#!/usr/bin/env bash

set -eu

tmp_directory=/tmp/transcode
lock_file=/tmp/music-transcode.lock

function die()
{
    printf '%s\n' "$1" >&2
    exit "${2-1}"
}

function transcode_to_mp3()
{
    input_directory="$1"
    input_file_name="$2"
    mp3_directory="$3"
    input_path="$input_directory/$input_file_name"
    output_file_name="$(echo "$input_file_name" | sed -E 's/(\.[^. ]+)?$/.mp3/g')"
    output_path="$mp3_directory/$output_file_name"

    output_directory="$(dirname "$output_path")"
    if [ ! -d "$output_directory" ] ; then
        echo "New Directory: \"$output_directory\""
        mkdir -p "$output_directory" || die "Could not create directory \"$output_directory\"."
    fi

    transcode=false

    if [ ! -f "$output_path" ] ; then
        echo "New MP3: \"$output_path\""
        transcode=true
    elif [ "$input_path" -nt "$output_path" ] ; then
        echo "Input file is newer: \"$output_path\""
        transcode=true
    fi

    if [ "$transcode" = true ] ; then
        input_type="$(file -b --mime-type "$input_path")"
        case "$input_type" in
            "audio/flac"|"audio/x-flac")
                tmp_path="$tmp_directory/$(basename "$output_path")"
                echo "Transcoding MP3..."
                ffmpeg -hide_banner -loglevel fatal -i "$input_path" -y -b:a 320k -qscale:a 2 -id3v2_version 3 -f mp3 "$tmp_path" < /dev/null || die "Failed to transcode to \"$tmp_path\"."
                mv -f "$tmp_path" "$output_path" || die "Could not move file to \"$output_path\"."
                ;;

            application/octet-stream)
                echo "Warning: Assuming \"$input_path\" is a MP3 file."
                ;&
            audio/mpeg)
                echo "Copying MP3..."
                cp -f "$input_path" "$output_path"
                ;;

            *)
                echo "Unsupported input type $input_type (\"$input_path\")"
                return 1
                ;;
        esac
    fi
}

function ogg_add_cover()
{
    ogg_file="$1"
    cover_file="$2"

    tmp_metafile="$tmp_directory/metadata"
    tmp_mdimg="$tmp_directory/image-with-header"

    cover_mime_type="$(file -b --mime-type "$cover_file")"

    description=""
    vorbiscomment --list --raw "$ogg_file" > "$tmp_metafile" && \
        sed -i -e '/^metadata_block_picture/d' "$tmp_metafile" && \
        echo -n "" > "$tmp_mdimg" && \
        printf "0: %.8x" 3 | xxd -r -g0 >> "$tmp_mdimg" && \
        printf "0: %.8x" "$(echo -n "$cover_mime_type" | wc -c)" | xxd -r -g0 >> "$tmp_mdimg" && \
        echo -n "$cover_mime_type" >> "$tmp_mdimg" && \
        printf "0: %.8x" "$(echo -n "$description" | wc -c)" | xxd -r -g0 >> "$tmp_mdimg" && \
        echo -n "$description" >> "$tmp_mdimg" && \
        printf "0: %.8x" 0 | xxd -r -g0  >> "$tmp_mdimg" && \
        printf "0: %.8x" 0 | xxd -r -g0  >> "$tmp_mdimg" && \
        printf "0: %.8x" 0 | xxd -r -g0  >> "$tmp_mdimg" && \
        printf "0: %.8x" 0 | xxd -r -g0  >> "$tmp_mdimg" && \
        printf "0: %.8x" "$(wc -c "$cover_file" | cut --delimiter=' ' --fields=1)" | xxd -r -g0 >> "$tmp_mdimg" && \
        cat "$tmp_cover" >> "$tmp_mdimg" && \
        echo "metadata_block_picture=$(base64 --wrap=0 < "$tmp_mdimg")" >> "$tmp_metafile" && \
        vorbiscomment --write --raw --commentfile "$tmp_metafile" "$ogg_file" && \
        rm "$tmp_metafile" "$tmp_mdimg"
}

function transcode_to_ogg()
{
    input_directory="$1"
    input_file_name="$2"
    ogg_directory="$3"
    input_path="$input_directory/$input_file_name"
    output_file_name="$(echo "$input_file_name" | sed -E 's/(\.[^. ]+)?$/.ogg/g')"
    output_path="$ogg_directory/$output_file_name"

    directory="$(dirname "$output_path")"
    if [ ! -d "$directory" ] ; then
        echo "New Directory: \"$directory\""
        mkdir -p "$directory" || die "Could not create directory \"$directory\"."
    fi

    transcode=false

    if [ ! -f "$output_path" ] ; then
        echo "New OGG: \"$output_path\""
        transcode=true
    elif [ "$input_path" -nt "$output_path" ] ; then
        echo "Input file is newer: \"$output_path\""
        transcode=true
    fi

    if [ "$transcode" = true ] ; then
        input_type="$(file -b --mime-type "$input_path")"

        tmp_ogg="$tmp_directory/$(basename "$output_path")"
        tmp_cover="$tmp_directory/cover"

        case "$input_type" in
            "audio/flac"|"audio/x-flac")
                echo "Transcoding OGG..."
                ffmpeg -hide_banner -loglevel fatal -i "$input_path" -y -map a -qscale:a 6 -id3v2_version 3 -f ogg "$tmp_ogg" < /dev/null || die "Could not transcode to \"$tmp_ogg\"."

                echo "Adding OGG cover image..."
                metaflac --export-picture-to="$tmp_cover" "$input_path" || die "Could not export cover image."
                ogg_add_cover "$tmp_ogg" "$tmp_cover" || die "Could not add cover image to \"$tmp_ogg\"."

                mv -f "$tmp_ogg" "$output_path" || die "Could not move file to \"$output_path\"."
                ;;

            application/octet-stream)
                echo "Warning: Assuming \"$input_path\" is a MP3 file."
                ;&
            audio/mpeg)
                echo "Transcoding OGG..."
                ffmpeg -hide_banner -loglevel fatal -i "$input_path" -y -map a -qscale:a 6 -id3v2_version 3 -f ogg "$tmp_ogg" || die "Could not transcode to \"$tmp_ogg\"."

                echo "Adding OGG cover image..."
                exiftool -Picture -b "$input_path" > "$tmp_cover" || die "Could not export cover image."
                ogg_add_cover "$tmp_ogg" "$tmp_cover" || die "Could not add cover image to \"$tmp_ogg\"."

                mv -f "$tmp_ogg" "$output_path" || die "Could not move file to \"$output_path\"."
                ;;

            *)
                echo "Unsupported input type $input_type (\"$input_path\")"
                return 1
                ;;
        esac
    fi
}

if [ -f "$lock_file" ] ; then
    echo "Another instance is already running. Exiting."
    echo "If you are certain this is the only instance, you can delete the lock file $lock_file"
    exit 2
else
    touch "$lock_file" || die "Could not create lock file."
fi

function cleanup()
{
    rm -f "$lock_file"
    rm -rf "$tmp_directory"
}

trap cleanup EXIT SIGTERM

if [ ! -d "$tmp_directory" ] ; then
    mkdir -p "$tmp_directory" || die "Could not create temporary directory \"$tmp_directory\"."
fi

mp3_out=''
ogg_out=''

while [ $# -gt 1 ] ; do
    case "$1" in
        '--mp3-out')
            mp3_out="$2"
            shift 2
            ;;
        '--ogg-out')
            ogg_out="$2"
            shift 2
            ;;
        '--')
            shift
            break
            ;;
        *)
            >&2 echo "Unknown argument: $1"
            exit 1
            ;;
    esac
done

if [ $# -lt 1 ] ; then
    >&2 echo "Missing input directory argument"
    exit 1
fi

input_directory="$1"

while IFS= read -r -d '' file; do
    if [ "$mp3_out" != '' ] ; then
        transcode_to_mp3 "$input_directory" "$file" "$mp3_out" || break
    fi
    if [ "$ogg_out" != '' ] ; then
        transcode_to_ogg "$input_directory" "$file" "$ogg_out" || break
    fi
done < <(
    find -P "$input_directory" \( -iname '*.flac' -or -iname '*.mp3' \) -printf '%P\0' | sort -z
)

echo "Done transcoding."