diff --git a/theme_qutebrowser b/theme_qutebrowser
index 508a218..a667858 100755
--- a/theme_qutebrowser
+++ b/theme_qutebrowser
@@ -1,97 +1,94 @@
 #!/usr/bin/env bash
 readonly dependency=("theova/base16-qutebrowser")
+readonly app="qutebrowser"
 
-path="$1"
-package="$2"
-theme="$3"
-permanent="$4"
+readonly path="$1"
+readonly package="$2"
+readonly theme="$3"
+readonly permanent="$4"
 
-file_exists() {
-  if [[ -f "$1" ]]; then
-    true
-  else
-    false
-  fi
-}
-# check for existence of pattern $2 in file $1
-line_exists() {
-  local file="$1"
-  local line="$2"
+# Safe sourcing: https://stackoverflow.com/a/12694189
+DIR="${BASH_SOURCE%/*}"
+if [[ ! -d "$DIR" ]]; then DIR="$PWD"; fi
+# shellcheck source=utilities.sh
+. "$DIR/utilities.sh"
 
-  if ! file_exists "$file" || ! grep -qe "$line" "$file"; then
-    false
-  else
-    true
-  fi
-}
-# prepare newline at eof to make adding newlines easier
-eol_exists_or_append() {
-  local file="$1"
-  local eof
-  eof=$(tail -c 1 "$file")
-
-  if [ -n "$eof" ]; then
-    printf "\\n" >>"$file"
-  fi
-}
-# append line $2 to file $1
-line_exists_or_append() {
-  local file="$1"
-  local line="$2"
-  local new="${3:-$2}"
-
-  if ! line_exists "$file" "$line"; then
-    eol_exists_or_append "$file"
-    echo "$new" >>"$file"
-  fi
-}
-check_tfile() {
-  if ! file_exists "$tfile"; then
-    dbg_msg="$dbg_msg theme $theme for qutebrowser not found.\n"
-    exit 1
-  fi
-}
-
-theme_qutebrowser() {
-  dbg_msg="QUTEBROWSER: $package - "
+## Main Entrypoint
+#
+#  Finds the right theme template file and starts theme
+#  switching and, if necessary, permanent setting processes.
+main() {
+  dbg_msg $app "Starting Processor"
   tfile="$path/$package/themes/default/base16-$theme.config.py"
 
-  check_tfile
+  if ! file_exists "$tfile"; then
+    dbg_msg $app "error" "Theme template $theme not found in package $package"
+    exit 1
+  fi
 
-  if [[ "$permanent" == "true" ]]; then set_qutebrowser_theme; fi
-  switch_qutebrowser_theme
+  if [[ "$permanent" == "true" ]]; then save; fi
+  theme
 
-  [[ "$DEBUG" == true ]] && echo "$dbg_msg"
+  dbg_msg $app "Processor Done"
 }
 
-switch_qutebrowser_theme() {
+## Theme switcher
+#
+#  Makes sure that if any application instance is
+#  currently running, it switches to new theme.
+theme() {
+  dbg_msg $app "Switching theme"
   # make sure qutebrowser is running
-  pgrep qutebrowser >/dev/null || return
+  pgrep qutebrowser >/dev/null || {
+    dbg_msg $app "warn" "No instance running, not switching theme"
+    return
+  }
   qutebrowser --loglevel error ":config-source $tfile"
+  dbg_msg $app "Successfully switched theme"
 }
 
-set_qutebrowser_theme() {
+## Theme setter
+#
+#  Takes care of permanently writing the desired
+#  base16 theme into application settings.
+save() {
+  dbg_msg $app "Saving theme"
   local qt_dir="${XDG_CONFIG_HOME:-/$HOME/.config}/qutebrowser"
 
   if [[ -d "$qt_dir" ]]; then
     cat "$tfile" >"$qt_dir/colorscheme.py"
+    dbg_msg $app "Saved theme to $qt_dir/colorscheme.py"
 
-    call_from_config "$qt_dir"
-
-    dbg_msg="$dbg_msg Set theme $theme\n"
+    include "$qt_dir"
+  else
+    dbg_msg $app "warn" "No qutebrowser configuration directory found"
   fi
 }
 
-call_from_config() {
+## Theme includer
+#
+#  Makes sure that theme is actually included in
+#  default application startup routine.
+#  This is the most invasive step of theming since it
+#  rewrites within existing configuration files.
+include() {
   local qt_dir="$1"
+  dbg_msg $app "Including theme in configuration"
 
   if file_exists "$qt_dir/config.py"; then
     line_exists_or_append "$qt_dir/config.py" "config.source('colorscheme.py')"
+    dbg_msg $app "Successfully included theme in configuration"
+  else
+    dbg_msg $app "warn" "No default configuration file found"
   fi
 }
 
+## Dependency Checker
+#
+#  Makes sure the processor is called for the correct
+#  base16 package, or refuses to run if it is not.
 if printf '%s\n' "${dependency[@]}" | grep -q -P "^$package$"; then
-  theme_qutebrowser
+  main
 else
-  printf "Processor does not work for %s, please use another." "$package"
+  dbg_msg $app "error" "Processor does not work for package $package"
 fi