/**
 * 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.hadoop.util;

import java.util.ArrayList;

/** Utility to assist with generation of progress reports.  Applications build
 * a hierarchy of {@link Progress} instances, each modelling a phase of
 * execution.  The root is constructed with {@link #Progress()}.  Nodes for
 * sub-phases are created by calling {@link #addPhase()}.
 */
public class Progress {
	private float[] weights = null;
	private String status = "";
	private float progress;
	private int currentPhase;
	private final ArrayList<Progress> phases = new ArrayList<Progress>();
	private Progress parent;
	private float progressPerPhase;

	/** Creates a new root node. */
	public Progress() {}

	public void setWeight(float[] weights) {
		if (weights.length == phases.size()) {
			float sum = 0f;
			for (int i = 0; i < weights.length; i++) {
				sum += weights[i];
			}
			this.weights = weights;
		}
	}
	/** Adds a named node to the tree. */
	public Progress addPhase(String status) {
		synchronized (phases) {
			Progress phase = addPhase();
			phase.setStatus(status);
			return phase;
		}
	}

	/** Adds a node to the tree. */
	public Progress addPhase() {
		synchronized (phases) {
			Progress phase = new Progress();
			phases.add(phase);
			phase.parent = this;
			progressPerPhase = 1.0f / (float)phases.size();
			return phase;
		}
	}

	/** Called during execution to move to the next phase at this level in the
	 * tree. */
	public void startNextPhase() {
		currentPhase++;
	}

	/** Returns the current sub-node executing. */
	public Progress phase() {
		synchronized (phases) {
			return phases.get(currentPhase);
		}
	}

	/** Completes this node, moving the parent node to its next child. */
	public void complete() {
		synchronized(phases) {
			// we have to traverse up to our parent, so be careful about locking.
			Progress myParent;
			progress = 1.0f;
			myParent = parent;
			if (myParent != null) {
				// this will synchronize on the parent, so we make sure we release
				// our lock before getting the parent's, since we're traversing 
				// against the normal traversal direction used by get() or toString().
				// We don't need transactional semantics, so we're OK doing this. 
				myParent.startNextPhase();
			}
		}
	}

	/** Called during execution on a leaf node to set its progress. */
	public void set(float progress) {
		this.progress = progress;
	}

	/** Returns the overall progress of the root. */
	// this method probably does not need to be synchronized as getINternal() is synchronized 
	// and the node's parent never changes. Still, it doesn't hurt. 
	public float get() {
		synchronized (phases) {
			Progress node = this;
			while (node.parent != null) {                 // find the root
				node = parent;
			}
			return node.getInternal();
		}
	}

	/** Computes progress in this node. */
	private float getInternal() {
		int phaseCount = phases.size();
		if (phaseCount != 0) {
			if (weights != null) {
				float weightedProgress = 0f;
				for (int i = 0; i < weights.length; i++) {
					weightedProgress += (phases.get(i).progress * weights[i]);
				}
				return weightedProgress;
			}
			else {
				float subProgress =
					currentPhase < phaseCount ? phase().getInternal() : 0.0f;
					return progressPerPhase*(currentPhase + subProgress);
			}
		} else {
			return progress;
		}
	}

	public void setStatus(String status) {
		this.status = status;
	}

	public String toString() {
		StringBuffer result = new StringBuffer();
		toString(result);
		return result.toString();
	}

	private void toString(StringBuffer buffer) {
		synchronized (phases) {
			buffer.append(status);
			if (phases.size() != 0 && currentPhase < phases.size()) {
				buffer.append(" > ");
				phase().toString(buffer);
			}
		}
	}

}