myscripts/install-discord-linux.sh

#!/usr/bin/bash

# BEGIN: Variables

ACTION=""
DOWNLOAD_URL='https://discord.com/api/download/stable?platform=linux&format=tar.gz'
VERSION_REGEX='[0-9]+\.[0-9]+\.[0-9]+'
INSTALL_DIR=~/.opt
EXISTING_INSTALL=$INSTALL_DIR/Discord
BUILD_FILE=$EXISTING_INSTALL/resources/build_info.json
DESKTOP_FILE=$EXISTING_INSTALL/discord.desktop
PACKAGE_DOWNLOAD_URL_BASE='https://dl.discordapp.net/apps/linux/{VERSION}/discord-{VERSION}.tar.gz'
ICON_DIR=~/.icons
DESKTOP_FILE_INSTALLED=0
[[ -f /usr/share/applications/discord.desktop ]] && DESKTOP_FILE_INSTALLED=1

# END: Variables


# BEGIN: Helper Functions

function get_remote_version(){
	local REMOTE_VERSION=`curl $DOWNLOAD_URL | grep -Eo $VERSION_REGEX | head -n 1`

	if [[ "$REMOTE_VERSION" ]]; then
		echo "$REMOTE_VERSION"
		return 0
	else
		echo "error: remote version not found"
		return 1
	fi
}

function do_download(){
	local VERSION="${1:?"do_download : Version was not provided"}"

	## If the provided version doesn't match the format #.#.#
	if [[ ! "$VERSION" =~ ^$VERSION_REGEX$ ]]; then
		echo "do_download : the version ($VERSION) provided, does not match format $VERSION_REGEX."
		exit 2
	fi

	## Making the URL to download the package
	### replacing all {VERSION} in PACKAGE_DOWNLOAD_URL_BASE with $REMOTE_VERSION using string substitution
	PACKAGE_DOWNLOAD_URL="${PACKAGE_DOWNLOAD_URL_BASE//\{VERSION\}/$REMOTE_VERSION}"

	## Getting filename from url
	### Removing all characters from the last / back to leave only the filename
	FILENAME="${PACKAGE_DOWNLOAD_URL/*\/}"

	## Downloading the discord package (tar.gz)
	curl "$PACKAGE_DOWNLOAD_URL" -o "$FILENAME" >/dev/null 2>&1
}

function update_desktop_file() {

	## Desktop file in the current/new install
	DESKTOP_FILE=$EXISTING_INSTALL/discord.desktop

	## Escaped becuase it would mess up the replacement syntax
	PATH_TO_REPLACE=\/usr\/bin
	PATH_REPLACEMENT=$EXISTING_INSTALL

	## Escaped becuase it would mess up the replacement syntax
	EXEC_TO_REPLACE=\/usr\/share\/discord\/Discord
	EXEC_REPLACEMENT=$EXISTING_INSTALL/Discord

	## Loading the desktop file contents into a variable to use replacement without sed
	DESKTOP_FILE_CONTENTS="$(<$DESKTOP_FILE)"

	## Replacing Path
	DESKTOP_FILE_CONTENTS="${DESKTOP_FILE_CONTENTS/$PATH_TO_REPLACE/$PATH_REPLACEMENT}"
	## Replacing Exec
	DESKTOP_FILE_CONTENTS="${DESKTOP_FILE_CONTENTS/$EXEC_TO_REPLACE/$EXEC_REPLACEMENT}"

	## Pushing replacement values to desktop file
	echo -e "$DESKTOP_FILE_CONTENTS" > $DESKTOP_FILE

}

function do_install() {

	cd "$INSTALL_DIR"

	REMOTE_VERSION=`get_remote_version`
	do_download "$REMOTE_VERSION"

	## Error handling in case curl couldn't do the download (or error in script)
	if [[ -f $FILENAME ]]; then
		tar xf "$FILENAME"
	else
		echo "$FILENAME failed to download. Exiting now"
		exit 1
	fi

	update_desktop_file

	## If your icon dir (configured above) exists in the env variable
	if [[ "$XDG_DATA_DIRS" != *$ICON_DIR* ]]; then
		export XDG_DATA_DIRS=$XDG_DATA_DIRS:$ICON_DIR
		if [[ $SHELL == *bash ]]; then
			echo 'export XDG_DATA_DIRS=$XDG_DATA_DIRS':$ICON_DIR > ~/.bashrc
		else 
			echo 'export XDG_DATA_DIRS=$XDG_DATA_DIRS':$ICON_DIR > ~/.profile

		fi
	fi

	[[ ! -d $ICON_DIR ]] && mkdir -p $ICON_DIR
	cp $EXISTING_INSTALL/discord.png $ICON_DIR/
	sudo desktop-file-isntall $DESKTOP_FILE
}

function do_upgrade(){
	cd "$INSTALL_DIR"

	REMOTE_VERSION=`get_remote_version`
	do_download "$REMOTE_VERSION"

	## FILENAME provided by do_download
	FILENAME="${FILENAME:?"do_upgrade : FILENAME not set by do_download"}"

	tar xf "$FILENAME"

	update_desktop_file

	if [[ $DESKTOP_FILE_INSTALLED -eq 0 ]]; then
		sudo desktop-file-install $DESKTOP_FILE
	fi
}

# END: Helper Functions



# BEGIN: Pre-Work Check

if [[ -d $EXISTING_INSTALL ]] && [[ -f $BUILD_FILE ]]; then
	LOCAL_VERSION=`grep -Eo $VERSION_REGEX $BUILD_FILE`
else
	ACTION=INSTALL
fi

REMOTE_VERSION=`get_remote_version`

# END: Pre-Work Check




# BEGIN: Work


## If ACTION hasn't already been set
if [[ ! $ACTION ]]; then

	## Use read to get version numbers in arrays
	OIFS=$IFS
	IFS='.'
	read -a local_versions  <<< "$LOCAL_VERSION"
	read -a remote_versions <<< "$REMOTE_VERSION"
	IFS=$OIFS

	## Check if the remote version is greater than the local
	for (( i=0; i<3; i++)); do
		## If at any point the remote version is greater than the local this will break and set NEEDS_UPGRADE flag
		if [[ ${local_versions[$i]} -lt ${remote_versions[$i]} ]]; then
			ACTION=UPGRADE
			break
		fi
	done
fi

case $ACTION in
	INSTALL)
		do_install
		;;

	UPGRADE)
		do_upgrade
		;;
esac


# END: Work