package audio

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

// FFmpeg converts any audio container to the strict format whisper wants: 16 kHz
// mono signed 16-bit PCM WAV (ADR-033). It ALWAYS transcodes, even when the input
// already is that format — a Teams export often is, and the transcode is then
// nearly free; assuming it would be the bug. This replaces whisper-server's
// --convert, whose --tmp-dir is created at process start and rots under macOS
// periodic cleanup.
type FFmpeg struct {
	// Bin is the ffmpeg executable ("ffmpeg" resolves via PATH).
	Bin string
}

// ToWAV writes src, converted, to dst. Video streams are dropped (-vn): by now the
// file has already been probed as audio-only, but a cover-art stream must not end
// up in the WAV.
func (f *FFmpeg) ToWAV(ctx context.Context, src, dst string) error {
	bin := f.Bin
	if bin == "" {
		bin = "ffmpeg"
	}
	cmd := exec.CommandContext(ctx, bin,
		"-y", "-v", "error", "-i", src, "-vn", "-ac", "1", "-ar", "16000", "-c:a", "pcm_s16le", "-f", "wav", dst)
	cmd.WaitDelay = killGrace
	if out, err := cmd.CombinedOutput(); err != nil {
		if ctxErr := ctx.Err(); ctxErr != nil {
			return fmt.Errorf("audio: ffmpeg: %w", ctxErr)
		}
		return fmt.Errorf("audio: ffmpeg: %w: %s", err, strings.TrimSpace(string(out)))
	}
	// A zero exit that wrote nothing is still a failure: never hand whisper a
	// missing file and let the error surface three layers later.
	if info, err := os.Stat(dst); err != nil || info.Size() == 0 {
		return fmt.Errorf("audio: ffmpeg wrote no output at %s", dst)
	}
	return nil
}