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/*
 * Copyright (c) 2016 Uber Technologies, Inc. ([email protected])
 *
 * 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.uber.hoodie.common.model;

import java.util.Map;
import org.apache.avro.Schema;
import org.apache.avro.generic.IndexedRecord;

import java.io.IOException;
import java.io.Serializable;
import java.util.Optional;

/**
 * Every Hoodie dataset has an implementation of the HoodieRecordPayload
 * This abstracts out callbacks which depend on record specific logic
 */
public interface HoodieRecordPayload extends Serializable {
    /**
     * When more than one HoodieRecord have the same HoodieKey, this function combines them
     * before attempting to insert/upsert (if combining turned on in HoodieClientConfig)
     */
    T preCombine(T another);

    /**
     *
     * This methods lets you write custom merging/combining logic to produce new values
     * as a function of current value on storage and whats contained in this object.
     *
     * eg:
     * 1) You are updating counters, you may want to add counts to currentValue and write back updated counts
     * 2) You may be reading DB redo logs, and merge them with current image for a database row on storage
     *
     * @param currentValue Current value in storage, to merge/combine this payload with
     * @param schema Schema used for record
     * @return new combined/merged value to be written back to storage. EMPTY to skip writing this record.
     */
    Optional combineAndGetUpdateValue(IndexedRecord currentValue, Schema schema) throws IOException;

    /**
     * Generates an avro record out of the given HoodieRecordPayload, to be written out to storage.
     * Called when writing a new value for the given HoodieKey, wherein there is no existing record in
     * storage to be combined against. (i.e insert)
     * Return EMPTY to skip writing this record.
     */
    Optional getInsertValue(Schema schema) throws IOException;

    /**
     * This method can be used to extract some metadata from HoodieRecordPayload. The metadata is passed
     * to {@code WriteStatus.markSuccess()} and {@code WriteStatus.markFailure()} in order to compute
     * some aggregate metrics using the metadata in the context of a write success or failure.
     */
    default Optional> getMetadata() {
        return Optional.empty();
    }
}