package firewall

import (
	"bufio"
	"context"
	"fmt"
	"net"
	"os"
	"strconv"
	"strings"

	dbus "github.com/coreos/go-systemd/dbus"
)

const (
	APFType  = "apf"
	APFConf  = "/etc/apf/conf.apf"
	APFAllow = "/etc/apf/allow_hosts.rules"
	APFDeny  = "/etc/apf/deny_hosts.rules"
	// APFPreroute and APFPostroute are apf's user routing-rule files, sourced as
	// shell during a (re)start. Like the pre-hook below, this backend uses them as a
	// raw-iptables fallback for rules apf's native config and allow/deny files cannot
	// express — here the routing-stage cases, which in practice are NAT: destination
	// NAT (DNAT/Redirect) is written into preroute.rules and source NAT
	// (SNAT/Masquerade) into postroute.rules.
	APFPreroute  = "/etc/apf/preroute.rules"
	APFPostroute = "/etc/apf/postroute.rules"
	// APFHook is apf's pre-hook, run after the flush but before apf adds its own
	// rules. This library writes the iptables rules for features apf's native
	// config cannot express directly into this hook.
	APFHook = "/etc/apf/hook_pre.sh"
)

// APF manages the firewall through apf's config files and a managed pre-hook.
type APF struct {
	ConfigChanged bool
	// rulePrefix is prepended to a rule's comment when it is written as a
	// full-line comment above a rule in allow_hosts.rules/deny_hosts.rules, so
	// rules this library creates can be told apart. conf.apf port/icmp-list
	// rules carry no per-rule comment and so ignore it.
	rulePrefix string
	// ipv6Enabled mirrors conf.apf's USE_IPV6. apf's own shell logic silently
	// no-ops a bare IPv6 host in allow_hosts.rules/deny_hosts.rules
	// (apf_trust.sh trust_hosts()) and the native IG_ICMPV6_TYPES/EG_ICMPV6_TYPES
	// lists (cports.common) whenever USE_IPV6 is not "1" (the shipped default),
	// so AddRule must reject those shapes rather than write a rule apf will
	// never enforce.
	ipv6Enabled bool
}

// NewAPF verifies apf is installed and active, then returns a manager bound to rulePrefix.
func NewAPF(ctx context.Context, rulePrefix string) (*APF, error) {
	apf := new(APF)
	apf.rulePrefix = rulePrefix

	// Connect to systemd dbus interface.
	var prop *dbus.Property
	conn, err := dbus.NewWithContext(ctx)
	if err == nil {
		defer conn.Close()
		// Find the systemd service for apf and confirm it was loaded.
		prop, _ = conn.GetUnitPropertyContext(ctx, "apf.service", "ActiveState")
	}

	// If the service is not active in SystemD, check SysV status.
	if prop == nil || prop.Value.Value() != "active" {
		// Run SysV check to see if APF is enabled there.
		results, err := runCommand(ctx, "chkconfig", "--list", "apf")
		if err != nil {
			return nil, fmt.Errorf("the apf service is not active on this server")
		}

		// Parse the result to see if apf is on.
		foundOn := false
		for _, line := range results {
			fields := strings.Fields(line)
			if len(fields) == 0 {
				continue
			}

			// If this is not the apf line, skip.
			if fields[0] != "apf" {
				continue
			}

			// Parse the runlevel:status output to check if any are on.
			for _, f := range fields {
				_, status, found := strings.Cut(f, ":")
				if found && status == "on" {
					foundOn = true
				}
			}
		}

		// If APF is not on, return result.
		if !foundOn {
			return nil, fmt.Errorf("the apf service is not active or enabled on this server")
		}
	}

	// Confirm config files exist.
	files := []string{APFConf, APFAllow, APFDeny}
	for _, f := range files {
		if _, err := os.Stat(f); err != nil {
			return nil, fmt.Errorf("the config file %s is missing", f)
		}
	}

	// Read whether apf's own IPv6 handling is turned on.
	useIPv6, err := readConfValue(APFConf, "USE_IPV6")
	if err != nil {
		return nil, fmt.Errorf("error reading %s: %s", APFConf, err)
	}
	apf.ipv6Enabled = useIPv6 == "1"

	// Return the new apf object.
	return apf, nil
}

// Type returns the backend identifier for apf.
// Type returns the backend identifier for apf.
func (f *APF) Type() string {
	return APFType
}

// hook returns the managed pre-hook script used to inject iptables rules for
// features apf's native config cannot express.
// Capabilities reports the firewall features apf supports.
func (f *APF) Capabilities() Capabilities {
	return Capabilities{
		Output:  true,
		Forward: true,
		// ICMPv6 mirrors ipv6Enabled: apf's native IG_ICMPV6_TYPES/EG_ICMPV6_TYPES
		// lists (what a plain, qualifier-free ICMPv6 rule uses) are a silent no-op
		// on the real firewall whenever conf.apf's USE_IPV6 is not "1" (confirmed
		// against a real apf install: ip6tables carries no rule for a type in
		// IG_ICMPV6_TYPES when USE_IPV6=0). A rule that also needs state/interface/
		// log/rate matching still works via the raw-iptables hook regardless.
		ICMPv6:         f.ipv6Enabled,
		PortList:       false,
		ConnState:      true,
		InterfaceMatch: true,
		Logging:        true,
		RateLimit:      true,
		ConnLimit:      true,
		NAT:            true,
		RuleOrdering:   false,
		DefaultPolicy:  false,
		RuleCounters:   false,
		AddressSets:    false,
		Comments:       true,
	}
}

// GetDefaultPolicy is unsupported: apf has no managed default-policy control.
// GetZone returns no zone; apf has no zone support.
func (f *APF) GetZone(ctx context.Context, iface string) (zoneName string, err error) {
	return "", nil
}

// parsePortToken parses a single apf port token: a port or an underscore
// range (e.g. "6000_7000").
// parsePortToken parses a single apf port token: a port or an underscore
// range (e.g. "6000_7000").
func (f *APF) parsePortToken(tok string) (PortRange, error) {
	lo, hi, isRange := strings.Cut(strings.TrimSpace(tok), "_")
	start, err := strconv.ParseUint(strings.TrimSpace(lo), 10, 16)
	if err != nil {
		return PortRange{}, fmt.Errorf("invalid port %q", lo)
	}
	pr := PortRange{Start: uint16(start), End: uint16(start)}
	if isRange {
		end, err := strconv.ParseUint(strings.TrimSpace(hi), 10, 16)
		if err != nil {
			return PortRange{}, fmt.Errorf("invalid port %q", hi)
		}
		pr.End = uint16(end)
		if pr.End < pr.Start {
			return PortRange{}, fmt.Errorf("port range end below start")
		}
	}
	return pr, nil
}

// portToken renders a port spec in apf notation: a port or an underscore
// range.
// ParseConnLimit decodes a conf.apf IG_TCP_CLIMIT/IG_UDP_CLIMIT value
// ("port:limit,...", port may be an underscore range) into connection-limit
// rules: apf caps concurrent connections per source and rejects the excess, so
// each entry becomes an inbound reject rule carrying a per-source ConnLimit.
func (f *APF) ParseConnLimit(val string, proto Protocol) (rules []*Rule) {
	for _, entry := range strings.Split(val, ",") {
		entry = strings.TrimSpace(entry)
		if entry == "" {
			continue
		}
		portTok, limitTok, ok := strings.Cut(entry, ":")
		if !ok {
			continue
		}
		pr, err := f.parsePortToken(strings.TrimSpace(portTok))
		if err != nil {
			continue
		}
		limit, err := strconv.ParseUint(strings.TrimSpace(limitTok), 10, 32)
		if err != nil {
			continue
		}
		// Like the CPORTS lists, IG_TCP_CLIMIT/IG_UDP_CLIMIT are dual-stack, so a
		// connection-limit entry carries no family of its own. Report FamilyAny so a
		// FamilyAny desired connlimit rule reconciles with its read-back. (APF has no
		// egress connection-limit config; connlimit applies only on the input chain.)
		rule := &Rule{
			Family:    FamilyAny,
			Proto:     proto,
			Action:    Reject,
			ConnLimit: &ConnLimit{Count: uint(limit), PerSource: true},
		}
		portSpecsToRule(rule, []PortRange{pr})
		rules = append(rules, rule)
	}
	return
}

// editConnLimit renders a CLIMIT config line with a rule's "port:limit" entry
// added or removed, preserving the other entries, and records a config change.
// ParseICMPTypes decodes an apf ICMP type list (IG_ICMP_TYPES/EG_ICMP_TYPES for
// proto ICMP, IG_ICMPV6_TYPES/EG_ICMPV6_TYPES for proto ICMPv6) into accept rules,
// one per type. The "all" wildcard (which apf applies as a typeless `-p icmp -j
// ACCEPT`) becomes a rule with a nil ICMPType, matching every type.
func (f *APF) ParseICMPTypes(val string, proto Protocol, out bool) (rules []*Rule) {
	fam := IPv4
	if proto == ICMPv6 {
		fam = IPv6
	}
	for _, tok := range strings.Split(val, ",") {
		tok = strings.TrimSpace(tok)
		if tok == "" {
			continue
		}
		rule := &Rule{Family: fam, Proto: proto, Direction: directionFromOutput(out), Action: Accept}
		if !strings.EqualFold(tok, "all") {
			n, ok := parseICMPTypeFamily(tok, proto == ICMPv6)
			if !ok {
				continue
			}
			rule.ICMPType = Ptr(n)
		}
		rules = append(rules, rule)
	}
	return
}

// splitAdvFields splits an apf advanced rule on ':' while leaving colons inside
// bracketed IPv6 addresses (e.g. [2001:db8::1]) intact.
// parseAddr parses an apf address value, stripping the bracket notation used
// to protect IPv6 addresses, and normalizing a zero-network to the empty (any)
// address. It reports the family, or false when the value is not an address.
func (f *APF) parseAddr(v string) (addr string, fam Family, ok bool) {
	if strings.HasPrefix(v, "[") && strings.HasSuffix(v, "]") {
		v = v[1 : len(v)-1]
	}
	_, network, err := net.ParseCIDR(v)
	ip := net.ParseIP(v)
	if err != nil && ip == nil {
		return "", FamilyAny, false
	}
	family := IPv4
	if (network != nil && network.IP.To4() == nil) || (ip != nil && ip.To4() == nil) {
		family = IPv6
	}
	// A zero network (0.0.0.0/0 or ::/0) means "any", represented as empty.
	if network != nil {
		ones, _ := network.Mask.Size()
		if ones == 0 && network.IP.IsUnspecified() {
			return "", family, true
		}
	}
	return v, family, true
}

// addrField renders an address for an advanced rule, wrapping an IPv6 address
// in brackets so it survives the colon-separated field format.
// parseStopAction maps a conf.apf ALL_STOP/TCP_STOP/UDP_STOP value to the
// action apf actually applies. "DROP", "REJECT" and "PROHIBIT" are valid;
// anything else (including empty) falls back to the stock default of DROP.
// PROHIBIT jumps to apf's own PROHIBIT chain, which rejects with an ICMP
// (un)reachable-prohibited response — the same reject-like semantics as
// REJECT, just a different ICMP code — so it maps to Reject rather than Drop;
// this model has no third action to give it.
func (f *APF) parseStopAction(val string) Action {
	switch strings.ToUpper(trimQuotes(strings.TrimSpace(val))) {
	case "REJECT", "PROHIBIT":
		return Reject
	default:
		return Drop
	}
}

// stopKey names the conf.apf setting apf actually applies to a deny of the
// given protocol. A bare-address deny_hosts entry (no protocol/port) is dropped
// by trust_hosts's own bare-host branch, which applies ALL_STOP directly. An
// advanced entry (proto:flow:s/d=port:s/d=ip) is instead routed through
// trust_entry_rule, which ignores ALL_STOP entirely and applies TCP_STOP for a
// tcp entry or UDP_STOP for a udp one (files/internals/apf_trust.sh). The three
// settings default to DROP and are otherwise fully independent, so an entry read
// or matched under the wrong key can report or accept the wrong action whenever
// an operator sets them differently.
// readStopAction reads the named STOP setting (ALL_STOP/TCP_STOP/UDP_STOP)
// from a conf.apf-format file, defaulting to the stock DROP when the key is
// absent or the file cannot be read. path is a parameter (rather than always
// APFConf) so this can be exercised against a fixture file in tests.
func (f *APF) readStopAction(path, key string) Action {
	action := Drop
	fd, err := os.Open(path)
	if err != nil {
		return action
	}
	defer func() { _ = fd.Close() }()

	scanner := bufio.NewScanner(fd)
	for scanner.Scan() {
		line := scanner.Text()
		if ci := strings.IndexByte(line, '#'); ci >= 0 {
			line = line[:ci]
		}
		k, val, found := strings.Cut(strings.TrimSpace(line), "=")
		if !found {
			continue
		}
		if strings.TrimSpace(k) != key {
			continue
		}
		action = f.parseStopAction(val)
	}
	return action
}

// denyActionFor reads conf.apf's setting for the given protocol (see
// stopKey) and returns the action apf actually applies to a deny of that
// protocol. deny_hosts encodes no action of its own, so a rule read back must
// be stamped with what apf actually applies — otherwise a Drop rule reads back
// as Reject, never compares equal to the desired rule, and churns on every Sync.
// stopKey names the conf.apf setting apf actually applies to a deny of the
// given protocol. A bare-address deny_hosts entry (no protocol/port) is dropped
// by trust_hosts's own bare-host branch, which applies ALL_STOP directly. An
// advanced entry (proto:flow:s/d=port:s/d=ip) is instead routed through
// trust_entry_rule, which ignores ALL_STOP entirely and applies TCP_STOP for a
// tcp entry or UDP_STOP for a udp one (files/internals/apf_trust.sh). The three
// settings default to DROP and are otherwise fully independent, so an entry read
// or matched under the wrong key can report or accept the wrong action whenever
// an operator sets them differently.
func (f *APF) stopKey(proto Protocol) string {
	switch proto {
	case TCP:
		return "TCP_STOP"
	case UDP:
		return "UDP_STOP"
	default:
		return "ALL_STOP"
	}
}

// readStopAction reads the named STOP setting (ALL_STOP/TCP_STOP/UDP_STOP)
// from a conf.apf-format file, defaulting to the stock DROP when the key is
// absent or the file cannot be read. path is a parameter (rather than always
// APFConf) so this can be exercised against a fixture file in tests.
// denyActionFor reads conf.apf's setting for the given protocol (see
// stopKey) and returns the action apf actually applies to a deny of that
// protocol. deny_hosts encodes no action of its own, so a rule read back must
// be stamped with what apf actually applies — otherwise a Drop rule reads back
// as Reject, never compares equal to the desired rule, and churns on every Sync.
func (f *APF) denyActionFor(proto Protocol) Action {
	return f.readStopAction(APFConf, f.stopKey(proto))
}

// resolveAction resolves the action to stamp on a rule parsed from — or
// matched against — allow_hosts/deny_hosts. base is Accept for allow_hosts
// (returned unchanged, since parseStopAction never yields Accept and
// allow_hosts has no per-protocol distinction) or the ALL_STOP-derived action
// for deny_hosts. A deny_hosts entry in apf's advanced syntax with a concrete
// tcp or udp protocol is not governed by ALL_STOP (see stopKey), so its
// action is re-derived from the matching TCP_STOP/UDP_STOP setting instead.
// resolveAction resolves the action to stamp on a rule parsed from — or
// matched against — allow_hosts/deny_hosts. base is Accept for allow_hosts
// (returned unchanged, since parseStopAction never yields Accept and
// allow_hosts has no per-protocol distinction) or the ALL_STOP-derived action
// for deny_hosts. A deny_hosts entry in apf's advanced syntax with a concrete
// tcp or udp protocol is not governed by ALL_STOP (see stopKey), so its
// action is re-derived from the matching TCP_STOP/UDP_STOP setting instead.
func (f *APF) resolveAction(base Action, proto Protocol) Action {
	if base == Accept {
		return base
	}
	switch proto {
	case TCP, UDP:
		return f.denyActionFor(proto)
	default:
		return base
	}
}

// ParseAdvRule decodes an apf advanced allow/deny rule of the form
// proto:flow:s/d=port:s/d=ip. IPv6 addresses use bracket notation.
// splitAdvFields splits an apf advanced rule on ':' while leaving colons inside
// bracketed IPv6 addresses (e.g. [2001:db8::1]) intact.
func (f *APF) splitAdvFields(s string) []string {
	var fields []string
	depth, start := 0, 0
	for i := 0; i < len(s); i++ {
		switch s[i] {
		case '[':
			depth++
		case ']':
			if depth > 0 {
				depth--
			}
		case ':':
			if depth == 0 {
				fields = append(fields, s[start:i])
				start = i + 1
			}
		}
	}
	return append(fields, s[start:])
}

// parseAddr parses an apf address value, stripping the bracket notation used
// to protect IPv6 addresses, and normalizing a zero-network to the empty (any)
// address. It reports the family, or false when the value is not an address.
// ParseAdvRule decodes an apf advanced allow/deny rule of the form
// proto:flow:s/d=port:s/d=ip. IPv6 addresses use bracket notation.
func (f *APF) ParseAdvRule(val string, action Action) (r *Rule) {
	r = &Rule{}

	for _, fld := range f.splitAdvFields(val) {
		switch {
		case strings.EqualFold(fld, "tcp"):
			r.Proto = TCP
		case strings.EqualFold(fld, "udp"):
			r.Proto = UDP
		case strings.EqualFold(fld, "in"):
			r.Direction = DirInput
		case strings.EqualFold(fld, "out"):
			r.Direction = DirOutput
		case strings.HasPrefix(fld, "s="):
			// The source field is either an address or, when it is not, a source
			// port (a single port or an underscore range; apf's port field takes
			// no comma list).
			v := strings.TrimPrefix(fld, "s=")
			if addr, fam, ok := f.parseAddr(v); ok {
				r.Family = fam
				r.Source = addr
				continue
			}
			pr, err := f.parsePortToken(v)
			if err != nil {
				return nil
			}
			sourcePortSpecsToRule(r, []PortRange{pr})
		case strings.HasPrefix(fld, "d="):
			// Mirror the s= branch: the destination field is either an address or a
			// single destination port (a single port or an underscore range; apf's
			// port field takes no comma list).
			v := strings.TrimPrefix(fld, "d=")
			if addr, fam, ok := f.parseAddr(v); ok {
				r.Family = fam
				r.Destination = addr
				continue
			}
			pr, err := f.parsePortToken(v)
			if err != nil {
				return nil
			}
			portSpecsToRule(r, []PortRange{pr})
		}
	}

	// The action depends on the protocol just parsed (see resolveAction), so
	// it is resolved last rather than stamped up front.
	r.Action = f.resolveAction(action, r.Proto)

	return
}

// MarshalAdvRule encodes a rule as an apf advanced allow/deny line. An apf
// advanced rule is tcp/udp only and must carry a source or destination address.
// ParseIPList reads an apf allow_hosts/deny_hosts file and returns the rules it holds.
func (f *APF) ParseIPList(filePath string, action Action) (rules []*Rule, err error) {
	// Read the allow_hosts/deny_hosts rule list.
	fd, err := os.Open(filePath)
	if err != nil {
		return nil, err
	}

	scanner := bufio.NewScanner(fd)
	// A full-line comment immediately above a rule is that rule's comment.
	// Consecutive comment lines accumulate (joined by a space); a blank line
	// detaches a comment from any rule that follows.
	var pendingComment string
	flushComment := func() (string, bool) {
		text, hasPrefix := prefixedComment(f.rulePrefix, pendingComment)
		pendingComment = ""
		return text, hasPrefix
	}
	for scanner.Scan() {
		raw := scanner.Text()
		trimmed := strings.TrimSpace(raw)

		// A full-line comment is held as a candidate rule comment.
		if trimmed != "" && strings.HasPrefix(trimmed, "#") {
			text := strings.TrimSpace(strings.TrimPrefix(trimmed, "#"))
			// A prefix tag starts a fresh comment block for the rule that
			// follows, so header/section comments above it are not absorbed into
			// the rule's comment and prefix detection stays reliable.
			if f.rulePrefix != "" && (text == f.rulePrefix || strings.HasPrefix(text, f.rulePrefix+" ")) {
				pendingComment = text
			} else if pendingComment != "" {
				pendingComment += " " + text
			} else {
				pendingComment = text
			}
			continue
		}

		// Strip an inline trailing comment (not a rule comment).
		if ci := strings.IndexByte(trimmed, '#'); ci >= 0 {
			trimmed = trimmed[:ci]
		}
		trimmed = strings.TrimSpace(trimmed)

		// A blank line detaches a pending comment from any later rule.
		if len(trimmed) == 0 {
			pendingComment = ""
			continue
		}

		comment, hasPrefix := flushComment()

		// An advanced rule carries s=/d= options; a bare line is a plain address
		// (which may itself be an IPv6 address containing colons).
		if strings.Contains(trimmed, "=") {
			rule := f.ParseAdvRule(trimmed, action)
			if rule == nil {
				continue
			}
			rule.Comment = comment
			rule.HasPrefix = hasPrefix
			rules = append(rules, rule)
		} else {
			// Try to parse IP.
			fam, ok := csfAddrFamily(trimmed)
			if !ok {
				continue
			}

			// A plain IP line matches the host in both directions, so it is one
			// bidirectional DirAny rule, authored in the inbound frame (Source=X).
			rules = append(rules, &Rule{
				Direction: DirAny,
				Family:    fam,
				Source:    trimmed,
				Action:    action,
				Comment:   comment,
				HasPrefix: hasPrefix,
			})
		}
	}

	_ = fd.Close()
	if serr := scanner.Err(); serr != nil {
		return nil, serr
	}
	return
}

// cPortsKey returns the conf.apf CPORTS list a tcp/udp port rule of the given
// direction lives in, or "" for a protocol with no such list.
// ParsePorts decodes an apf comma-separated port list into accept rules, one per port entry.
func (f *APF) ParsePorts(val string, proto Protocol, out bool) (rules []*Rule) {
	for _, port := range strings.Split(val, ",") {
		port = strings.TrimSpace(port)
		if port == "" {
			continue
		}

		pr, err := f.parsePortToken(port)
		if err != nil {
			continue
		}
		// apf's IG_*_CPORTS/EG_*_CPORTS lists are dual-stack — a single list applied
		// to both the ip and ip6 tables — so a port entry carries no family of its
		// own. Report FamilyAny (not IPv4) so a FamilyAny desired rule, which a bare
		// tcp/udp port carries by default, reconciles with its own read-back.
		rule := &Rule{
			Family:    FamilyAny,
			Proto:     proto,
			Direction: directionFromOutput(out),
			Action:    Accept,
		}
		portSpecsToRule(rule, []PortRange{pr})
		rules = append(rules, rule)
	}
	return
}

// ParseICMPTypes decodes an apf ICMP type list (IG_ICMP_TYPES/EG_ICMP_TYPES for
// proto ICMP, IG_ICMPV6_TYPES/EG_ICMPV6_TYPES for proto ICMPv6) into accept rules,
// one per type. The "all" wildcard (which apf applies as a typeless `-p icmp -j
// ACCEPT`) becomes a rule with a nil ICMPType, matching every type.
// hook returns the managed pre-hook script used to inject iptables rules for
// features apf's native config cannot express.
func (f *APF) hook() *hookScript {
	return &hookScript{
		rulePrefix: f.rulePrefix,
		hookPath:   APFHook,
		hookPerm:   0750,
	}
}

// GetZone returns no zone; apf has no zone support.
// GetRules returns the current filter rules read from conf.apf, the allow/deny lists, and the pre-hook.
func (f *APF) GetRules(ctx context.Context, zoneName string) (rules []*Rule, err error) {
	// Read rules from conf.apf
	fd, err := os.Open(APFConf)
	if err != nil {
		return nil, err
	}

	// denyAction is the action apf applies to a bare-address deny (conf.apf
	// ALL_STOP, default DROP). Capture it in this same pass so the deny list can
	// be stamped without re-reading conf.apf for that common case; a tcp/udp
	// advanced deny_hosts entry is re-resolved from TCP_STOP/UDP_STOP instead (see
	// resolveAction, used by ParseAdvRule as ParseIPList parses each line).
	denyAction := Drop

	// Scan each line.
	scanner := bufio.NewScanner(fd)
	for scanner.Scan() {
		// Get the line.
		line := scanner.Text()

		// Remove comments.
		ci := strings.IndexByte(line, '#')
		if ci >= 0 {
			line = line[:ci]
		}

		// Trim spaces.
		line = strings.TrimSpace(line)

		// Ignore zero lines.
		if len(line) == 0 {
			continue
		}

		// Parse key/value.
		key, val, found := strings.Cut(line, "=")
		if !found {
			continue
		}
		key = strings.TrimSpace(key)
		val = trimQuotes(strings.TrimSpace(val))

		// Parse rules.
		switch key {
		case "ALL_STOP":
			denyAction = f.parseStopAction(val)
		case "IG_TCP_CPORTS":
			rules = append(rules, f.ParsePorts(val, TCP, false)...)
		case "IG_UDP_CPORTS":
			rules = append(rules, f.ParsePorts(val, UDP, false)...)
		case "EG_TCP_CPORTS":
			rules = append(rules, f.ParsePorts(val, TCP, true)...)
		case "EG_UDP_CPORTS":
			rules = append(rules, f.ParsePorts(val, UDP, true)...)
		case "IG_ICMP_TYPES":
			rules = append(rules, f.ParseICMPTypes(val, ICMP, false)...)
		case "EG_ICMP_TYPES":
			rules = append(rules, f.ParseICMPTypes(val, ICMP, true)...)
		case "IG_ICMPV6_TYPES":
			rules = append(rules, f.ParseICMPTypes(val, ICMPv6, false)...)
		case "EG_ICMPV6_TYPES":
			rules = append(rules, f.ParseICMPTypes(val, ICMPv6, true)...)
		case "IG_TCP_CLIMIT":
			rules = append(rules, f.ParseConnLimit(val, TCP)...)
		case "IG_UDP_CLIMIT":
			rules = append(rules, f.ParseConnLimit(val, UDP)...)
		}
	}

	_ = fd.Close()
	if err := scanner.Err(); err != nil {
		return nil, err
	}

	// Read the allowed IP rule list.
	ipRules, err := f.ParseIPList(APFAllow, Accept)
	if err != nil {
		return nil, err
	}
	rules = append(rules, ipRules...)

	// Read the denied IP rule list, stamped with the action apf actually applies
	// (captured above from conf.apf ALL_STOP, default DROP) rather than a fixed
	// Reject, so a managed Drop rule reads back as Drop and reconciles without churn.
	ipRules, err = f.ParseIPList(APFDeny, denyAction)
	if err != nil {
		return nil, err
	}
	rules = append(rules, ipRules...)

	// Read the iptables rules injected through the apf pre-hook (state,
	// interface, logging, rate-limit, icmpv6).
	hookRules, err := f.hook().getRules()
	if err != nil {
		return nil, err
	}
	rules = append(rules, hookRules...)

	// Merge rules across families so a v4/v6 hook pair collapses to one rule, then
	// collapse each input/output twin into one DirAny rule — a plain allow_hosts/
	// deny_hosts IP, read as an inbound (source) rule plus an outbound (destination)
	// rule, reads back as the single bidirectional line it was written as.
	rules = mergeFamilies(rules)
	rules = mergeDirections(rules)
	return
}

// removeBareHostOneWay removes a one-way bare-address host rule. Such a rule is
// stored either as its own hook rule or as one direction of a bidirectional plain
// allow_hosts/deny_hosts line (a DirAny rule). When a matching plain line exists,
// split it: drop the line and re-add the surviving opposite direction as a hook rule
// so the untargeted direction keeps its coverage.
// portToken renders a port spec in apf notation: a port or an underscore
// range.
func (f *APF) portToken(pr PortRange) string {
	pr = pr.normalized()
	if pr.Start == pr.End {
		return strconv.FormatUint(uint64(pr.Start), 10)
	}
	return fmt.Sprintf("%d_%d", pr.Start, pr.End)
}

// ParsePorts decodes an apf comma-separated port list into accept rules, one per port entry.
// editConnLimit renders a CLIMIT config line with a rule's "port:limit" entry
// added or removed, preserving the other entries, and records a config change.
func (f *APF) editConnLimit(key, val string, r *Rule, remove bool) string {
	portTok := f.portToken(r.PortSpecs()[0])
	var kept []string
	present := false
	for _, tok := range strings.Split(val, ",") {
		tok = strings.TrimSpace(tok)
		if tok == "" {
			continue
		}
		p, _, ok := strings.Cut(tok, ":")
		if ok && strings.TrimSpace(p) == portTok {
			present = true
			if remove {
				f.ConfigChanged = true
				continue
			}
			// Replace the entry in place. Record a config change only when the
			// count actually differs so Reload runs apf --restart to apply the new
			// limit; an unchanged count must not trigger a spurious restart.
			newTok := fmt.Sprintf("%s:%d", portTok, r.ConnLimit.Count)
			if strings.TrimSpace(tok) != newTok {
				f.ConfigChanged = true
			}
			kept = append(kept, newTok)
			continue
		}
		kept = append(kept, tok)
	}
	if !remove && !present {
		kept = append(kept, fmt.Sprintf("%s:%d", portTok, r.ConnLimit.Count))
		f.ConfigChanged = true
	}
	return fmt.Sprintf(`%s="%s"`, key, strings.Join(kept, ","))
}

// icmpTokens returns the conf.apf type token(s) an icmp/icmpv6 accept rule
// contributes to its type list: the numeric type, or "all" when the rule matches
// every type (a nil ICMPType, which apf applies as a typeless `-p icmp -j ACCEPT`).
// icmpTokens returns the conf.apf type token(s) an icmp/icmpv6 accept rule
// contributes to its type list: the numeric type, or "all" when the rule matches
// every type (a nil ICMPType, which apf applies as a typeless `-p icmp -j ACCEPT`).
func (f *APF) icmpTokens(r *Rule) []string {
	if r.ICMPType == nil {
		return []string{"all"}
	}
	return []string{strconv.Itoa(int(*r.ICMPType))}
}

// portTokens renders the rule's ports as apf config tokens.
// isConnLimitRule reports whether a rule maps onto conf.apf's
// IG_TCP_CLIMIT/IG_UDP_CLIMIT: a per-source cap on concurrent inbound
// connections to a single tcp/udp port (or range) with no address, rejecting the
// excess.
func (f *APF) isConnLimitRule(r *Rule) bool {
	return r.ConnLimit != nil && r.ConnLimit.PerSource &&
		!r.IsOutput() && (r.Proto == TCP || r.Proto == UDP) &&
		r.Source == "" && r.Destination == "" &&
		len(r.PortSpecs()) == 1 && r.Action == Reject
}

// ParseConnLimit decodes a conf.apf IG_TCP_CLIMIT/IG_UDP_CLIMIT value
// ("port:limit,...", port may be an underscore range) into connection-limit
// rules: apf caps concurrent connections per source and rejects the excess, so
// each entry becomes an inbound reject rule carrying a per-source ConnLimit.
// portTokens renders the rule's ports as apf config tokens.
func (f *APF) portTokens(r *Rule) []string {
	specs := r.PortSpecs()
	tokens := make([]string, len(specs))
	for i, sp := range specs {
		tokens[i] = f.portToken(sp)
	}
	return tokens
}

// EditRulePort returns the conf.apf line with the rule's tokens added to or removed from the list that key manages.
// EditRulePort returns the conf.apf line with the rule's tokens added to or removed from the list that key manages.
func (f *APF) EditRulePort(orig, key, val string, r *Rule, remove bool) string {
	// A connection-limit rule is expressed solely through the CLIMIT config; it
	// must never also add or remove its port from an accept port list, or
	// RemoveRule would close a port the caller never opened and a round-trip
	// would report a spurious accept rule alongside the connlimit.
	if r.ConnLimit != nil && key != "IG_TCP_CLIMIT" && key != "IG_UDP_CLIMIT" {
		return orig
	}

	// Determine which config list this key manages and the tokens the rule
	// contributes to it. Non-matching keys are returned untouched.
	var wantTokens []string
	switch key {
	case "IG_TCP_CPORTS":
		if r.IsOutput() || r.Proto != TCP {
			return orig
		}
		wantTokens = f.portTokens(r)
	case "IG_UDP_CPORTS":
		if r.IsOutput() || r.Proto != UDP {
			return orig
		}
		wantTokens = f.portTokens(r)
	case "EG_TCP_CPORTS":
		if !r.IsOutput() || r.Proto != TCP {
			return orig
		}
		wantTokens = f.portTokens(r)
	case "EG_UDP_CPORTS":
		if !r.IsOutput() || r.Proto != UDP {
			return orig
		}
		wantTokens = f.portTokens(r)
	case "IG_ICMP_TYPES":
		if r.IsOutput() || r.Proto != ICMP {
			return orig
		}
		wantTokens = f.icmpTokens(r)
	case "EG_ICMP_TYPES":
		if !r.IsOutput() || r.Proto != ICMP {
			return orig
		}
		wantTokens = f.icmpTokens(r)
	case "IG_ICMPV6_TYPES":
		if r.IsOutput() || r.Proto != ICMPv6 {
			return orig
		}
		wantTokens = f.icmpTokens(r)
	case "EG_ICMPV6_TYPES":
		if !r.IsOutput() || r.Proto != ICMPv6 {
			return orig
		}
		wantTokens = f.icmpTokens(r)
	case "IG_TCP_CLIMIT":
		// CLIMIT tokens are "port:limit", edited independently of the port lists.
		if !f.isConnLimitRule(r) || r.Proto != TCP {
			return orig
		}
		return f.editConnLimit(key, val, r, remove)
	case "IG_UDP_CLIMIT":
		if !f.isConnLimitRule(r) || r.Proto != UDP {
			return orig
		}
		return f.editConnLimit(key, val, r, remove)
	default:
		return orig
	}

	// Canonicalize tokens for comparison. An ICMP-type list may hold either a
	// numeric type or a name (e.g. "echo-request"), and the read path resolves names
	// to numbers; comparing the list's raw token against the numeric token this code
	// emits would never match a name-based (foreign) entry, so a remove would keep it
	// and an add would append a numeric duplicate. Fold each token to its resolved
	// number, using the family the key implies; other keys
	// compare verbatim.
	canon := func(tok string) string { return tok }
	switch key {
	case "IG_ICMP_TYPES", "EG_ICMP_TYPES", "IG_ICMPV6_TYPES", "EG_ICMPV6_TYPES":
		v6 := key == "IG_ICMPV6_TYPES" || key == "EG_ICMPV6_TYPES"
		canon = func(tok string) string {
			if n, ok := parseICMPTypeFamily(tok, v6); ok {
				return strconv.Itoa(int(n))
			}
			return tok
		}
	}

	// Add or remove the rule's tokens from the comma list, preserving any others.
	// Three collections cooperate here:
	//   - want:    the canonical form of every token this rule contributes, so a
	//              remove can recognize an existing token as "ours" regardless of
	//              how it was spelled in the file.
	//   - present: the canonical form of every token we decide to keep, so the
	//              add pass can tell whether one of the rule's tokens is already
	//              in the list and must not be appended a second time.
	//   - kept:    the tokens, in original spelling, that survive into the
	//              rewritten list. This is the actual output.
	// want and present are keyed by canonical form (comparison identity); kept
	// holds the verbatim tokens (what we write back).
	want := make(map[string]bool, len(wantTokens))
	for _, w := range wantTokens {
		want[canon(w)] = true
	}
	present := make(map[string]bool)
	var kept []string

	// Pass 1: walk the existing config list. Each token is either dropped (only
	// on a remove, and only when it is one of the rule's own tokens) or kept.
	// We keep the original spelling but track it by canonical form so pass 2 can
	// dedupe against it.
	for _, tok := range strings.Split(val, ",") {
		tok = strings.TrimSpace(tok)
		if tok == "" {
			continue
		}
		c := canon(tok)
		// On a remove, an existing token that matches one of the rule's tokens is
		// the one we are deleting: skip it and flag the file as changed.
		if remove && want[c] {
			f.ConfigChanged = true
			continue
		}
		// Otherwise the token stays. Record its canonical form so the add pass
		// below treats it as already present.
		kept = append(kept, tok)
		present[c] = true
	}

	// Pass 2 (add only): append any of the rule's tokens that the existing list
	// did not already contain. present carries forward from pass 1, so a token
	// the file already had is skipped and we never write a duplicate.
	if !remove {
		for _, w := range wantTokens {
			if cw := canon(w); !present[cw] {
				kept = append(kept, w)
				present[cw] = true
				f.ConfigChanged = true
			}
		}
	}

	// Re-create the configuration with the new list.
	return fmt.Sprintf(`%s="%s"`, key, strings.Join(kept, ","))
}

// EditConf adds or removes a rule in conf.apf, rewriting the file in place.
// EditConf adds or removes a rule in conf.apf, rewriting the file in place.
func (f *APF) EditConf(ctx context.Context, r *Rule, remove bool) error {
	// For port only rules, open the standard config file.
	fd, err := os.Open(APFConf)
	if err != nil {
		return err
	}

	// Stage the rewrite, preserving conf.apf's mode and ownership.
	af, err := newAtomicFile(APFConf, 0644)
	if err != nil {
		_ = fd.Close()
		return err
	}
	defer af.Abort()

	// Parse config one line at a time, adding the port rule.
	scanner := bufio.NewScanner(fd)
	for scanner.Scan() {
		// Get the line.
		orig := scanner.Text()
		line := orig

		// Remove comments.
		ci := strings.IndexByte(line, '#')
		if ci >= 0 {
			line = line[:ci]
		}

		// Trim spaces.
		line = strings.TrimSpace(line)

		// Ignore zero lines.
		if len(line) == 0 {
			_, _ = fmt.Fprintln(af, orig)
			continue
		}

		// Parse key/value.
		key, val, found := strings.Cut(line, "=")
		if !found {
			_, _ = fmt.Fprintln(af, orig)
			continue
		}
		key = strings.TrimSpace(key)
		val = trimQuotes(strings.TrimSpace(val))

		// Parse rules.
		orig = f.EditRulePort(orig, key, val, r, remove)
		_, _ = fmt.Fprintln(af, orig)
	}

	_ = fd.Close()

	// A read error means the rewritten file is truncated; discard it.
	if serr := scanner.Err(); serr != nil {
		return serr
	}

	// Move new file into place, preserving mode and ownership.
	return af.Commit()
}

// nativeICMPv6 reports whether an ICMPv6 rule can be carried by apf's native
// IG_ICMPV6_TYPES/EG_ICMPV6_TYPES lists (an address-less accept, optionally typed)
// and so belongs in conf.apf rather than the raw-iptables hook. The shared
// ruleNeedsHook diverts every ICMPv6 rule to the hook — correct for csf, which has
// no native v6 type list — so apf overrides that only for the rules its config can
// actually express, leaving an ICMPv6 rule that also needs state/interface/log/
// rate matching (which conf.apf cannot carry) on the hook path.
// addrField renders an address for an advanced rule, wrapping an IPv6 address
// in brackets so it survives the colon-separated field format.
func (f *APF) addrField(addr string) string {
	if strings.Contains(addr, ":") {
		return "[" + addr + "]"
	}
	return addr
}

// parseStopAction maps a conf.apf ALL_STOP/TCP_STOP/UDP_STOP value to the
// action apf actually applies. "DROP", "REJECT" and "PROHIBIT" are valid;
// anything else (including empty) falls back to the stock default of DROP.
// PROHIBIT jumps to apf's own PROHIBIT chain, which rejects with an ICMP
// (un)reachable-prohibited response — the same reject-like semantics as
// REJECT, just a different ICMP code — so it maps to Reject rather than Drop;
// this model has no third action to give it.
// MarshalAdvRule encodes a rule as an apf advanced allow/deny line. An apf
// advanced rule is tcp/udp only and must carry a source or destination address.
func (f *APF) MarshalAdvRule(r *Rule) (string, error) {
	if r.Proto.IsICMP() {
		return "", fmt.Errorf("apf advanced rules do not support icmp")
	}
	if r.Source == "" && r.Destination == "" {
		return "", fmt.Errorf("an apf advanced rule requires a source or destination address")
	}
	// apf's advanced rule holds a single address field, so a rule matching both a
	// source and a destination cannot be expressed; reject it rather than silently
	// dropping the destination (which would install a broader rule than asked and
	// leave the rule unremovable). Mirrors the dual-port guard below.
	if r.Source != "" && r.Destination != "" {
		return "", fmt.Errorf("apf advanced rules cannot match both a source and destination address")
	}
	// apf's port field takes a single port or an underscore range (no comma list),
	// and there is a single port-flow field, so a rule cannot match both a source
	// and a destination port at once.
	if len(r.PortSpecs()) > 1 || len(r.SourcePortSpecs()) > 1 {
		return "", fmt.Errorf("apf advanced rules do not support a port list in this model")
	}
	if r.HasPorts() && r.HasSourcePorts() {
		return "", fmt.Errorf("apf advanced rules cannot match both a source and destination port")
	}

	var parts []string
	switch r.Proto {
	case TCP:
		parts = append(parts, "tcp")
	case UDP:
		parts = append(parts, "udp")
	}
	if r.IsOutput() {
		parts = append(parts, "out")
	} else {
		parts = append(parts, "in")
	}
	// The port-flow field: a source port or a destination port.
	if specs := r.SourcePortSpecs(); len(specs) == 1 {
		parts = append(parts, "s="+f.portToken(specs[0]))
	} else if specs := r.PortSpecs(); len(specs) == 1 {
		parts = append(parts, "d="+f.portToken(specs[0]))
	}
	if r.Source != "" {
		parts = append(parts, "s="+f.addrField(r.Source))
	} else if r.Destination != "" {
		parts = append(parts, "d="+f.addrField(r.Destination))
	}
	return strings.Join(parts, ":"), nil
}

// ParseIPList reads an apf allow_hosts/deny_hosts file and returns the rules it holds.
// EditIPList adds or removes a rule in an apf allow_hosts/deny_hosts file, rewriting it in place.
func (f *APF) EditIPList(ctx context.Context, filePath string, action Action, r *Rule, remove bool) error {
	// Read the allow_hosts/deny_hosts rule list.
	fd, err := os.Open(filePath)
	if err != nil {
		return err
	}

	// Stage the rewrite, preserving the list file's mode and ownership.
	af, err := newAtomicFile(filePath, 0644)
	if err != nil {
		_ = fd.Close()
		return err
	}
	defer af.Abort()

	scanner := bufio.NewScanner(fd)
	exists := false
	// A deny_hosts entry takes on the drop/reject action set in apf.conf (and
	// allow_hosts is accept), so a rule read back is stamped with the file's
	// action. Resolve the incoming rule's action the same way via resolveAction
	// before matching.
	match := *r
	match.Action = f.resolveAction(action, r.Proto)

	// pending holds the full-line comments seen immediately above a rule, so they
	// can be dropped together with a removed rule (they are its comment) or written
	// ahead of a kept one. A blank line detaches them.
	var pending []string
	flush := func() {
		for _, c := range pending {
			_, _ = fmt.Fprintln(af, c)
		}
		pending = nil
	}
	drop := func() { pending = nil }

	// Read the file line by line.
	for scanner.Scan() {
		orig := scanner.Text()
		trimmed := strings.TrimSpace(orig)

		// A full-line comment is held as a candidate rule comment.
		if trimmed != "" && strings.HasPrefix(trimmed, "#") {
			// Mirror ParseIPList: a prefix tag starts a fresh comment block, so
			// any header/section comments above it are not part of the rule's comment
			// and must survive its removal. Flush them now and begin the rule's block
			// at the tag, so drop() only discards the tag and the rule's own comment.
			if f.rulePrefix != "" {
				if text := strings.TrimSpace(strings.TrimPrefix(trimmed, "#")); text == f.rulePrefix || strings.HasPrefix(text, f.rulePrefix+" ") {
					flush()
				}
			}
			pending = append(pending, orig)
			continue
		}

		// Strip an inline trailing comment for matching, but preserve the
		// original line (with its inline note) when copying it through.
		line := trimmed
		if ci := strings.IndexByte(line, '#'); ci >= 0 {
			line = line[:ci]
		}
		line = strings.TrimSpace(line)

		// A blank line detaches a pending comment; write it and the blank.
		if len(line) == 0 {
			flush()
			_, _ = fmt.Fprintln(af, orig)
			continue
		}

		if strings.Contains(line, "=") {
			rule := f.ParseAdvRule(line, action)
			if rule == nil {
				flush()
				_, _ = fmt.Fprintln(af, orig)
				continue
			}
			// Match family-aware: the address-less "port-only deny" form parses to
			// Source="" for both families, so a bare EqualBase would let an IPv4 line
			// stand in for its IPv6 twin. EqualForDedup/EqualForRemoval fold in the
			// family coverage the add and remove paths respectively need.
			var famMatch bool
			if remove {
				famMatch = rule.EqualForRemoval(&match, true)
			} else {
				famMatch = rule.EqualForDedup(&match, true)
			}
			if famMatch {
				exists = true
				if !remove {
					flush()
					_, _ = fmt.Fprintln(af, orig)
				} else {
					drop()
					f.ConfigChanged = true
				}
			} else {
				flush()
				_, _ = fmt.Fprintln(af, orig)
			}
		} else {
			// Try to parse IP.
			fam, ok := csfAddrFamily(line)
			if !ok {
				flush()
				_, _ = fmt.Fprintln(af, orig)
				continue
			}

			// A plain IP line is one bidirectional DirAny rule; match the target
			// against it in the inbound frame (canonicalMatch), so a DirAny or a
			// concrete-direction input/output target that names this host lines up.
			plainRule := &Rule{
				Direction: DirAny,
				Family:    fam,
				Source:    line,
				Action:    action,
			}
			if plainRule.EqualBase(match.canonicalMatch(), false) {
				exists = true
				if !remove {
					flush()
					_, _ = fmt.Fprintln(af, orig)
				} else {
					drop()
					f.ConfigChanged = true
				}
			} else {
				flush()
				_, _ = fmt.Fprintln(af, orig)
			}
		}
	}
	// Write any trailing comments that followed the last rule.
	flush()

	// If not exists and not remove, try adding the rule.
	if !exists && !remove {
		writeComment := func() {
			if c := combineComment(f.rulePrefix, r.Comment); c != "" {
				_, _ = fmt.Fprintln(af, "# "+c)
			}
		}
		hasIP := r.Source != "" || r.Destination != ""
		switch {
		case hasIP && (r.HasPorts() || r.HasSourcePorts()):
			// A port rule with an address is an advanced rule.
			line, err := f.MarshalAdvRule(r)
			if err != nil {
				_ = fd.Close()
				return err
			}
			f.ConfigChanged = true
			writeComment()
			_, _ = fmt.Fprintln(af, line)
		case hasIP:
			// A bare all-protocol host allow/deny: a single address matching every
			// protocol. apf's trust files hold no other portless address shape — a
			// concrete-protocol host or a source+destination pair — so AddRule diverts
			// those to the raw-iptables hook (hostNeedsHook) and never reaches here
			// with one. A direct caller of this exported writer that supplies such a
			// shape gets a best-effort single-address write, not a guard.
			f.ConfigChanged = true
			writeComment()
			if r.Source != "" {
				_, _ = fmt.Fprintln(af, r.Source)
			} else {
				_, _ = fmt.Fprintln(af, r.Destination)
			}
		case action != Accept && r.HasPorts():
			// A port-only deny is written as an advanced rule against any address,
			// which apf requires in the field position. apf's port field holds a
			// single port or underscore range only; a multi-port list has no advanced-
			// rule form, so AddRule diverts it to the hook (needsHook) and this
			// branch only sees a single port/range. A direct caller supplying a list
			// gets a best-effort single-port write.
			specs := r.PortSpecs()
			// apf requires an address in the field position, so a port-only deny
			// uses the "any" network as a placeholder. That literal is family-
			// specific (0.0.0.0/0 vs ::/0) and read back with its family, so emit
			// the placeholder matching the rule's family. A family-neutral rule has
			// no single literal, so cover both families — mergeFamilies collapses
			// the v4/v6 pair back to FamilyAny on read, keeping the rule both
			// readable and removable rather than silently becoming IPv4-only.
			writeAny := func(placeholder string) {
				var tokens []string
				if r.Proto != ProtocolAny {
					tokens = append(tokens, r.Proto.String())
				}
				if r.IsOutput() {
					tokens = append(tokens, "out")
				} else {
					tokens = append(tokens, "in")
				}
				tokens = append(tokens, "d="+f.portToken(specs[0]))
				if r.IsOutput() {
					tokens = append(tokens, "d="+placeholder)
				} else {
					tokens = append(tokens, "s="+placeholder)
				}
				writeComment()
				_, _ = fmt.Fprintln(af, strings.Join(tokens, ":"))
			}
			switch r.impliedFamily() {
			case IPv6:
				writeAny("[::/0]")
			case IPv4:
				writeAny("0.0.0.0/0")
			default:
				writeAny("0.0.0.0/0")
				writeAny("[::/0]")
			}
			f.ConfigChanged = true
		}
	}

	_ = fd.Close()

	// A read error means the rewritten file is truncated; discard it.
	if serr := scanner.Err(); serr != nil {
		return serr
	}

	// Move new file into place, preserving mode and ownership.
	return af.Commit()
}

// removePlainHost drops the bidirectional plain allow_hosts/deny_hosts line backing
// the DirAny rule e, choosing the list by the rule's action.
// isConfRule reports whether a rule is managed in conf.apf: an address-less
// accept rule of ports (TCP/UDP lists) or ICMP/ICMPv6 types (a nil type is the
// "all" wildcard).
func (f *APF) isConfRule(r *Rule) bool {
	if r.Source != "" || r.Destination != "" || r.Action != Accept {
		return false
	}
	return r.HasPorts() || r.Proto == ICMP || r.Proto == ICMPv6
}

// isConnLimitRule reports whether a rule maps onto conf.apf's
// IG_TCP_CLIMIT/IG_UDP_CLIMIT: a per-source cap on concurrent inbound
// connections to a single tcp/udp port (or range) with no address, rejecting the
// excess.
// nativeICMPv6 reports whether an ICMPv6 rule can be carried by apf's native
// IG_ICMPV6_TYPES/EG_ICMPV6_TYPES lists (an address-less accept, optionally typed)
// and so belongs in conf.apf rather than the raw-iptables hook. The shared
// ruleNeedsHook diverts every ICMPv6 rule to the hook — correct for csf, which has
// no native v6 type list — so apf overrides that only for the rules its config can
// actually express, leaving an ICMPv6 rule that also needs state/interface/log/
// rate matching (which conf.apf cannot carry) on the hook path.
func (f *APF) nativeICMPv6(r *Rule) bool {
	return r.Proto == ICMPv6 && r.State == 0 && r.InInterface == "" && r.OutInterface == "" &&
		!r.Log && r.RateLimit == nil && f.isConfRule(r)
}

// ipv6Unavailable reports whether adding r would silently write something
// apf itself never enforces: a bare IPv6 host in allow_hosts.rules/
// deny_hosts.rules, or a native ICMPv6 type, are both no-op'd by apf's own
// shell logic when conf.apf's USE_IPV6 is not "1". A rule diverted to the
// raw-iptables hook is unaffected — the hook runs ip6tables directly, outside
// apf's USE_IPV6-gated logic — so this only applies to the two native paths.
// ipv6Unavailable reports whether adding r would silently write something
// apf itself never enforces: a bare IPv6 host in allow_hosts.rules/
// deny_hosts.rules, or a native ICMPv6 type, are both no-op'd by apf's own
// shell logic when conf.apf's USE_IPV6 is not "1". A rule diverted to the
// raw-iptables hook is unaffected — the hook runs ip6tables directly, outside
// apf's USE_IPV6-gated logic — so this only applies to the two native paths.
func (f *APF) ipv6Unavailable(r *Rule) bool {
	if f.ipv6Enabled {
		return false
	}
	if f.nativeICMPv6(r) {
		return true
	}
	return r.impliedFamily() == IPv6 && (r.Source != "" || r.Destination != "")
}

// barePortAccept reports whether a rule is an address-less tcp/udp port accept —
// the shape apf stores either in a dual-stack conf.apf CPORTS list (a FamilyAny
// port) or, per family, through the raw-iptables hook (a single-family port, or a
// FamilyAny that GetRules merged back from a v4+v6 hook pair). Both the add-time hook
// decision (dualStackPortNeedsHook) and the remove-time split/clear
// (removeDualStackPort) build on it.
// barePortAccept reports whether a rule is an address-less tcp/udp port accept —
// the shape apf stores either in a dual-stack conf.apf CPORTS list (a FamilyAny
// port) or, per family, through the raw-iptables hook (a single-family port, or a
// FamilyAny that GetRules merged back from a v4+v6 hook pair). Both the add-time hook
// decision (dualStackPortNeedsHook) and the remove-time split/clear
// (removeDualStackPort) build on it.
func (f *APF) barePortAccept(r *Rule) bool {
	return (r.Proto == TCP || r.Proto == UDP) && r.HasPorts() &&
		r.Source == "" && r.Destination == "" && r.Action == Accept
}

// dualStackPortNeedsHook reports whether a bare tcp/udp port accept pinned to a
// single family must be injected through the hook. apf's IG_*_CPORTS/EG_*_CPORTS
// lists are dual-stack — one list applied to both the ip and ip6 tables — so they
// express only a FamilyAny port (unlike csf, whose TCP_IN/TCP6_IN split the
// families). A single-family one is written per-family through the hook instead,
// whose iptables (or ip6tables) rule carries just that family; removing one family
// of a FamilyAny CPORTS entry splits it (see removeDualStackPort). ICMP keeps its
// concrete family (its type lists are per-family), so this gates on a port match.
// dualStackPortNeedsHook reports whether a bare tcp/udp port accept pinned to a
// single family must be injected through the hook. apf's IG_*_CPORTS/EG_*_CPORTS
// lists are dual-stack — one list applied to both the ip and ip6 tables — so they
// express only a FamilyAny port (unlike csf, whose TCP_IN/TCP6_IN split the
// families). A single-family one is written per-family through the hook instead,
// whose iptables (or ip6tables) rule carries just that family; removing one family
// of a FamilyAny CPORTS entry splits it (see removeDualStackPort). ICMP keeps its
// concrete family (its type lists are per-family), so this gates on a port match.
func (f *APF) dualStackPortNeedsHook(r *Rule) bool {
	return f.barePortAccept(r) && r.impliedFamily() != FamilyAny
}

// needsHook reports whether a rule must be injected through the apf pre-hook as a
// raw iptables rule because apf's native config cannot express it. It is the single
// gate between the hook path and apf's config files: everything it rejects (returns
// true) is written to the hook, everything it accepts (returns false) maps onto
// conf.apf or the allow_hosts/deny_hosts trust files. The shared shapes
// (ruleNeedsHook, bareHostOneWay, hostNeedsHook) and the two apf shapes RemoveRule
// reuses to route a split (dualStackPortNeedsHook, nativeICMPv6) keep their own
// predicates; the apf-only, single-use port/source-port/connlimit/icmp tests are
// inlined here as their sole caller.
// needsHook reports whether a rule must be injected through the apf pre-hook as a
// raw iptables rule because apf's native config cannot express it. It is the single
// gate between the hook path and apf's config files: everything it rejects (returns
// true) is written to the hook, everything it accepts (returns false) maps onto
// conf.apf or the allow_hosts/deny_hosts trust files. The shared shapes
// (ruleNeedsHook, bareHostOneWay, hostNeedsHook) and the two apf shapes RemoveRule
// reuses to route a split (dualStackPortNeedsHook, nativeICMPv6) keep their own
// predicates; the apf-only, single-use port/source-port/connlimit/icmp tests are
// inlined here as their sole caller.
func (f *APF) needsHook(r *Rule) bool {
	// Features apf's native config cannot model — connection state, per-rule
	// interface, logging, rate limiting, forward-chain routing, ICMPv6, or a
	// transport apf does not carry (see ruleNeedsHook) — go to the hook. An ICMPv6
	// type rule is the exception: apf carries it natively in IG_ICMPV6_TYPES/
	// EG_ICMPV6_TYPES (see nativeICMPv6), so it stays out.
	if ruleNeedsHook(r) && !f.nativeICMPv6(r) {
		return true
	}
	// A one-way bare host has no trust-file form (a plain line is bidirectional, an
	// advanced rule needs a port), and a concrete-protocol host or a source+
	// destination pair likewise has none (see hostNeedsHook); all go to the hook.
	if bareHostOneWay(r) || hostNeedsHook(r) {
		return true
	}
	// A multi-port tcp/udp list apf's config cannot carry: its advanced rule holds a
	// single port or one underscore range, and the only native multi-port shape is an
	// address-less accept (isConfRule, carried by the IG_*_CPORTS comma lists);
	// every other list goes to the hook's iptables multiport match.
	if (r.Proto == TCP || r.Proto == UDP) &&
		(len(r.PortSpecs()) > 1 || len(r.SourcePortSpecs()) > 1) && !f.isConfRule(r) {
		return true
	}
	// A source-port match with no address has no advanced-rule form (advanced rules
	// require an address); iptables matches --sport directly, so it goes to the hook.
	if r.HasSourcePorts() && r.Source == "" && r.Destination == "" &&
		(r.Proto == TCP || r.Proto == UDP) {
		return true
	}
	// A connection limit conf.apf's IG_*_CLIMIT cannot express — anything but a
	// per-source cap on a single address-less inbound tcp/udp port rejecting the
	// excess (isConnLimitRule) — goes to the hook's `-m connlimit` match.
	if r.ConnLimit != nil && !f.isConnLimitRule(r) {
		return true
	}
	// An ICMPv4 rule apf's IG_ICMP_TYPES/EG_ICMP_TYPES lists cannot express (they
	// match a type on the whole zone, so only an address-less accept is native, and
	// one carrying an address or a non-accept action is not) goes to the hook's
	// `iptables -p icmp` match. ICMPv6 is routed by ruleNeedsHook above, not here.
	if r.Proto == ICMP && !f.isConfRule(r) {
		return true
	}
	// A bare protocol match with no address and no port has no native apf construct —
	// the trust files key on an address and conf.apf's lists on a port or icmp type —
	// but iptables expresses it directly, so it goes to the hook (see
	// bareProtoNeedsHook). A native address-less ICMP/ICMPv6 accept is excluded there;
	// connection limits and every other addressed/ported shape are routed above.
	if bareProtoNeedsHook(r) {
		return true
	}
	// A single-family bare tcp/udp port accept: apf's CPORTS lists are dual-stack, so
	// only a FamilyAny port is native; a single-family one is written per-family
	// through the hook (see dualStackPortNeedsHook, which RemoveRule also uses).
	return f.dualStackPortNeedsHook(r)
}

// EditIPList adds or removes a rule in an apf allow_hosts/deny_hosts file, rewriting it in place.
// addRule is AddRule's implementation, with the IPv6 gate optional. Restore
// passes enforceIPv6Gate false so it can reproduce a Backup snapshot's exact
// prior state, including inert entries the gate would reject as fresh no-op
// writes.
func (f *APF) addRule(ctx context.Context, zoneName string, r *Rule, enforceIPv6Gate bool) error {
	// A DirAny rule maps to a single native construct only as a bare-host plain line;
	// every other DirAny shape fans out into a concrete input rule plus its swapped
	// output rule, each routed independently (a half may itself need the hook).
	if r.Direction == DirAny && !dirAnyPlainLine(r) {
		for _, sub := range expandDirections(r) {
			if err := f.addRule(ctx, zoneName, sub, enforceIPv6Gate); err != nil {
				return err
			}
		}
		return nil
	}

	// Any shape apf's native config cannot express (a stateful/interface/logged/
	// rate-limited rule, a one-way or concrete-protocol host, a source+destination
	// pair, a multi-port list, an address-less source-port match, a non-native
	// connection limit, a non-native ICMPv4 rule, or a single-family port accept) is
	// injected as a raw iptables rule through the apf pre-hook. See needsHook for
	// each clause; everything past this gate maps onto apf's own config files.
	if f.needsHook(r) {
		changed, err := f.hook().edit(r, false)
		f.ConfigChanged = f.ConfigChanged || changed
		return err
	}
	if enforceIPv6Gate && f.ipv6Unavailable(r) {
		return fmt.Errorf("apf's IPv6 handling is disabled (conf.apf USE_IPV6 is not \"1\"): %w", ErrUnsupported)
	}
	if err := iptablesRuleValid(r); err != nil {
		return fmt.Errorf("%v: %w", err, ErrUnsupported)
	}

	// A native connection-limit rule maps onto conf.apf's IG_*_CLIMIT lists (a
	// non-native one was diverted to the hook above by needsHook).
	if r.ConnLimit != nil {
		return f.EditConf(ctx, r, false)
	}

	// Address-less accept rules (dual-stack port lists, icmp types) live in conf.apf.
	if f.isConfRule(r) {
		return f.EditConf(ctx, r, false)
	}

	// Otherwise edit allow_hosts.rules for accepts, deny_hosts.rules for denies. A
	// bare protocol match (no address, no port) never reaches here — needsHook routed
	// it to the pre-hook above — so every rule at this point carries an address.
	if r.Action == Accept {
		return f.EditIPList(ctx, APFAllow, Accept, r, false)
	}
	// A deny_hosts entry carries no action of its own: apf applies conf.apf's ALL_STOP
	// action to a bare-address entry, or its TCP_STOP/UDP_STOP action to a tcp/udp
	// advanced one (see stopKey). A deny whose action matches that is written natively;
	// one that differs has no native form, so it is injected through the pre-hook
	// instead, whose iptables rule carries the exact action. A DirAny bare-host deny is
	// expanded to its two concrete directions first, since each hook line is one-way.
	denyAction := f.denyActionFor(r.Proto)
	if r.Action != denyAction {
		for _, sub := range expandDirections(r) {
			changed, err := f.hook().edit(sub, false)
			f.ConfigChanged = f.ConfigChanged || changed
			if err != nil {
				return err
			}
		}
		return nil
	}
	return f.EditIPList(ctx, APFDeny, denyAction, r, false)
}

// AddRule adds a rule to apf, routing it to conf.apf, the allow/deny lists, or the pre-hook.
// AddRule adds a rule to apf, routing it to conf.apf, the allow/deny lists, or the pre-hook.
func (f *APF) AddRule(ctx context.Context, zoneName string, r *Rule) error {
	return f.addRule(ctx, zoneName, r, true)
}

// RemoveRule removes a rule from apf, routing it to the config file or pre-hook that holds it.
// InsertRule is unsupported: APF organizes rules in config files, not an ordered list.
func (f *APF) InsertRule(ctx context.Context, zoneName string, position int, r *Rule) error {
	return unsupportedOrdering(f.Type())
}

// InsertNATRule is unsupported: APF stores NAT in a config file it applies as a
// whole, with no explicit ordering.
// MoveRule is unsupported for the same reason as InsertRule.
func (f *APF) MoveRule(ctx context.Context, zoneName string, r *Rule, position int) error {
	return unsupportedOrdering(f.Type())
}

// Capabilities reports the firewall features apf supports.
// removePlainHost drops the bidirectional plain allow_hosts/deny_hosts line backing
// the DirAny rule e, choosing the list by the rule's action.
func (f *APF) removePlainHost(ctx context.Context, e *Rule) error {
	if e.Action == Accept {
		return f.EditIPList(ctx, APFAllow, Accept, e, true)
	}
	return f.EditIPList(ctx, APFDeny, f.denyActionFor(e.Proto), e, true)
}

// removeDualStackPort removes a single-family bare tcp/udp port accept. Such a rule
// is stored either as its own per-family hook rule or as one family of a dual-stack
// conf.apf CPORTS entry (a FamilyAny port). Read the CPORTS list the port would live
// in — not the merged rule view, which cannot tell a genuine CPORTS entry from a
// pair of single-family hook rules — and split it when present: drop the dual-stack
// entry and re-add the surviving opposite family as a hook rule, so the untargeted
// family keeps its coverage. Otherwise the rule is a per-family hook rule.
// removeBareHostOneWay removes a one-way bare-address host rule. Such a rule is
// stored either as its own hook rule or as one direction of a bidirectional plain
// allow_hosts/deny_hosts line (a DirAny rule). When a matching plain line exists,
// split it: drop the line and re-add the surviving opposite direction as a hook rule
// so the untargeted direction keeps its coverage.
func (f *APF) removeBareHostOneWay(ctx context.Context, zoneName string, r *Rule) error {
	existing, err := f.GetRules(ctx, zoneName)
	if err != nil {
		return err
	}
	for _, e := range existing {
		if !e.IsAny() || !e.EqualForRemoval(r, true) {
			continue
		}
		// The host is stored as a bidirectional plain line; drop it, then re-add the
		// surviving direction as a hook rule.
		if err := f.removePlainHost(ctx, e); err != nil {
			return err
		}
		if s := splitDualRowDirection(e, r); s != nil {
			changed, err := f.hook().edit(s, false)
			f.ConfigChanged = f.ConfigChanged || changed
			return err
		}
		return nil
	}
	// Not stored as a plain line; remove the one-way hook rule.
	changed, err := f.hook().edit(r, true)
	f.ConfigChanged = f.ConfigChanged || changed
	return err
}

// addRule is AddRule's implementation, with the IPv6 gate optional. Restore
// passes enforceIPv6Gate false so it can reproduce a Backup snapshot's exact
// prior state, including inert entries the gate would reject as fresh no-op
// writes.
// cPortsKey returns the conf.apf CPORTS list a tcp/udp port rule of the given
// direction lives in, or "" for a protocol with no such list.
func (f *APF) cPortsKey(proto Protocol, output bool) string {
	dir := "IG"
	if output {
		dir = "EG"
	}
	switch proto {
	case TCP:
		return dir + "_TCP_CPORTS"
	case UDP:
		return dir + "_UDP_CPORTS"
	}
	return ""
}

// natFile returns the routing file a NAT rule belongs in: source NAT is
// applied in POSTROUTING (postroute.rules), destination NAT in PREROUTING
// (preroute.rules).
// removeDualStackPort removes a single-family bare tcp/udp port accept. Such a rule
// is stored either as its own per-family hook rule or as one family of a dual-stack
// conf.apf CPORTS entry (a FamilyAny port). Read the CPORTS list the port would live
// in — not the merged rule view, which cannot tell a genuine CPORTS entry from a
// pair of single-family hook rules — and split it when present: drop the dual-stack
// entry and re-add the surviving opposite family as a hook rule, so the untargeted
// family keeps its coverage. Otherwise the rule is a per-family hook rule.
func (f *APF) removeDualStackPort(ctx context.Context, r *Rule) error {
	val, err := readConfValue(APFConf, f.cPortsKey(r.Proto, r.IsOutput()))
	if err != nil {
		return err
	}
	inCPorts := false
	for _, e := range f.ParsePorts(val, r.Proto, r.IsOutput()) {
		if e.EqualForRemoval(r, true) {
			inCPorts = true
			break
		}
	}
	if inCPorts {
		// Drop the dual-stack CPORTS entry (family-agnostic), then re-add the
		// surviving opposite family through the hook.
		if err := f.EditConf(ctx, r, true); err != nil {
			return err
		}
		surviving := *r
		surviving.Family = oppositeFamily(r.impliedFamily())
		changed, err := f.hook().edit(&surviving, false)
		f.ConfigChanged = f.ConfigChanged || changed
		return err
	}
	// Not stored in CPORTS; remove the per-family hook rule.
	changed, err := f.hook().edit(r, true)
	f.ConfigChanged = f.ConfigChanged || changed
	return err
}

// removeFamilyAnyPort removes a FamilyAny address-less bare tcp/udp port accept. Its
// two families live in a dual-stack conf.apf CPORTS entry (a genuine FamilyAny add),
// in a v4+v6 pair in the hook (two separate concrete-family adds that GetRules merged
// back into one FamilyAny rule), or split across both. The merged read cannot tell
// which, so remove the rule from both backings — EditConf drops it from the CPORTS
// list and the hook edit drops both per-family rows, and each no-ops when the rule is
// absent — clearing the whole merged rule wherever it lives. Unlike the single-family
// removeDualStackPort there is no untargeted family to preserve, so nothing is re-added.
// removeFamilyAnyPort removes a FamilyAny address-less bare tcp/udp port accept. Its
// two families live in a dual-stack conf.apf CPORTS entry (a genuine FamilyAny add),
// in a v4+v6 pair in the hook (two separate concrete-family adds that GetRules merged
// back into one FamilyAny rule), or split across both. The merged read cannot tell
// which, so remove the rule from both backings — EditConf drops it from the CPORTS
// list and the hook edit drops both per-family rows, and each no-ops when the rule is
// absent — clearing the whole merged rule wherever it lives. Unlike the single-family
// removeDualStackPort there is no untargeted family to preserve, so nothing is re-added.
func (f *APF) removeFamilyAnyPort(ctx context.Context, r *Rule) error {
	if err := f.EditConf(ctx, r, true); err != nil {
		return err
	}
	changed, err := f.hook().edit(r, true)
	f.ConfigChanged = f.ConfigChanged || changed
	return err
}

// GetRules returns the current filter rules read from conf.apf, the allow/deny lists, and the pre-hook.
// RemoveRule removes a rule from apf, routing it to the config file or pre-hook that holds it.
func (f *APF) RemoveRule(ctx context.Context, zoneName string, r *Rule) error {
	// A non-plain-line DirAny target fans out into its two concrete-direction rules,
	// mirroring addRule, so each half is removed from wherever it was written.
	if r.Direction == DirAny && !dirAnyPlainLine(r) {
		for _, sub := range expandDirections(r) {
			if err := f.RemoveRule(ctx, zoneName, sub); err != nil {
				return err
			}
		}
		return nil
	}

	// Clear any hook copy of the rule first, no matter how apf stores it. A rule apf
	// carries only in the hook (stateful/interface/logged/rate-limited/icmpv6/
	// hook-only-proto) lives nowhere else, so this is its entire removal; a natively-
	// expressible rule may still have a stray hook copy — the library's own
	// differing-action deny (see AddRule) or a hand-added duplicate for a shape apf can
	// also express natively — that must be cleared before the native entry below. DirAny
	// is expanded so both one-way hook lines are matched; a rule with no hook copy makes
	// this a harmless no-op.
	var err error
	for _, sub := range expandDirections(r) {
		changed, e := f.hook().edit(sub, true)
		f.ConfigChanged = f.ConfigChanged || changed
		if e != nil {
			err = e
			break
		}
	}
	// A rule apf carries only in the hook has no native entry to fall through to, so
	// return once its hook copy is cleared (or on any hook error). Returning here also
	// keeps such a rule out of the split scans below, whose plain-line/CPORTS checks
	// could wrongly split an unrelated coexisting native entry. A native ICMPv6 type
	// rule lives in conf.apf, not the hook, so it is excluded and routed there below.
	if (ruleNeedsHook(r) && !f.nativeICMPv6(r)) || err != nil {
		return err
	}
	// A one-way bare host rule is stored either as its own hook rule or as one
	// direction of a bidirectional plain line; removing it may need to split the
	// plain line (see removeBareHostOneWay).
	if bareHostOneWay(r) {
		return f.removeBareHostOneWay(ctx, zoneName, r)
	}
	// A single-family bare tcp/udp port accept is stored either as its own per-family
	// hook rule or as one family of a dual-stack CPORTS entry; removing it may need to
	// split that entry (see removeDualStackPort).
	if f.dualStackPortNeedsHook(r) {
		return f.removeDualStackPort(ctx, r)
	}
	// A FamilyAny bare tcp/udp port accept is stored in a dual-stack CPORTS entry, in a
	// v4+v6 hook pair (separate concrete-family adds GetRules merged back), or split
	// across both; removeFamilyAnyPort clears it from every backing (see there).
	if f.barePortAccept(r) {
		return f.removeFamilyAnyPort(ctx, r)
	}
	// Every other shape apf's native config cannot express (see needsHook) has already
	// had its hook copy cleared above and has no native entry to split, so it is done.
	if f.needsHook(r) {
		return nil
	}
	if err := iptablesRuleValid(r); err != nil {
		return fmt.Errorf("%v: %w", err, ErrUnsupported)
	}

	// A native connection-limit rule maps onto conf.apf's IG_*_CLIMIT lists.
	if r.ConnLimit != nil {
		return f.EditConf(ctx, r, true)
	}

	// Address-less accept rules (dual-stack port lists, icmp types) live in conf.apf.
	if f.isConfRule(r) {
		return f.EditConf(ctx, r, true)
	}

	// Otherwise edit allow_hosts.rules for accepts, deny_hosts.rules for denies.
	if r.Action == Accept {
		return f.EditIPList(ctx, APFAllow, Accept, r, true)
	}
	return f.EditIPList(ctx, APFDeny, f.denyActionFor(r.Proto), r, true)
}

// Backup captures the current filter and NAT rules managed by this backend.
// parseNATLine decodes a raw iptables nat command line back into a NATRule,
// reporting whether the line is one this backend recognizes.
func (f *APF) parseNATLine(line string) (*NATRule, bool) {
	line = strings.TrimSpace(line)
	var fam Family
	var rest string
	switch {
	case strings.HasPrefix(line, "iptables -t nat "):
		fam, rest = IPv4, strings.TrimPrefix(line, "iptables -t nat ")
	case strings.HasPrefix(line, "ip6tables -t nat "):
		fam, rest = IPv6, strings.TrimPrefix(line, "ip6tables -t nat ")
	default:
		return nil, false
	}
	ipt := &IPTables{rulePrefix: f.rulePrefix}
	r, err := ipt.UnmarshalNATRule(rest, fam)
	if err != nil {
		return nil, false
	}
	return r, true
}

// parseNATFile reads a routing-rules file and returns the NAT rules it holds.
// parseNATFile reads a routing-rules file and returns the NAT rules it holds.
func (f *APF) parseNATFile(path string) ([]*NATRule, error) {
	fd, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}
	defer func() { _ = fd.Close() }()

	var rules []*NATRule
	scanner := bufio.NewScanner(fd)
	for scanner.Scan() {
		line := scanner.Text()
		if ci := strings.IndexByte(line, '#'); ci >= 0 {
			line = line[:ci]
		}
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		if r, ok := f.parseNATLine(line); ok {
			rules = append(rules, r)
		}
	}
	if err := scanner.Err(); err != nil {
		return nil, err
	}
	return rules, nil
}

// GetNATRules returns the NAT rules held in apf's preroute and postroute routing files.
// GetNATRules returns the NAT rules held in apf's preroute and postroute routing files.
func (f *APF) GetNATRules(ctx context.Context, zoneName string) ([]*NATRule, error) {
	var rules []*NATRule
	for _, path := range []string{APFPreroute, APFPostroute} {
		parsed, err := f.parseNATFile(path)
		if err != nil {
			return nil, err
		}
		rules = append(rules, parsed...)
	}
	// APF's routing files hold raw iptables nat commands, so a rule this library
	// added carries the configured prefix in its -m comment tag and UnmarshalNATRule
	// derives HasPrefix from it (an empty prefix writes no tag, so HasPrefix is
	// false; a rule hand-added without the tag likewise reports false).
	merged := mergeNATFamilies(rules)
	return merged, nil
}

// editNATFile adds or removes a NAT rule's command line(s) in a routing file.
// A family-agnostic rule occupies one line per family; both are added or dropped
// together. It records whether a reload is needed.
// natFamilies lists the address families a NAT rule is written for: a rule
// pinned to a family touches only that command; a family-agnostic rule (e.g. a
// portless masquerade) is written for both v4 and v6.
func (f *APF) natFamilies(r *NATRule) []Family {
	switch r.impliedFamily() {
	case IPv4:
		return []Family{IPv4}
	case IPv6:
		return []Family{IPv6}
	default:
		return []Family{IPv4, IPv6}
	}
}

// natLine encodes a NAT rule as a raw iptables/ip6tables nat-table command
// line for the given family, the form apf's shell-sourced routing files expect.
// natFile returns the routing file a NAT rule belongs in: source NAT is
// applied in POSTROUTING (postroute.rules), destination NAT in PREROUTING
// (preroute.rules).
func (f *APF) natFile(r *NATRule) string {
	if r.Kind.isSource() {
		return APFPostroute
	}
	return APFPreroute
}

// natCommand returns the iptables command name for a family.
// natCommand returns the iptables command name for a family.
func (f *APF) natCommand(fam Family) string {
	if fam == IPv6 {
		return "ip6tables"
	}
	return "iptables"
}

// natFamilies lists the address families a NAT rule is written for: a rule
// pinned to a family touches only that command; a family-agnostic rule (e.g. a
// portless masquerade) is written for both v4 and v6.
// natLine encodes a NAT rule as a raw iptables/ip6tables nat-table command
// line for the given family, the form apf's shell-sourced routing files expect.
func (f *APF) natLine(r *NATRule, fam Family) (string, error) {
	ipt := &IPTables{rulePrefix: f.rulePrefix}
	rc := *r
	rc.Family = fam
	spec, err := ipt.MarshalNATRule(&rc)
	if err != nil {
		return "", err
	}
	return f.natCommand(fam) + " -t nat " + spec, nil
}

// parseNATLine decodes a raw iptables nat command line back into a NATRule,
// reporting whether the line is one this backend recognizes.
// editNATFile adds or removes a NAT rule's command line(s) in a routing file.
// A family-agnostic rule occupies one line per family; both are added or dropped
// together. It records whether a reload is needed.
func (f *APF) editNATFile(r *NATRule, remove bool) error {
	path := f.natFile(r)

	// The line(s) this rule contributes, one per family it targets.
	want := make(map[string]bool)
	for _, fam := range f.natFamilies(r) {
		line, err := f.natLine(r, fam)
		if err != nil {
			return err
		}
		want[line] = true
	}

	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			if remove {
				return nil
			}
			data = nil
		} else {
			return err
		}
	}
	lines := strings.Split(string(data), "\n")
	// Drop the trailing empty element left by a final newline so repeated adds do
	// not accumulate blank lines.
	if len(lines) > 0 && lines[len(lines)-1] == "" {
		lines = lines[:len(lines)-1]
	}

	out := make([]string, 0, len(lines)+len(want))
	present := make(map[string]bool)
	changed := false
	for _, raw := range lines {
		body := raw
		if ci := strings.IndexByte(body, '#'); ci >= 0 {
			body = body[:ci]
		}
		body = strings.TrimSpace(body)
		// Match either the exact line we would write or an equivalent NAT rule. On a
		// match, record which of our want-lines this existing line satisfies so the
		// add path below does not append a duplicate: an exact match satisfies its own
		// text; a fuzzy (equivalent) match satisfies the want-line for the same family.
		matched := false
		satisfied := ""
		if want[body] {
			matched, satisfied = true, body
		} else if body != "" {
			// The fuzzy fallback (an equivalent line whose text differs from ours)
			// must stay family-aware (EqualForRemoval): a family-agnostic rule fans
			// into a v4 and a v6 line in the same direction file, so without the gate
			// a family-scoped removal would also drop the opposite family's twin.
			if existing, ok := f.parseNATLine(body); ok && existing.EqualForRemoval(r) {
				matched = true
				// The equivalent want-line is the one for this existing line's family;
				// mark it satisfied so its duplicate is not appended below. Recompute it
				// (rather than reuse body) since body is the existing spelling, not ours.
				if line, lerr := f.natLine(r, existing.impliedFamily()); lerr == nil {
					satisfied = line
				}
			}
		}
		if matched {
			if remove {
				changed = true
				continue
			}
			if satisfied != "" {
				present[satisfied] = true
			}
		}
		out = append(out, raw)
	}

	if remove {
		if !changed {
			return nil
		}
	} else {
		added := false
		for line := range want {
			if !present[line] {
				out = append(out, line)
				added = true
			}
		}
		if !added {
			return nil
		}
	}

	content := strings.Join(out, "\n")
	if !strings.HasSuffix(content, "\n") {
		content += "\n"
	}
	if err := writeConfigFile(path, []byte(content), 0600); err != nil {
		return err
	}
	f.ConfigChanged = true
	return nil
}

// AddNATRule adds a NAT rule to apf's preroute or postroute routing file.
// AddNATRule adds a NAT rule to apf's preroute or postroute routing file.
func (f *APF) AddNATRule(ctx context.Context, zoneName string, r *NATRule) error {
	if err := r.validate(); err != nil {
		return err
	}
	return f.editNATFile(r, false)
}

// RemoveNATRule removes a NAT rule from apf's preroute or postroute routing file.
// InsertNATRule is unsupported: APF stores NAT in a config file it applies as a
// whole, with no explicit ordering.
func (f *APF) InsertNATRule(ctx context.Context, zoneName string, position int, r *NATRule) error {
	return unsupportedOrdering(f.Type())
}

// MoveRule is unsupported for the same reason as InsertRule.
// RemoveNATRule removes a NAT rule from apf's preroute or postroute routing file.
func (f *APF) RemoveNATRule(ctx context.Context, zoneName string, r *NATRule) error {
	if err := r.validate(); err != nil {
		return err
	}
	return f.editNATFile(r, true)
}

// isConfRule reports whether a rule is managed in conf.apf: an address-less
// accept rule of ports (TCP/UDP lists) or ICMP/ICMPv6 types (a nil type is the
// "all" wildcard).
// Backup captures the current filter and NAT rules managed by this backend.
func (f *APF) Backup(ctx context.Context, zoneName string) (*Backup, error) {
	rules, err := f.GetRules(ctx, zoneName)
	if err != nil {
		return nil, err
	}
	natRules, err := f.GetNATRules(ctx, zoneName)
	if err != nil {
		return nil, err
	}
	// Backup captures the full filter and NAT rule state; Restore removes the
	// current rules and re-adds these, so every rule read is preserved.
	return &Backup{Rules: rules, NATRules: natRules}, nil
}

// Restore replaces the managed rules with the contents of a Backup.
// Restore replaces the managed rules with the contents of a Backup.
func (f *APF) Restore(ctx context.Context, zoneName string, backup *Backup) error {
	if backup == nil {
		return fmt.Errorf("backup cannot be nil")
	}

	// Remove existing rules.
	existing, err := f.GetRules(ctx, zoneName)
	if err != nil {
		return err
	}
	for _, r := range existing {
		if err := f.RemoveRule(ctx, zoneName, r); err != nil {
			return err
		}
	}
	existingNAT, err := f.GetNATRules(ctx, zoneName)
	if err != nil {
		return err
	}
	for _, r := range existingNAT {
		if err := f.RemoveNATRule(ctx, zoneName, r); err != nil {
			return err
		}
	}

	// Re-add rules from backup.
	for _, r := range backup.Rules {
		if err := f.addRule(ctx, zoneName, r, false); err != nil {
			return err
		}
	}
	for _, r := range backup.NATRules {
		if err := f.AddNATRule(ctx, zoneName, r); err != nil {
			return err
		}
	}
	return nil
}

// Reload restarts apf to apply config changes, but only when a mutation changed its files.
// GetDefaultPolicy is unsupported: apf has no managed default-policy control.
func (f *APF) GetDefaultPolicy(ctx context.Context, zoneName string) (*DefaultPolicy, error) {
	return nil, unsupportedPolicy(f.Type())
}

// SetDefaultPolicy is unsupported: apf has no managed default-policy control.
// SetDefaultPolicy is unsupported: apf has no managed default-policy control.
func (f *APF) SetDefaultPolicy(ctx context.Context, zoneName string, policy *DefaultPolicy) error {
	return unsupportedPolicy(f.Type())
}

// GetAddressSets is unsupported: apf has no address-set support.
// GetAddressSets is unsupported: apf has no address-set support.
func (f *APF) GetAddressSets(ctx context.Context) ([]*AddressSet, error) {
	return nil, unsupportedSet(f.Type())
}

// GetAddressSet is unsupported: apf has no address-set support.
// GetAddressSet is unsupported: apf has no address-set support.
func (f *APF) GetAddressSet(ctx context.Context, name string) (*AddressSet, error) {
	return nil, unsupportedSet(f.Type())
}

// AddAddressSet is unsupported: apf has no address-set support.
// AddAddressSet is unsupported: apf has no address-set support.
func (f *APF) AddAddressSet(ctx context.Context, set *AddressSet) error {
	return unsupportedSet(f.Type())
}

// RemoveAddressSet is unsupported: apf has no address-set support.
// RemoveAddressSet is unsupported: apf has no address-set support.
func (f *APF) RemoveAddressSet(ctx context.Context, name string) error {
	return unsupportedSet(f.Type())
}

// AddAddressSetEntry is unsupported: apf has no address-set support.
// AddAddressSetEntry is unsupported: apf has no address-set support.
func (f *APF) AddAddressSetEntry(ctx context.Context, name, entry string) error {
	return unsupportedSet(f.Type())
}

// RemoveAddressSetEntry is unsupported: apf has no address-set support.
// RemoveAddressSetEntry is unsupported: apf has no address-set support.
func (f *APF) RemoveAddressSetEntry(ctx context.Context, name, entry string) error {
	return unsupportedSet(f.Type())
}

// Reload restarts apf to apply config changes, but only when a mutation changed its files.
func (f *APF) Reload(ctx context.Context) error {
	// apf --restart rewrites and reloads the whole ruleset, which is disruptive, so
	// only restart when a mutation actually changed apf's config files.
	if f.ConfigChanged {
		_, err := runCommand(ctx, "/etc/apf/apf", "--restart")
		if err != nil {
			return err
		}
	}
	return nil
}

// Close releases resources held by the manager; apf holds none.
// Close releases resources held by the manager; apf holds none.
func (f *APF) Close(ctx context.Context) error {
	return nil
}

// InsertRule is unsupported: APF organizes rules in config files, not an ordered list.