/*
 * Copyright 2005-2011 the original author or authors.
 * 
 * Licensed 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.wamblee.xmlrouter.impl;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.wamblee.xmlrouter.config.Transformation;

/**
 * This class manages transformations and computes the shortest transformations
 * paths based on the provided transformations.
 * 
 * @author Erik Brakkee
 * 
 */
public class TransformationPaths {

    private Collection<Transformation> transformations;
    private List<String> vertices;
    private TransformationPath[][] matrix;

    /**
     * Construct the transformations.
     */
    public TransformationPaths(Collection<Transformation> aTransformations) {
        transformations = aTransformations;
        vertices = new ArrayList<String>();
        matrix = new TransformationPath[0][0];
        computeTransformationSequences();
    }

    /**
     * Gets the possible target types based on an input type.
     * 
     * @param aType
     *            Input type.
     * @return Possible target types.
     */
    public Collection<String> getPossibleTargetTypes(String aType) {
        int index = vertices.indexOf(aType);
        Set<String> res = new HashSet<String>();
        for (int j = 0; j < vertices.size(); j++) {
            if (matrix[index][j] != null) {
                String value = matrix[index][j].getToType();
                if (value == null) {
                    value = aType;
                }
                res.add(value);
            }
        }
        res.add(aType);
        return res;
    }

    /**
     * Gets the transformation path from A to B.
     * 
     * @param aFrom
     *            From
     * @param aTo
     *            To
     * @return Transformatkon path or null if not found.
     */
    public TransformationPath getPath(String aFrom, String aTo) {
        int i = vertices.indexOf(aFrom);
        if (i < 0) {
            if (aFrom.equals(aTo)) {
                return new TransformationPath();
            }
            return null;
        }

        int j = vertices.indexOf(aTo);
        if (j < 0) {
            return null;
        }
        return matrix[i][j];
    }

    /**
     * Computest the transformation sequences using Floyd's algorithm.
     */
    private void computeTransformationSequences() {
        vertices = new ArrayList<String>();

        // Obtain possible starting points.
        Set<String> v = new HashSet<String>();
        for (Transformation transformation : transformations) {
            v.add(transformation.getFromType());
            v.add(transformation.getToType());
        }

        vertices.addAll(v);

        matrix = new TransformationPath[vertices.size()][vertices.size()];

        // Floyd's algorithm.
        int nvertices = vertices.size();
        for (int i = 0; i < nvertices; i++) {
            matrix[i][i] = new TransformationPath();
        }
        for (Transformation transformation : transformations) {
            int from = vertices.indexOf(transformation.getFromType());
            int to = vertices.indexOf(transformation.getToType());
            TransformationPath path = new TransformationPath(transformation);
            matrix[from][to] = path;
        }

        for (int k = 0; k < nvertices; k++) {
            for (int i = 0; i < nvertices; i++) {
                for (int j = 0; j < nvertices; j++) {
                    // if the path from i to j through k is shorter then the
                    // existing path then
                    // replace it.
                    int lij = getPathLength(i, j);
                    int lik = getPathLength(i, k);
                    int lkj = getPathLength(k, j);
                    if (lik + lkj < lij) {
                        matrix[i][j] = matrix[i][k].appendPath(matrix[k][j]);
                    }
                }
            }
        }
    }

    private int getPathLength(int i, int j) {
        // We use MAX_INT/3 as infinity. This ensures that the default integer
        // comparison in Floyd's algorithm does not lead to overflow.
        return matrix[i][j] == null ? Integer.MAX_VALUE / 3 : matrix[i][j]
            .size();
    }

    @Override
    public String toString() {
        StringBuffer buf = new StringBuffer();
        buf.append("Transformations(");
        int nvertices = vertices.size();
        for (int i = 0; i < nvertices; i++) {
            for (int j = 0; j < nvertices; j++) {
                TransformationPath path = matrix[i][j];
                if (path != null) {
                    buf.append(vertices.get(i));
                    buf.append(" -> ");
                    buf.append(vertices.get(j));
                    buf.append(": ");
                    buf.append(path);
                    buf.append("\n");
                }
            }
        }
        buf.append(")");
        return buf.toString();
    }
}