Add styler theming framework

Sets up basic theming program styler which can be called to change
theming of various applications.

styler/.local/bin/styler

@@ -0,0 +1,115 @@
+#!/usr/bin/env bash
+
+readonly BASE_PATH="${STYLER_DATA_PATH:-${XDG_DATA_HOME:-$HOME/.local/share}/styler}"
+readonly DEBUG="${STYLER_ENABLE_DEBUG_MODE:-false}"
+
+readonly PACKAGE_PATH="$BASE_PATH/packages"
+readonly PROCESSOR_PATH="$BASE_PATH/processors"
+
+main() {
+  local cmd=""
+  local ret=0
+
+  case "$1" in
+  -s | --set | set)
+    cmd="set_theme"
+    ;;
+  -v | --version | version)
+    printf "Program theming script.\n\n©Marty Oehme\n\nVersion: 0.1.0\n"
+    exit 0
+    ;;
+  -h | --help | help | *)
+    cmd="usage"
+    ;;
+  esac
+  shift
+
+  $cmd "$1"
+  ret=$((ret + $?))
+  exit $ret
+}
+
+usage() {
+  printf "%s\n" \
+    "" \
+    " styler -      Quickly switch your linux style." \
+    "               Uses base16 themes to quickly set them for a variety of applications." \
+    "" \
+    " Usage: styler [-hv | set base16-themename]" \
+    "" \
+    " Options:" \
+    "" \
+    "     -s | set        Set the theme. Use any valid base16 theme name (without base16- prefix)." \
+    "" \
+    "     -h | help       Print out this help." \
+    "" \
+    "     -v | version    Print out program information." \
+    "" \
+    ""
+}
+
+# retrieves all relevant packages from BASE_PATH/packages
+# 'relevant' here means they follow github pattern of author/repository
+get_packages() {
+  for author in "$PACKAGE_PATH"/*; do
+    # TODO should eventually be used to either distinguish between author/pkg and pkg packages
+    # or to spit out a warning if they should not be used.
+    # if grep -q -e '^base16-' <<<"$(basename -- "$author")"; then
+    #   echo ERROR
+    # fi
+    for package in "$author"/*; do
+      [[ -e "$author" ]] || break
+      [[ -d "$package" ]] || break
+      printf "%s/%s\n" "$(basename -- "$author")" "$(basename -- "$package")"
+    done
+  done
+}
+
+# retrieves all processors from BASE_PATH/processors
+# 'relevant' here means they follow github pattern of author/repository
+get_processors() {
+  for processor in "$PROCESSOR_PATH"/*; do
+    [[ -e "$processor" ]] || break
+    [[ -f "$processor" ]] || break
+    printf "%s\n" "$(basename -- "$processor")"
+  done
+}
+
+set_theme() {
+  local theme="$1"
+
+  local packages
+  packages="$(get_packages)"
+  if [[ -z "$packages" ]]; then
+    printf "ERROR: No base16 packages installed. Please install at least 1 base16 package in %s/.\n" "$PACKAGE_PATH" >&2
+    exit 1
+  fi
+
+  local processors
+  processors="$(get_processors)"
+  if [[ -z "$processors" ]]; then
+    printf "ERROR: No application processors installed. Please install at least one processor in %s/.\n" "$PROCESSOR_PATH" >&2
+    exit 1
+  fi
+
+  for pkg in $packages; do
+    local appext
+
+    # filter the application a package targets, since base16 packages
+    # carry standard names this removes everything before base16-
+    # the result is the application it targets
+    # shellcheck disable=SC2001
+    appext=$(sed "s|^[[:alnum:]]\{1,\}/base16-||" <<<"$pkg")
+
+    # Compares application extension with existing processors and runs the appropriate processor if found
+    processor="$PROCESSOR_PATH/theme_$appext"
+    if [[ -f "$processor" ]]; then
+      "$processor" "$PACKAGE_PATH" "$pkg" "$theme"
+    else
+      printf "WARN: No processor found for application %s in %s. Make sure you install a processor for the application.\n" "$appext" "$PROCESSOR_PATH/" >&2
+    fi
+
+  done
+}
+
+main "$@"