/*
 * SSSync, a Simple and Stupid Synchronizer for data with multi-valued attributes
 * Copyright (C) 2014  Ludovic Pouzenc <ludovic@pouzenc.fr>
 *  
 * This file is part of SSSync.
 *
 *  SSSync is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  SSSync is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with SSSync.  If not, see <http://www.gnu.org/licenses/>
 */

package sync;


import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;

import org.apache.log4j.Logger;

import data.MVDataEntry;
import data.io.MVDataReader;
import data.io.MVDataWriter;

/**
 * Basic one-way synchronization code. Uses MVDataEntry semantics.
 * Each entry has a key and a set of multi-valued attributes, like LDAP entries.
 * Data source is a MVDataReader. Multiple source could be used via MVDataCombiner.
 * <br/><br/>
 * <b>Warnings :</b> needs MVDataReaders that give key-sorted results. This sync will try
 * to delete entries that exists on destination side and don't exist at source side.
 * Extra attributes in existing entries on destination side are preserved.
 * Look like useful for account's failure password count for instance.
 * <br/><br/>
 * <b>Notes :</b> Null value and empty strings are not allowed in MVDataEntry, so they are not sync'ed.
 * 
 * @author lpouzenc
 */
public class BasicSyncTask extends AbstractSyncTask {
	private static final Logger logger = Logger.getLogger(BasicSyncTask.class.getName());

	/**
	 * Source data stream (read-only)
	 */
	private final MVDataReader srcReader;
	/**
	 * Destination data stream (read)
	 */
	private final MVDataReader dstReader;
	/**
	 * Destination data stream (write) 
	 */
	private final MVDataWriter dstWriter;

	/**
	 * If true, disable removal of data on destination side even if detected as obsolete 
	 */
	private boolean skipEntryDelete;

	
	private int maxInserts;
	private int maxUpdates;
	private int maxDeletes;

	private transient int curInserts;
	private transient int curUpdates;
	private transient int curDeletes;
	

	/**
	 * BasicSyncTask constructor
	 * Assumes that the *Readers have iterators that returns entries sorted by lexicographical ascending key
	 * @param taskName Friendly name of this task (for tracing in log files) 
	 * @param srcReader Source data stream (read-only)
	 * @param dstReader Destination data stream (read)
	 * @param dstWriter Destination data stream (write) 
	 */
	public BasicSyncTask(String taskName, boolean skipDelete, MVDataReader srcReader, MVDataReader dstReader, MVDataWriter dstWriter) {
		this.taskName = taskName;
		this.srcReader = srcReader;
		this.dstReader = dstReader;
		this.dstWriter = dstWriter;
		
		this.maxInserts = 0;
		this.maxUpdates = 0;
		this.maxDeletes = 0;
	}
	
	public Boolean call() {
		logger.info("task " + taskName + " : starting " + (dryRun?"dry-run":"real") + " pass");
		// Better stack traces "call()" don't say "what"
		boolean success = syncTaskRun();
		logger.info("task " + taskName + " : " + (success?"terminated successfully":"aborted"));

		return success;
	}	

	private boolean syncTaskRun() {
		curInserts=0;
		curUpdates=0;
		curDeletes=0;
		dstWriter.setDryRun(dryRun);
		
		Iterator<MVDataEntry> itSrc = srcReader.iterator();
		Iterator<MVDataEntry> itDst = dstReader.iterator();
		MVDataEntry src = null, dst = null;
		boolean srcExhausted = false;
		boolean dstExhausted = false;
		boolean abort = false;
		boolean done = false;
		while ( !abort && !done ) {

			// Look-ahead srcReader if previous has been "poped" (or if never read yet)
			if ( src == null ) {
				if ( !srcExhausted ) {
					srcExhausted = !itSrc.hasNext();
				}
				if ( !srcExhausted ) {
					try {
						src=itSrc.next();
						logger.trace("src read : " + src);
					} catch (Exception e) {
						logger.error("Read failure detected on " + srcReader.getDataSourceName() + ". Aborting.", e);
						// Escape from the while loop
						abort=true; continue;
					}
				}
			}
			
			// Look-ahead dstReader if previous has been "poped" (or if never read yet)
			if ( dst == null ) {
				if ( !dstExhausted ) {
					dstExhausted = !itDst.hasNext();
				}
				if ( !dstExhausted ) {
					try {
						dst = itDst.next();
						logger.trace("dst read : " + dst);
					} catch (NoSuchElementException e) {
						logger.error("Read failure detected on " + dstReader.getDataSourceName() + ". Aborting.", e);
						// Escape from the while loop
						abort=true; continue;
					}
				}
			}

			// Error-free cases (no problems while reading data)
			int compare;
			if ( !srcExhausted && !dstExhausted ) {
				// General case : check order precedence to take an action
				compare = src.compareTo(dst);
			} else if ( !srcExhausted && dstExhausted ) {
				// Particular case : dst is exhausted, it's like ( src < dst )
				compare=-1;
			} else if ( srcExhausted && !dstExhausted ) {
				// Particular case : src is exhausted, it's like ( src > dst )
				compare=1;
			} else /* ( srcExhausted && dstExhausted ) */ {
				// Particular case : everything is synchronized
				// Exit gracefully the while loop
				done=true; continue;
			}
			
			logger.trace("compare : " + compare);
			
			boolean actionRealized = false;
			// Take an action (insert/update/delete)
			if ( compare < 0 ) {
				actionRealized = _insert(src);
				src = null;
				// preserve dst until src key is not greater
			} else if ( compare > 0 ) {
				// dst current entry doesn't exists anymore (src key is greater than dst key)
				actionRealized = _delete(dst);
				// preserve src until dst key is not greater
				dst = null;
			} else /* ( compare == 0 ) */ {
				// src current entry already exists in dst, update it if necessary
				Set<String> changedAttr = src.getChangedAttributes(dst);
				if ( ! changedAttr.isEmpty() ) {
					actionRealized = _update(src,dst,changedAttr);
				} else {
					// Already up-to-date, nothing to do
					actionRealized = true;
				}
				// Both src and dst have been used
				src = null;
				dst = null;
			}
			abort = !actionRealized;
		} /* while */

		return !abort;
	} /* _taskRunSync() */

	private boolean _insert(MVDataEntry entry) {
				
		if ( maxInserts > 0 && curInserts >= maxInserts ) {
			logger.error("Max insert limit reached (" + maxInserts + ")" );
			return false;
		}
		
		logger.debug("dstWriter : Action\n-> Insert " + entry);
		try {
			dstWriter.insert(entry);
		} catch (Exception e) {
			logger.error("Exception occured while inserting", e);
			return false;
		}
		
		curInserts++;
		return true;
	}

	private boolean _update(MVDataEntry updatedEntry, MVDataEntry originalEntry, Set<String> attrToUpdate) {
		if ( maxUpdates > 0 && curUpdates >= maxUpdates ) {
			logger.error("Max update limit reached (" + maxUpdates + ")");
			return false;
		}

		logger.debug("dstWriter : Action\n-> Update " + updatedEntry + "\n->  changed attributes : " + attrToUpdate);
		try {
			dstWriter.update(updatedEntry, originalEntry, attrToUpdate);
		} catch (Exception e) {
			logger.error("Exception occured while updating", e);
			return false;
		}
	
		curUpdates++;
		return true;
	}
	
	private boolean _delete(MVDataEntry entry) {
		if ( skipEntryDelete ) {
			logger.info("dstWriter : skipping deletion for key " + entry.getKey());
			return true;
		} 
		
		if ( maxDeletes > 0 && curDeletes >= maxDeletes ) {
			logger.error("Max delete limit reached (" + maxDeletes + ")");
			return false;
		}
		logger.debug("dstWriter : Action\n-> Delete " + entry);
		try {
			dstWriter.delete(entry);
		} catch (Exception e) {
			logger.error("Exception occured while deleting", e);
			return false;
		}
		
		curDeletes++;
		return true;
	}

	// Boring accessors

	/**
	 * Setter to fix limits about operations counts (safeguard)
	 * @param maxInserts
	 * @param maxUpdates
	 * @param maxDeletes
	 */
	public void setOperationLimits(int maxInserts, int maxUpdates, int maxDeletes) {
		this.maxInserts = maxInserts;
		this.maxUpdates = maxUpdates;
		this.maxDeletes = maxDeletes;
	}

	/**
	 * @return the skipEntryDelete
	 */
	public boolean isSkipEntryDelete() {
		return skipEntryDelete;
	}

	/**
	 * @param skipEntryDelete the skipEntryDelete to set
	 */
	public void setSkipEntryDelete(boolean skipEntryDelete) {
		this.skipEntryDelete = skipEntryDelete;
	}

}