package main

import (
	"context"
	"fmt"
	"sync"
	"time"
)

// Source is a control input that drives a device's zones. Each source is bound
// to one device and arbitrates for control via the device's Apply.
type Source interface {
	// Name returns the source's configured name.
	Name() string
	// Start begins receiving and applying control input.
	Start(ctx context.Context) error
	// Stop releases the source's resources.
	Stop()
}

// NewSource constructs the source implementation for the given configuration,
// bound to its target device.
func NewSource(cfg *SourceConfig, dev *Device) (Source, error) {
	if dev == nil {
		return nil, fmt.Errorf("device %q not found", cfg.Device)
	}
	hold := time.Duration(cfg.HoldSec * float64(time.Second))
	// DMX is a stream of instantaneous level data — the console owns the crossfade
	//  — so default DMX sources to an instant fade when none is configured; other
	//  sources fall back to the device's fade.
	fade := cfg.Fade
	if fade == "" && (cfg.Type == "sacn" || cfg.Type == "artnet") {
		fade = "00:00"
	}
	binding := dev.RegisterSource(cfg.Name, cfg.Priority, hold, fade)

	switch cfg.Type {
	case "mqtt":
		return newMQTTSource(cfg, dev, binding), nil
	case "osc":
		return newOSCSource(cfg, dev, binding), nil
	case "sacn":
		disp, err := newDMXDispatcher(dev, binding, cfg.SACN.DMXMap)
		if err != nil {
			return nil, err
		}
		return newSACNSource(cfg, dev, disp), nil
	case "artnet":
		disp, err := newDMXDispatcher(dev, binding, cfg.ArtNet.DMXMap)
		if err != nil {
			return nil, err
		}
		return newArtNetSource(cfg, dev, disp), nil
	default:
		return nil, fmt.Errorf("unknown source type %q", cfg.Type)
	}
}

// dmxBinding maps a DMX channel (0-indexed offset into the universe) to a target
// zone for level control.
type dmxBinding struct {
	channel int
	target  int
}

// sceneSelectBinding maps a DMX channel to scene activation by value: the channel's
// value selects the scene (1..maxScene) to trigger, and 0 means no action. It fires
// when the value changes, so it acts as a momentary trigger rather than a level.
type sceneSelectBinding struct {
	channel  int
	maxScene int
}

// dmxDispatcher applies a DMX universe frame to a device: zone channels set zone
// levels, scene-select channels trigger scenes by value.
type dmxDispatcher struct {
	dev           *Device
	binding       *sourceBinding
	zoneBindings  []dmxBinding
	sceneBindings []sceneSelectBinding

	mu   sync.Mutex
	prev []byte // Previous frame, for scene change detection.
}

// newDMXDispatcher builds a dispatcher from the DMX channel map. It notes scene
// control on the device so scene monitoring is enabled.
func newDMXDispatcher(dev *Device, binding *sourceBinding, m DMXMap) (*dmxDispatcher, error) {
	zones, scenes, err := buildDMXMap(m, dev.Zones())
	if err != nil {
		return nil, err
	}
	if len(scenes) > 0 {
		dev.NoteSceneControl()
	}
	return &dmxDispatcher{
		dev:           dev,
		binding:       binding,
		zoneBindings:  zones,
		sceneBindings: scenes,
	}, nil
}

// dispatch applies a universe frame to the device.
func (d *dmxDispatcher) dispatch(data []byte) {
	// Snapshot the previous frame and store the current one for edge detection.
	d.mu.Lock()
	prev := d.prev
	cur := make([]byte, len(data))
	copy(cur, data)
	d.prev = cur
	d.mu.Unlock()

	// Zone channels: apply each mapped zone's level, leaving zones this source
	//  doesn't map untouched rather than forcing them to zero.
	if len(d.zoneBindings) > 0 {
		levels := make(map[int]byte, len(d.zoneBindings))
		for _, zb := range d.zoneBindings {
			if zb.channel < len(data) && zb.target >= 1 && zb.target <= d.dev.Zones() {
				levels[zb.target] = data[zb.channel]
			}
		}
		d.dev.ApplyZoneLevels(d.binding, levels)
	}

	// Scene-select channels: trigger a scene when the channel's value changes to a
	//  non-zero scene number. Holding a value doesn't re-fire; sweeping a fader
	//  through the channel fires each scene it passes, so set it deliberately.
	for _, sb := range d.sceneBindings {
		if sb.channel >= len(data) {
			continue
		}
		scene := int(data[sb.channel])
		prevScene := 0
		if sb.channel < len(prev) {
			prevScene = int(prev[sb.channel])
		}
		if scene != prevScene && scene >= 1 && scene <= sb.maxScene {
			d.dev.ApplyScene(d.binding, scene)
		}
	}
}

// refreshActivity re-asserts the source's zone activity so a continuously
// streaming universe keeps its arbitration lock between value changes. Scene-select
// channels trigger on change and carry their own hold, so only zone-driving
// dispatchers need this.
func (d *dmxDispatcher) refreshActivity() {
	if len(d.zoneBindings) > 0 {
		d.dev.RefreshZoneActivity(d.binding)
	}
}

// release drives every zone this dispatcher owns to 0, mirroring a DMX source
// going away: an unsourced universe collapses to all-zeros, so a console release
// blacks the zones out instead of latching the last value. Scene-select channels
// are left untouched; they trigger on change. The previous-frame state is cleared
// so a returning identical look re-applies.
func (d *dmxDispatcher) release() {
	if len(d.zoneBindings) == 0 {
		return
	}
	levels := make(map[int]byte, len(d.zoneBindings))
	for _, zb := range d.zoneBindings {
		if zb.target >= 1 && zb.target <= d.dev.Zones() {
			levels[zb.target] = 0
		}
	}
	d.dev.ApplyZoneLevels(d.binding, levels)

	d.mu.Lock()
	d.prev = nil
	d.mu.Unlock()
}

// buildDMXMap resolves a DMX channel map into zone bindings and scene-select
// bindings. An explicit channels list takes precedence; otherwise the zones are
// laid out sequentially from the start address, followed by a single scene-select
// channel when scenes are enabled.
func buildDMXMap(m DMXMap, deviceZones int) (zones []dmxBinding, scenes []sceneSelectBinding, err error) {
	// Explicit per-channel map.
	if len(m.Channels) > 0 {
		for _, c := range m.Channels {
			if c.Channel < 1 || c.Channel > 512 {
				return nil, nil, fmt.Errorf("channel %d: must be 1-512", c.Channel)
			}
			idx := c.Channel - 1 // 1-indexed DMX address to 0-indexed offset.
			switch c.Type {
			case "zone":
				if c.Zone < 1 || c.Zone > deviceZones {
					return nil, nil, fmt.Errorf("channel %d: zone %d out of range 1-%d", c.Channel, c.Zone, deviceZones)
				}
				zones = append(zones, dmxBinding{channel: idx, target: c.Zone})
			case "scene":
				scenes = append(scenes, sceneSelectBinding{channel: idx, maxScene: qseMaxScene})
			default:
				return nil, nil, fmt.Errorf("channel %d: unknown type %q", c.Channel, c.Type)
			}
		}
		return zones, scenes, nil
	}

	// Sequential layout: zones from the start address, then one scene-select channel.
	zoneCount := m.Zones
	if zoneCount == 0 {
		zoneCount = deviceZones
	}
	if m.StartAddress < 0 {
		return nil, nil, fmt.Errorf("start_address %d: must be >= 0", m.StartAddress)
	}
	if m.Scenes < 0 || m.Scenes > qseMaxScene {
		return nil, nil, fmt.Errorf("scenes %d: must be 0-%d", m.Scenes, qseMaxScene)
	}
	// One channel carries the scene selector when scenes are enabled.
	sceneChannels := 0
	if m.Scenes > 0 {
		sceneChannels = 1
	}
	// Reject a layout that runs past the 512-channel universe, which would
	//  otherwise silently drop the out-of-range channels at dispatch.
	if last := m.StartAddress + zoneCount + sceneChannels; last > 512 {
		return nil, nil, fmt.Errorf("sequential layout runs to channel %d, past the 512-channel universe", last)
	}
	addr := m.StartAddress
	for z := 1; z <= zoneCount; z++ {
		zones = append(zones, dmxBinding{channel: addr, target: z})
		addr++
	}
	if m.Scenes > 0 {
		scenes = append(scenes, sceneSelectBinding{channel: addr, maxScene: m.Scenes})
	}
	return zones, scenes, nil
}