#!/bin/bash

# Copyright (C) 2009 Przemyslaw Pawelczyk <przemoc@gmail.com>
#           (C) 2017 Jan Schulz <jasc@gmx.net>             
##
## This script is licensed under the terms of the MIT license.
## https://opensource.org/licenses/MIT

# Fail on all errors
set -o pipefail

# We always start in the current users home directory so that names always start there
cd ~


### ARGUMENT PARSING ###
SCRIPT=${0}

if [[ -z ${2} ]] || [[ ! -d ${2} ]] ; then
	echo "Need a directory name in the current users home directory as second argument. Aborting."
	exit 1
fi

DIRECTORY=$2

if [[ -z ${1} ]] ; then
	echo "Need a command as first argument. Aborting."
	exit 1
else
	if [[ "sync" == "${1}" ]] ; then
		COMMAND=sync
	elif [[ "listen" == "${1}" ]] ; then
		COMMAND=listen
	else
		echo "Unknown command. Aborting."
		exit 1
	fi
fi


### LOCKFILE BOILERPLATE ###
LOCKFILE="/run/user/$(id -u)/$(basename $0)_${DIRECTORY//\//_}"
LOCKFD=99

# PRIVATE
_lock()             { flock -$1 $LOCKFD; }
_no_more_locking()  { _lock u; _lock xn && rm -f $LOCKFILE; }
_prepare_locking()  { eval "exec $LOCKFD>\"$LOCKFILE\""; trap _no_more_locking EXIT; }

# ON START
_prepare_locking

# PUBLIC
exlock_now()        { _lock xn; }  # obtain an exclusive lock immediately or fail
exlock()            { _lock x; }   # obtain an exclusive lock
shlock()            { _lock s; }   # obtain a shared lock
unlock()            { _lock u; }   # drop a lock

### SYNC SCRIPT ###
# Idea: only let one script run, but if the sync script is called a second time 
# make sure we sync a second time, too

sync_directory() {
	_directory=${1}
	if ping -c1 -W1 -q accounts.google.com >/dev/null 2>&1; then
	    true
	    # pass
	else
	    echo "Google drive server not reachable..."
	    exit 0
	fi

	reset_timer_and_exit() { echo "Retriggered google drive sync" && touch -m $LOCKFILE && exit; }

	exlock_now || reset_timer_and_exit

	TIME_AT_START=0
	TIME_AT_END=1
	while [[ ${TIME_AT_START} -lt ${TIME_AT_END} ]]; do
	    echo "Syncing ${_directory}..." 
	    TIME_AT_START=$(stat -c %Y $LOCKFILE)
	    grive -p ${_directory} 2>&1 | grep -v -E "^Reading local directories$|^Reading remote server file list$|^Synchronizing files$|^Finished!$"
	    TIME_AT_END=$(stat -c %Y $LOCKFILE)
	    echo "Sync of ${_directory} done." 
	done

	# always exit ok, so that we never go into a wrong systemd state
	exit 0
}

### LISTEN TO DIRECTORY CHANGES ###


listen_directory() {
	_directory=${1}

	type inotifywait >/dev/null 2>&1 || { echo >&2 "I require inotifywait but it's not installed. Aborting."; exit 1; }

	echo "Listening for changes in ~/${_directory}"

	while true #run indefinitely
	do 
		# Use a different call to not need to change exit into return
		inotifywait -q -r -e modify,attrib,close_write,move,create,delete --exclude ".grive_state|.grive" ${_directory} > /dev/null 2>&1 && ${SCRIPT} sync ${_directory}
	done

	# always exit ok, so that we never go into a wrong systemd state
	exit 0
}

if [[ ${COMMAND} == listen ]] ; then
	listen_directory ${DIRECTORY}
else
	sync_directory ${DIRECTORY}
fi

# always exit ok, so that we never go into a wrong systemd state
exit 0