#!/usr/bin/env bash

set -o nounset
set -E

required_commands="exiftool identify oxipng parallel"
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

MAX_DAYS="${MAX_DAYS:-7}"
if [[ "${MAX_DAYS}" =~ ^[0-9]+$ ]]; then
  max_mins="$(("${MAX_DAYS}"*60*24))"
  export -p max_mins
else
  echo "MAX_DAYS must be a positive integer value"

  exit 1
fi

DEBUG=${DEBUG:-0}
if [[ ${DEBUG} -eq 1 ]]; then
  echo "DEBUG: Running single threaded"
  parallel_thread_count=1
  oxipng_thread_count=1
else
  parallel_thread_count=8
  oxipng_thread_count=4
fi
export -p DEBUG
export -p parallel_thread_count
export -p oxipng_thread_count

lock_file="/run/user/$(id -ru)/optimize-pngs.lock"
if [ -f "${lock_file}" ]; then
  echo "Process already running at pid $(cat "${lock_file}")."

  exit 0
fi
echo "$$" > "${lock_file}"

function cleanup {
  if ! { rm "${lock_file}"; }; then
    echo "Cleanup failed. You may need to manually remove ${lock_file}."
  fi
}
trap cleanup EXIT

base_dir="$(mktemp -d)"
if [[ ${DEBUG} -eq 1 ]]; then
  echo "DEBUG: Temporary files will be written to ${base_dir}"
fi
export -p base_dir

commands="${base_dir}/commands.txt"
if [[ ${DEBUG} -eq 1 ]]; then
  echo "DEBUG: Storing commands for $(pwd) in ${commands}"
fi
export -p commands

optimize_png() {
    if [ "$#" -ne 2 ]; then
    echo -e "\nUsage: ${0} <temporary directory> <file path>\n"

    exit 1
  fi

  local temp_dir
  temp_dir="${1}"

  local file_path
  file_path="${2}"

  local stored_checksum
  stored_checksum="$(exiftool -ignoreMinorErrors -short -short -short -Comment "${file_path}")"

  local current_checksum
  current_checksum="$(identify -quiet -format '%#\n' "${file_path}")"

  local new_file
  new_file="${temp_dir}${file_path}"

  if [ "${current_checksum}" == "${stored_checksum}" ]; then
    if [[ ${DEBUG} -eq 1 ]]; then
      echo "DEBUG: Stored and calculated checksums match for ${file_path}"
    fi

    return
  fi

  if oxipng --opt 2 --quiet --alpha --keep="tEXt,display" --zopfli --out "${new_file}" --threads "${oxipng_thread_count}" "${file_path}"; then
    local old_size
    old_size=$(du -b "${file_path}" | awk '{print $1}')
    
    local old_size_human
    old_size_human=$(du -h "${file_path}" | awk '{print $1}')
    
    local new_size
    new_size=$(du -b "${new_file}" | awk '{print $1}')

    local new_size_human
    new_size_human=$(du -h "${new_file}" | awk '{print $1}')

    local new_percentage
    new_percentage=$(echo "scale=2; ${new_size}/${old_size}*100" | bc)

    local rounded_percentage
    rounded_percentage=$(printf "%.0f" "${new_percentage}")

    local new_checksum
    new_checksum=$(identify -quiet -format '%#\n' "${new_file}")

    exiftool -ignoreMinorErrors -Comment="${new_checksum}" "${new_file}" >/dev/null 2>&1

    echo "Reduced file size of ${file_path} from ${old_size_human} to ${new_size_human} (${rounded_percentage}%)"

    if [[ ${DEBUG} -eq 1 ]]; then
      SHELLNOCASEMATCH=$(shopt -p nocasematch; true)
      shopt -s nocasematch
      read -r -p 'Replace with optimized file? [y/N]: ' keep_file
      if [[ "${keep_file}" == "n" ]]; then
        echo "DEBUG: Not modifying ${file_path}."

        $SHELLNOCASEMATCH

        return
      else
        echo "DEBUG: Replacing ${file_path} with optimized version."
      fi
      $SHELLNOCASEMATCH
    fi

    mv "${new_file}" "${file_path}"
  fi
}
export -f -p optimize_png

optimize_pngs() {
  if [ "$#" -ne 2 ]; then
    echo -e "\nUsage: ${0} <temporary directory> <target path>\n"

    exit 1
  fi

  local base_dir
  base_dir="${1}"

  local target_path
  target_path="${2}"

  if [[ ${DEBUG} -eq 1 ]]; then
    echo "DEBUG: Target path is ${target_path}"
  fi

  temp_dir="${base_dir}${target_path}"
  mkdir -p "${temp_dir}"
  if [[ ${DEBUG} -eq 1 ]]; then
    echo "DEBUG: Created temporary directory ${temp_dir} for ${target_path}"
  fi

  local commands
  commands="${temp_dir}/commands.txt"
  if [[ ${DEBUG} -eq 1 ]]; then
    echo "DEBUG: Storing commands for ${target_path} in ${commands}"
  fi

  while read -r input_file; do
    if [ -f "${input_file}" ]; then
      printf 'bash -c \"optimize_png %q %q\"\n' "${temp_dir}" "${input_file}" >> "${commands}"
    fi
  done <<< "$(find "${target_path}" -mindepth 1 -maxdepth 1 -type f -name '*.png' -mmin -"${max_mins}" -print)"

  if [ -s "${commands}" ]; then
    parallel --line-buffer --no-notice --jobs "${parallel_thread_count}" < "${commands}"
  fi
}
export -f -p optimize_pngs

while read -r path; do
  printf 'bash -c \"optimize_pngs %q %q\"\n' "${base_dir}" "${path}" >> "${commands}"
done <<< "$(find "$(pwd -P)" -type d)"

parallel --line-buffer --no-notice --jobs "${parallel_thread_count}" < "${commands}"

SHELLNOCASEMATCH=$(shopt -p nocasematch; true)
shopt -s nocasematch
read -r -p 'Delete temporary directory? [y/N]: ' remove_temp_dir
if [[ "${remove_temp_dir}" == "y" ]]; then
  rm -rf "${base_dir}"
fi
$SHELLNOCASEMATCH