#!/usr/bin/env bash

# exit if a command fails
set -o errexit

# exit if required variables are not set
set -o nounset

# number of threads to use
if [[ ${DEBUG} -eq 1 ]]; then
  echo "Running single thread for debugging"
  parallel_thread_count=1
  export oxipng_thread_count=1
else
  parallel_thread_count=8
  export oxipng_thread_count=4
fi

# commands required for script execution
required_commands="oxipng parallel"

function check_dependencies() {
  local missing_counter
  missing_counter=0
  for command in ${required_commands}; do
    if ! hash "${command}" >/dev/null 2>&1; then
      printf "Command not found in PATH: %s\n" "${command}" >&2
      ((missing_counter++))
    fi
  done
  if ((missing_counter > 0)); then
    printf "%d or more commands are missing from PATH. Exiting.\n" "${missing_counter}" >&2
    exit 1
  fi
}

# make sure the correct number of arguments are passed; if not, output syntax and exit
if [ "$#" -ne 1 ]; then
  echo -e "\nUsage: ${0} <temporary directory>\n"
  exit 1
fi

# set base directory (passed from invoking command)
base_dir="${1}"

# skip optimizing the optimization directories
if [[ "$(pwd)" == *".optimized" ]]; then
  if [[ ${DEBUG} -eq 1 ]]; then
    echo "Skipping optimization directory"
  fi
  exit 0
fi

# store current directory
current_dir="$(pwd)"
export current_dir
if [[ ${DEBUG} -eq 1 ]]; then
  echo "Current directory is ${current_dir}"
fi

# create directory for file hashes
hash_dir="${current_dir}/.optimized"
export hash_dir
mkdir -p "${hash_dir}"
if [[ ${DEBUG} -eq 1 ]]; then
  echo "Hash directory is ${hash_dir}"
fi

# create matching filesystem hierarchy in tempdir
temp_dir="${base_dir}$(readlink -f .)"
export temp_dir
mkdir -p "${temp_dir}"
if [[ ${DEBUG} -eq 1 ]]; then
  echo "Created temporary directory ${temp_dir} for ${current_dir}"
fi

# create temporary file to store pending commands
commands="${temp_dir}/commands.txt"
if [[ ${DEBUG} -eq 1 ]]; then
  echo "Storing commands for ${current_dir} in ${commands}"
fi

# attempt to optimize png, and store hash of output file if successful
function optimize_png() {
  local file_name
  file_name="${1}"

  local stored_hash
  stored_hash="${hash_dir}/${file_name}.hash"

  local current_hash
  current_hash="${temp_dir}/${file_name}.hash"

  local new_file
  new_file="${temp_dir}/${file_name}"

  local old_file
  old_file="${current_dir}/${file_name}"

  sha256sum "${old_file}" | cut -d " " -f 1 > "${current_hash}"

  if [ -f "${stored_hash}" ] && cmp -s "${current_hash}" "${stored_hash}"; then
    if [[ ${DEBUG} -eq 1 ]]; then
      echo "${current_hash} matches ${stored_hash}"
    fi
    return
  fi

  if [[ ${DEBUG} -eq 1 ]]; then
    echo "${current_hash} does not match ${stored_hash}"
    return
  fi

  if oxipng --opt 2 --quiet --zopfli --out "${new_file}" --strip safe --threads "${oxipng_thread_count}" "${old_file}"; then
    mv "${new_file}" "${old_file}"
    sha256sum "${old_file}" | cut -d " " -f 1 > "${current_hash}"
    mv "${current_hash}" "${stored_hash}"
  fi

  if [[ ${DEBUG} -eq 1 ]]; then
    sleep 1
  fi
}
export -f optimize_png

# generate list of commands to run
for input_file in *.png; do
  if [ -f "${input_file}" ]; then
    echo "optimize_png \"${input_file}\"" >> "${commands}"
  fi
done

# run commands in parallel
if [ -s "${commands}" ]; then
  parallel --no-notice --jobs "${parallel_thread_count}" < "${commands}"
fi