#!/bin/bash

# Check for ffmpeg dependency
if ! command -v ffmpeg &> /dev/null; then
    echo "ffmpeg could not be found. Please install ffmpeg to use this script."
    exit 1
fi

# Number of concurrent ffmpeg processes
N=${1:-8}

# Semaphore file for limiting concurrent processes
semaphore=/tmp/ffmpeg.lock

# Opening the semaphore file descriptor on 9
exec 9>"$semaphore"

# Function to run an ffmpeg command with semaphore locking
run_ffmpeg() {
  # Wait for a semaphore slot to become available
  flock -x 9

  # Execute the ffmpeg command
  ffmpeg -y -i "$1" -af "loudnorm=I=-16:LRA=11:measured_I=-20:measured_LRA=16,volume=0.8" "$2"
  if [ $? -ne 0 ]; then
    echo "An error occurred with ffmpeg processing $1"
    # Release the semaphore slot on error as well
    flock -u 9
    return 1
  fi

  # Release the semaphore slot
  flock -u 9
}

# Create the semaphore file if it does not exist
touch "$semaphore"
if [ ! -f "$semaphore" ]; then
    echo "Failed to create semaphore file."
    exit 1
fi

# Processing each .opus file
find . -maxdepth 1 -type f -name '*.m4a' | while read -r file; do
  wav_file="${file/%.m4a/.wav}"
  if [ ! -f "$wav_file" ]; then
    echo "Processing $file..."
    run_ffmpeg "$file" "$wav_file" &

    # Ensure N parallel ffmpeg processes
    while [ $(jobs -p | wc -l) -ge "$N" ]; do
      wait -n
    done
  fi
done

# Wait for all background jobs to finish
wait

# Close the semaphore file descriptor and remove the file
exec 9>&-
rm -f "$semaphore"