/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.flink.runtime.operators.resettable;

import java.io.IOException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
import org.apache.flink.runtime.memory.MemoryAllocationException;
import org.apache.flink.runtime.memory.MemoryManager;
import org.apache.flink.runtime.util.ResettableMutableObjectIterator;
import org.apache.flink.util.MutableObjectIterator;

/**
 * Implementation of an iterator that fetches a block of data into main memory and offers resettable
 * access to the data in that block.
 * 
 */
public class BlockResettableMutableObjectIterator<T> extends AbstractBlockResettableIterator<T>
	implements ResettableMutableObjectIterator<T>
{
	public static final Logger LOG = LoggerFactory.getLogger(BlockResettableMutableObjectIterator.class);
	
	// ------------------------------------------------------------------------
	
	private final MutableObjectIterator<T> input;
	
	private boolean readPhase;
	
	private boolean leftOverReturned;
	
	private boolean fullWriteBuffer;
	
	private boolean noMoreBlocks;
	
	private T leftOverRecord;
	
	// ------------------------------------------------------------------------
	
	public BlockResettableMutableObjectIterator(MemoryManager memoryManager,
			MutableObjectIterator<T> input,	TypeSerializer<T> serializer,
			int numMemoryPages, AbstractInvokable ownerTask)
	throws MemoryAllocationException
	{
		super(serializer, memoryManager, numMemoryPages, ownerTask);
		
		this.input = input;
		this.leftOverRecord = serializer.createInstance();
		this.leftOverReturned = true;
	}
	
	// --------------------------------------------------------------------------------------------


	@Override
	public T next(T target) throws IOException {
		// check for the left over element
		if (this.readPhase) {
			return getNextRecord(target);
		} else {
			// writing phase. check for leftover first
			if (this.leftOverReturned) {
				// get next record
				if ((target = this.input.next(target)) != null) {
					if (writeNextRecord(target)) {
						return target;
					} else {
						// did not fit into memory, keep as leftover
						this.leftOverRecord = this.serializer.copy(target, this.leftOverRecord);
						this.leftOverReturned = false;
						this.fullWriteBuffer = true;
						return null;
					}
				} else {
					this.noMoreBlocks = true;
					return null;
				}
			} else if (this.fullWriteBuffer) {
				return null;
			} else {
				this.leftOverReturned = true;
				target = this.serializer.copy(this.leftOverRecord, target);
				return target;
			}
		}
	}

	@Override
	public T next() throws IOException {
		// check for the left over element
		if (this.readPhase) {
			return getNextRecord();
		} else {
			// writing phase. check for leftover first
			T result = null;
			if (this.leftOverReturned) {
				// get next record
				if ((result = this.input.next()) != null) {
					if (writeNextRecord(result)) {
						return result;
					} else {
						// did not fit into memory, keep as leftover
						this.leftOverRecord = this.serializer.copy(result);
						this.leftOverReturned = false;
						this.fullWriteBuffer = true;
						return null;
					}
				} else {
					this.noMoreBlocks = true;
					return null;
				}
			} else if (this.fullWriteBuffer) {
				return null;
			} else {
				this.leftOverReturned = true;
				return this.leftOverRecord;
			}
		}
	}



	public void reset() {
		// a reset always goes to the read phase
		this.readPhase = true;
		super.reset();
	}
	

	@Override
	public boolean nextBlock() throws IOException {
		// check the state
		if (this.closed) {
			throw new IllegalStateException("Iterator has been closed.");
		}
		
		// check whether more blocks are available
		if (this.noMoreBlocks) {
			return false;
		}

		// reset the views in the superclass
		super.nextBlock();
		
		// if there is no leftover record, get a record such that we guarantee to advance
		if (this.leftOverReturned || !this.fullWriteBuffer) {
			if ((this.leftOverRecord = this.input.next(this.leftOverRecord)) != null) {
				this.leftOverReturned = false;
			} else {
				this.noMoreBlocks = true;
				this.fullWriteBuffer = true;
				this.readPhase = false;
				return false;
			}
		}

		// write the leftover record
		if (!writeNextRecord(this.leftOverRecord)) {
			throw new IOException("BlockResettableIterator could not serialize record into fresh memory block: " +
					"Record is too large.");
		}
		this.readPhase = false;
		this.fullWriteBuffer = false;
		
		return true;
	}
	
	/**
	 * Checks, whether the input that is blocked by this iterator, has further elements
	 * available. This method may be used to forecast (for example at the point where a
	 * block is full) whether there will be more data (possibly in another block).
	 * 
	 * @return True, if there will be more data, false otherwise.
	 */
	public boolean hasFurtherInput() {
		return !this.noMoreBlocks; 
	}
	

	public void close() {
		// suggest that we are in the read phase. because nothing is in the current block,
		// read requests will fail
		this.readPhase = true;
		super.close();
	}
}