package org.insa.graph.io;

import java.io.DataInputStream;
import java.io.IOException;
import java.util.ArrayList;

import org.insa.graph.Graph;
import org.insa.graph.Node;
import org.insa.graph.Path;

public class BinaryPathReader extends BinaryReader implements AbstractPathReader {

	// Map version and magic number targeted for this reader.
	private static final int VERSION = 1;
	private static final int MAGIC_NUMBER = 0xdecafe;

	public BinaryPathReader(DataInputStream dis) {
		super(MAGIC_NUMBER, VERSION, dis);
	}

	@Override
	public Path readPath(Graph graph) throws Exception {
		
		// Read and check magic number and version.
		checkMagicNumberOrThrow(dis.readInt());
		checkVersionOrThrow(dis.readInt());
		
		// Read map ID and check against graph.
		int mapId = dis.readInt();
		
		if (mapId != graph.getMapId()) {
			throw new MapMismatchException(mapId, graph.getMapId());
		}
		
		// Number of nodes in the path (without first and last).
		int nbNodes = dis.readInt();
		
		ArrayList<Node> nodes = new ArrayList<Node>(nbNodes + 2);
		
		// Read first node
		nodes.add(readNode(graph));
		
		// Read last node
		Node lastNode = readNode(graph);
		
		// Read intermediate nodes:
		for (int node = 0; node < nbNodes; ++node) {
			nodes.add(readNode(graph));
		}
		
		// Add last node
		nodes.add(lastNode);
		
		return new Path(graph, nodes);
	}

	/**
	 * Read a node from the stream and returns id.
	 * 
	 * @return
	 * @throws IOException 
	 */
	protected Node readNode(Graph graph) throws IOException {
		// Discard zone.
		dis.readUnsignedByte();
		
		return graph.getNodes().get(read24bits());
	}

}