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/*
* 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 data.filters;
import java.util.Iterator;
import java.util.NoSuchElementException;
import data.MVDataEntry;
import data.io.AbstractMVDataReader;
import data.io.MVDataReader;
/**
* Combines arbitrary number of MVData* sources while behaving same as AbstractMVDataReader.
* This could enable a sync implementation to merge multiple sources
* before sync'ing in a transparent manner.
* To prevent memory consumption, this assumes that all sources will be read
* with lexicographical ascending order on the "key" field.
*
* @author lpouzenc
*/
public class MVDataCombiner extends AbstractMVDataReader {
public enum MVDataCombineMode { PRIMARY_SOURCE, MERGE_APPEND, MERGE_REPLACE, OVERRIDE };
private final MVDataReader[] readers;
private final MVDataCombineMode[] mergeModes;
private transient Iterator<MVDataEntry>[] readerIterators;
private transient MVDataEntry[] lookAheadData;
private transient String lastKey;
public MVDataCombiner(String dataSourceName, MVDataReader[] readers, MVDataCombineMode mergeModes[]) {
if ( readers == null || mergeModes == null || (mergeModes.length != readers.length) ) {
throw new IllegalArgumentException("readers and mergeModes arrays should have same size");
}
if ( ! (mergeModes.length > 0) || mergeModes[0] != MVDataCombineMode.PRIMARY_SOURCE ) {
throw new IllegalArgumentException("MVDataCombiner first mergeModes should always be PRIMARY_SOURCE");
}
this.dataSourceName = dataSourceName;
this.readers = readers.clone();
this.mergeModes = mergeModes.clone();
}
/**
* {@inheritDoc}
*/
@Override
@SuppressWarnings("unchecked") /* for new Iterator[...] */
public Iterator<MVDataEntry> iterator() {
// Be cautious to reset everything
readerIterators = new Iterator[readers.length];
for (int i=0; i<readers.length;i++) {
readerIterators[i] = readers[i].iterator();
}
lookAheadData = new MVDataEntry[readers.length];
lastKey = null;
return this;
}
/**
* {@inheritDoc}
*/
@Override
public boolean hasNext() {
for ( MVDataEntry line : lookAheadData ) {
if ( line != null ) { return true; }
}
for ( MVDataReader reader : readers ) {
if ( reader.hasNext() ) { return true; }
}
return false;
}
/**
* {@inheritDoc}
*/
@Override
public MVDataEntry next() {
final String currentKey = lookAheadAll();
// Check if there was unsorted lines in source data
if ( lastKey != null && (currentKey.compareTo(lastKey) < 0) ) {
//XXX : this is checked here and in SafeDataReader (redundant), but both are optionnal...
throw new UnsupportedOperationException("At least one data source is out of order. " +
"Data sources are excepted to be read sorted by MVDataEntry key (ascending lexicogrpahical order)");
}
// Merge all data sources for key currentKey
MVDataEntry result = null;
for ( int i=0; i<lookAheadData.length; i++) {
if ( lookAheadData[i] != null && lookAheadData[i].getKey().equals(currentKey) ) {
if ( result == null ) {
result = lookAheadData[i];
} else {
//XXX : some items in LDAP could have constrains like : "not multi-valued". Force MERGE_REPLACE mode ?
//FIXME : honor all Combine modes
result.mergeValues( (mergeModes[i] == MVDataCombineMode.MERGE_APPEND ),lookAheadData[i]);
}
lookAheadData[i]=null; // "Pop" the used entry
}
}
lastKey = currentKey;
return result;
}
private String lookAheadAll() {
String minKey=null;
// Feed the look-ahead buffer (look forward by 1 value for each reader)
for ( int i=0; i<lookAheadData.length; i++) {
if ( lookAheadData[i] == null && readerIterators[i].hasNext() ) {
lookAheadData[i] = readerIterators[i].next();
}
}
// Find the least RelData key from look-ahead buffers
for (MVDataEntry entry: lookAheadData) {
if ( entry != null ) {
final String minKeyCandidate = entry.getKey();
if ( minKey == null || minKey.compareTo(minKeyCandidate) > 0 ) {
minKey = minKeyCandidate;
}
}
}
// Sanity checks
if ( minKey == null ) {
// Every reader is empty and look-ahead buffer is empty (hasNext() should have said false)
throw new NoSuchElementException();
}
return minKey;
}
// Boring accessors
public String getLastKey() {
return lastKey;
}
}
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