/*
 * (C) Copyright 2006-2011 Nuxeo SA (http://nuxeo.com/) and others.
 *
 * 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.
 *
 * Contributors:
 *     Florent Guillaume
 */
package org.nuxeo.ecm.core.storage.sql;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import javax.transaction.xa.XAException;
import javax.transaction.xa.Xid;

import org.apache.commons.collections.map.AbstractReferenceMap;
import org.apache.commons.collections.map.ReferenceMap;
import org.nuxeo.ecm.core.storage.sql.ACLRow.ACLRowPositionComparator;
import org.nuxeo.runtime.metrics.MetricsService;

import com.codahale.metrics.Counter;
import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.SharedMetricRegistries;
import com.codahale.metrics.Timer;

/**
 * A {@link RowMapper} that has an internal cache.
 * <p>
 * The cache only holds {@link Row}s that are known to be identical to what's in the underlying {@link RowMapper}.
 */
public class SoftRefCachingRowMapper implements RowMapper {

    private static final String ABSENT = "__ABSENT__\0\0\0";

    /**
     * The cached rows. All held data is identical to what is present in the underlying {@link RowMapper} and could be
     * refetched if needed.
     * <p>
     * The values are either {@link Row} for fragments present in the database, or a row with tableName {@link #ABSENT}
     * to denote a fragment known to be absent from the database.
     * <p>
     * This cache is memory-sensitive (all values are soft-referenced), a fragment can always be refetched if the GC
     * collects it.
     */
    // we use a new Row instance for the absent case to avoid keeping other
    // references to it which would prevent its GCing
    private final Map<RowId, Row> cache;

    private Model model;

    /**
     * The {@link RowMapper} to which operations that cannot be processed from the cache are delegated.
     */
    private RowMapper rowMapper;

    /**
     * The local invalidations due to writes through this mapper that should be propagated to other sessions at
     * post-commit time.
     */
    private final Invalidations localInvalidations;

    /**
     * The queue of cache invalidations received from other session, to process at pre-transaction time.
     */
    // public for unit tests
    public final InvalidationsQueue cacheQueue;

    /**
     * The propagator of invalidations to other mappers.
     */
    private InvalidationsPropagator cachePropagator;

    /**
     * Cache statistics
     *
     * @since 5.7
     */
    protected final MetricRegistry registry = SharedMetricRegistries.getOrCreate(MetricsService.class.getName());

    protected Counter cacheHitCount;

    protected Timer cacheGetTimer;

    // sor means system of record (database access)
    protected Counter sorRows;

    protected Timer sorGetTimer;

    @SuppressWarnings("unchecked")
    public SoftRefCachingRowMapper() {
        cache = new ReferenceMap(AbstractReferenceMap.HARD, AbstractReferenceMap.SOFT);
        localInvalidations = new Invalidations();
        cacheQueue = new InvalidationsQueue("mapper-" + this);
    }

    public void initialize(String repositoryName, Model model, RowMapper rowMapper,
            InvalidationsPropagator cachePropagator, Map<String, String> properties) {
        this.model = model;
        this.rowMapper = rowMapper;
        this.cachePropagator = cachePropagator;
        cachePropagator.addQueue(cacheQueue);
        setMetrics(repositoryName);
    }

    protected void setMetrics(String repositoryName) {
        cacheHitCount = registry.counter(MetricRegistry.name("nuxeo", "repositories", repositoryName, "caches",
                "soft-ref", "hits"));
        cacheGetTimer = registry.timer(MetricRegistry.name("nuxeo", "repositories", repositoryName, "caches",
                "soft-ref", "get"));
        sorRows = registry.counter(MetricRegistry.name("nuxeo", "repositories", repositoryName, "caches", "soft-ref",
                "sor", "rows"));
        sorGetTimer = registry.timer(MetricRegistry.name("nuxeo", "repositories", repositoryName, "caches", "soft-ref",
                "sor", "get"));
    }

    public void close() {
        clearCache();
        cachePropagator.removeQueue(cacheQueue);
    }

    @Override
    public Serializable generateNewId() {
        return rowMapper.generateNewId();
    }

    /*
     * ----- Cache -----
     */

    protected static boolean isAbsent(Row row) {
        return row.tableName == ABSENT; // == is ok
    }

    protected void cachePut(Row row) {
        row = row.clone();
        // for ACL collections, make sure the order is correct
        // (without the cache, the query to get a list of collection does an
        // ORDER BY pos, so users of the cache must get the same behavior)
        if (row.isCollection() && row.values.length > 0 && row.values[0] instanceof ACLRow) {
            row.values = sortACLRows((ACLRow[]) row.values);
        }
        cache.put(new RowId(row), row);
    }

    protected ACLRow[] sortACLRows(ACLRow[] acls) {
        List<ACLRow> list = new ArrayList<ACLRow>(Arrays.asList(acls));
        Collections.sort(list, ACLRowPositionComparator.INSTANCE);
        ACLRow[] res = new ACLRow[acls.length];
        return list.toArray(res);
    }

    protected void cachePutAbsent(RowId rowId) {
        cache.put(new RowId(rowId), new Row(ABSENT, (Serializable) null));
    }

    protected void cachePutAbsentIfNull(RowId rowId, Row row) {
        if (row != null) {
            cachePut(row);
        } else {
            cachePutAbsent(rowId);
        }
    }

    protected void cachePutAbsentIfRowId(RowId rowId) {
        if (rowId instanceof Row) {
            cachePut((Row) rowId);
        } else {
            cachePutAbsent(rowId);
        }
    }

    protected Row cacheGet(RowId rowId) {
        final Timer.Context context = cacheGetTimer.time();
        try {
            Row row = cache.get(rowId);
            if (row != null && !isAbsent(row)) {
                row = row.clone();
            }
            if (row != null) {
                cacheHitCount.inc();
            }
            return row;
        } finally {
            context.stop();
        }
    }

    protected void cacheRemove(RowId rowId) {
        cache.remove(rowId);
    }

    /*
     * ----- Invalidations / Cache Management -----
     */

    @Override
    public Invalidations receiveInvalidations() {
        // invalidations from the underlying mapper (cluster)
        // already propagated to our invalidations queue
        rowMapper.receiveInvalidations();

        Invalidations invalidations = cacheQueue.getInvalidations();

        // invalidate our cache
        if (invalidations.all) {
            clearCache();
        }
        if (invalidations.modified != null) {
            for (RowId rowId : invalidations.modified) {
                cacheRemove(rowId);
            }
        }
        if (invalidations.deleted != null) {
            for (RowId rowId : invalidations.deleted) {
                cachePutAbsent(rowId);
            }
        }

        return invalidations.isEmpty() ? null : invalidations;
    }

    // propagate invalidations
    @Override
    public void sendInvalidations(Invalidations invalidations) {
        // add local invalidations
        if (!localInvalidations.isEmpty()) {
            if (invalidations == null) {
                invalidations = new Invalidations();
            }
            invalidations.add(localInvalidations);
            localInvalidations.clear();
        }

        if (invalidations != null && !invalidations.isEmpty()) {
            // send to underlying mapper
            rowMapper.sendInvalidations(invalidations);

            // queue to other local mappers' caches
            cachePropagator.propagateInvalidations(invalidations, cacheQueue);
        }
    }

    @Override
    public void clearCache() {
        cache.clear();
        sorRows.dec(sorRows.getCount());
        localInvalidations.clear();
        rowMapper.clearCache();
    }

    @Override
    public long getCacheSize() {
        return cache.size();
    }

    @Override
    public void rollback(Xid xid) throws XAException {
        try {
            rowMapper.rollback(xid);
        } finally {
            clearCache();
        }
    }

    /*
     * ----- Batch -----
     */

    /*
     * Use those from the cache if available, read from the mapper for the rest.
     */
    @Override
    public List<? extends RowId> read(Collection<RowId> rowIds, boolean cacheOnly) {
        List<RowId> res = new ArrayList<RowId>(rowIds.size());
        // find which are in cache, and which not
        List<RowId> todo = new LinkedList<RowId>();
        for (RowId rowId : rowIds) {
            Row row = cacheGet(rowId);
            if (row == null) {
                if (cacheOnly) {
                    res.add(new RowId(rowId));
                } else {
                    todo.add(rowId);
                }
            } else if (isAbsent(row)) {
                res.add(new RowId(rowId));
            } else {
                res.add(row);
            }
        }
        if (!todo.isEmpty()) {
            final Timer.Context context = sorGetTimer.time();
            try {
                // ask missing ones to underlying row mapper
                List<? extends RowId> fetched = rowMapper.read(todo, cacheOnly);
                // add them to the cache
                for (RowId rowId : fetched) {
                    cachePutAbsentIfRowId(rowId);
                }
                // merge results
                res.addAll(fetched);
                sorRows.inc(fetched.size());
            } finally {
                context.stop();
            }
        }
        return res;
    }

    /*
     * Save in the cache then pass all the writes to the mapper.
     */
    @Override
    public void write(RowBatch batch) {
        for (Row row : batch.creates) {
            cachePut(row);
            // we need to send modified invalidations for created
            // fragments because other session's ABSENT fragments have
            // to be invalidated
            localInvalidations.addModified(new RowId(row));
        }
        for (RowUpdate rowu : batch.updates) {
            cachePut(rowu.row);
            localInvalidations.addModified(new RowId(rowu.row));
        }
        for (RowId rowId : batch.deletes) {
            if (rowId instanceof Row) {
                throw new AssertionError();
            }
            cachePutAbsent(rowId);
            localInvalidations.addDeleted(rowId);
        }
        for (RowId rowId : batch.deletesDependent) {
            if (rowId instanceof Row) {
                throw new AssertionError();
            }
            cachePutAbsent(rowId);
            localInvalidations.addDeleted(rowId);
        }

        // propagate to underlying mapper
        rowMapper.write(batch);
    }

    /*
     * ----- Read -----
     */

    @Override
    public Row readSimpleRow(RowId rowId) {
        Row row = cacheGet(rowId);
        if (row == null) {
            row = rowMapper.readSimpleRow(rowId);
            cachePutAbsentIfNull(rowId, row);
            return row;
        } else if (isAbsent(row)) {
            return null;
        } else {
            return row;
        }
    }

    @Override
    public Map<String, String> getBinaryFulltext(RowId rowId) {
        return rowMapper.getBinaryFulltext(rowId);
    }

    @Override
    public Serializable[] readCollectionRowArray(RowId rowId) {
        Row row = cacheGet(rowId);
        if (row == null) {
            Serializable[] array = rowMapper.readCollectionRowArray(rowId);
            assert array != null;
            row = new Row(rowId.tableName, rowId.id, array);
            cachePut(row);
            return row.values;
        } else if (isAbsent(row)) {
            return null;
        } else {
            return row.values;
        }
    }

    @Override
    public List<Row> readSelectionRows(SelectionType selType, Serializable selId, Serializable filter,
            Serializable criterion, boolean limitToOne) {
        List<Row> rows = rowMapper.readSelectionRows(selType, selId, filter, criterion, limitToOne);
        for (Row row : rows) {
            cachePut(row);
        }
        return rows;
    }

    /*
     * ----- Copy -----
     */

    @Override
    public CopyResult copy(IdWithTypes source, Serializable destParentId, String destName, Row overwriteRow) {
        CopyResult result = rowMapper.copy(source, destParentId, destName, overwriteRow);
        Invalidations invalidations = result.invalidations;
        if (invalidations.modified != null) {
            for (RowId rowId : invalidations.modified) {
                cacheRemove(rowId);
                localInvalidations.addModified(new RowId(rowId));
            }
        }
        if (invalidations.deleted != null) {
            for (RowId rowId : invalidations.deleted) {
                cacheRemove(rowId);
                localInvalidations.addDeleted(rowId);
            }
        }
        return result;
    }

    @Override
    public List<NodeInfo> remove(NodeInfo rootInfo) {
        List<NodeInfo> infos = rowMapper.remove(rootInfo);
        for (NodeInfo info : infos) {
            for (String fragmentName : model.getTypeFragments(new IdWithTypes(info.id, info.primaryType, null))) {
                RowId rowId = new RowId(fragmentName, info.id);
                cacheRemove(rowId);
                localInvalidations.addDeleted(rowId);
            }
        }
        // we only put as absent the root fragment, to avoid polluting the cache
        // with lots of absent info. the rest is removed entirely
        cachePutAbsent(new RowId(Model.HIER_TABLE_NAME, rootInfo.id));
        return infos;
    }

}