package runner

import (
	"context"
	"fmt"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
)

// RunSnapshot renders a single frame of compName from aepPath and writes a PNG
// still, returning its path. It reuses the render pipeline shape: aerender emits
// the comp's output module (lossless AVI/MOV) for one frame, then ffmpeg extracts
// a single PNG. Requires aerender (aePath) and ffmpeg on the node.
func RunSnapshot(ctx context.Context, aePath, aepPath, compName string, frame int, workDir string) (string, error) {
	if aePath == "" {
		return "", fmt.Errorf("AE path required for snapshot render")
	}
	if compName == "" {
		return "", fmt.Errorf("comp name required for snapshot render")
	}
	if err := os.MkdirAll(workDir, 0o755); err != nil {
		return "", fmt.Errorf("workdir: %w", err)
	}
	out := filepath.Join(workDir, "snap.avi")
	_ = os.Remove(out)

	// -s/-e bound the render to a single frame; aerender writes via the comp's
	// output module (cmd.Dir = project folder so relative footage resolves).
	args := []string{
		"-project", aepPath, "-comp", compName,
		"-s", strconv.Itoa(frame), "-e", strconv.Itoa(frame),
		"-output", out,
	}
	log.Printf("[snapshot] aerender %v", args)
	cmd := exec.CommandContext(ctx, aePath, args...)
	cmd.Dir = filepath.Dir(aepPath)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	if err := cmd.Run(); err != nil {
		return "", fmt.Errorf("aerender: %w", err)
	}
	actual := findRenderedOutput(out)
	if actual == "" {
		return "", fmt.Errorf("aerender produced no output for comp %q", compName)
	}

	ff := ffmpegPath()
	if ff == "" {
		return "", fmt.Errorf("ffmpeg not found (set FFMPEG_PATH or place ffmpeg.exe next to the agent)")
	}
	png := filepath.Join(workDir, "snap.png")
	_ = os.Remove(png)
	ffArgs := []string{"-y", "-i", actual, "-frames:v", "1", png}
	log.Printf("[snapshot] ffmpeg %v", ffArgs)
	fc := exec.CommandContext(ctx, ff, ffArgs...)
	fc.Stdout = os.Stdout
	fc.Stderr = os.Stderr
	if err := fc.Run(); err != nil {
		return "", fmt.Errorf("ffmpeg still: %w", err)
	}
	_ = os.Remove(actual) // drop the intermediate render
	if st, err := os.Stat(png); err != nil || st.Size() == 0 {
		return "", fmt.Errorf("no snapshot image produced")
	}
	return png, nil
}