// author: spijet (https://github.com/spijet/)
// author: sentriz (https://github.com/sentriz/)

//nolint:gochecknoglobals
package transcode

import (
	"context"
	"fmt"
	"io"
	"os/exec"
	"time"

	"github.com/google/shlex"
)

type Transcoder interface {
	Transcode(ctx context.Context, profile Profile, in string) (io.ReadCloser, error)
}

var UserProfiles = map[string]Profile{
	"mp3":      MP3,
	"mp3_rg":   MP3RG,
	"opus_car": OpusCar,
	"opus":     Opus,
	"opus_rg":  OpusRG,
}

// Store as simple strings, since we may let the user provide their own profiles soon
var (
	MP3   = NewProfile("audio/mpeg", 128, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libmp3lame -af "volume=replaygain=track:replaygain_preamp=6dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -metadata replaygain_album_gain= -metadata replaygain_album_peak= -metadata replaygain_track_gain= -metadata replaygain_track_peak= -metadata r128_album_gain= -metadata r128_track_gain= -f mp3 -`)
	MP3RG = NewProfile("audio/mpeg", 128, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libmp3lame -af "volume=replaygain=track:replaygain_preamp=6dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -metadata replaygain_album_gain= -metadata replaygain_album_peak= -metadata replaygain_track_gain= -metadata replaygain_track_peak= -metadata r128_album_gain= -metadata r128_track_gain= -f mp3 -`)

	// this sets a baseline gain which results in the final track being +3~5dB louder than
	// Foobar2000's default ReplayGain target volume.
	// this makes it easier to listen to music in a car, where all other
	// sources are usually ten thousand times louder than RG-adjusted music.
	//
	// opus always forces output to 48kHz sampling rate, but we can still use upsampling
	// to increase RG and alimiter's peak limiting precision, which is desirable in some
	// cases. ffmpeg's `soxr` resampler is quite fast on x86-64: it takes around 5 seconds
	// on my Ryzen 3600 to transcode an 8-minute FLAC with 2x upsample and RG applied.
	//
	// -- @spijet
	OpusCar = NewProfile("audio/ogg", 96, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libopus -vbr on -af "aresample=96000:resampler=soxr, volume=replaygain=track:replaygain_preamp=15dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -f opus -`)
	Opus    = NewProfile("audio/ogg", 96, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libopus -vbr on -af "volume=replaygain=track:replaygain_preamp=6dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -metadata replaygain_album_gain= -metadata replaygain_album_peak= -metadata replaygain_track_gain= -metadata replaygain_track_peak= -metadata r128_album_gain= -metadata r128_track_gain= -f opus -`)
	OpusRG  = NewProfile("audio/ogg", 96, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libopus -vbr on -af "volume=replaygain=track:replaygain_preamp=6dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -metadata replaygain_album_gain= -metadata replaygain_album_peak= -metadata replaygain_track_gain= -metadata replaygain_track_peak= -metadata r128_album_gain= -metadata r128_track_gain= -f opus -`)

	PCM16le = NewProfile("audio/wav", 0, `ffmpeg -v 0 -i <file> -ss <seek> -c:a pcm_s16le -ac 2 -f s16le -`)
)

type BitRate int // kb/s

type Profile struct {
	bitrate BitRate // the default bitrate, but the user can request a different one
	seek    time.Duration
	mime    string
	exec    string
}

func (p *Profile) BitRate() BitRate    { return p.bitrate }
func (p *Profile) Seek() time.Duration { return p.seek }
func (p *Profile) MIME() string        { return p.mime }

func NewProfile(mime string, bitrate BitRate, exec string) Profile {
	return Profile{mime: mime, bitrate: bitrate, exec: exec}
}

func WithBitrate(p Profile, bitRate BitRate) Profile {
	p.bitrate = bitRate
	return p
}
func WithSeek(p Profile, seek time.Duration) Profile {
	p.seek = seek
	return p
}

var ErrNoProfileParts = fmt.Errorf("not enough profile parts")

func parseProfile(profile Profile, in string) (string, []string, error) {
	parts, err := shlex.Split(profile.exec)
	if err != nil {
		return "", nil, fmt.Errorf("split command: %w", err)
	}
	if len(parts) == 0 {
		return "", nil, ErrNoProfileParts
	}
	name, err := exec.LookPath(parts[0])
	if err != nil {
		return "", nil, fmt.Errorf("find name: %w", err)
	}

	var args []string
	for _, p := range parts[1:] {
		switch p {
		case "<file>":
			args = append(args, in)
		case "<seek>":
			args = append(args, fmt.Sprintf("%dus", profile.Seek().Microseconds()))
		case "<bitrate>":
			args = append(args, fmt.Sprintf("%dk", profile.BitRate()))
		default:
			args = append(args, p)
		}
	}

	return name, args, nil
}

// GuessExpectedSize guesses how big the transcoded file will be in bytes.
// Handy if we want to send a Content-Length header to the client before
// the transcode has finished. This way, clients like DSub can render their
// scrub bar and duration as the track is streaming.
//
// The estimate should overshoot a bit (2s in this case) otherwise some HTTP
// clients will shit their trousers given some unexpected bytes.
func GuessExpectedSize(profile Profile, length time.Duration) int {
	if length == 0 {
		return 0
	}

	bytesPerSec := int(profile.BitRate() * 1000 / 8)

	var guess int
	guess += bytesPerSec * int(length.Seconds()-profile.seek.Seconds())
	guess += bytesPerSec * 2 // 2s pading
	guess += 10000           // 10kb byte padding
	return guess
}