#!/bin/bash -eu

function merge_dbs {
		
	# Takes file name as only argument
	function check_for_diff_errors {
		
		if grep -q '^<<<<<<<' $1;
		then
			echo "ERROR: The merged database contains conficts."
			echo "       Please search the $1 file for the occurrence of '^<<<<<<<' and resolve the conflicts manually."
	
			echo "Did you fix the conflicts? (yes/no)"
			read
			if [ "$REPLY" = yes ]
			then
				check_for_diff_errors $1
			else
				echo "Cannot continue without a merged database. Exiting."
				exit 1
			fi		
		fi	
	}
	
	DB1=$(readlink -vnf $1)
	LAST_MERGE_DB=$(readlink -vnf $2)
	DB2=$(readlink -vnf $3)
	touch $4
	DEST=$(readlink -vnf $4)
	
	mkdir -p merge_dbs
	cd merge_dbs
	
	# Strip all data and comments
	DATA_PATTERN="INSERT INTO .* VALUES"
	COMMENTS_PATTERN='..!40103 SET TIME_ZONE=@OLD_TIME_ZONE ..;\|..!40101 SET SQL_MODE=@OLD_SQL_MODE ..;\|..!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS ..;\|..!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS ..;\|..!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT ..;\|..!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS ..;\|..!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION ..;\|..!40111 SET SQL_NOTES=@OLD_SQL_NOTES ..;\|Dump completed on'
	
	SED_STRIP_AUTO_INCREMENT="s/\().*\) AUTO_INCREMENT=[0-9]\+\(.*\)/\1\2/"
	
	echo "Merging the new schema structure..."
	grep -v "${DATA_PATTERN}\|${COMMENTS_PATTERN}" $DB1 | sed "$SED_STRIP_AUTO_INCREMENT" > db1_schema.sql
	grep -v "${DATA_PATTERN}\|${COMMENTS_PATTERN}" $LAST_MERGE_DB | sed "$SED_STRIP_AUTO_INCREMENT" > last_merge_schema.sql
	grep -v "${DATA_PATTERN}\|${COMMENTS_PATTERN}" $DB2 | sed "$SED_STRIP_AUTO_INCREMENT" > db2_schema.sql
	
	# Save the comments; to be appended to the final merged file later
	grep "${COMMENTS_PATTERN}" $DB2 > comments.sql
	
	# Build the new schema structure
	if ! diff3 -E --merge db1_schema.sql last_merge_schema.sql db2_schema.sql > merged_schema.sql
	then
		check_for_diff_errors 'merged_schema.sql'
	fi
	
	
	
	# List tables in the new schema
	FILTERED_TABLES="cache\|sessions\|history\|watchdog"
	#                                             table list             ignore some talbes      	  just the name + \|                          remove line breaks and last \| characters                          
	MERGED_SCHEMA_TABLES=`cat merged_schema.sql | grep 'CREATE TABLE ' | grep -v "$FILTERED_TABLES" | sed 's/CREATE TABLE \`\(.*\)\` (/\1\\\|/g' | tr -d '\n'  | sed 's/..$//'`
	
	# Get data for the new schema tables, keeping the locks, but not disabling keys since we actually want to perform integrity check when we insert the data
	grep '\(LOCK TABLES.*\|..!40000 ALTER TABLE .* DISABLE KEYS ..;\|INSERT INTO `\('${MERGED_SCHEMA_TABLES}'\)` VALUES\|..!40000 ALTER TABLE .* ENABLE KEYS ..;\|UNLOCK TABLES.*\)' $DB1 > db1_filtered_data.sql
	grep '\(LOCK TABLES.*\|..!40000 ALTER TABLE .* DISABLE KEYS ..;\|INSERT INTO `\('${MERGED_SCHEMA_TABLES}'\)` VALUES\|..!40000 ALTER TABLE .* ENABLE KEYS ..;\|UNLOCK TABLES.*\)' $LAST_MERGE_DB > last_merge_filtered_data.sql
	grep '\(LOCK TABLES.*\|..!40000 ALTER TABLE .* DISABLE KEYS ..;\|INSERT INTO `\('${MERGED_SCHEMA_TABLES}'\)` VALUES\|..!40000 ALTER TABLE .* ENABLE KEYS ..;\|UNLOCK TABLES.*\)' $DB2 > db2_filtered_data.sql
	
	echo "Merging the new database data..."
	# Merge the data
	if ! diff3 -E --merge db1_filtered_data.sql last_merge_filtered_data.sql db2_filtered_data.sql > merged_data.sql
	then
		check_for_diff_errors 'merged_data.sql'
	fi

	echo "Combining schema structure and data..."
	# Append the data and the comments to the schema
	cat merged_data.sql >> merged_schema.sql
	cat comments.sql >> merged_schema.sql
	
	# We're done
	mv merged_schema.sql $DEST
	
	cd ..
	rm -rf merge_dbs
}