package hudson.model;

import org.kohsuke.stapler.StaplerRequest;
import org.kohsuke.stapler.StaplerResponse;
import org.kohsuke.graph_layouter.Layout;
import org.kohsuke.graph_layouter.Navigator;
import org.kohsuke.graph_layouter.Direction;

import javax.servlet.ServletOutputStream;
import javax.imageio.ImageIO;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.HashSet;
import java.util.Stack;
import java.util.Map.Entry;
import java.io.IOException;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Rectangle;
import java.awt.Graphics2D;
import java.awt.Color;
import java.awt.Point;
import java.awt.HeadlessException;
import java.awt.FontMetrics;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;

/**
 * Maintains the build dependencies between {@link AbstractProject}s
 * for efficient dependency computation.
 *
 * <p>
 * The "master" data of dependencies are owned/persisted/maintained by
 * individual {@link AbstractProject}s, but because of that, it's relatively
 * slow  to compute backward edges.
 *
 * <p>
 * This class builds the complete bi-directional dependency graph
 * by collecting information from all {@link AbstractProject}s.
 *
 * <p>
 * Once built, {@link DependencyGraph} is immutable, and every time
 * there's a change (which is relatively rare), a new instance
 * will be created. This eliminates the need of synchronization.
 *
 * @author Kohsuke Kawaguchi
 */
public final class DependencyGraph {

    private Map<AbstractProject, List<AbstractProject>> forward = new HashMap<AbstractProject, List<AbstractProject>>();
    private Map<AbstractProject, List<AbstractProject>> backward = new HashMap<AbstractProject, List<AbstractProject>>();

    private boolean built;

    /**
     * Builds the dependency graph.
     */
    public DependencyGraph() {
        for( AbstractProject p : Hudson.getInstance().getAllItems(AbstractProject.class) )
            p.buildDependencyGraph(this);

        forward = finalize(forward);
        backward = finalize(backward);

        built = true;
    }

    /**
     * Special constructor for creating an empty graph
     */
    private DependencyGraph(boolean dummy) {
        forward = backward = Collections.emptyMap();
        built = true;
    }

    /**
     * Gets all the immediate downstream projects (IOW forward edges) of the given project.
     *
     * @return
     *      can be empty but never null.
     */
    public List<AbstractProject> getDownstream(AbstractProject p) {
        return get(forward,p);
    }

    /**
     * Gets all the immediate upstream projects (IOW backward edges) of the given project.
     *
     * @return
     *      can be empty but never null.
     */
    public List<AbstractProject> getUpstream(AbstractProject p) {
        return get(backward,p);
    }

    private List<AbstractProject> get(Map<AbstractProject, List<AbstractProject>> map, AbstractProject src) {
        List<AbstractProject> v = map.get(src);
        if(v!=null) return v;
        else        return Collections.emptyList();
    }

    /**
     * Called during the dependency graph build phase to add a dependency edge.
     */
    public void addDependency(AbstractProject from, AbstractProject to) {
        if(built)
            throw new IllegalStateException();
        add(forward,from,to);
        add(backward,to,from);
    }

    public void addDependency(AbstractProject from, Collection<? extends AbstractProject> to) {
        for (AbstractProject p : to)
            addDependency(from,p);
    }

    public void addDependency(Collection<? extends AbstractProject> from, AbstractProject to) {
        for (AbstractProject p : from)
            addDependency(p,to);
    }

    /**
     * Returns true if a project has a non-direct dependency to another project.
     * <p>
     * A non-direct dependency is a path of dependency "edge"s from the source to the destination,
     * where the length is greater than 1.
     */
    public boolean hasIndirectDependencies(AbstractProject src, AbstractProject dst) {
        Set<AbstractProject> visited = new HashSet<AbstractProject>();
        Stack<AbstractProject> queue = new Stack<AbstractProject>();

        queue.addAll(getDownstream(src));
        queue.remove(dst);

        while(!queue.isEmpty()) {
            AbstractProject p = queue.pop();
            if(p==dst)
                return true;
            if(visited.add(p))
                queue.addAll(getDownstream(p));
        }

        return false;
    }

    /**
     * Gets all the direct and indirect upstream dependencies of the given project.
     */
    public Set<AbstractProject> getTransitiveUpstream(AbstractProject src) {
        return getTransitive(backward,src);
    }

    /**
     * Gets all the direct and indirect downstream dependencies of the given project.
     */
    public Set<AbstractProject> getTransitiveDownstream(AbstractProject src) {
        return getTransitive(forward,src);
    }

    private Set<AbstractProject> getTransitive(Map<AbstractProject, List<AbstractProject>> direction, AbstractProject src) {
        Set<AbstractProject> visited = new HashSet<AbstractProject>();
        Stack<AbstractProject> queue = new Stack<AbstractProject>();

        queue.add(src);

        while(!queue.isEmpty()) {
            AbstractProject p = queue.pop();

            for (AbstractProject child : get(direction,p)) {
                if(visited.add(child))
                    queue.add(child);
            }
        }

        return visited;
    }

    private void add(Map<AbstractProject, List<AbstractProject>> map, AbstractProject src, AbstractProject dst) {
        List<AbstractProject> set = map.get(src);
        if(set==null) {
            set = new ArrayList<AbstractProject>();
            map.put(src,set);
        }
        set.add(dst);
    }

    private Map<AbstractProject, List<AbstractProject>> finalize(Map<AbstractProject, List<AbstractProject>> m) {
        for (Entry<AbstractProject, List<AbstractProject>> e : m.entrySet()) {
            Collections.sort( e.getValue(), NAME_COMPARATOR );
            e.setValue( Collections.unmodifiableList(e.getValue()) );
        }
        return Collections.unmodifiableMap(m);
    }

    /**
     * Experimental visualization of project dependencies.
     */
    public void doGraph( StaplerRequest req, StaplerResponse rsp ) throws IOException {
        try {

            // creates a dummy graphics just so that we can measure font metrics
            BufferedImage emptyImage = new BufferedImage(1,1, BufferedImage.TYPE_INT_RGB );
            Graphics2D graphics = emptyImage.createGraphics();
            graphics.setFont(FONT);
            final FontMetrics fontMetrics = graphics.getFontMetrics();

            // TODO: timestamp check
            Layout<AbstractProject> layout = new Layout<AbstractProject>(new Navigator<AbstractProject>() {
                public Collection<AbstractProject> vertices() {
                    // only include projects that have some dependency
                    List<AbstractProject> r = new ArrayList<AbstractProject>();
                    for (AbstractProject p : Hudson.getInstance().getAllItems(AbstractProject.class)) {
                        if(!getDownstream(p).isEmpty() || !getUpstream(p).isEmpty())
                            r.add(p);
                    }
                    return r;
                }

                public Collection<AbstractProject> edge(AbstractProject p) {
                    return getDownstream(p);
                }

                public Dimension getSize(AbstractProject p) {
                    int w = fontMetrics.stringWidth(p.getDisplayName()) + MARGIN*2;
                    return new Dimension(w, fontMetrics.getHeight() + MARGIN*2);
                }
            }, Direction.LEFTRIGHT);

            Rectangle area = layout.calcDrawingArea();
            area.grow(4,4); // give it a bit of margin
            BufferedImage image = new BufferedImage(area.width, area.height, BufferedImage.TYPE_INT_RGB );
            Graphics2D g2 = image.createGraphics();
            g2.setTransform(AffineTransform.getTranslateInstance(-area.x,-area.y));
            g2.setPaint(Color.WHITE);
            g2.fill(area);
            g2.setFont(FONT);

            g2.setPaint(Color.BLACK);
            for( AbstractProject p : layout.vertices() ) {
                final Point sp = center(layout.vertex(p));

                for (AbstractProject q : layout.edges(p)) {
                    Point cur=sp;
                    for( Point pt : layout.edge(p,q) ) {
                        g2.drawLine(cur.x, cur.y, pt.x, pt.y);
                        cur=pt;
                    }

                    final Point ep = center(layout.vertex(q));
                    g2.drawLine(cur.x, cur.y, ep.x, ep.y);
                }
            }

            int diff = fontMetrics.getAscent()+fontMetrics.getLeading()/2;
            
            for( AbstractProject p : layout.vertices() ) {
                Rectangle r = layout.vertex(p);
                g2.setPaint(Color.WHITE);
                g2.fillRect(r.x, r.y, r.width, r.height);
                g2.setPaint(Color.BLACK);
                g2.drawRect(r.x, r.y, r.width, r.height);
                g2.drawString(p.getDisplayName(), r.x+MARGIN, r.y+MARGIN+ diff);
            }

            rsp.setContentType("image/png");
            ServletOutputStream os = rsp.getOutputStream();
            ImageIO.write(image, "PNG", os);
            os.close();
        } catch(HeadlessException e) {
            // not available. send out error message
            rsp.sendRedirect2(req.getContextPath()+"/images/headless.png");
        }
    }

    private Point center(Rectangle r) {
        return new Point(r.x+r.width/2,r.y+r.height/2);
    }

    private static final Font FONT = new Font("TimesRoman", Font.PLAIN, 10);
    /**
     * Margins between the project name and its bounding box.
     */
    private static final int MARGIN = 4;


    private static final Comparator<AbstractProject> NAME_COMPARATOR = new Comparator<AbstractProject>() {
        public int compare(AbstractProject lhs, AbstractProject rhs) {
            return lhs.getName().compareTo(rhs.getName());
        }
    };

    public static final DependencyGraph EMPTY = new DependencyGraph(false);
}