feat(bin): update scripts to function format

local/bin/x-thumbgen

@@ -1,39 +1,69 @@
 #!/usr/bin/env bash
-# Generate thumbnails using magick
+# Generate thumbnails using ImageMagick (magick)
 # https://imagemagick.org/script/download.php
 #
-# Defaults to current directory creating thumbs with 1000x1000
-# images with 200px white borders around the original image.
+# Defaults to current directory creating thumbnails with 1000x1000
+# dimensions and 200px white borders around the original image.
 #
 # Defaults can be overridden with ENV variables like this:
 # $ THMB_BACKGROUND=black x-thumbgen ~/images/
 #
 # Created by: Ismo Vuorinen <https://github.com/ivuorinen> 2015
 
-: "${THMB_SOURCE:=$1}"
+set -euo pipefail
+
+# Default values
+: "${THMB_SOURCE:=${1:-}}"
 : "${THMB_BACKGROUND:=white}"
 : "${THMB_RESIZE:=800x800}"
 : "${THMB_EXTENT:=1000x1000}"
 
-[ $# -eq 0 ] && {
+# Print usage information
+usage()
+{
   echo "Usage: $0 /full/path/to/image/folder"
   exit 1
 }
 
-if [ "$THMB_SOURCE" == "" ] || [ ! -d "$THMB_SOURCE" ]; then
-  THMB_SOURCE=$(pwd)
-fi
+# Check if ImageMagick is installed
+check_magick_installed()
+{
+  if ! command -v magick &> /dev/null; then
+    echo "magick not found in PATH, https://imagemagick.org/script/download.php"
+    exit 1
+  fi
+}
 
-if command -v magick &> /dev/null; then
+# Generate thumbnails
+generate_thumbnails()
+{
+  local source=$1
 
   magick \
-    "$THMB_SOURCE/*" \
+    "${source}/*" \
     -resize "$THMB_RESIZE" \
     -background "$THMB_BACKGROUND" \
     -gravity center \
     -extent "$THMB_EXTENT" \
     -set filename:fname '%t_thumb.%e' +adjoin '%[filename:fname]'
+}
 
-else
-  echo "magick not found in PATH, https://imagemagick.org/script/download.php"
-fi
+# Main function
+main()
+{
+  # Validate input
+  if [ -z "$THMB_SOURCE" ]; then
+    usage
+  fi
+
+  # Check if the source directory is valid
+  if [ ! -d "$THMB_SOURCE" ]; then
+    echo "Invalid directory: $THMB_SOURCE"
+    exit 1
+  fi
+
+  check_magick_installed
+  generate_thumbnails "$THMB_SOURCE"
+}
+
+main "$@"