pre_install() {
	# Oracle Group Names and GIDs
	ORACLE_GIDS=('54321' '54322' '54323' '54324' '54325' '54326' '54330')
	ORACLE_GROUP_NAMES=('oinstall' 'dba' 'oper' 'backupdba' 'dgdba' 'kmdba' 'racdba')

	# Check if All the Users and Groups exist
	if getent passwd oracle || getent passwd 54321;then
		echo "The user oracle with uid 54321 exists!" >&2
		exit 1
	fi
	for ((i = 0; i < ${#ORACLE_GIDS[@]}; ++i));do
		if getent group ${ORACLE_GROUP_NAMES[i]} || getent group ${ORACLE_GIDS[i]};then
			echo "The group ${ORACLE_GROUP_NAMES[i]} with gid ${ORACLE_GIDS[i]} exists!" >&2
			exit 2
		fi
	done

	# Create All Required Users and Groups
	for ((i = 0; i < ${#ORACLE_GIDS[@]}; ++i));do
		groupadd --system --gid ${ORACLE_GIDS[i]} ${ORACLE_GROUP_NAMES[i]}
	done
	useradd --system --uid 54321 --gid 54321 --home-dir /var/lib/oracle \
		--groups $(echo ${ORACLE_GROUP_NAMES[@]:1:${#ORACLE_GROUP_NAMES[@]}} | sed 's/ /,/g') oracle
}

post_install() {
	# Fix Permissions
	chown -R oracle:oinstall /opt/oracle /etc/oratab /var/lib/oracle

	# Create Default Database Listener
	su -s /bin/bash oracle -c '/opt/oracle/product/18c/dbhomeXE/bin/netca -silent \
		-orahome /opt/oracle/product/18c/dbhomeXE -instype typical -inscomp client,oraclenet,javavm,server,ano \
		-responseFile /opt/oracle/product/18c/dbhomeXE/network/install/netca_typ.rsp -insprtcl tcp -cfg local \
		-authadp NO_VALUE -orahnam OraHomeXE -listenerparameters DEFAULT_SERVICE=XE'

	# Create Default Pluggable Database
	cat <<- 'EOF'

		[Info] Use the following with root command to set password and create default pluggable database:
		su -s /bin/bash oracle -c '/opt/oracle/product/18c/dbhomeXE/bin/dbca -silent \
			-createDatabase -gdbName XE -templateName XE_Database.dbc -characterSet AL32UTF8 \
			-createAsContainerDatabase true -numberOfPDBs 1 -sid XE -pdbName XEPDB1 \
			-J-Doracle.assistants.dbca.validate.ConfigurationParams=false -emConfiguration DBEXPRESS \
			-emExpressPort 5500 -J-Doracle.assistants.dbca.validate.DBCredentials=false -sampleSchema true \
			-customScripts /opt/oracle/product/18c/dbhomeXE/assistants/dbca/postdb_creation.sql'

	EOF
}

pre_remove() {
	# Terminate All Processes
	PIDs=$(ps aux | grep -E '^oracle' | grep -v grep | awk '{print $2}')
	if [ "$PIDs" ];then
		kill -SIGKILL $PIDs
	fi
}

post_remove() {
	# Oracle Group Names and GIDs
	ORACLE_GROUP_NAMES=('oinstall' 'dba' 'oper' 'backupdba' 'dgdba' 'kmdba' 'racdba')

	# Remove Oracle Users and Groups
	userdel oracle
	for gp in ${ORACLE_GROUP_NAMES[@]};do
		groupdel $gp
	done

	# Remove Database Files
	rm -rf /opt/oracle /var/lib/oracle
}