package recording

import (
	"database/sql"
	"encoding/json"
	"log/slog"
	"strconv"
	"sync"
	"time"

	"github.com/gofiber/websocket/v2"
	"github.com/klauspost/compress/zstd"
)

// PlayerCmd is a client→server playback control message.
type PlayerCmd struct {
	Cmd   string  `json:"cmd"`
	Ms    int64   `json:"ms,omitempty"`
	Value float64 `json:"value,omitempty"`
}

// Player streams a single recording over a websocket with seek/pause/speed
// controls. Frames are streamed from SQLite in a sliding window so memory use
// is bounded.
type Player struct {
	db          *sql.DB
	conn        *websocket.Conn
	recordingID int64
	totalFrames int
	durationMs  int64
	dec         *zstd.Decoder

	mu         sync.Mutex
	speed      float64
	playing    bool
	positionMs int64

	cmdCh  chan PlayerCmd
	stopCh chan struct{}
}

// NewPlayer constructs a Player bound to a websocket connection.
func NewPlayer(db *sql.DB, conn *websocket.Conn, id int64) (*Player, error) {
	dec, err := zstd.NewReader(nil)
	if err != nil {
		return nil, err
	}
	return &Player{
		db:          db,
		conn:        conn,
		recordingID: id,
		dec:         dec,
		speed:       1.0,
		playing:     true,
		cmdCh:       make(chan PlayerCmd, 16),
		stopCh:      make(chan struct{}),
	}, nil
}

func (p *Player) sendJSON(v any) error {
	b, err := json.Marshal(v)
	if err != nil {
		return err
	}
	return p.conn.WriteMessage(websocket.TextMessage, b)
}

func (p *Player) sendErr(msg string) { _ = p.sendJSON(map[string]any{"error": msg}) }

func (p *Player) sendState() {
	p.mu.Lock()
	playing, speed, pos := p.playing, p.speed, p.positionMs
	p.mu.Unlock()
	_ = p.sendJSON(map[string]any{
		"type": "playback_state", "playing": playing, "speed": speed, "position_ms": pos,
	})
}

// Run executes the playback loop. It returns when playback ends, the client
// stops it, or the connection drops.
func (p *Player) Run() {
	defer p.dec.Close()

	var name string
	if err := p.db.QueryRow(`SELECT name FROM recordings WHERE id = ?`, p.recordingID).Scan(&name); err != nil {
		p.sendErr("recording not found")
		return
	}
	if err := p.db.QueryRow(`SELECT COUNT(*), COALESCE(MAX(offset_ms),0) FROM frames WHERE recording_id = ?`, p.recordingID).
		Scan(&p.totalFrames, &p.durationMs); err != nil {
		p.sendErr("failed to read recording")
		return
	}
	if p.totalFrames == 0 {
		p.sendErr("no frames in recording")
		return
	}

	_ = p.sendJSON(map[string]any{
		"type": "playback_start", "name": name,
		"frames": p.totalFrames, "duration_ms": p.durationMs,
	})

	go p.readCommands()

	const prefetch = 256
	type frame struct {
		ms    int64
		data  []byte
		codec int
	}
	var buf []frame
	cursor := int64(-1)
	frameIdx := 0

	refill := func(fromMs int64) error {
		buf = buf[:0]
		rows, err := p.db.Query(
			`SELECT offset_ms, data, codec FROM frames WHERE recording_id = ? AND offset_ms >= ? ORDER BY offset_ms LIMIT ?`,
			p.recordingID, fromMs, prefetch)
		if err != nil {
			return err
		}
		defer rows.Close()
		for rows.Next() {
			var f frame
			if err := rows.Scan(&f.ms, &f.data, &f.codec); err != nil {
				continue
			}
			buf = append(buf, f)
		}
		return nil
	}

	doSeek := func(targetMs int64) {
		if targetMs < 0 {
			targetMs = 0
		}
		if targetMs > p.durationMs {
			targetMs = p.durationMs
		}
		p.mu.Lock()
		p.positionMs = targetMs
		p.mu.Unlock()
		cursor = targetMs - 1
		buf = buf[:0]
		var idx int
		if err := p.db.QueryRow(
			`SELECT COUNT(*) FROM frames WHERE recording_id = ? AND offset_ms < ?`,
			p.recordingID, targetMs).Scan(&idx); err == nil {
			frameIdx = idx
		}
		p.sendState()
	}

	if err := refill(0); err != nil {
		p.sendErr("read error")
		return
	}
	p.sendState()

	anchorWall := time.Now()
	anchorPos := int64(0)

	timer := time.NewTimer(time.Hour)
	defer timer.Stop()

	armTimer := func() {
		p.mu.Lock()
		playing, speed, pos := p.playing, p.speed, p.positionMs
		p.mu.Unlock()

		if !playing || len(buf) == 0 {
			if !timer.Stop() {
				select {
				case <-timer.C:
				default:
				}
			}
			timer.Reset(time.Hour)
			return
		}
		next := buf[0]
		delta := time.Duration(float64(next.ms-pos)/speed) * time.Millisecond
		if delta < 0 {
			delta = 0
		}
		if !timer.Stop() {
			select {
			case <-timer.C:
			default:
			}
		}
		timer.Reset(delta)
	}

	armTimer()

	stateBroadcast := time.NewTicker(250 * time.Millisecond)
	defer stateBroadcast.Stop()

	for {
		select {
		case <-p.stopCh:
			return

		case cmd := <-p.cmdCh:
			switch cmd.Cmd {
			case "play":
				p.mu.Lock()
				if !p.playing {
					p.playing = true
					anchorWall = time.Now()
					anchorPos = p.positionMs
				}
				p.mu.Unlock()
				p.sendState()
				armTimer()
			case "pause":
				p.mu.Lock()
				if p.playing {
					elapsed := time.Since(anchorWall)
					p.positionMs = anchorPos + int64(float64(elapsed.Milliseconds())*p.speed)
					if p.positionMs > p.durationMs {
						p.positionMs = p.durationMs
					}
					p.playing = false
				}
				p.mu.Unlock()
				p.sendState()
				armTimer()
			case "speed":
				p.mu.Lock()
				if cmd.Value > 0 && cmd.Value <= 16 {
					if p.playing {
						elapsed := time.Since(anchorWall)
						p.positionMs = anchorPos + int64(float64(elapsed.Milliseconds())*p.speed)
					}
					p.speed = cmd.Value
					anchorWall = time.Now()
					anchorPos = p.positionMs
				}
				p.mu.Unlock()
				p.sendState()
				armTimer()
			case "seek":
				doSeek(cmd.Ms)
				if err := refill(cmd.Ms); err != nil {
					p.sendErr("read error")
					return
				}
				p.mu.Lock()
				anchorWall = time.Now()
				anchorPos = p.positionMs
				p.mu.Unlock()
				armTimer()
			case "stop":
				return
			}

		case <-stateBroadcast.C:
			p.mu.Lock()
			if p.playing {
				elapsed := time.Since(anchorWall)
				p.positionMs = anchorPos + int64(float64(elapsed.Milliseconds())*p.speed)
				if p.positionMs > p.durationMs {
					p.positionMs = p.durationMs
				}
			}
			p.mu.Unlock()
			p.sendState()

		case <-timer.C:
			p.mu.Lock()
			if !p.playing {
				p.mu.Unlock()
				armTimer()
				continue
			}
			elapsed := time.Since(anchorWall)
			pos := anchorPos + int64(float64(elapsed.Milliseconds())*p.speed)
			p.positionMs = pos
			p.mu.Unlock()

			for len(buf) > 0 && buf[0].ms <= p.positionMs {
				f := buf[0]
				buf = buf[1:]
				data := f.data
				if f.codec == 1 {
					out, err := p.dec.DecodeAll(f.data, nil)
					if err != nil {
						slog.Warn("frame decode failed", "err", err)
						continue
					}
					data = out
				}
				frameIdx++
				msg := append([]byte(nil), `{"type":"playback_frame","offset_ms":`...)
				msg = strconv.AppendInt(msg, f.ms, 10)
				msg = append(msg, `,"frame":`...)
				msg = strconv.AppendInt(msg, int64(frameIdx), 10)
				msg = append(msg, `,"data":`...)
				msg = append(msg, data...)
				msg = append(msg, '}')
				if err := p.conn.WriteMessage(websocket.TextMessage, msg); err != nil {
					return
				}
				cursor = f.ms
			}

			if len(buf) == 0 {
				if err := refill(cursor + 1); err != nil {
					p.sendErr("read error")
					return
				}
				if len(buf) == 0 {
					_ = p.sendJSON(map[string]any{"type": "playback_end"})
					return
				}
			}
			armTimer()
		}
	}
}

func (p *Player) readCommands() {
	for {
		_, msg, err := p.conn.ReadMessage()
		if err != nil {
			close(p.stopCh)
			return
		}
		var cmd PlayerCmd
		if err := json.Unmarshal(msg, &cmd); err != nil {
			continue
		}
		select {
		case p.cmdCh <- cmd:
		default:
		}
	}
}