package media

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

type ffmpegReader struct {
	io.ReadCloser

	cmd       *exec.Cmd
	stdErrBuf *bytes.Buffer
}

func newFfmpegReader(ctx context.Context, input io.Reader, arg ...string) (*ffmpegReader, error) {
	var stdErr bytes.Buffer

	cmd := exec.CommandContext(ctx, "ffmpeg", arg...)
	cmd.Stdin = input
	cmd.Stderr = &stdErr

	r, err := cmd.StdoutPipe()
	if err != nil {
		return nil, fmt.Errorf("error creating pipe: %v", err)
	}

	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("error starting ffmpeg: %v, output: %s", err, stdErr.String())
	}

	return &ffmpegReader{ReadCloser: r, cmd: cmd, stdErrBuf: &stdErr}, nil
}

func (r *ffmpegReader) Cancel() error {
	if err := r.cmd.Process.Kill(); err != nil {
		return fmt.Errorf("error killing ffmpeg process: %v", err)
	}
	return nil
}

func (r *ffmpegReader) Close() error {
	state, err := r.cmd.Process.Wait()

	if err != nil {
		return fmt.Errorf("error returned from ffmpeg process: %v", err)
	}

	if state.ExitCode() != 0 {
		return fmt.Errorf("non-zero status %d returned from ffmpeg process, output: %s", state.ExitCode(), r.stdErrBuf.String())
	}

	return nil
}