#!/usr/bin/env bash

APPNAME=$(basename $0 | sed "s/\.sh$//")

# -----------------------------------------------------------------------------
# Log functions
# -----------------------------------------------------------------------------

fn_log_info()  { echo "$APPNAME: $1"; }
fn_log_warn()  { echo "$APPNAME: [WARNING] $1" 1>&2; }
fn_log_error() { echo "$APPNAME: [ERROR] $1" 1>&2; }
fn_log_info_cmd()  {
	if [ -n "$SSH_CMD" ]; then
		echo "$APPNAME: $SSH_CMD '$1'";
	else
		echo "$APPNAME: $1";
	fi
}

# -----------------------------------------------------------------------------
# Make sure everything really stops when CTRL+C is pressed
# -----------------------------------------------------------------------------

fn_terminate_script() {
	fn_log_info "SIGINT caught."
	exit 1
}

trap 'fn_terminate_script' SIGINT

# -----------------------------------------------------------------------------
# Small utility functions for reducing code duplication
# -----------------------------------------------------------------------------
fn_display_usage() {
	echo "Usage: $(basename $0) [OPTION]... <SOURCE> <[USER@HOST:]DESTINATION> [exclude-pattern-file]"
	echo ""
	echo "Options"
	echo " -p, --port           SSH port."
	echo " -h, --help           Display this help message."
	echo " --rsync-get-flags    Display the default rsync flags that are used for backup."
	echo " --rsync-set-flags    Set the rsync flags that are going to be used for backup."
	echo " --log-dir            Set the log file directory. If this flag is set, generated files will"
	echo "                      not be managed by the script - in particular they will not be"
	echo "                      automatically deleted."
	echo "                      Default: $LOG_DIR"
	echo ""
	echo "For more detailed help, please see the README file:"
	echo ""
	echo "https://github.com/laurent22/rsync-time-backup/blob/master/README.md"
}

fn_parse_date() {
	# Converts YYYY-MM-DD-HHMMSS to YYYY-MM-DD HH:MM:SS and then to Unix Epoch.
	case "$OSTYPE" in
		linux*) date -d "${1:0:10} ${1:11:2}:${1:13:2}:${1:15:2}" +%s ;;
		cygwin*) date -d "${1:0:10} ${1:11:2}:${1:13:2}:${1:15:2}" +%s ;;
		darwin*) date -j -f "%Y-%m-%d-%H%M%S" "$1" "+%s" ;;
		FreeBSD*) date -j -f "%Y-%m-%d-%H%M%S" "$1" "+%s" ;;
	esac
}

fn_find_backups() {
	fn_run_cmd "find "$DEST_FOLDER" -type d -name "????-??-??-??????" -prune | sort -r"
}

fn_expire_backup() {
	# Double-check that we're on a backup destination to be completely
	# sure we're deleting the right folder
	if [ -z "$(fn_find_backup_marker "$(dirname -- "$1")")" ]; then
		fn_log_error "$1 is not on a backup destination - aborting."
		exit 1
	fi

	fn_log_info "Expiring $1"
	fn_rm "$1"
}

fn_parse_ssh() {
	if [[ "$DEST_FOLDER" =~ ^[A-Za-z0-9\._%\+\-]+@[A-Za-z0-9.\-]+\:.+$ ]]
	then
		SSH_USER=$(echo "$DEST_FOLDER" | sed -E  's/^([A-Za-z0-9\._%\+\-]+)@([A-Za-z0-9.\-]+)\:(.+)$/\1/')
		SSH_HOST=$(echo "$DEST_FOLDER" | sed -E  's/^([A-Za-z0-9\._%\+\-]+)@([A-Za-z0-9.\-]+)\:(.+)$/\2/')
		SSH_DEST_FOLDER=$(echo "$DEST_FOLDER" | sed -E  's/^([A-Za-z0-9\._%\+\-]+)@([A-Za-z0-9.\-]+)\:(.+)$/\3/')
		SSH_CMD="ssh -p $SSH_PORT ${SSH_USER}@${SSH_HOST}"
		SSH_FOLDER_PREFIX="${SSH_USER}@${SSH_HOST}:"
	fi
}

fn_run_cmd() {
	if [ -n "$SSH_CMD" ]
	then
		eval "$SSH_CMD '$1'"
	else
		eval $1
	fi
}

fn_find() {
	fn_run_cmd "find '$1'"  2>/dev/null
}

fn_get_absolute_path() {
	fn_run_cmd "cd '$1';pwd"
}

fn_mkdir() {
	fn_run_cmd "mkdir -p -- '$1'"
}

fn_rm() {
	if [[ -d $1 ]]; then
		# when deleting a directory use rsync for performance reasons
		fn_run_cmd "mkdir -p /tmp/rsync-time-backup-emptydir"
		fn_run_cmd "rsync -a --delete /tmp/rsync-time-backup-emptydir/ '$1'"
		fn_run_cmd "rm -rf /tmp/rsync-time-backup-emptydir '$1'"
	else
		# when deleting a file use regular rm
		fn_run_cmd "rm -f '$1'"
	fi
}

fn_touch() {
	fn_run_cmd "touch -- '$1'"
}

fn_ln() {
	fn_run_cmd "ln -s -- '$1' '$2'"
}

# -----------------------------------------------------------------------------
# Source and destination information
# -----------------------------------------------------------------------------
SSH_USER=""
SSH_HOST=""
SSH_DEST_FOLDER=""
SSH_CMD=""
SSH_FOLDER_PREFIX=""
SSH_PORT="22"

SRC_FOLDER=""
DEST_FOLDER=""
EXCLUSION_FILE=""
LOG_DIR="$HOME/.$APPNAME"
AUTO_DELETE_LOG="1"

RSYNC_FLAGS="-D --compress --numeric-ids --links --hard-links --one-file-system --itemize-changes --times --recursive --perms --owner --group --stats --human-readable"

while :; do
	case $1 in
		-h|-\?|--help)
			fn_display_usage
			exit
			;;
		-p|--port)
			shift
			SSH_PORT=$1
			;;
		--rsync-get-flags)
			shift
			echo $RSYNC_FLAGS
			exit
			;;
		--rsync-set-flags)
			shift
			RSYNC_FLAGS="$1"
			;;
		--log-dir)
			shift
			LOG_DIR="$1"
			AUTO_DELETE_LOG="0"
			;;
		--)
			shift
			SRC_FOLDER="$1"
			DEST_FOLDER="$2"
			EXCLUSION_FILE="$3"
			break
			;;
		-?*)
			fn_log_error "Unknown option: \"$1\""
			fn_log_info ""
			fn_display_usage
			exit 1
			;;
		*)
			SRC_FOLDER="$1"
			DEST_FOLDER="$2"
			EXCLUSION_FILE="$3"
			break
	esac

	shift
done

# Display usage information if required arguments are not passed
if [[ -z "$SRC_FOLDER" || -z "$DEST_FOLDER" ]]; then
	fn_display_usage
	exit 1
fi

# Strips off last slash. Note that it means the root folder "/"
# will be represented as an empty string "", which is fine
# with the current script (since a "/" is added when needed)
# but still something to keep in mind.
# Don't think it would with DEST_FOLDER set to "/" though,
# but there's probably not a use case for this anyway.
SRC_FOLDER="${SRC_FOLDER%/}"
DEST_FOLDER="${DEST_FOLDER%/}"

fn_parse_ssh

if [ -n "$SSH_DEST_FOLDER" ]; then
	DEST_FOLDER="$SSH_DEST_FOLDER"
fi

for ARG in "$SRC_FOLDER" "$DEST_FOLDER" "$EXCLUSION_FILE"; do
	if [[ "$ARG" == *"'"* ]]; then
		fn_log_error 'Source and destination directories may not contain single quote characters.'
		exit 1
	fi
done

# -----------------------------------------------------------------------------
# Check that the destination drive is a backup drive
# -----------------------------------------------------------------------------

# TODO: check that the destination supports hard links

fn_backup_marker_path() { echo "$1/backup.marker"; }
fn_find_backup_marker() { fn_find "$(fn_backup_marker_path "$1")" 2>/dev/null; }

if [ -z "$(fn_find_backup_marker "$DEST_FOLDER")" ]; then
	fn_log_info "Safety check failed - the destination does not appear to be a backup folder or drive (marker file not found)."
	fn_log_info "If it is indeed a backup folder, you may add the marker file by running the following command:"
	fn_log_info ""
	fn_log_info_cmd "mkdir -p -- \"$DEST_FOLDER\" ; touch \"$(fn_backup_marker_path "$DEST_FOLDER")\""
	fn_log_info ""
	exit 1
fi

# -----------------------------------------------------------------------------
# Setup additional variables
# -----------------------------------------------------------------------------

# Date logic
NOW=$(date +"%Y-%m-%d-%H%M%S")
EPOCH=$(date "+%s")
KEEP_ALL_DATE=$((EPOCH - 86400))       # 1 day ago
KEEP_DAILIES_DATE=$((EPOCH - 2678400)) # 31 days ago

export IFS=$'\n' # Better for handling spaces in filenames.
DEST="$DEST_FOLDER/$NOW"
PREVIOUS_DEST="$(fn_find_backups | head -n 1)"
INPROGRESS_FILE="$DEST_FOLDER/backup.inprogress"
MYPID="$$"

# -----------------------------------------------------------------------------
# Create log folder if it doesn't exist
# -----------------------------------------------------------------------------

if [ ! -d "$LOG_DIR" ]; then
	fn_log_info "Creating log folder in '$LOG_DIR'..."
	mkdir -- "$LOG_DIR"
fi

# -----------------------------------------------------------------------------
# Handle case where a previous backup failed or was interrupted.
# -----------------------------------------------------------------------------

if [ -n "$(fn_find "$INPROGRESS_FILE")" ]; then
	if [ "$OSTYPE" == "cygwin" ]; then
		# TODO: Cygwin reports the name of currently running Bash scripts as just "/usr/bin/bash"
		# TODO: so the pgrep solution below won't work. Need to use "procps -wwFAH", grep
		# TODO: the script name, and extract the process ID from it.
		fn_log_warn "Cygwin only: Previous backup task has either been interrupted or it might still be active, but there is currently no check for this. Assuming that the task was simply interrupted."
	else 
		RUNNINGPID="$(fn_run_cmd "cat $INPROGRESS_FILE")"
		if [ "$RUNNINGPID" = "$(pgrep "$APPNAME")" ]; then
			fn_log_error "Previous backup task is still active - aborting."
			exit 1
		fi
	fi

	if [ -n "$PREVIOUS_DEST" ]; then
		# - Last backup is moved to current backup folder so that it can be resumed.
		# - 2nd to last backup becomes last backup.
		fn_log_info "$SSH_FOLDER_PREFIX$INPROGRESS_FILE already exists - the previous backup failed or was interrupted. Backup will resume from there."
		fn_run_cmd "mv -- $PREVIOUS_DEST $DEST"
		if [ "$(fn_find_backups | wc -l)" -gt 1 ]; then
			PREVIOUS_DEST="$(fn_find_backups | sed -n '2p')"
		else
			PREVIOUS_DEST=""
		fi
		# update PID to current process to avoid multiple concurrent resumes
		fn_run_cmd "echo $MYPID > $INPROGRESS_FILE"
	fi
fi

# Run in a loop to handle the "No space left on device" logic.
while : ; do

	# -----------------------------------------------------------------------------
	# Check if we are doing an incremental backup (if previous backup exists).
	# -----------------------------------------------------------------------------

	LINK_DEST_OPTION=""
	if [ -z "$PREVIOUS_DEST" ]; then
		fn_log_info "No previous backup - creating new one."
	else
		# If the path is relative, it needs to be relative to the destination. To keep
		# it simple, just use an absolute path. See http://serverfault.com/a/210058/118679
		PREVIOUS_DEST="$(fn_get_absolute_path "$PREVIOUS_DEST")"
		fn_log_info "Previous backup found - doing incremental backup from $SSH_FOLDER_PREFIX$PREVIOUS_DEST"
		LINK_DEST_OPTION="--link-dest='$PREVIOUS_DEST'"
	fi

	# -----------------------------------------------------------------------------
	# Create destination folder if it doesn't already exists
	# -----------------------------------------------------------------------------

	if [ -z "$(fn_find "$DEST -type d" 2>/dev/null)" ]; then
		fn_log_info "Creating destination $SSH_FOLDER_PREFIX$DEST"
		fn_mkdir "$DEST"
	fi

	# -----------------------------------------------------------------------------
	# Purge certain old backups before beginning new backup.
	# -----------------------------------------------------------------------------

	# Default value for $PREV ensures that the most recent backup is never deleted.
	PREV="0000-00-00-000000"
	for FILENAME in $(fn_find_backups | sort -r); do
		BACKUP_DATE=$(basename "$FILENAME")
		TIMESTAMP=$(fn_parse_date $BACKUP_DATE)

		# Skip if failed to parse date...
		if [ -z "$TIMESTAMP" ]; then
			fn_log_warn "Could not parse date: $FILENAME"
			continue
		fi

		if   [ $TIMESTAMP -ge $KEEP_ALL_DATE ]; then
			true
		elif [ $TIMESTAMP -ge $KEEP_DAILIES_DATE ]; then
			# Delete all but the most recent of each day.
			[ "${BACKUP_DATE:0:10}" == "${PREV:0:10}" ] && fn_expire_backup "$FILENAME"
		else
			# Delete all but the most recent of each month.
			[ "${BACKUP_DATE:0:7}" == "${PREV:0:7}" ] && fn_expire_backup "$FILENAME"
		fi

		PREV=$BACKUP_DATE
	done

	# -----------------------------------------------------------------------------
	# Start backup
	# -----------------------------------------------------------------------------

	LOG_FILE="$LOG_DIR/$(date +"%Y-%m-%d-%H%M%S").log"

	fn_log_info "Starting backup..."
	fn_log_info "From: $SRC_FOLDER/"
	fn_log_info "To:   $SSH_FOLDER_PREFIX$DEST/"

	CMD="rsync"
	if [ -n "$SSH_CMD" ]; then
		CMD="$CMD  -e 'ssh -p $SSH_PORT -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null'"
	fi
	CMD="$CMD $RSYNC_FLAGS"
	CMD="$CMD --log-file '$LOG_FILE'"
	if [ -n "$EXCLUSION_FILE" ]; then
		# We've already checked that $EXCLUSION_FILE doesn't contain a single quote
		CMD="$CMD --exclude-from '$EXCLUSION_FILE'"
	fi
	CMD="$CMD $LINK_DEST_OPTION"
	CMD="$CMD -- '$SRC_FOLDER/' '$SSH_FOLDER_PREFIX$DEST/'"

	fn_log_info "Running command:"
	fn_log_info "$CMD"

	fn_run_cmd "echo $MYPID > $INPROGRESS_FILE"

	eval $CMD

	# -----------------------------------------------------------------------------
	# Check if we ran out of space
	# -----------------------------------------------------------------------------

	NO_SPACE_LEFT="$(grep "No space left on device (28)\|Result too large (34)" "$LOG_FILE")"

	if [ -n "$NO_SPACE_LEFT" ]; then
		fn_log_warn "No space left on device - removing oldest backup and resuming."

		if [[ "$(fn_find_backups | wc -l)" -lt "2" ]]; then
			fn_log_error "No space left on device, and no old backup to delete."
			exit 1
		fi

		fn_expire_backup "$(fn_find_backups | tail -n 1)"

		# Resume backup
		continue
	fi

	# -----------------------------------------------------------------------------
	# Check whether rsync reported any errors
	# -----------------------------------------------------------------------------

	if [ -n "$(grep "rsync error:" "$LOG_FILE")" ]; then
		fn_log_error "Rsync reported an error. Run this command for more details: grep -E 'rsync:|rsync error:' '$LOG_FILE'"
		exit 1
	fi

	if [ -n "$(grep "rsync:" "$LOG_FILE")" ]; then
		fn_log_warn "Rsync reported a warning. Run this command for more details: grep -E 'rsync:|rsync error:' '$LOG_FILE'"
	fi

	# -----------------------------------------------------------------------------
	# Add symlink to last successful backup
	# -----------------------------------------------------------------------------

	fn_rm "$DEST_FOLDER/latest"
	fn_ln "$(basename -- "$DEST")" "$DEST_FOLDER/latest"

	fn_rm "$INPROGRESS_FILE"
	if [[ $AUTO_DELETE_LOG == "1" ]]; then
		rm -f -- "$LOG_FILE"
	fi

	fn_log_info "Backup completed without errors."

	exit 0
done