#!/usr/bin/env bash

LIBRARY="${1:-.}"
mapfile -t FILES < <(
    find "$LIBRARY" -type f \( \
        -iname "*.mp3" -o \
        -iname "*.m4b" -o \
        -iname "*.m4a" \
    \)
)
TOTAL=${#FILES[@]}
PROCESSED=0
for f in "${FILES[@]}"; do
    ((PROCESSED++))
    if (( PROCESSED % 100 == 0 )); then
        echo "Progress: $PROCESSED/$TOTAL files processed"
    fi

    comment=$(ffprobe -v error \
        -show_entries format_tags=comment \
        -of default=nw=1:nk=1 \
        -- "$f")
    shopt -s nocasematch

[[ $comment =~ (read[[:space:]]+by|spoken[[:space:]]+by|narrated[[:space:]]+by|gesprochen[[:space:]]+von|gelesen[[:space:]]+von)[[:space:]]+([^.$'\n']*) ]] ||  continue

    composer="${BASH_REMATCH[2]}"
composer="${composer%"${composer##*[!.,[:space:]]}"}"
    printf '[%d/%d] [%s] %s | OLD="%s" | NEW="%s
"\n' "$PROCESSED" "$TOTAL" "Update" "$f" "$comment" "$composer"    

    dir=$(dirname -- "$f")
    base=$(basename -- "$f")
    ext="${base##*.}"

    case "${ext,,}" in
        mp3) format=mp3 ;;
        m4a|m4b) format=ipod ;;
        *) continue ;;
    esac

    tmp=$(mktemp -p "$dir" ".${base}.XXXXXX") || {
        echo "Couldn't create temporary file in $dir" >&2
        continue
    }

    if ffmpeg -nostdin -v error -y \
        -i "$f" \
        -map 0 \
        -map_metadata 0 \
        -c copy \
        -metadata composer="$composer" \
        -metadata comment= \
        -f "$format" \
        "$tmp"
    then
        mv -f -- "$tmp" "$f"
    else
        echo "FAILED: $f" >&2
        rm -f -- "$tmp"
    fi
done