import java.awt.Graphics;
import java.awt.Polygon;

public class Face
{
	public Vertex vertex;
	public Segment segment;
	public Face prev;
	public Face next;
	public Face twin;
	
	public Face() {
	}
	
	public Face(Vertex v) {
		this.vertex = v;
	}
	
	public Face(int x, int y, int w, int h) {
		this.addVertex(new Vertex(x  , y  ));
		this.addVertex(new Vertex(x  , y+h));
		this.addVertex(new Vertex(x+w, y+h));
		this.addVertex(new Vertex(x+w, y  ));
	}
	
	public void draw(Graphics g) {
		Face cur_face = this;
		do {
			cur_face.segment.h.draw(g);
			cur_face = cur_face.next;
		} while (cur_face != this);
	}
	
	public void fill(Graphics g) {
		Polygon poly = new Polygon();
		Face cur_face = this;
		do {
			poly.addPoint((int) cur_face.vertex.x, (int) cur_face.vertex.y);
			cur_face = cur_face.next;
		} while (cur_face != this);
		g.fillPolygon(poly);
	}
	
	public Segment clip(Segment s) {
		// returns the part of <s> contained in <this>
		Face cur_face = this;
		do {
			s = s.clip(cur_face.segment.h);
			cur_face = cur_face.next;
		} while (cur_face != this && s != null);
		return s;
	}
	
	public Face[] split(Segment s) {
		// return the two halves of <this> after it is split by <s>
		// faces[0] = in front part
		// faces[1] = in back part
		Face [] faces = new Face[2];
		faces[0] = new Face();
		faces[1] = new Face();
		int left_vertices = 0;
		int right_vertices = 0;
		// traverse all segments, clip to the halfspace of <s>
		Face cur_face = this;
		do {
			int e1 = s.h.eval(cur_face.vertex);
			// check where to put the first vertex
			if (e1 == Parameters.IN_FRONT || e1 == Parameters.COINCIDENT) {
				faces[0].addVertex(cur_face.vertex);
				left_vertices++;
			}
			if (e1 == Parameters.IN_BACK || e1 == Parameters.COINCIDENT) {
				faces[1].addVertex(cur_face.vertex);
				right_vertices++;
			}
			// if the segment is spanning <s> introduce new vertices 
			if (s.h.eval(cur_face.segment) == Parameters.SPANNING) {
				Vertex new_vertex = cur_face.segment.intersect(s);
				faces[0].addVertex(new_vertex);
				left_vertices++;
				faces[1].addVertex(new_vertex);
				right_vertices++;
			}
			cur_face = cur_face.next;
		} while (cur_face != this);
		if (left_vertices < 3) faces[0] = null;
		if (right_vertices < 3) faces[1] = null;
		return faces;
	}
	
	public void addVertex(Vertex v) {
		if (this.vertex == null) {
			this.vertex = v;
			this.prev = this;
			this.next = this;
			this.twin = new Face(this.vertex);
		}
		else {
			Face new_face = new Face(v);
			// link the prev side of the new entry
			new_face.prev = this.prev;
			this.prev.next = new_face;
			// link the next side of the new entry
			new_face.next = this;
			this.prev = new_face;
			// recompute the edges
			new_face.prev.segment = new Segment(new_face.prev.vertex, new_face.vertex);
			new_face.segment = new Segment(new_face.vertex, new_face.next.vertex);
			// now do everything for the twins
			// create them:
			new_face.twin = new Face(new_face.next.vertex);
			new_face.twin.segment = new Segment(new_face.next.vertex, new_face.vertex);
			new_face.prev.twin.vertex = new_face.vertex;
			new_face.prev.twin.segment = new Segment(new_face.vertex, new_face.prev.vertex);
			// link them:
			new_face.twin.prev = new_face.next.twin;
			new_face.next.twin.next = new_face.twin;
			new_face.twin.next = new_face.prev.twin;
			new_face.prev.twin.prev = new_face.twin;
		}
	}	
}