scripts/reduce_bitrate.sh

#!/usr/bin/env bash

TARGET_BITRATE="192k"
ROOT_DIR="."
DRY_RUN=0
CLEANUP_BACKUPS=0

GREEN="\033[1;32m"
BLUE="\033[1;34m"
YELLOW="\033[1;33m"
RED="\033[1;31m"
DIM="\033[2m"
RESET="\033[0m"

usage() {
    echo -e "${BLUE}Usage:${RESET} $0 [-n] [-d DIR] [-c]"
    echo -e "  -n        Dry-run (only show files that would be converted)"
    echo -e "  -d DIR    Working directory (default: current directory)"
    echo -e "  -c        Remove .bak files after successful run"
    echo -e "  -h        Show this help"
}

log_step() { echo -e "\n${BLUE}▶${RESET} $*"; }
log_info() { echo -e "${BLUE}ℹ${RESET}  $*"; }
log_warn() { echo -e "${YELLOW}⚠${RESET}  $*"; }
log_error() { echo -e "${RED}✖${RESET}  $*"; }
log_success() { echo -e "${GREEN}✔${RESET}  $*"; }

get_total_size_mb() {
    local dir="$1"
    find "$dir" -name "*.mp3" -print0 | xargs -0 stat -c '%s' 2>/dev/null | \
        awk '{sum += $1} END {printf "%.2f MB\n", sum/1024/1024}'
}

get_bitrate_kbps() {
    local file="$1"
    local metadata

    metadata=$(ffprobe -v error -select_streams a:0 -show_entries stream=bit_rate \
        -of default=noprint_wrappers=1:nokey=1 "$file" < /dev/null 2>/dev/null)

    if ! [[ "$metadata" =~ ^[0-9]+$ ]]; then
        metadata=$(ffprobe -v error -show_entries format=bit_rate \
            -of default=noprint_wrappers=1:nokey=1 "$file" < /dev/null 2>/dev/null)
    fi

    if [[ "$metadata" =~ ^[0-9]+$ ]]; then
        echo $((metadata / 1024))
        return 0
    fi

    return 1
}

restore_metadata() {
    local source_file="$1"
    local target_file="$2"

    id3cp "$source_file" "$target_file" >/dev/null 2>&1
    return $?
}

process_file() {
    local file="$1"
    local current_bitrate
    local backup_file
    local temp_file

    current_bitrate=$(get_bitrate_kbps "$file") || {
        log_warn "Could not read bitrate for: ${file}"
        ((warn_count++))
        return 0
    }

    if [ "$current_bitrate" -le "${TARGET_BITRATE%k}" ]; then
        log_info "Skip (already <= ${TARGET_BITRATE}): ${file}"
        ((skip_count++))
        return 0
    fi

    if [ "$DRY_RUN" -eq 1 ]; then
        log_info "Would convert (${current_bitrate} kbps ➜ ${TARGET_BITRATE}): ${file}"
        ((dry_run_count++))
        return 0
    fi

    backup_file="${file%.mp3}.bak"
    if [ ! -f "$backup_file" ]; then
        cp "$file" "$backup_file"
        log_success "Backup created: ${backup_file}"
    fi

    temp_file="${file%.mp3}_temp_$$.mp3"
    if ffmpeg -nostdin -y -i "$file" -b:a "${TARGET_BITRATE}" -id3v2_version 3 "$temp_file" > /dev/null 2>&1; then
        mv "$temp_file" "$file"

        # Restore all metadata from backup file
        if restore_metadata "$backup_file" "$file"; then
            log_success "Converted: ${file} (${current_bitrate} kbps ➜ ${TARGET_BITRATE}) ✅"
            ((converted_count++))
        else
            log_error "Metadata restoration failed: ${file}"
            # Revert to backup since metadata restoration failed
            cp "$backup_file" "$file"
            log_warn "Reverted to backup (conversion skipped due to metadata error)"
            ((error_count++))
        fi
    else
        rm -f "$temp_file"
        log_error "ffmpeg failed: ${file}"
        ((error_count++))
    fi
}

# ==================== MAIN ====================

while getopts ":nd:ch" opt; do
    case "$opt" in
        n) DRY_RUN=1 ;;
        d) ROOT_DIR="$OPTARG" ;;
        c) CLEANUP_BACKUPS=1 ;;
        h)
            usage
            exit 0
            ;;
        *)
            usage
            exit 1
            ;;
    esac
done

if ! command -v ffprobe >/dev/null 2>&1 || ! command -v ffmpeg >/dev/null 2>&1; then
    log_error "ffprobe/ffmpeg not found. Please install ffmpeg."
    exit 1
fi

if ! command -v id3cp >/dev/null 2>&1; then
    log_error "id3cp not found. Please install id3lib (Arch: id3lib, Debian/Ubuntu: libid3-tools)."
    exit 1
fi

if [ ! -d "$ROOT_DIR" ]; then
    log_error "Directory not found: ${ROOT_DIR}"
    exit 1
fi

log_step "Starting Bitrate Reduction"
log_info "Target bitrate: ${TARGET_BITRATE}"
log_info "Working directory: ${ROOT_DIR}"
if [ "$DRY_RUN" -eq 1 ]; then
    log_info "Dry-run: enabled"
fi
if [ "$CLEANUP_BACKUPS" -eq 1 ]; then
    log_info "Cleanup backups: enabled"
fi

total_before=$(get_total_size_mb "$ROOT_DIR")
log_info "Total MP3 size before: ${total_before:-0.00 MB}"

converted_count=0
skip_count=0
warn_count=0
error_count=0
dry_run_count=0
file_count=0

log_step "Scanning for MP3 files..."
while IFS= read -r -d '' file; do
    ((file_count++))
    process_file "$file"
done < <(find "$ROOT_DIR" -type f -name "*.mp3" -print0)

if [ "$file_count" -eq 0 ]; then
    log_warn "No MP3 files found in ${ROOT_DIR}"
fi

total_after=$(get_total_size_mb "$ROOT_DIR")
log_info "Total MP3 size after: ${total_after:-0.00 MB}"

log_step "Summary"
log_info "Files scanned: ${file_count}"
log_info "Converted: ${converted_count}"
log_info "Skipped: ${skip_count}"
log_info "Dry-run matches: ${dry_run_count}"
log_info "Warnings: ${warn_count}"
if [ "$error_count" -gt 0 ]; then
    log_error "Errors: ${error_count}"
else
    log_success "Errors: 0"
fi

if [ "$CLEANUP_BACKUPS" -eq 1 ] && [ "$DRY_RUN" -eq 0 ] && [ "$error_count" -eq 0 ]; then
    log_step "Cleaning up backups"
    find "$ROOT_DIR" -name "*.bak" -type f -delete
    log_success "All .bak files removed"
elif [ "$CLEANUP_BACKUPS" -eq 1 ] && [ "$DRY_RUN" -eq 1 ]; then
    log_warn "Cleanup skipped in dry-run mode"
elif [ "$CLEANUP_BACKUPS" -eq 1 ] && [ "$error_count" -gt 0 ]; then
    log_warn "Cleanup skipped due to errors"
fi

log_step "Done 🎉"