using System;

namespace EllipseTruncate {

	public class ConcentricGrid {

		Ellipse ellipse;

		double step;

		Point b0, b1, b2;

		public ConcentricGrid(Ellipse ellipse, double step, Point b0, Point b1, Point b2) {

			this.ellipse = ellipse;

			this.step = step;

			this.b0 = b0; this.b1 = b1; this.b2 = b2;

		}

		public void calcBounds(out double min, out double max) {

			Point o = ellipse.matrixInv*b0;

			Point dx = ellipse.matrixInv.turn(b1 - b0);

			Point dy = ellipse.matrixInv.turn(b2 - b0);

			max = 0.0;

			min = double.PositiveInfinity;

			// distance to points

			Point[] corners = new Point[] { o, o+dx, o+dx+dy, o+dy };

			foreach(Point p in corners) {

				double k = p.len();

				if (k < min) min = k;

				if (k > max) max = k;

			}

			// distance to sides

			Point[] lines = new Point[] { dx, dy, -1.0*dx, -1.0*dy };

			int positive = 0, negative = 0;

			for(int i = 0; i < 4; ++i) {

				double len2 = lines[i].lenSqr();

				if (len2 <= Geometry.precisionSqr) continue;

				double k = corners[i]*lines[i].rotate90()/Math.Sqrt(len2);

				if (k > Geometry.precision) ++positive;

				if (k < Geometry.precision) ++negative;

				double l = -(corners[i]*lines[i]);

				if (l <= Geometry.precision || l >= len2 - Geometry.precision) continue;

				k = Math.Abs(k);

				if (k < min) min = k;

				if (k > max) max = k;

			}

			// if center is inside bounds

			if (min < 0.0 || positive == 0 || negative == 0) min = 0.0;

		}

		public void draw(Cairo.Context context) {

			double r2 = Math.Min(

				ellipse.matrix.row0().lenSqr(),

				ellipse.matrix.row1().lenSqr() );

			if (r2 <= Geometry.precisionSqr) return;

			double actualStep = step/Math.Sqrt(r2);

			double min, max;

			calcBounds(out min, out max);

			if (max <= min) return;

			if (max - min > 1e5) return;

			int minI = (int)Math.Ceiling((min - 1.0)/actualStep + Geometry.precision);

			int maxI = (int)Math.Ceiling((max - 1.0)/actualStep - Geometry.precision);

			for(int i = minI; i < maxI; ++i) {

				double scale = i*actualStep + 1.0;

				Ellipse e = new Ellipse( ellipse.matrix.scale(scale) );

				e.drawFull(context, true);

				e.drawTruncated(context, b0, b1, b2, true);

			}

		}

	}

}