#!/usr/bin/env bash

root="${1:-.}"
mode="${2:-}"
THRESHOLD=40
find "$root" \( -iname '*.mp3' -o -iname '*.m4a' -o -iname '*.m4b' \) -print0 |
while IFS= read -r -d '' f; do

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

    description=$(ffprobe -v error \
        -show_entries format_tags=description \
        -of default=nw=1:nk=1 \
        -- "$f")
    # trim comment
    comment="${comment#"${comment%%[![:space:]]*}"}"
    comment="${comment%"${comment##*[![:space:]]}"}"

    # ---- DELETE MODE ----
    if [[ "$mode" == "--delete" && -n "$comment" && ${#comment} -lt $THRESHOLD ]]; then
        tmp=$(mktemp -p "$(dirname -- "$f")" ".fftmp.XXXXXX.${f##*.}") || continue

        echo "Removing short comment: $f"
        echo "  comment: $comment"

        ffmpeg -nostdin -v error -y \
            -i "$f" \
            -map 0 \
            -map_metadata 0 \
            -c copy \
            -metadata comment= \
            "$tmp" &&
        mv -f -- "$tmp" "$f" || {
            echo "FAILED: $f" >&2
            rm -f -- "$tmp"
        }

        continue
    fi

    # ---- SCAN MODE ----
    # only show short non-empty tags (<20 chars)
    for tag in comment description; do
        value="${!tag}"

        value="${value#"${value%%[![:space:]]*}"}"
        value="${value%"${value##*[![:space:]]}"}"

        if [[ -n "$value" && ${#value} -lt $THRESHOLD ]]; then
            printf "%s\n  %s: %s\n\n" "$f" "$tag" "$value"
        fi
    done

done