using System;
using Azimuth;
using UnitTestSharp;

namespace Blacklight.Bezier.UnitTests
{
    public class CubicPieceTests : TestFixture
    {
        public static readonly CubicPiece Wave = new CubicPiece(new Vector(0, 0), new Vector(1, 2), new Vector(3, -1),
            new Vector(4, 0));

        public class CtorTests : TestFixture
        {
            public void AssignsAllFourControlPoints()
            {
                var piece = new CubicPiece(new Vector(1, 2), new Vector(3, 4), new Vector(5, 6), new Vector(7, 8));
                CheckEqual(new Vector(1, 2), piece.P0);
                CheckEqual(new Vector(3, 4), piece.P1);
                CheckEqual(new Vector(5, 6), piece.P2);
                CheckEqual(new Vector(7, 8), piece.P3);
            }
        }

        public class FromQuadraticTests : TestFixture
        {
            public void KeepsTheEndpoints()
            {
                CubicPiece piece = CubicPiece.FromQuadratic(new Vector(1, 2), new Vector(3, 5), new Vector(7, 4));
                CheckEqual(new Vector(1, 2), piece.P0);
                CheckEqual(new Vector(7, 4), piece.P3);
            }

            public void TracesTheQuadraticAtTheSameParameter()
            {
                var start = new Vector(1, 2);
                var control = new Vector(3, 5);
                var end = new Vector(7, 4);
                CubicPiece piece = CubicPiece.FromQuadratic(start, control, end);
                for (double t = 0; t <= 1; t += 0.125)
                {
                    double u = 1 - t;
                    Vector quadratic = u * u * start + 2 * u * t * control + t * t * end;
                    CheckGreater(1e-14, (piece.PointAt(t) - quadratic).Length().Value);
                }
            }
        }

        public class PointAtTests : TestFixture
        {
            public void Zero_IsTheFirstControlPoint()
            {
                CheckEqual(new Vector(0, 0), Wave.PointAt(0));
            }

            public void One_IsTheLastControlPoint()
            {
                CheckEqual(new Vector(4, 0), Wave.PointAt(1));
            }

            public void Half_WeighsTheInnerControlPointsThreeToOne()
            {
                CheckEqual(new Vector((0 + 3 * 1 + 3 * 3 + 4) / 8.0, (0 + 3 * 2 - 3 * 1 + 0) / 8.0),
                    Wave.PointAt(0.5));
            }
        }

        public class DerivativeAtTests : TestFixture
        {
            public void Zero_IsThreeTimesTheFirstLeg()
            {
                CheckEqual(new Vector(3, 6), Wave.DerivativeAt(0));
            }

            public void One_IsThreeTimesTheLastLeg()
            {
                CheckEqual(new Vector(3, 3), Wave.DerivativeAt(1));
            }

            public void Interior_MatchesAFiniteDifference()
            {
                const double step = 1e-6;
                Vector difference = (Wave.PointAt(0.3 + step) - Wave.PointAt(0.3 - step)) / (2 * step);
                CheckGreater(1e-8, (difference - Wave.DerivativeAt(0.3)).Length().Value);
            }
        }

        public class SecondDerivativeAtTests : TestFixture
        {
            public void Zero_IsSixTimesTheFirstTwoLegsDifference()
            {
                CheckEqual(6 * (new Vector(2, -3) - new Vector(1, 2)), Wave.SecondDerivativeAt(0));
            }

            public void One_IsSixTimesTheLastTwoLegsDifference()
            {
                CheckEqual(6 * (new Vector(1, 1) - new Vector(2, -3)), Wave.SecondDerivativeAt(1));
            }

            public void Interior_MatchesAFiniteDifference()
            {
                const double step = 1e-6;
                Vector difference = (Wave.DerivativeAt(0.3 + step) - Wave.DerivativeAt(0.3 - step)) / (2 * step);
                CheckGreater(1e-7, (difference - Wave.SecondDerivativeAt(0.3)).Length().Value);
            }
        }

        public class SegmentTests : TestFixture
        {
            public void TracesThePieceBetweenTheTwoParameters()
            {
                CubicPiece segment = Wave.Segment(0.2, 0.7);
                for (double s = 0; s <= 1; s += 0.125)
                {
                    CheckGreater(1e-14, (segment.PointAt(s) - Wave.PointAt(0.2 + 0.5 * s)).Length().Value);
                }
            }

            public void Reversed_TracesItBackwards()
            {
                CubicPiece segment = Wave.Segment(0.7, 0.2);
                CheckGreater(1e-14, (segment.PointAt(0.25) - Wave.PointAt(0.575)).Length().Value);
            }
        }
    }
}