#!/usr/bin/env bash

# Usage:
# ./mp3_transfer.sh -s 1.3 /mnt/mp3player file1.m4a file2.m4a ...

set -e

# Default speed
SPEED=1.0

# Parse options
while getopts ":s:" opt; do
  case $opt in
    s)
      SPEED=$OPTARG
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      exit 1
      ;;
    :)
      echo "Option -$OPTARG requires a value." >&2
      exit 1
      ;;
  esac
done

# Shift past the options
shift $((OPTIND -1))

# Check arguments
if [ "$#" -lt 2 ]; then
  echo "Usage: $0 [-s speed] MOUNT_POINT FILE1 [FILE2 ...]"
  exit 1
fi

MOUNT_POINT=$1
shift
FILES=("$@")

# Check mount point exists
if [ ! -d "$MOUNT_POINT" ]; then
  echo "Error: Mount point '$MOUNT_POINT' does not exist."
  exit 1
fi

# Estimate required space
TOTAL_SIZE=0
for f in "${FILES[@]}"; do
  if [ ! -f "$f" ]; then
    echo "Warning: File '$f' does not exist, skipping."
    continue
  fi
  # Get file size in bytes
  FILE_SIZE=$(stat --printf="%s" "$f")
  # Estimate mp3 output size: roughly 1/2 of original m4a (adjust if needed)
  TOTAL_SIZE=$((TOTAL_SIZE + FILE_SIZE / 2))
done

# Get available space in bytes
AVAILABLE=$(df --output=avail "$MOUNT_POINT" | tail -n 1)
AVAILABLE=$((AVAILABLE * 1024))  # df reports in KB

if [ "$TOTAL_SIZE" -gt "$AVAILABLE" ]; then
  echo "Error: Not enough space on device. Required: $TOTAL_SIZE bytes, Available: $AVAILABLE bytes"
  exit 1
fi

echo "Enough space available. Starting conversion..."

sanitize_filename() {
  local name="$1"
  # Remove path, keep only base name
  name=$(basename "$name")
  # Remove any extension
  name=${name%.*}
  # Replace spaces and special chars with underscore
  name=$(echo "$name" | tr ' ' '_' | tr -cd '[:alnum:]_-')
  # Truncate to max 50 chars
  echo "${name:0:50}"
}

# Convert and copy files
for f in "${FILES[@]}"; do
  if [ ! -f "$f" ]; then
    continue
  fi

  # Determine the next prefix
  existing_prefixes=$(ls "$MOUNT_POINT" | grep -E '^[0-9].*\.mp3$' | sed -E 's/^([0-9]).*/\1/' | sort -n | uniq)
  for i in {0..9}; do
    if ! echo "$existing_prefixes" | grep -q "^$i$"; then
      PREFIX=$i
      break
    fi
  done

  echo "Using prefix: $PREFIX"

  BASENAME=$(sanitize_filename "$f")
  OUT_PATTERN="$MOUNT_POINT/${PREFIX}_%03d_${BASENAME}.mp3"

  echo "Converting '$f' to '$OUT_PATTERN' at speed $SPEED..."

  ffmpeg -nostdin -i "$f" \
    -filter:a "atempo=$SPEED" \
    -ar 22050 -ac 1 -c:a libmp3lame -b:a 32k \
    -f segment -segment_time 300 \
    "$OUT_PATTERN"

  # Update prefix for next file
  # Count how many segments were created
  SEG_COUNT=$(ls "$MOUNT_POINT" | grep -E "^${PREFIX}[0-9]{2}_" | wc -l)
  PREFIX=$((PREFIX + SEG_COUNT))
done

echo "All files processed successfully."