/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.index.internal.gbptree;

import static java.lang.String.format;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.neo4j.index.internal.gbptree.DataTree.W_BATCHED_SINGLE_THREADED;
import static org.neo4j.index.internal.gbptree.GBPTreeTestUtil.consistencyCheckStrict;
import static org.neo4j.io.pagecache.context.CursorContext.NULL_CONTEXT;
import static org.neo4j.test.utils.PageCacheConfig.config;

import java.io.IOException;
import java.lang.reflect.Array;
import java.nio.file.OpenOption;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.stream.Collectors;
import org.eclipse.collections.api.factory.Sets;
import org.eclipse.collections.api.set.ImmutableSet;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.neo4j.io.fs.EphemeralFileSystemAbstraction;
import org.neo4j.io.pagecache.PageCache;
import org.neo4j.io.pagecache.tracing.DatabaseFlushEvent;
import org.neo4j.io.pagecache.tracing.FileFlushEvent;
import org.neo4j.test.RandomSupport;
import org.neo4j.test.extension.Inject;
import org.neo4j.test.extension.RandomExtension;
import org.neo4j.test.extension.testdirectory.EphemeralTestDirectoryExtension;
import org.neo4j.test.utils.PageCacheSupport;
import org.neo4j.test.utils.TestDirectory;

@EphemeralTestDirectoryExtension
@ExtendWith(RandomExtension.class)
abstract class GBPTreeRecoveryITBase<KEY, VALUE> {
    private static final int PAGE_SIZE = 512;

    @Inject
    private EphemeralFileSystemAbstraction fs;

    @Inject
    private TestDirectory directory;

    @Inject
    private RandomSupport random;

    private final PageCacheSupport pageCacheSupport =
            new PageCacheSupport(config().withPageSize(PAGE_SIZE).withAccessChecks(true));
    private final Action CHECKPOINT = new CheckpointAction();

    // Test config
    private int loadCountTransactions;
    private int minInsertCountPerBatch;
    private int maxInsertCountPerBatch;
    private int minRemoveCountPerBatch;
    private int maxRemoveCountPerBatch;
    private TestLayout<KEY, VALUE> layout;

    /* Global variables for recoverFromAnything test */
    private boolean recoverFromAnythingInitialized;
    private int keyRange;

    @BeforeEach
    void setUp() {
        try (var pageCache = createPageCache()) {
            this.layout = getLayout(random, GBPTreeTestUtil.calculatePayloadSize(pageCache, getOpenOptions()));
        }
        loadCountTransactions = random.intBetween(300, 1_000);
        minInsertCountPerBatch = 30;
        maxInsertCountPerBatch = 200;
        minRemoveCountPerBatch = 5;
        maxRemoveCountPerBatch = 20;
    }

    protected abstract TestLayout<KEY, VALUE> getLayout(RandomSupport random, int pageSize);

    ImmutableSet<OpenOption> getOpenOptions() {
        return Sets.immutable.empty();
    }

    @Test
    void shouldRecoverFromCrashBeforeFirstCheckpoint() throws Exception {
        // GIVEN
        // a tree with only small amount of data that has not yet seen checkpoint from outside
        KEY key = key(1L);
        VALUE value = value(10L);
        Path file = directory.file("index");
        {
            try (PageCache pageCache = createPageCache();
                    GBPTree<KEY, VALUE> index = createIndex(pageCache, file);
                    Writer<KEY, VALUE> writer = index.writer(W_BATCHED_SINGLE_THREADED, NULL_CONTEXT)) {
                writer.put(key, value);
                pageCache.flushAndForce(DatabaseFlushEvent.NULL);
                // No checkpoint
            }
        }

        // WHEN
        try (PageCache pageCache = createPageCache();
                GBPTree<KEY, VALUE> index = createIndex(pageCache, file)) {
            try (Writer<KEY, VALUE> writer = index.writer(W_BATCHED_SINGLE_THREADED, NULL_CONTEXT)) {
                writer.put(key, value);
            }

            // THEN
            // we should end up with a consistent index
            consistencyCheckStrict(index);

            // ... containing all the stuff load says
            try (Seeker<KEY, VALUE> cursor = index.seek(key(Long.MIN_VALUE), key(Long.MAX_VALUE), NULL_CONTEXT)) {
                assertTrue(cursor.next());
                assertEqualsKey(key, cursor.key());
                assertEqualsValue(value, cursor.value());
            }
        }
    }

    @Test
    void shouldRecoverFromAnythingReplayExactFromCheckpointHighKeyContention() throws Exception {
        initializeRecoveryFromAnythingTest(100);
        doShouldRecoverFromAnything(true);
    }

    @Test
    void shouldRecoverFromAnythingReplayFromBeforeLastCheckpointHighKeyContention() throws Exception {
        initializeRecoveryFromAnythingTest(100);
        doShouldRecoverFromAnything(false);
    }

    @Test
    void shouldRecoverFromAnythingReplayExactFromCheckpointLowKeyContention() throws Exception {
        initializeRecoveryFromAnythingTest(1_000_000);
        doShouldRecoverFromAnything(true);
    }

    @Test
    void shouldRecoverFromAnythingReplayFromBeforeLastCheckpointLowKeyContention() throws Exception {
        initializeRecoveryFromAnythingTest(1_000_000);
        doShouldRecoverFromAnything(false);
    }

    private void initializeRecoveryFromAnythingTest(int keyRange) {
        recoverFromAnythingInitialized = true;
        this.keyRange = keyRange;
    }

    private void assertInitialized() {
        assertTrue(recoverFromAnythingInitialized);
    }

    private void doShouldRecoverFromAnything(boolean replayRecoveryExactlyFromCheckpoint) throws Exception {
        assertInitialized();
        // GIVEN
        // a tree which has had random updates and checkpoints in it, load generated with specific seed
        Path file = directory.file("index");
        List<Action> load = generateLoad();
        List<Action> shuffledLoad = randomCausalAwareShuffle(load);
        int lastCheckPointIndex = indexOfLastCheckpoint(load);

        {
            // _,_,_,_,_,_,_,c,_,_,_,_,_,_,_,_,_,_,_,_,_,_,_,_,c,_,_,_,_,_,_,_,_,_,_,_
            //                                                 ^             ^
            //                                                 |             |------------ crash flush index
            //                                                 |-------------------------- last checkpoint index
            //

            PageCache pageCache = createPageCache();
            GBPTree<KEY, VALUE> index = createIndex(pageCache, file);
            // Execute all actions up to and including last checkpoint ...
            execute(shuffledLoad.subList(0, lastCheckPointIndex + 1), index);
            // ... a random amount of the remaining "unsafe" actions ...
            int numberOfRemainingActions = shuffledLoad.size() - lastCheckPointIndex - 1;
            int crashFlushIndex = lastCheckPointIndex + random.nextInt(numberOfRemainingActions) + 1;
            execute(shuffledLoad.subList(lastCheckPointIndex + 1, crashFlushIndex), index);
            // ... flush ...
            pageCache.flushAndForce(DatabaseFlushEvent.NULL);
            // ... execute the remaining actions
            execute(shuffledLoad.subList(crashFlushIndex, shuffledLoad.size()), index);
            // ... and finally crash

            EphemeralFileSystemAbstraction snapshot = fs.snapshot();
            try {
                index.close();
                pageCache.close();
            } finally {
                fs.close();
                fs = snapshot;
            }
        }

        // WHEN doing recovery
        List<Action> recoveryActions;
        if (replayRecoveryExactlyFromCheckpoint) {
            recoveryActions = recoveryActions(load, lastCheckPointIndex + 1);
        } else {
            recoveryActions = recoveryActions(load, random.nextInt(lastCheckPointIndex + 1));
        }

        // first crashing during recovery
        int numberOfCrashesDuringRecovery = random.intBetween(0, 3);
        for (int i = 0; i < numberOfCrashesDuringRecovery; i++) {
            try (PageCache pageCache = createPageCache();
                    GBPTree<KEY, VALUE> index = createIndex(pageCache, file)) {
                int numberOfActionsToRecoverBeforeCrashing = random.intBetween(1, recoveryActions.size());
                recover(recoveryActions.subList(0, numberOfActionsToRecoverBeforeCrashing), index);
                // ... crash
            }
        }

        // to finally apply all actions after last checkpoint and verify tree
        try (PageCache pageCache = createPageCache();
                GBPTree<KEY, VALUE> index = createIndex(pageCache, file)) {
            recover(recoveryActions, index);

            // THEN
            // we should end up with a consistent index containing all the stuff load says
            consistencyCheckStrict(index);
            long[ /*key,value,key,value...*/] aggregate = expectedSortedAggregatedDataFromGeneratedLoad(load);
            try (Seeker<KEY, VALUE> cursor = index.seek(key(Long.MIN_VALUE), key(Long.MAX_VALUE), NULL_CONTEXT)) {
                for (int i = 0; i < aggregate.length; ) {
                    assertTrue(cursor.next());
                    assertEqualsKey(key(aggregate[i++]), cursor.key());
                    assertEqualsValue(value(aggregate[i++]), cursor.value());
                }
                assertFalse(cursor.next());
            }
        }
    }

    /**
     * Shuffle actions without breaking causal dependencies, i.e. without affecting the end result
     * of the data ending up in the tree. Checkpoints cannot move.
     *
     * On an integration level with neo4j, this is done because of the nature of how concurrent transactions
     * are applied in random order and recovery applies transactions in order of transaction id.
     */
    private List<Action> randomCausalAwareShuffle(List<Action> actions) {
        //noinspection unchecked
        Action[] arrayToShuffle = actions.toArray((Action[]) Array.newInstance(Action.class, actions.size()));
        int size = arrayToShuffle.length;
        int numberOfActionsToShuffle = random.nextInt(size / 2);

        for (int i = 0; i < numberOfActionsToShuffle; i++) {
            int actionIndexToMove = random.nextInt(size);
            int stride = random.nextBoolean() ? 1 : -1;
            int maxNumberOfSteps = random.nextInt(10) + 1;

            for (int steps = 0; steps < maxNumberOfSteps; steps++) {
                Action actionToMove = arrayToShuffle[actionIndexToMove];
                int actionIndexToSwap = actionIndexToMove + stride;
                if (actionIndexToSwap < 0 || actionIndexToSwap >= size) {
                    break;
                }
                Action actionToSwap = arrayToShuffle[actionIndexToSwap];

                if (actionToMove.hasCausalDependencyWith(actionToSwap)) {
                    break;
                }

                arrayToShuffle[actionIndexToMove] = actionToSwap;
                arrayToShuffle[actionIndexToSwap] = actionToMove;

                actionIndexToMove = actionIndexToSwap;
            }
        }
        return Arrays.asList(arrayToShuffle);
    }

    private List<Action> recoveryActions(List<Action> load, int fromIndex) {
        return load.subList(fromIndex, load.size()).stream()
                .filter(action -> !action.isCheckpoint())
                .collect(Collectors.toList());
    }

    private void recover(List<Action> load, GBPTree<KEY, VALUE> index) throws IOException {
        execute(load, index);
    }

    private void execute(List<Action> load, GBPTree<KEY, VALUE> index) throws IOException {
        for (Action action : load) {
            action.execute(index);
        }
    }

    private long[] expectedSortedAggregatedDataFromGeneratedLoad(List<Action> load) {
        TreeMap<Long, Long> map = new TreeMap<>();
        for (Action action : load) {
            long[] data = action.data();
            if (data != null) {
                for (int i = 0; i < data.length; ) {
                    long key = data[i++];
                    long value = data[i++];
                    if (action.type() == ActionType.INSERT) {
                        map.put(key, value);
                    } else if (action.type() == ActionType.REMOVE) {
                        map.remove(key);
                    } else {
                        throw new UnsupportedOperationException(action.toString());
                    }
                }
            }
        }

        @SuppressWarnings("unchecked")
        Map.Entry<Long, Long>[] entries = map.entrySet().toArray(new Map.Entry[0]);
        long[] result = new long[entries.length * 2];
        for (int i = 0, c = 0; i < entries.length; i++) {
            result[c++] = entries[i].getKey();
            result[c++] = entries[i].getValue();
        }
        return result;
    }

    private int indexOfLastCheckpoint(List<Action> actions) {
        int i = 0;
        int lastCheckpoint = -1;
        for (Action action : actions) {
            if (action.isCheckpoint()) {
                lastCheckpoint = i;
            }
            i++;
        }
        return lastCheckpoint;
    }

    private List<Action> generateLoad() {
        List<Action> actions = new ArrayList<>(loadCountTransactions);
        boolean hasCheckPoint = false;
        for (int i = 0; i < loadCountTransactions; i++) {
            Action action = randomAction(true);
            actions.add(action);
            if (action == CHECKPOINT) {
                hasCheckPoint = true;
            }
        }

        // Guarantee that there's at least one check point, i.e. if there's none then append one at the end
        if (!hasCheckPoint) {
            actions.add(CHECKPOINT);
        }

        // Guarantee that there are at least some non-checkpoint actions after last checkpoint
        if (actions.get(actions.size() - 1) == CHECKPOINT) {
            int additional = random.intBetween(1, 10);
            for (int i = 0; i < additional; i++) {
                actions.add(randomAction(false));
            }
        }
        return actions;
    }

    private Action randomAction(boolean allowCheckPoint) {
        float randomized = random.nextFloat();
        if (randomized <= 0.7) {
            // put
            long[] data = modificationData(minInsertCountPerBatch, maxInsertCountPerBatch);
            return new InsertAction(data);
        } else if (randomized <= 0.95 || !allowCheckPoint) {
            // remove
            long[] data = modificationData(minRemoveCountPerBatch, maxRemoveCountPerBatch);
            return new RemoveAction(data);
        } else {
            return CHECKPOINT;
        }
    }

    private long[] modificationData(int min, int max) {
        int count = random.intBetween(min, max);
        long[] data = new long[count * 2];
        for (int i = 0, c = 0; i < count; i++) {
            data[c++] = random.intBetween(0, keyRange); // key
            data[c++] = random.intBetween(0, keyRange); // value
        }
        return data;
    }

    private GBPTree<KEY, VALUE> createIndex(PageCache pageCache, Path file) {
        return new GBPTreeBuilder<>(pageCache, fs, file, layout)
                .with(getOpenOptions())
                .build();
    }

    private PageCache createPageCache() {
        return pageCacheSupport.getPageCache(fs);
    }

    enum ActionType {
        INSERT,
        REMOVE,
        CHECKPOINT
    }

    abstract class Action {
        long[] data;
        Set<Long> allKeys;

        Action(long[] data) {
            this.data = data;
            this.allKeys = keySet(data);
        }

        long[] data() {
            return data;
        }

        abstract void execute(GBPTree<KEY, VALUE> index) throws IOException;

        abstract boolean isCheckpoint();

        abstract boolean hasCausalDependencyWith(Action other);

        private Set<Long> keySet(long[] data) {
            Set<Long> keys = new TreeSet<>();
            for (int i = 0; i < data.length; i += 2) {
                keys.add(data[i]);
            }
            return keys;
        }

        abstract ActionType type();
    }

    abstract class DataAction extends Action {
        DataAction(long[] data) {
            super(data);
        }

        @Override
        boolean isCheckpoint() {
            return false;
        }

        @Override
        public boolean hasCausalDependencyWith(Action other) {
            if (other.isCheckpoint()) {
                return true;
            }

            Set<Long> intersection = new TreeSet<>(allKeys);
            intersection.retainAll(other.allKeys);

            return !intersection.isEmpty();
        }
    }

    class InsertAction extends DataAction {
        InsertAction(long[] data) {
            super(data);
        }

        @Override
        public void execute(GBPTree<KEY, VALUE> index) throws IOException {
            try (Writer<KEY, VALUE> writer = index.writer(W_BATCHED_SINGLE_THREADED, NULL_CONTEXT)) {
                for (int i = 0; i < data.length; ) {
                    writer.put(key(data[i++]), value(data[i++]));
                }
            }
        }

        @Override
        ActionType type() {
            return ActionType.INSERT;
        }
    }

    class RemoveAction extends DataAction {
        RemoveAction(long[] data) {
            super(data);
        }

        @Override
        public void execute(GBPTree<KEY, VALUE> index) throws IOException {
            try (Writer<KEY, VALUE> writer = index.writer(W_BATCHED_SINGLE_THREADED, NULL_CONTEXT)) {
                for (int i = 0; i < data.length; ) {
                    KEY key = key(data[i++]);
                    i++; // value
                    writer.remove(key);
                }
            }
        }

        @Override
        ActionType type() {
            return ActionType.REMOVE;
        }
    }

    class CheckpointAction extends Action {
        CheckpointAction() {
            super(new long[0]);
        }

        @Override
        public void execute(GBPTree<KEY, VALUE> index) throws IOException {
            index.checkpoint(FileFlushEvent.NULL, NULL_CONTEXT);
        }

        @Override
        boolean isCheckpoint() {
            return true;
        }

        @Override
        public boolean hasCausalDependencyWith(Action other) {
            return true;
        }

        @Override
        ActionType type() {
            return ActionType.CHECKPOINT;
        }
    }

    private KEY key(long seed) {
        return layout.key(seed);
    }

    private VALUE value(long seed) {
        return layout.value(seed);
    }

    private void assertEqualsKey(KEY expected, KEY actual) {
        assertEquals(
                0,
                layout.compare(expected, actual),
                format("expected equal, expected=%s, actual=%s", expected, actual));
    }

    private void assertEqualsValue(VALUE expected, VALUE actual) {
        assertEquals(
                0,
                layout.compareValue(expected, actual),
                format("expected equal, expected=%s, actual=%s", expected, actual));
    }
}
