package main

import (
	"context"
	"flag"
	"fmt"
	"hash/crc32"
	"io"
	"io/ioutil"
	"net/http"
	"os"
	"os/exec"
	"path/filepath"
)

type config struct {
	youtubeDl         string
	mkvmerge          string
	overrideOutput    string
	deleteTemporaries bool
}

func performDownload(ctx context.Context, cfg *config, targetUrl string) error {

	//

	var content []byte
	var err error
	if targetUrl == "-" {
		// Read HTML page from stdin
		content, err = ioutil.ReadAll(os.Stdin)
		if err != nil {
			return err
		}
	} else {
		// Download HTML page from URL
		resp, err := http.Get(targetUrl)
		if err != nil {
			return err
		}
		content, err = ioutil.ReadAll(resp.Body)
		if err != nil {
			return err
		}
		_ = resp.Body.Close() // swallow error
	}

	ltc, err := NewLoadTupContent(content)
	if err != nil {
		return err
	}

	err = ltc.Validate()
	if err != nil {
		return err
	}

	// Create temporary directory
	tmpdir, err := ioutil.TempDir("", "loadtup-dl-")
	if err != nil {
		return err
	}
	if cfg.deleteTemporaries {
		defer os.RemoveAll(tmpdir)
	}

	// Download the video
	ytdl := exec.CommandContext(ctx, cfg.youtubeDl, `-f`, `bestvideo+bestaudio`, "https://youtu.be/"+ltc.VideoID, `--merge-output-format`, `mkv`, "-o", filepath.Join(tmpdir, "downloaded"))
	ytdl.Stdout = os.Stdout
	ytdl.Stderr = os.Stderr
	err = ytdl.Run()
	if err != nil {
		return err
	}

	// Determine video's total length

	// Create the subtitle file (clamped to total length)

	fh, err := os.OpenFile(filepath.Join(tmpdir, "subtitles.srt"), os.O_CREATE|os.O_WRONLY, 0600)
	if err != nil {
		return err
	}

	err = ltc.WriteSRT(fh)
	fh.Close()
	if err != nil {
		return err
	}

	// Mux the subtitles into the file

	mkvm := exec.CommandContext(ctx, cfg.mkvmerge, `-o`, filepath.Join(tmpdir, "muxed.mkv"), filepath.Join(tmpdir, "downloaded.mkv"), filepath.Join(tmpdir, "subtitles.srt"))
	mkvm.Stdout = os.Stdout
	mkvm.Stderr = os.Stderr
	err = mkvm.Run()
	if err != nil {
		return err
	}

	// Determine final filename
	outputFile := cfg.overrideOutput
	if outputFile == "" {
		// Generate the CRC32 and put it into the filename
		hw := NewCRCwriter(crc32.IEEE, ioutil.Discard)
		fhm, err := os.OpenFile(filepath.Join(tmpdir, "muxed.mkv"), os.O_RDONLY, 0400)
		if err != nil {
			return err
		}
		_, err = io.Copy(hw, fhm)
		fhm.Close()
		if err != nil {
			return err
		}

		outputFile = fmt.Sprintf(`[Loadtup] %s [%08X].mkv`, ltc.Title, hw.Sum())
	}

	err = os.Rename(filepath.Join(tmpdir, "muxed.mkv"), outputFile)
	if err != nil {
		return err
	}

	// Done

	return nil
}

func usage() {
	fmt.Fprintln(os.Stderr, `Usage: loadtup-dl [options] [--] URL|- [URL...]

Supported URLs take the form 'https://loadtup.com/abcdefghijk'. Use a hyphen to
read equivalent loadtup.com HTML content from stdin.

Options:
  --youtube-dl PATH          Override path to youtube-dl
  --mkvmerge PATH            Override path to mkvmerge
  --output PATH              Override output filename
                             (only valid for a single URL)
  --delete-temporary=false   Preserve temporary files
`)
	os.Exit(1)
}

func main() {

	ctx := context.Background()

	cfg := config{}

	flag.StringVar(&cfg.youtubeDl, "youtube-dl", "youtube-dl", "")
	flag.StringVar(&cfg.mkvmerge, "mkvmerge", "mkvmerge", "")
	flag.StringVar(&cfg.overrideOutput, "output", "", "")
	flag.BoolVar(&cfg.deleteTemporaries, "delete-temporary", true, "")
	flag.Usage = usage
	flag.Parse()

	if len(flag.Args()) == 0 {
		usage() // n.b. calls os.Exit(1)
	}

	if len(flag.Args()) > 1 && cfg.overrideOutput != "" {
		fmt.Fprintln(os.Stderr, "Can't use --output when supplying multiple URLs")
		os.Exit(1)
	}

	for _, targetUrl := range flag.Args() {
		err := performDownload(ctx, &cfg, targetUrl)
		if err != nil {
			fmt.Fprintln(os.Stderr, err.Error())
			os.Exit(1)
		}
	}

}