#!/bin/bash

# Exit out if the same script is already running in the background
pidof -sq -o %PPID -x "$(basename "$0")" && exit

# Setting read-only variables
declare -r datadir="$HOME"/.local/share/fix-zombie-appicons
declare -r backup_dir="$datadir"/backup
declare -r datafile="$datadir"/tweaked-desktop-files

# Desktop files stored here will take precedence over the other ones
declare -r home_local_applications_dir="$HOME/.local/share/applications"

# Go through each item in $XDG_DATA_DIRS to find all other directories
# except home_local_applications_dir where desktop files are stored, and
# save these to other_applications_dirs
while read -r dir; do
	full_dir_path=${dir%/}/applications
	other_applications_dirs+=("$full_dir_path")

	# Directories inside user's home directory
	[[ "$full_dir_path" = "$HOME"/* ]] && dirs_inside_user_home+=("$full_dir_path")

done < <(echo "$XDG_DATA_DIRS" | tr ':' '\n' | sort -u | grep -vFx "$home_local_applications_dir")

declare -r other_applications_dirs dirs_inside_user_home

# Create tempfile which is used by the fix_desktop_files function
tempfile="$(mktemp)"
trap 'rm $tempfile' EXIT # Delete tempfile when the script exits
declare -r tempfile

# This function will check for new desktop files in home_local_applications_dir and
# record them in datafile if the same file is found in any of the other_applications_dirs.
detect_new_desktop_files() {
	for file in "$home_local_applications_dir"/*.desktop; do
		# This is added as a failsafe to ensure its a file and not a directory
		[ -d "$file" ] && continue
		filename=$(basename "$file")
		# Continue looping if the filename is already recorded in the datafile
		grep -xq "$filename" "$datafile" && continue
		# If the same file is present in any of the other_applications_dirs then add its filename to datafile
		for dir in "${other_applications_dirs[@]}"; do
			[ -f "$dir/$filename" ] && echo "$filename" >> "$datafile" && break
		done
	done
}

# The following function will:
#    1. Go through all the files recorded in datafile and move them to backup_dir if
#       the same file is not found in other_applications_dirs anymore.
#    2. Go through all the bakked up files in backup_dir and move them back to
#       its original_file_path if the same file is present in any of
#       the other_applications_dirs. This will not overwrite if a new
#       file already exists at original_file_path.

fix_desktop_files() {
	# This is added as a failsafe to avoid overwriting datafile in case the file got edited during this period
	local -r last_modified_time=$(stat -c "%Y" "$datafile")
	# Copy datafile to tempfile because its not possible to directly edit the file inside a while-read loop
	[ -f "$datafile" ] && cp "$datafile" "$tempfile" && local -r datafile_copied='true'
	local -i line_number=0

	# Loop through each line in datafile
	[ "$datafile_copied" = 'true' ] && while IFS='' read -r filename; do
		line_number+=1
		file="$home_local_applications_dir/$filename"
		# If the file don't exist anymore then remove the line from datafile (as tempfile) and continue looping
		[ -f "$file" ] || { sed -i "${line_number}d" "$tempfile" && line_number+=-1 ; continue; }

		# If the same file is not present in any of the other_applications_dirs then move the file to backup_dir
		unset file_exists
		for dir in "${other_applications_dirs[@]}"; do
			[ -f "$dir/$filename" ] && file_exists='true' && break
		done
		[ "$file_exists" != 'true' ] && mv "$file" "$backup_dir/$filename.bak"
	done < "$datafile"

	# Write the contents from tempfile back to datafile after sorting and removing duplicate lines
	[ "$datafile_copied" = 'true' ] && [ "$(stat -c '%Y' "$datafile")" = "$last_modified_time" ] && sort -u "$tempfile" > "$datafile"

	for bakfile in "$backup_dir"/*.desktop.bak; do
		filename=$(basename "${bakfile%.bak}")
		original_file_path="$home_local_applications_dir/$filename"

		# Continue looping if a new file is already present at the original_file_path,
		# this will prevent the backup from overwriting the new file
		[ -f "$original_file_path" ] && continue

		# If the same bakked up file is present in any of the other_applications_dirs then move it back to its original_file_path
		for dir in "${other_applications_dirs[@]}"; do
			[ -f "$dir/$filename" ] && mv "$bakfile" "$original_file_path" && break
		done
	done
}

# Create some directories in the user's home directory if they don't already exist
mkdir -p "$datadir" "$backup_dir" "$home_local_applications_dir" ||
	{ echo "failed to make directories $datadir, $backup_dir & $home_local_applications_dir"; exit 1; }

# Try to create dirs_inside_user_home if they don't already exist
[ ${#dirs_inside_user_home[@]} -gt 0 ] && mkdir -p "${dirs_inside_user_home[@]}"

# Check which directories currently exist on the user's system so that inotifywait can monitor them for changes
for dir in "$home_local_applications_dir" "${other_applications_dirs[@]}"; do
	[ -d "$dir" ] && currently_existing_dirs+=("$dir")
done

# Both functions will be run once when the script first starts
detect_new_desktop_files
fix_desktop_files

# Inotifywait monitors currently_existing_dirs and the functions are run each time when there is a change in relevant directories
while IFS='' read -r line; do
	if [ "$line" = "$home_local_applications_dir/" ]; then
		detect_new_desktop_files
	else
		fix_desktop_files
	fi
done < <(inotifywait -qm --format '%w' --include '\.desktop$' -e 'move,move_self,create,delete,delete_self,unmount' "${currently_existing_dirs[@]}")