/*
 * Copyright (C) 2020 ActiveJ LLC.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.activej.etl;

import io.activej.ot.TransformResult;
import io.activej.ot.TransformResult.ConflictResolution;
import io.activej.ot.system.OTSystem;
import io.activej.ot.system.OTSystemImpl;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import static io.activej.common.Checks.checkArgument;
import static io.activej.common.Checks.checkState;
import static io.activej.common.Utils.*;

public class LogOT {
	public static <T> OTSystem<LogDiff<T>> createLogOT(OTSystem<T> otSystem) {
		return OTSystemImpl.<LogDiff<T>>builder()
			.withTransformFunction(LogDiff.class, LogDiff.class, (left, right) -> {
				Set<String> intersection = intersection(left.getPositions().keySet(), right.getPositions().keySet());
				if (intersection.isEmpty()) {
					TransformResult<T> transformed = otSystem.transform(left.getDiffs(), right.getDiffs());
					if (transformed.hasConflict()) {
						return TransformResult.conflict(transformed.resolution);
					}
					return TransformResult.of(
						LogDiff.of(right.getPositions(), transformed.left),
						LogDiff.of(left.getPositions(), transformed.right));
				}

				int comparison = 0;
				for (String log : intersection) {
					LogPositionDiff leftPosition = left.getPositions().get(log);
					LogPositionDiff rightPosition = right.getPositions().get(log);
					checkArgument(leftPosition.from().equals(rightPosition.from()),
						"'From' values should be equal for left and right log positions");
					comparison += leftPosition.compareTo(rightPosition);
				}

				return TransformResult.conflict(comparison > 0 ? ConflictResolution.LEFT : ConflictResolution.RIGHT);
			})
			.withEmptyPredicate(LogDiff.class, commit -> commit.getPositions().isEmpty() && commit.getDiffs().stream().allMatch(otSystem::isEmpty))
			.withSquashFunction(LogDiff.class, LogDiff.class, (commit1, commit2) -> {
				Map<String, LogPositionDiff> positions = new HashMap<>(commit1.getPositions());
				for (Entry<String, LogPositionDiff> entry : commit2.getPositions().entrySet()) {
					String log = entry.getKey();
					LogPositionDiff positionDiff1 = positions.get(log);
					LogPositionDiff positionDiff2 = entry.getValue();
					if (positionDiff1 != null) {
						checkState(positionDiff1.to().equals(positionDiff2.from()),
							"'To' value of the first log position should be equal to 'From' value of the second log position");
						positionDiff2 = new LogPositionDiff(positionDiff1.from(), positionDiff2.to());
					}
					if (!positionDiff2.isEmpty()) {
						positions.put(log, positionDiff2);
					} else {
						positions.remove(log);
					}
				}
				List<T> ops = concat(commit1.getDiffs(), commit2.getDiffs());
				return LogDiff.of(positions, otSystem.squash(ops));
			})
			.withInvertFunction(LogDiff.class, commit -> List.of(LogDiff.of(
				commit.getPositions().entrySet().stream()
					.collect(entriesToLinkedHashMap(LogPositionDiff::inverse)),
				otSystem.invert(commit.getDiffs()))))
			.build();
	}

}
