// backend\assets_sprite.go

package main

import (
	"bytes"
	"context"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"syscall"
)

const (
	previewSpriteCols       = 20
	previewSpriteRows       = 12
	previewSpriteFrameCount = previewSpriteCols * previewSpriteRows
	previewSpriteCellW      = 320
	previewSpriteCellH      = 180
)

func fixedPreviewSpriteLayout() (cols, rows, count, cellW, cellH int) {
	return previewSpriteCols, previewSpriteRows, previewSpriteFrameCount, previewSpriteCellW, previewSpriteCellH
}

func previewSpriteStepSeconds(durationSec float64) float64 {
	if durationSec <= 0 {
		return 5
	}

	// 120 Zellen = 119 Abstände.
	// Wir ziehen ein kleines Stück vom Ende ab, damit ffmpeg
	// nicht "hinter" dem letzten gültigen Frame sampelt.
	usableDur := durationSec - 0.10
	if usableDur <= 0 {
		usableDur = durationSec
	}

	step := usableDur / float64(previewSpriteFrameCount-1)

	// Nicht künstlich auf 0.5s anheben:
	// genau das erzeugt bei kürzeren Videos zu wenige Frames
	// und damit schwarze Rest-Zellen im Sprite.
	if step < 0.05 {
		step = 0.05
	}

	return step
}

// generatePreviewSpriteJPG erzeugt ein statisches JPG-Spritesheet aus einem Video.
// ffmpeg muss im PATH verfügbar sein.
func generatePreviewSpriteJPG(
	ctx context.Context,
	videoPath string,
	outPath string,
	cols int,
	rows int,
	stepSec float64,
	cellW int,
	cellH int,
) error {
	videoPath = strings.TrimSpace(videoPath)
	outPath = strings.TrimSpace(outPath)

	if videoPath == "" {
		return fmt.Errorf("generatePreviewSpriteJPG: empty videoPath")
	}
	if outPath == "" {
		return fmt.Errorf("generatePreviewSpriteJPG: empty outPath")
	}
	if cols <= 0 || rows <= 0 {
		return fmt.Errorf("generatePreviewSpriteJPG: invalid grid %dx%d", cols, rows)
	}
	if stepSec <= 0 {
		return fmt.Errorf("generatePreviewSpriteJPG: invalid stepSec %.3f", stepSec)
	}
	if cellW <= 0 || cellH <= 0 {
		return fmt.Errorf("generatePreviewSpriteJPG: invalid cell size %dx%d", cellW, cellH)
	}

	if err := os.MkdirAll(filepath.Dir(outPath), 0o755); err != nil {
		return fmt.Errorf("mkdir sprite dir: %w", err)
	}

	ext := filepath.Ext(outPath)
	if ext == "" {
		ext = ".jpg"
	}
	base := strings.TrimSuffix(outPath, ext)
	tmpPath := base + ".tmp" + ext

	// alte temp-Datei vorsichtshalber vorher entfernen
	_ = os.Remove(tmpPath)

	// bei JEDEM Fehler temp wieder aufräumen
	renameOK := false
	defer func() {
		if !renameOK {
			_ = os.Remove(tmpPath)
		}
	}()

	ffmpegPath := strings.TrimSpace(getSettings().FFmpegPath)
	if ffmpegPath == "" {
		ffmpegPath = "ffmpeg"
	}

	// robustere Filterkette
	vf := fmt.Sprintf(
		"fps=fps=1/%f:start_time=0:round=up,"+
			"scale=%d:%d:force_original_aspect_ratio=decrease:flags=bilinear,"+
			"pad=%d:%d:(ow-iw)/2:(oh-ih)/2:black,"+
			"setsar=1,"+
			"tile=%dx%d:margin=0:padding=0",
		stepSec,
		cellW, cellH,
		cellW, cellH,
		cols, rows,
	)

	args := []string{
		"-hide_banner",
		"-y",
	}
	args = append(args, ffmpegInputTol...)
	args = append(args,
		"-i", videoPath,
		"-an",
		"-sn",
		"-threads", "2",
		"-vf", vf,
		"-frames:v", "1",
		"-update", "1",
		"-c:v", "mjpeg",
		"-q:v", "3",
		tmpPath,
	)

	cmd := exec.CommandContext(ctx, ffmpegPath, args...)
	cmd.SysProcAttr = &syscall.SysProcAttr{
		HideWindow:    true,
		CreationFlags: 0x08000000, // CREATE_NO_WINDOW
	}

	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	if err := ctx.Err(); err != nil {
		return err
	}

	err := cmd.Run()

	if err != nil {
		if ctx.Err() != nil {
			return ctx.Err()
		}

		msgErr := strings.TrimSpace(stderr.String())
		if msgErr == "" {
			msgErr = "(kein stderr)"
		}

		return fmt.Errorf(
			"ffmpeg sprite failed for %q -> %q: %w | args=%q | stderr=%s",
			videoPath,
			tmpPath,
			err,
			strings.Join(cmd.Args, " "),
			msgErr,
		)
	}

	fi, err := os.Stat(tmpPath)
	if err != nil {
		return fmt.Errorf("sprite temp stat failed: %w", err)
	}
	if fi.IsDir() || fi.Size() <= 0 {
		return fmt.Errorf("sprite temp file invalid/empty")
	}

	_ = os.Remove(outPath)
	if err := os.Rename(tmpPath, outPath); err != nil {
		return fmt.Errorf("sprite rename failed: %w", err)
	}

	renameOK = true
	return nil
}