Minor code refinements

Clean up some parts of the code without affecting each script's
functionality.  Improve the documentation.

bin/bin/own_script_notify_send_mpc_status

@@ -21,32 +21,39 @@
 # Assign this executable to a key binding for your convenience.  This
 # file is part of my dotfiles: https://gitlab.com/protesilaos/dotfiles
 #
-# Dependency for sending desktop notifications:
+# Debian buster dependency for sending desktop notifications:
 # 	apt install libnotify-bin
 #
-# Optional dependency to display album art:
+# Optional dependencies to display album art:
 # 	apt install playerctl mpDris2
 
 # Fetch album art information using playerctl, if it is installed.  Else
 # display generic icon.
 if [ "$(command -v playerctl 2> /dev/null)" ]; then
+	# TODO use paramater expansion instead of sed
 	album_art=$(playerctl metadata 'mpris:artUrl' --player=mpd | sed 's,file://,,')
 else
 	# else use the "rhythmbox" icon from the available icon theme
 	album_art='rhythmbox'
 fi
 
+# The square brackets are meant to display their content only if the
+# included metatag is available.  This is documented in `man mpc`.
+mpc_format="$(mpc --format '%artist% - %title%\n%album%[ (%date%)]' current)"
+
 # This script accepts "cli" as a single argument, in which case it
 # prints the notification to the terminal (stdout).  Otherwise it sends
 # a desktop notification (if the dependency is already installed).
 if [ "$1" == "cli" ]; then
-	echo -e "$(mpc --format '%artist% - %title%\\n%album% (%date%)' current)"\\n"Album art: $album_art"
+	echo "$mpc_format"
+	echo "Album art: $album_art"
 else
 	if [ "$(command -v notify-send 2> /dev/null)" ]; then
-		notify-send -i "$album_art" "Now Playing" "$(mpc --format '%artist% - %title%\\n%album% (%date%)' current)"
+		notify-send -i "$album_art" "Now Playing" "$mpc_format"
 	else
-		echo -e "ERROR. Missing dependency 'libnotify-bin'.\
-		\\nThis is the package that provides the 'notify-send' command.\
-		\\nCannot send message to the notification daemon without it."
+		echo "ERROR. Missing Debian buster dependency 'libnotify-bin'"
+		echo "Cannot send desktop notification"
+		echo "Aborting"
+		exit 1
 	fi
 fi

bin/bin/tempusmenu

@@ -44,24 +44,38 @@
 # General variables {{{
 # ---------------------
 
-# Array with all available tempus themes.  The `sed` command cleans up
-# the output, stripping it of surrounding text. As for `sort`, it just
-# presents the output in alphabetical order.
-tempus_themes_array=$(find "$HOME/.local/share/my_colours/shell/" -type f -printf "%f\\n" | sed -e 's/tempus_\([a-z]*\).sh/\1/g' | sort)
+# We use this logic to check and then pass to the rest of the script the
+# colour values and the custom font.  If the files are not available,
+# the script exits with an error.
+source_file() {
+	if [ -f "$1" ]; then
+		source "$1"
+	else
+		echo "ERROR: Could not find active $2"
+		echo "Aborting"
+		exit 1
+	fi
+}
 
 # Pass custom colours to the `dmenu` command.  These will style the
 # background and foreground values using shell variables.  That file is
 # used in other places as well to offer a convenient way of styling
 # multiple tools in a that is centralised and straightforward.
-# TODO make this conditional
-source "$HOME/.local/share/my_colours/active-tempus-theme.sh"
+my_colours="$HOME/.local/share/my_colours/active-tempus-theme.sh"
+source_file "$my_colours" 'Tempus theme'
 
 # Get the system-wide custom font.  This is done with other `dmenu`
 # scripts as well to provide for an easy way to style them all at once.
 # The actual font is a `fontconfig` alias.  See my dotfiles under
 # "fontconfig".
-# TODO make this conditional
-source "$HOME/.local/share/my_custom_ui_font.sh"
+my_font="$HOME/.local/share/my_custom_ui_font.sh"
+source_file "$my_font" 'UI font'
+
+# TODO use parameter expansion instead of sed
+# Array with all available tempus themes.  The `sed` command cleans up
+# the output, stripping it of surrounding text. As for `sort`, it just
+# presents the output in alphabetical order.
+tempus_themes_array=$(find "$HOME/.local/share/my_colours/shell/" -type f -printf "%f\\n" | sed -e 's/tempus_\([a-z]*\).sh/\1/g' | sort)
 
 # }}}