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/*
 * (c) Copyright 2018 Palantir Technologies Inc. All rights reserved.
 *
 * 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 com.palantir.atlasdb.keyvalue.dbkvs.impl;

import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.Caffeine;
import com.palantir.atlasdb.keyvalue.api.TableReference;
import com.palantir.atlasdb.table.description.TableMetadata;
import java.time.Duration;
import javax.annotation.Nullable;

public class TableMetadataCache {
    private static final TableMetadata EMPTY = TableMetadata.allDefault();

    private final Cache cache = Caffeine.newBuilder()
            .maximumSize(10000)
            .expireAfterWrite(Duration.ofHours(1))
            .build();
    private final DbTableFactory dbTables;

    public TableMetadataCache(DbTableFactory dbTables) {
        this.dbTables = dbTables;
    }

    @Nullable
    @SuppressWarnings("ImmutablesReferenceEquality")
    public TableMetadata getTableMetadata(TableReference tableRef, ConnectionSupplier conns) {
        TableMetadata metadataOrEmpty = getOrReturnEmpty(tableRef, conns);
        if (metadataOrEmpty == EMPTY) {
            return null;
        } else {
            return metadataOrEmpty;
        }
    }

    @SuppressWarnings("ImmutablesReferenceEquality")
    private TableMetadata getOrReturnEmpty(TableReference tableRef, ConnectionSupplier conns) {
        TableMetadata cached = cache.getIfPresent(tableRef);
        if (cached != null) {
            return cached;
        } else {
            byte[] rawMetadata = dbTables.createMetadata(tableRef, conns).getMetadata();
            TableMetadata hydrated = hydrateMetadata(rawMetadata);
            cache.put(tableRef, hydrated);
            return hydrated;
        }
    }

    private TableMetadata hydrateMetadata(byte[] rawMetadata) {
        if (rawMetadata == null || rawMetadata.length == 0) {
            return EMPTY;
        } else {
            return TableMetadata.BYTES_HYDRATOR.hydrateFromBytes(rawMetadata);
        }
    }
}