#!/usr/bin/env bash
#
# Generate thumbnails using ImageMagick (magick) with MIME type filtering.
# https://imagemagick.org/script/download.php
#
# This script recursively processes images in a given directory (and its subdirectories)
# by using the `mimetype` command to detect file types. Files with MIME types that are not
# supported by ImageMagick (as defined in the ALLOWED_MIMETYPES array) are skipped.
#
# Defaults (can be overridden by environment variables or command-line options):
#   THUMB_SOURCE: Directory with images (provided as a positional argument)
#   THUMB_OUTPUT: Directory to store thumbnails (default: same as THUMB_SOURCE)
#   THUMB_BACKGROUND: Background color (default: white)
#   THUMB_RESIZE: Resize dimensions (default: 800x800)
#   THUMB_EXTENT: Canvas dimensions (default: 1000x1000)
#   THUMB_SUFFIX: Suffix appended to filename (default: _thumb)
#
# Options:
#   -o output_directory  Specify the output directory for thumbnails (default: same as source).
#   -s suffix            Specify a custom suffix for thumbnail filenames (default: _thumb).
#   -h, --help           Display this help message and exit.
#
# Example:
#   THUMB_BACKGROUND=black x-thumbgen.sh -o ~/thumbnails ~/images/
#
# Author: Ismo Vuorinen <https://github.com/ivuorinen> 2015
# Improved in 2025

set -euo pipefail

usage()
{
  cat << EOF
Usage: $0 [options] source_directory

Options:
  -o output_directory  Specify the output directory for thumbnails (default: same as source).
  -s suffix            Specify a custom suffix for thumbnail filenames (default: _thumb).
  -h, --help           Display this help message and exit.
EOF
  exit 1
}

# Default values (can be overridden by ENV variables)
THUMB_SOURCE=""
THUMB_OUTPUT=""
THUMB_BACKGROUND="${THUMB_BACKGROUND:-white}"
THUMB_RESIZE="${THUMB_RESIZE:-800x800}"
THUMB_EXTENT="${THUMB_EXTENT:-1000x1000}"
THUMB_SUFFIX="${THUMB_SUFFIX:-_thumb}"

# List of MIME types supported by ImageMagick (adjust as needed)
ALLOWED_MIMETYPES=("image/jpeg" "image/png" "image/gif" "image/bmp" "image/tiff" "image/webp")

check_magick_installed()
{
  if ! command -v magick &> /dev/null; then
    echo "Error: 'magick' command not found. Please install ImageMagick from https://imagemagick.org/script/download.php" >&2
    exit 1
  fi
}

check_mimetype_installed()
{
  if ! command -v mimetype &> /dev/null; then
    echo "Error: 'mimetype' command not found. Please install it (e.g. via 'sudo apt install libfile-mimeinfo-perl' on Debian/Ubuntu)." >&2
    exit 1
  fi
}

# Helper function to check if a given MIME type is allowed
is_supported_mimetype()
{
  local mt=$1
  for allowed in "${ALLOWED_MIMETYPES[@]}"; do
    if [[ "$mt" == "$allowed" ]]; then
      return 0
    fi
  done
  return 1
}

# Parse command-line options using getopts
parse_options()
{
  while getopts ":o:s:h-:" opt; do
    case $opt in
      o)
        THUMB_OUTPUT="$OPTARG"
        ;;
      s)
        THUMB_SUFFIX="$OPTARG"
        ;;
      h)
        usage
        ;;
      -)
        if [[ "$OPTARG" == "help" ]]; then
          usage
        else
          echo "Error: Unknown option --$OPTARG" >&2
          usage
        fi
        ;;
      \?)
        echo "Error: Invalid option -$OPTARG" >&2
        usage
        ;;
      :)
        echo "Error: Option -$OPTARG requires an argument." >&2
        usage
        ;;
    esac
  done
  shift $((OPTIND - 1))

  # The remaining argument should be the source directory.
  if [ $# -lt 1 ]; then
    echo "Error: Source directory is required." >&2
    usage
  fi

  THUMB_SOURCE="$1"
}

# Generate thumbnails recursively using find and filtering by MIME type
generate_thumbnails()
{
  local source_dir=$1
  local output_dir=$2

  # Ensure the output directory exists (create if necessary)
  if [ ! -d "$output_dir" ]; then
    mkdir -p "$output_dir"
  fi

  # Recursively find all files.
  while IFS= read -r -d '' file; do
    # Use mimetype to determine the file's MIME type.
    file_mimetype=$(mimetype -b "$file")
    if ! is_supported_mimetype "$file_mimetype"; then
      echo "Skipping unsupported MIME type '$file_mimetype' for file: $file" >&2
      continue
    fi

    # Determine the relative path with respect to the source directory.
    rel_path="${file#$source_dir/}"
    dir="$(dirname "$rel_path")"
    base="$(basename "$rel_path")"
    filename="${base%.*}"
    ext="${base##*.}"

    # Create corresponding output subdirectory
    out_dir="${output_dir}/${dir}"
    mkdir -p "$out_dir"
    outfile="${out_dir}/${filename}${THUMB_SUFFIX}.${ext}"

    echo "Processing '$file' -> '$outfile'..."
    magick "$file" \
      -resize "$THUMB_RESIZE" \
      -background "$THUMB_BACKGROUND" \
      -gravity center \
      -extent "$THUMB_EXTENT" \
      "$outfile"
  done < <(find "$source_dir" -type f -print0)
}

main()
{
  parse_options "$@"

  if [ -z "$THUMB_SOURCE" ]; then
    echo "Error: Source directory not specified." >&2
    usage
  fi

  if [ ! -d "$THUMB_SOURCE" ]; then
    echo "Error: Source directory '$THUMB_SOURCE' does not exist or is not accessible." >&2
    exit 1
  fi

  # If output directory is not specified, default to the source directory.
  if [ -z "$THUMB_OUTPUT" ]; then
    THUMB_OUTPUT="$THUMB_SOURCE"
  fi

  check_magick_installed
  check_mimetype_installed
  generate_thumbnails "$THUMB_SOURCE" "$THUMB_OUTPUT"
}

main "$@"