// Package ffmpeg implements driven.AudioEncoder: WAV framing done by hand,
// then a shell-out to the system ffmpeg binary to transcode to AAC/M4A,
// matching uma-tts-api's pydub `.export(..., format="ipod")` step
// (mimetype audio/aac, despite the "ipod" format name being an M4A/AAC
// container alias).
package ffmpeg

import (
	"bytes"
	"context"
	"fmt"
	"os"
	"os/exec"
)

type Encoder struct{}

func NewEncoder() *Encoder {
	return &Encoder{}
}

// Encode transcodes PCM samples to AAC. The output goes to a temp file
// rather than a stdout pipe because the M4A/MP4 muxer needs a seekable
// destination to write its moov atom.
func (e *Encoder) Encode(ctx context.Context, pcm []float32, sampleRate int) ([]byte, string, error) {
	wavBytes := encodeWAV(pcm, sampleRate)

	tmpFile, err := os.CreateTemp("", "tts-gateway-*.m4a")
	if err != nil {
		return nil, "", fmt.Errorf("ffmpeg: create temp output file: %w", err)
	}
	tmpPath := tmpFile.Name()
	_ = tmpFile.Close()
	defer os.Remove(tmpPath)

	cmd := exec.CommandContext(ctx, "ffmpeg",
		"-y",
		"-f", "wav", "-i", "pipe:0",
		"-f", "ipod",
		tmpPath,
	)
	cmd.Stdin = bytes.NewReader(wavBytes)
	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		return nil, "", fmt.Errorf("ffmpeg: transcode failed: %w: %s", err, stderr.String())
	}

	data, err := os.ReadFile(tmpPath)
	if err != nil {
		return nil, "", fmt.Errorf("ffmpeg: read transcoded output: %w", err)
	}
	return data, "audio/aac", nil
}