// Remotion render engine.
//
// FlatRender supports two template engines that both produce a web-playable MP4:
//
//   - AfterEffects (EngineAfterEffects) — aerender.exe renders a .aep template,
//     bindings are written into the project first; see runner.go / binder.go.
//   - Remotion     (EngineRemotion)     — a code-based React/Remotion composition
//     is rendered with `npx remotion render`; bindings become --props; this file.
//
// The two engines are interchangeable from the job loop's point of view: Run()
// dispatches on Job.Engine and each returns the path to an MP4 on disk.
package runner

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"runtime"
	"strconv"
	"strings"
	"sync/atomic"
	"time"
)

// Engine identifiers. These mirror the values the orchestrator stores per
// template (content.templates.render_engine) and sends on the claimed job.
const (
	EngineAfterEffects = "AfterEffects"
	EngineRemotion     = "Remotion"
)

// Remotion prints "Rendered <done>/<total>" while drawing frames and
// "Stitched <done>/<total>" while muxing them into the MP4. We parse both to
// build a real percentage.
var (
	reRemRendered = regexp.MustCompile(`Rendered\s+(\d+)/(\d+)`)
	reRemStitched = regexp.MustCompile(`Stitched\s+(\d+)/(\d+)`)
)

// npxCmd returns the platform-appropriate npx launcher.
func npxCmd() string {
	if runtime.GOOS == "windows" {
		return "npx.cmd"
	}
	return "npx"
}

// remotionProps maps the user's bindings into a Remotion props JSON object.
// For code-based templates the binding Key is the composition's schema field
// (logoText, accentColor, …) and Value is the user's edited string. Anything the
// user didn't touch falls back to the composition's defaultProps.
func remotionProps(job *Job) (string, error) {
	// FlexStory (scene engine) passthrough: the orchestrator already built the full
	// props object (scenes:[{blockId,durationSec,props}] + theme colours) as a single
	// "__flexprops__" binding. Use it verbatim — it's a complete JSON object, not a
	// flat key/value map.
	for _, b := range job.Bindings {
		if b.Key == "__flexprops__" {
			return b.Value, nil
		}
	}
	props := make(map[string]string, len(job.Bindings))
	for _, b := range job.Bindings {
		if b.Key == "" {
			continue
		}
		props[b.Key] = b.Value
	}
	data, err := json.Marshal(props)
	if err != nil {
		return "", err
	}
	return string(data), nil
}

// crlfSplit is a bufio.SplitFunc that breaks on either \n or \r so we capture
// each progress-bar repaint (Remotion redraws the bar with \r, not \n).
func crlfSplit(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}
	for i, b := range data {
		if b == '\n' || b == '\r' {
			return i + 1, data[:i], nil
		}
	}
	if atEOF {
		return len(data), data, nil
	}
	return 0, nil, nil // request more data
}

// RunRemotion renders a code-based (Remotion) template to MP4.
//
//   - remotionDir is the Remotion project root (has package.json + src/index.ts).
//   - job.CompName is the Remotion composition id (e.g. "KineticQuote").
//   - job.Bindings become --props.
//   - job.Resolution selects an output height tier (free=360p … 4k).
//
// Returns the path to the rendered MP4. Progress + periodic previews are streamed
// through the same callbacks the AE engine uses, so the UI is engine-agnostic.
func RunRemotion(ctx context.Context, remotionDir string, job *Job, outputPath string, onProgress ProgressFn, onPreview PreviewFn) (string, error) {
	if remotionDir == "" {
		return "", fmt.Errorf("remotion project dir not set (REMOTION_PROJECT_DIR)")
	}
	if job.CompName == "" {
		return "", fmt.Errorf("remotion render requires a composition id (CompName)")
	}
	if st, err := os.Stat(remotionDir); err != nil || !st.IsDir() {
		return "", fmt.Errorf("remotion project dir not found: %s", remotionDir)
	}

	propsJSON, err := remotionProps(job)
	if err != nil {
		return "", fmt.Errorf("build props: %w", err)
	}

	// Render at the composition's native resolution, then downscale to the quality
	// tier with ffmpeg (scale=-2:h preserves aspect). Remotion's --height flag
	// overrides height but keeps the native width, which squishes non-matching
	// aspect ratios — so we deliberately scale in the same ffmpeg post-step the AE
	// engine uses. This also keeps one place to stamp the free-tier watermark later.
	nativePath := strings.TrimSuffix(outputPath, filepath.Ext(outputPath)) + ".native.mp4"
	entry := filepath.Join("src", "index.ts")
	args := []string{
		"remotion", "render", entry, job.CompName, nativePath,
		"--props=" + propsJSON,
		"--log=info",
	}

	log.Printf("[remotion] job %s → comp %q, props %s (cwd=%s)", job.JobID, job.CompName, propsJSON, remotionDir)
	cmd := exec.CommandContext(ctx, npxCmd(), args...)
	cmd.Dir = remotionDir

	// Merge stdout+stderr into one pipe — Remotion writes the progress bar to
	// stderr and structured logs to stdout; we want both.
	pr, pw := io.Pipe()
	cmd.Stdout = pw
	cmd.Stderr = pw

	var curFrame, totalFrames, stitched, totalStitch int64
	var phase atomic.Int32 // 0=bundling 1=rendering 2=stitching
	go func() {
		sc := bufio.NewScanner(pr)
		sc.Buffer(make([]byte, 64*1024), 1024*1024)
		sc.Split(crlfSplit)
		for sc.Scan() {
			line := strings.TrimSpace(sc.Text())
			if line == "" {
				continue
			}
			_, _ = io.WriteString(os.Stdout, "[remotion] "+line+"\n")
			if m := reRemRendered.FindStringSubmatch(line); m != nil {
				cur, _ := strconv.ParseInt(m[1], 10, 64)
				tot, _ := strconv.ParseInt(m[2], 10, 64)
				atomic.StoreInt64(&curFrame, cur)
				atomic.StoreInt64(&totalFrames, tot)
				phase.Store(1)
			}
			if m := reRemStitched.FindStringSubmatch(line); m != nil {
				cur, _ := strconv.ParseInt(m[1], 10, 64)
				tot, _ := strconv.ParseInt(m[2], 10, 64)
				atomic.StoreInt64(&stitched, cur)
				atomic.StoreInt64(&totalStitch, tot)
				phase.Store(2)
			}
		}
	}()

	if err := cmd.Start(); err != nil {
		_ = pw.Close()
		return "", fmt.Errorf("start remotion: %w", err)
	}

	done := make(chan error, 1)
	go func() {
		werr := cmd.Wait()
		_ = pw.Close() // unblock the scanner goroutine
		done <- werr
	}()

	_ = onProgress(ctx, 4, "در حال آماده‌سازی قالب…") // "Preparing template…"
	ticker := time.NewTicker(2 * time.Second)
	defer ticker.Stop()
	lastPreview := time.Time{}

	for {
		select {
		case werr := <-done:
			if werr != nil {
				return "", fmt.Errorf("remotion render exit: %w", werr)
			}
			if st, serr := os.Stat(nativePath); serr != nil || st.Size() == 0 {
				return "", fmt.Errorf("remotion finished but produced no output at %s", nativePath)
			}
			// Downscale to the quality tier (aspect-preserving). When ffmpeg is
			// missing or the tier is unknown, ship the native render unchanged.
			h := resolutionHeight(job.Resolution)
			if h > 0 && ffmpegPath() != "" {
				_ = onProgress(ctx, 96, "در حال بهینه‌سازی کیفیت…") // "Optimizing quality…"
				mp4, terr := transcodeToMP4(ctx, nativePath, outputPath, h)
				if terr != nil {
					log.Printf("[remotion] tier transcode failed (%v) — shipping native render", terr)
					_ = onProgress(ctx, 98, "اتمام رندر")
					return nativePath, nil
				}
				_ = os.Remove(nativePath)
				_ = onProgress(ctx, 98, "اتمام رندر")
				return mp4, nil
			}
			_ = onProgress(ctx, 98, "اتمام رندر")
			return nativePath, nil
		case <-ticker.C:
			pct, msg := remotionProgress(phase.Load(),
				atomic.LoadInt64(&curFrame), atomic.LoadInt64(&totalFrames),
				atomic.LoadInt64(&stitched), atomic.LoadInt64(&totalStitch))
			_ = onProgress(ctx, pct, msg)
			if onPreview != nil && time.Since(lastPreview) >= 8*time.Second {
				lastPreview = time.Now()
				if perr := onPreview(ctx, GeneratePreviewB64(pct, job.Quality, job.Resolution)); perr != nil {
					log.Printf("[remotion] preview push error: %v", perr)
				}
			}
		case <-ctx.Done():
			_ = cmd.Process.Kill()
			return "", ctx.Err()
		}
	}
}

// remotionProgress maps the render phase + frame counts to a 4–96 percentage
// (leaving headroom for the orchestrator's upload step) plus a Persian message.
func remotionProgress(phase int32, cur, total, stch, stchTotal int64) (int, string) {
	switch phase {
	case 2: // stitching → 70..96
		if stchTotal > 0 {
			frac := float64(stch) / float64(stchTotal)
			return 70 + int(frac*26), fmt.Sprintf("در حال ساخت ویدیو… %d از %d", stch, stchTotal)
		}
		return 70, "در حال ساخت ویدیو…"
	case 1: // rendering frames → 8..70
		if total > 0 {
			frac := float64(cur) / float64(total)
			return 8 + int(frac*62), fmt.Sprintf("در حال رندر… فریم %d از %d", cur, total)
		}
		return 8, "در حال رندر…"
	default: // bundling
		return 5, "در حال کامپایل قالب…"
	}
}