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/*
 * Copyright (c) 2017 simplity.org
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package org.simplity.aggr;

import org.simplity.kernel.data.FieldsInterface;
import org.simplity.service.ServiceContext;

/**
 * Functionality required to accumulate/aggregate column value/s across rows.
 * init() is invoked once for a table/sheet/rows. accumulate() is called for
 * each row of data and writeOut() is called as and when the accumulated value
 * is to be written out. For example when the group-by fields change, or when
 * there are no more rows
 *
 * @author simplity.org
 *
 */
public interface AggregationWorker {
	/**
	 * set-up shop and get ready to start aggregation process. Utility for a
	 * class to reset in case it is re-used across aggregation cycles.
	 * Implementations should put safety against init() when accumulation is in
	 * progress. Best practice would be a reset() and then init()
	 *
	 * @param ctx
	 *            service context
	 */
	public void init(ServiceContext ctx);

	/**
	 * called with fields from the current row of data. Main method for keep
	 * accumulating data
	 *
	 * @param currentRow
	 *            fields from current row being aggregated
	 * @param ctx
	 *            service context
	 */
	public void accumulate(FieldsInterface currentRow, ServiceContext ctx);

	/**
	 * end of rows for the current accumulation. Write-out your result, and get
	 * ready for the next accumulation. Note that init is NOT called after this.
	 * Also, this is called when there are no more rows
	 *
	 * @param outputRow
	 * @param ctx
	 */
	public void writeOut(FieldsInterface outputRow, ServiceContext ctx);

	/**
	 * invoked in case the accumulated value is to be discarded (opposite of
	 * writeOut)
	 *
	 * @param ctx
	 */
	public void discard(ServiceContext ctx);

	/**
	 * reset to a state as if this was never called earlier..
	 *
	 * @param ctx
	 */
	public void reset(ServiceContext ctx);
}