#!/bin/bash
set -e
PATH=$(dirname "$0"):$PATH
source rpc.bash

datadir=data
default_replica_host_file=$datadir/default-replica-host
replication_password_file=$datadir/replication-password

if [ -r "$default_replica_host_file" ]
then
	read default_replica_host < "$default_replica_host_file"
fi

gen_password()
{
	generated_password_length=32
	generated_password=$(tr -cd a-zA-Z0-9 < /dev/urandom |
		head -c "$generated_password_length")
	[ "${#generated_password}" -eq "$generated_password_length" ]
	printf '%s\n' "$generated_password"
}

if ! [ -e "$replication_password_file" ]
then
	gen_password > "$replication_password_file"
fi

if [ -r "$replication_password_file" ]
then
	read replication_password < "$replication_password_file" 
	[ "${#replication_password}" -ge 30 ]
fi

primary_host=$(hostname --fqdn)
replica_host=${1:-$default_replica_host}
replication_user=replication

[ "$primary_host" ]
[ "$replica_host" ]
[ "$replication_password" ]

run_primary()
{
	(set -x
	: primary : $1 $2 ${3:+ ...})
	BASH_RPC_REMOTE_DEST=$primary_host remote_run_function "$@"
}

run_replica()
{
	(set -x
	: replica : $1 $2 ${3:+ ...})
	BASH_RPC_REMOTE_DEST=$replica_host remote_run_function "$@"
}

show_hostnames()
{
	printf \
		"==> %s %s <==\n    %s\n" \
		"$(hostname -A)" \
		"$(hostname -I)" \
		"$(uptime)"
}

check_db()
{
	show_hostnames
	mariadb --skip-reconnect -t <<END
select @@hostname, @@server_id, @@gtid_slave_pos, @@sql_log_bin;
END
}

create_backup()
{
	set -e
	mariabackup_target_dir=/var/mariadb/backup
	binlog_info_file=$mariabackup_target_dir/xtrabackup_binlog_info 
	[ -e "$binlog_info_file" ] && return
	mkdir -p "$mariabackup_target_dir"
	marialog=$(mktemp)
	e=0
	(set -- \
		-u root \
		--target-dir="$mariabackup_target_dir"
	exec >"$marialog" 2>&1
	set -x
	mariabackup --backup --rsync "$@"
	mariabackup --prepare "$@") || e=$?
	if [ "$e" = 0 -a -e "$binlog_info_file" ]
	then
		tail -v -n2 "$marialog" >&2
		rm "$marialog"
	else
		cat "$marialog" >&2
		false
	fi
}

delete_backup()
{
	set -x
	rm -r /var/mariadb/backup
}

send_backup()
{
	mariabackup_target_dir=/var/mariadb/backup
	set -x
	rsync -zaR -- /./"${mariabackup_target_dir#/}" "$1":/
}

stop_database_server_and_remove_database_files()
{
	livedb=/var/lib/mysql
	set -e
	if [ -e "$livedb" ]
	then
		if [ "$(systemctl is-active mariadb)" = active ]
		then
			systemctl stop mariadb
		fi
		livedb_backup=$livedb~$(date -Ins)
		mv -v -T -- "$livedb" "$livedb_backup"
		mkdir "$livedb"
		chown --reference="$livedb_backup" "$livedb"
		chmod --reference="$livedb_backup" "$livedb"
	fi
}

restore_from_backup()
{
	mariabackup_target_dir=/var/mariadb/backup
	set -e

	stop_database_server_and_remove_database_files

	marialog=$(mktemp)
	exec >"$marialog" 2>&1
	set -- \
		-u root \
		--target-dir="$mariabackup_target_dir"
	if mariabackup --move-back "$@"
	then
		tail -v -n2 "$marialog" >&2
		# Can't believe mariabackup
		# is so primitive as to
		# recommend this chown in its
		# documentation
		chown -R mysql:mysql /var/lib/mysql
		systemctl start mariadb
	else
		cat "$marialog" >&2
	fi

}

enable_replication()
{
	primary_host=$1
	replication_user=$2
	replication_password=$3
	mariabackup_target_dir=/var/mariadb/backup
	binlog_info_file=$mariabackup_target_dir/xtrabackup_binlog_info 
	set -e
	read master_log_file master_log_pos gtid_slave_pos < $binlog_info_file
	tee /dev/stderr <<END | mariadb --skip-reconnect -t
STOP SLAVE;
SET GLOBAL gtid_slave_pos = "$gtid_slave_pos";
CHANGE MASTER TO
  MASTER_HOST='$primary_host',
  MASTER_USER='$replication_user',
  MASTER_PASSWORD='$replication_password',
  MASTER_USE_GTID=slave_pos;
START SLAVE;
SHOW SLAVE STATUS\G
END
	set -x
	rm -r /var/mariadb/backup
}

create_replication_user()
{
	mariadb --skip-reconnect -t <<END
CREATE OR REPLACE USER '$2'@'$1' IDENTIFIED BY '$3';
GRANT REPLICATION SLAVE ON *.*  TO '$2'@'$1';
END
}

showvars()
{
	for h in "$@"
	do
		run_$h mariadb --skip-reconnect -t <<END
select VARIABLE_NAME,SESSION_VALUE,GLOBAL_VALUE 
from INFORMATION_SCHEMA.SYSTEM_VARIABLES
where VARIABLE_NAME LIKE '%SLAVE%' \G
END
	done
}

set -e
run_primary check_db
run_replica check_db
: showvars replica
: exit

run_primary create_replication_user \
	"$replica_host" \
	"$replication_user" \
	"$replication_password"
run_primary create_backup
run_primary send_backup "$replica_host"
run_replica restore_from_backup
run_replica enable_replication \
	"$primary_host" \
	"$replication_user" \
	"$replication_password"
run_replica check_db
run_primary delete_backup
run_primary check_db