#!/usr/bin/bash

# BEGIN: Variables

DEBUG=1
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
LOCAL_APPLICATION_DIR=~/.local/share/applications
EXISTING_INSTALL=$INSTALL_DIR/Discord
BUILD_FILE=$EXISTING_INSTALL/resources/build_info.json
DESKTOP_FILE=$EXISTING_INSTALL/discord.desktop
INSTALLED_DESKTOP_FILE=$LOCAL_APPLICATION_DIR/discord.desktop
PACKAGE_DOWNLOAD_URL_BASE='https://dl.discordapp.net/apps/linux/{VERSION}/discord-{VERSION}.tar.gz'
ICON_DIR=~/.local/share/icons
DESKTOP_FILE_NEEDS_UPDATE=0

# END: Variables


# BEGIN: Helper Functions

function log () {
	if [[ $DEBUG -eq 1 ]]; then 
		local DATE=`date` 
		local MESSAGE="${1:?"log: Message not provided"}"
		echo "$DATE : $MESSAGE"
	fi
}

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

	if [[ "$REMOTE_VERSION" ]]; then
		echo "$REMOTE_VERSION"
		return 0
	else
		log "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
		log "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\}/$REMOTE_VERSION}"
	log "Download url created ($PACKAGE_DOWNLOAD_URL)"

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

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

function update_desktop_file() {

	log "Updating 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
	log "Desktop file has been updated"

}

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
		log "$FILENAME failed to download. Exiting now"
		exit 3
	fi

	update_desktop_file

	[[ ! -d $ICON_DIR ]] && mkdir -p $ICON_DIR
	cp $EXISTING_INSTALL/discord.png $ICON_DIR/
}

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
}

# END: Helper Functions



# BEGIN: Pre-Work Check

if [[ -d $EXISTING_INSTALL ]] && [[ -f $BUILD_FILE ]]; then
	LOCAL_VERSION=`grep -Eo $VERSION_REGEX $BUILD_FILE`
	log "Local version was found to be ($LOCAL_VERSION)"
else
	ACTION=INSTALL
fi

REMOTE_VERSION=`get_remote_version`
log "Retrieved remote version ($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


# BEGIN: End Work Check

## If discord isn't already setup, go ahead and mark it for install/update
if [[ ! -f $INSTALLED_DESKTOP_FILE ]]; then
	log "Desktop file not found in the local applications dir ($LOCAL_APPLICATION_DIR) installing now"
	DESKTOP_FILE_NEEDS_UPDATE=1

else
	# If there is a change for any reason update it 
	if [[ "$(<$DESKTOP_FILE)" != "$(<$INSTALLED_DESKTOP_FILE)" ]]; then
		log "Desktop file for new version of discord has changed. Updating the existing installation"
		DESKTOP_FILE_NEEDS_UPDATE=1
	fi
fi

if [[ $DESKTOP_FILE_NEEDS_UPDATE -eq 1 ]]; then 
	log "Updating/Installing desktop file"
	desktop-file-install --dir=$LOCAL_APPLICATION_DIR $DESKTOP_FILE

	if [[ $? -ne 0 ]]; then
		log "There was an issue with installtion"
	else
		log "Desktop file was successfully installed"
	fi
fi

# END: End Work Check