package recording

import (
	"database/sql"
	"log/slog"
	"time"

	"github.com/klauspost/compress/zstd"

	"git.destefano.cloud/texasmade/RocketLeagueBot-Renderer/internal/hub"
	"git.destefano.cloud/texasmade/RocketLeagueBot-Renderer/internal/stats"
)

const (
	flushBatchSize = 64
	flushInterval  = 100 * time.Millisecond
	framesChanCap  = 1024
	idleTimeout    = 5 * time.Second
)

type rawFrame struct {
	t    time.Time
	data []byte
}

// Recorder receives raw UDP frames and persists them in batched, optionally
// zstd-compressed inserts to SQLite. A single writer goroutine owns the DB
// handles so there is no contention on the UDP hot path.
type Recorder struct {
	db       *sql.DB
	hub      *hub.Hub
	frames   chan rawFrame
	compress bool
	enc      *zstd.Encoder

	// session bookkeeping (writer-goroutine-owned)
	sessionID   int64
	sessionName string
	startTime   time.Time
	frameCount  int
	lastFrameAt time.Time

	insertFrame   *sql.Stmt
	insertSession *sql.Stmt
	updateSession *sql.Stmt

	doneCh    chan struct{}
	stoppedCh chan struct{}
}

// NewRecorder constructs a Recorder. Call Start to launch the writer goroutine.
func NewRecorder(db *sql.DB, h *hub.Hub, compress bool) (*Recorder, error) {
	r := &Recorder{
		db:        db,
		hub:       h,
		frames:    make(chan rawFrame, framesChanCap),
		compress:  compress,
		doneCh:    make(chan struct{}),
		stoppedCh: make(chan struct{}),
	}
	var err error
	if r.insertFrame, err = db.Prepare(`INSERT INTO frames(recording_id, offset_ms, data, codec) VALUES(?,?,?,?)`); err != nil {
		return nil, err
	}
	if r.insertSession, err = db.Prepare(`INSERT INTO recordings(name) VALUES(?)`); err != nil {
		return nil, err
	}
	if r.updateSession, err = db.Prepare(`UPDATE recordings SET frames=?, duration_ms=? WHERE id=?`); err != nil {
		return nil, err
	}
	if compress {
		enc, err := zstd.NewWriter(nil, zstd.WithEncoderLevel(zstd.SpeedDefault))
		if err != nil {
			return nil, err
		}
		r.enc = enc
	}
	return r, nil
}

// Submit hands a UDP packet to the recorder. Non-blocking: if the queue is
// full the frame is dropped and counted in stats.FramesDropped.
func (r *Recorder) Submit(data []byte) {
	cp := make([]byte, len(data))
	copy(cp, data)
	select {
	case r.frames <- rawFrame{t: time.Now(), data: cp}:
	default:
		stats.Global.FramesDropped.Add(1)
	}
}

// Start launches the writer goroutine. Stop must be called to flush.
func (r *Recorder) Start() { go r.run() }

// Stop signals the writer to drain the queue and exit, then waits for it.
func (r *Recorder) Stop() {
	close(r.doneCh)
	<-r.stoppedCh
}

func (r *Recorder) run() {
	defer close(r.stoppedCh)

	ticker := time.NewTicker(flushInterval)
	defer ticker.Stop()
	idleCheck := time.NewTicker(idleTimeout / 2)
	defer idleCheck.Stop()

	batch := make([]rawFrame, 0, flushBatchSize)
	flush := func() {
		if len(batch) == 0 {
			return
		}
		if err := r.writeBatch(batch); err != nil {
			slog.Error("flush batch failed", "err", err, "n", len(batch))
		}
		batch = batch[:0]
	}

	for {
		select {
		case <-r.doneCh:
		drain:
			for {
				select {
				case f := <-r.frames:
					batch = append(batch, f)
					if len(batch) >= flushBatchSize {
						flush()
					}
				default:
					break drain
				}
			}
			flush()
			r.finalizeSession()
			return

		case f := <-r.frames:
			batch = append(batch, f)
			if len(batch) >= flushBatchSize {
				flush()
			}

		case <-ticker.C:
			flush()

		case <-idleCheck.C:
			if r.sessionID != 0 && time.Since(r.lastFrameAt) > idleTimeout {
				flush()
				r.finalizeSession()
			}
		}
	}
}

// writeBatch persists frames within a single transaction. If no session is
// active, one is started using the first frame's timestamp.
func (r *Recorder) writeBatch(batch []rawFrame) error {
	tx, err := r.db.Begin()
	if err != nil {
		return err
	}

	if r.sessionID == 0 {
		first := batch[0].t
		r.sessionName = first.Format("2006-01-02_15-04-05")
		res, err := tx.Stmt(r.insertSession).Exec(r.sessionName)
		if err != nil {
			_ = tx.Rollback()
			return err
		}
		r.sessionID, _ = res.LastInsertId()
		r.startTime = first
		r.frameCount = 0
		slog.Info("recording started", "name", r.sessionName, "id", r.sessionID)
		r.hub.PublishEvent(map[string]any{
			"type": "event", "kind": "recording_started",
			"recording": map[string]any{"id": r.sessionID, "name": r.sessionName},
		})
	}

	stmt := tx.Stmt(r.insertFrame)
	for _, f := range batch {
		payload := f.data
		codec := 0
		stats.Global.BytesBeforeCompr.Add(int64(len(payload)))
		if r.compress && r.enc != nil {
			payload = r.enc.EncodeAll(f.data, make([]byte, 0, len(f.data)/2+64))
			codec = 1
		}
		stats.Global.BytesAfterCompr.Add(int64(len(payload)))
		offset := f.t.Sub(r.startTime).Milliseconds()
		if _, err := stmt.Exec(r.sessionID, offset, payload, codec); err != nil {
			_ = tx.Rollback()
			return err
		}
		r.frameCount++
		r.lastFrameAt = f.t
		stats.Global.FramesWritten.Add(1)
	}
	return tx.Commit()
}

func (r *Recorder) finalizeSession() {
	if r.sessionID == 0 {
		return
	}
	duration := r.lastFrameAt.Sub(r.startTime).Milliseconds()
	if _, err := r.updateSession.Exec(r.frameCount, duration, r.sessionID); err != nil {
		slog.Error("finalize session failed", "err", err)
	}
	slog.Info("recording stopped", "name", r.sessionName, "frames", r.frameCount, "duration_ms", duration)
	r.hub.PublishEvent(map[string]any{
		"type": "event", "kind": "recording_stopped",
		"recording": map[string]any{
			"id": r.sessionID, "name": r.sessionName,
			"frames": r.frameCount, "duration_ms": duration,
		},
	})
	r.sessionID = 0
	r.sessionName = ""
	r.frameCount = 0
}

// CurrentSession returns a snapshot of the active recording, or zero values
// if none. Reads are not strictly synchronized; slight staleness is acceptable
// for the /api/stats endpoint.
func (r *Recorder) CurrentSession() (id int64, name string, frames int, elapsedMs int64) {
	id = r.sessionID
	name = r.sessionName
	frames = r.frameCount
	if id != 0 {
		elapsedMs = time.Since(r.startTime).Milliseconds()
	}
	return
}