/*
 * 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.io.csv;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.SortedSet;
import java.util.TreeSet;

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVRecord;

import data.MVDataEntry;
import data.io.AbstractMVDataReader;

/**
 * Stream-oriented reader from a particular CSV file.
 * Always returns lines/items sorted by lexicographical ascending key.
 * 
 * @author lpouzenc
 */
public class CSVDataReader extends AbstractMVDataReader {

	public static final String CSV_DEMO = 
			//"key,attr,values\n" +
			"line3,hello,all;the;others\n" +
			"line1,from,csv1;csv1bis\n" +
			"line2,hello,all;the;world\n" +
			"line1,attr2,csv1\n" +
			",,\n";
	
	public static final CSVFormat DEFAULT_CSV_FORMAT = CSVFormat.EXCEL
			.withHeader("key","attr","values")
			.withIgnoreSurroundingSpaces(true);
	
	private final CSVFormat format;
	private final Reader dataSourceStream;
	
	private transient MVDataEntry nextEntry;
	private transient CSVRecord nextCSVRecord;
	private transient Iterator<CSVRecord> csvIt;


	/**
	 * Constructs a CSVDataReader object for parsing a CSV input given via dataSourceStream.
	 * @param dataSourceName A short string representing this reader (for logging)
	 * @param dataSourceStream A java.io.Reader from which read the actual CSV data, typically a FileReader 
	 * @param alreadySorted If false, memory cost is around 3 times the CSV file size !
	 * @param format Specify the exact format used to encode the CSV file (separators, escaping...)
	 * @throws IOException
	 */
	public CSVDataReader(String dataSourceName, Reader dataSourceStream, boolean alreadySorted, CSVFormat format) throws IOException {
		this.dataSourceName = dataSourceName;
		this.format = format;
		
		if ( alreadySorted ) {
			this.dataSourceStream = dataSourceStream;
		} else {
			BufferedReader bufReader;
			if ( dataSourceStream instanceof BufferedReader ) {
				bufReader = (BufferedReader) dataSourceStream;
			} else {
				bufReader = new BufferedReader(dataSourceStream);
			}
			this.dataSourceStream = readAndSortLines(bufReader);
		}
	}

	/**
	 * Constructs a CSVDataReader object with default CSV format (for CSVParser).
	 * @param dataSourceName A short string representing this reader (for logging)
	 * @param dataSourceStream A java.io.Reader from which read the actual CSV data, typically a FileReader
	 * @param alreadySorted If false, memory cost is around 3 times the CSV file size !
	 * @throws IOException 
	 */
	public CSVDataReader(String dataSourceName, Reader dataSourceStream, boolean alreadySorted) throws IOException {
		this(dataSourceName, dataSourceStream, alreadySorted, DEFAULT_CSV_FORMAT);
	}
	
	/**
	 * {@inheritDoc}
	 * Note : multiple iterators on the same instance are not supported
	 */
	@Override
	public Iterator<MVDataEntry> iterator() {
		// When a new iterator is requested, everything should be reset
		CSVParser parser;
		try {
			dataSourceStream.reset();
			parser = new CSVParser(dataSourceStream, format);
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
		csvIt = parser.iterator();
		nextCSVRecord = null;
		nextEntry = null;
		return this;
	}
	
	/**
	 * {@inheritDoc}
	 */
	@Override
	public boolean hasNext() {
		if ( nextEntry == null ) {
			lookAhead();
		}
		return ( nextEntry != null );  
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public MVDataEntry next() {
		if ( !hasNext() ) {
			throw new NoSuchElementException();
		}
		// Pop the lookahead record
		MVDataEntry res = nextEntry;
		nextEntry=null;
		// And return it
		return res;
	}
	
	/**
	 * In-memory File sorting, return as a single String
	 * @param reader
	 * @return
	 * @throws IOException
	 */
	private Reader readAndSortLines(BufferedReader bufReader) throws IOException {
		// Put all the CSV in memory, in a SortedSet
		SortedSet<String> lineSet = new TreeSet<String>();
		String inputLine;
		int totalCSVSize=0;
		while ((inputLine = bufReader.readLine()) != null) {
			lineSet.add(inputLine);
			totalCSVSize += inputLine.length() + 1;
		}
		bufReader.close(); // Closes also dataSourceStream

		// Put all sorted lines in a String
		StringBuilder allLines = new StringBuilder(totalCSVSize);
		for ( String line: lineSet) {
			allLines.append(line + "\n");
		}
		lineSet = null; // Could help the GC if the input file is huge
		
		// Build a Java Reader from that String
		return new StringReader(allLines.toString());
	}
	
	/**
	 * A MVDataEntry could be represented on many CSV lines.
	 * The key is repeated, the attr could change, the values should change (for given key/attr pair)
	 */
	private void lookAhead() {
		MVDataEntry currEntry = null;
		
		boolean abort=(nextCSVRecord==null && !csvIt.hasNext()); // Nothing to crunch
		boolean done=(nextEntry!=null); // Already looked ahead
		while (!abort && !done) {
			// Try to get a valid CSVRecord
			if ( nextCSVRecord == null ) {
				nextCSVRecord = nextValidCSVRecord();
			}
			// If no more CSV data
			if ( nextCSVRecord == null ) {
				// Maybe we have a remaining entry to return
				if ( currEntry != null ) {
					done=true; continue;
				} else {
					abort=true; continue;
				}
			}
			
			// Now we have a valid CSV line to put in a MVDataEntry
			String newKey = nextCSVRecord.get("key");
			

			// If no MVDataEntry yet, it's time to create it (we have data to put into)
			if ( currEntry == null ) {
				currEntry = new MVDataEntry(newKey);
			}
			// If CSV line key matches MVDataEntry key, appends attr/values on it
			// XXX Tricky code : following condition is always true if the previous one is true
			if ( currEntry.getKey().equals(newKey) ) {
				currEntry.splitAndPut(nextCSVRecord.get("attr"), nextCSVRecord.get("values"), ";");
				nextCSVRecord = null; // Record consumed
			} else {
				// Keys are different, we are done (and we have remaining CSV data in nextCSVRecord)
				done=true; continue;
			}
		}
		
		nextEntry = done?currEntry:null;
	}
	
	/**
	 * Seek for the next valid record in the CSV file
	 * @return the next valid CSVRecord
	 */
	private CSVRecord nextValidCSVRecord() {
		CSVRecord res = null;
		boolean abort = !csvIt.hasNext();
		boolean done = false;
		while (!abort && !done) {
			// Try to read a CSV line
			res = (csvIt.hasNext())?csvIt.next():null;

			// Break if nothing readable
			if ( res == null ) {
				abort=true; continue;
			}
			
			// Skip invalid and empty lines
			String key = res.get("key");
			if ( key != null && ! key.isEmpty() ) {
				done=true; continue;
			}
		}
		
		return done?res:null;
	}
}