using System;
using System.Collections.Generic;
using System.Linq;
using Chernobyl.Mathematics.Movement;
using Chernobyl.Mathematics.Vectors;
using NUnit.Framework;

namespace Chernobyl.Mathematics.Geometry
{
    /// <summary>
    /// A helper test fixture base class that is used to test types that
    /// implement <see cref="IArc"/> interface.
    /// </summary>
    public abstract class ArcTests
    {
        [Test, Description("A test to ensure that the IArc throws an  " +
            "ArgumentOutOfRangeException if client code attempts to construct " +
            "the IArc with zero points.")]
        public void ZeroPointsArgumentOutOfRangeException()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => CreateArc(new ITransform[0]));
        }

        [Test, Description("A test to ensure that the IArc throws an  " +
            "ArgumentOutOfRangeException if client code attempts to construct " +
            "the IArc with one point.")]
        public void OnePointArgumentOutOfRangeException()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => CreateArc(new ITransform[1]));
        }

        [Test, Description("A test to ensure that the IArc is properly constructed " +
            "if given two points.")]
        public void TwoPointsCreation()
        {
            IArc arc = CreateArc(new ITransform[2]);

            Assert.AreEqual(2, arc.Count(), "Unexpected number of " +
                "ITransform instances in the returned IArc.");
        }

        [Test, Description("A test to ensure that the IArc throws an " +
            "ArgumentOutOfRangeException if client code attempts to construct " +
            "the IArc with less than one line segments.")]
        public void ZeroLineSegmentsArgumentOutOfRangeException()
        {
            Assert.Throws<ArgumentOutOfRangeException>(() => CreateArc((IEnumerable<ILineSegment>)new ILineSegment[0]));
        }

        [Test, Description("A test to ensure that the IArc throws an " +
            "ArgumentException if client code attempts to construct " +
            "the IArc with line segments that do not connect together.")]
        public void UnconnectedLineSegmentsArgumentException()
        {
            ITransform point1 = new MatrixTransform();
            point1.Position = new Vector3(0, 0, 0);

            ITransform point2 = new MatrixTransform();
            point2.Position = new Vector3(5, 0, 0);

            ITransform point3 = new MatrixTransform();
            point3.Position = new Vector3(6, 0, 0);

            ITransform point4 = new MatrixTransform();
            point4.Position = new Vector3(10, 0, 0);

            ILineSegment[] lines = {
                new LineSegment(point1, point2),
                new LineSegment(point3, point4),
            };

            Assert.Throws<ArgumentException>(() => CreateArc((IEnumerable<ILineSegment>)lines));
        }

        [Test, Description("A test to ensure that the IArc is created " +
            "properly when given only one line segment.")]
        public void OneLineSegmentsConstruction()
        {
            const int uniquePointCount = 2;

            ITransform point1 = new MatrixTransform();
            point1.Position = new Vector3(0, 0, 0);

            ITransform point2 = new MatrixTransform();
            point2.Position = new Vector3(5, 0, 0);

            ILineSegment[] lines = {
                new LineSegment(point1, point2)
            };

            IArc arc = CreateArc((IEnumerable<ILineSegment>)lines);

            Assert.AreEqual(uniquePointCount, arc.Count(),
                "The are too few or too many points in the arc.");

            Assert.AreEqual(point1.Position, arc.ElementAt(0).Position,
                "The first arc point is not the point that was expected.");
            Assert.AreEqual(point2.Position, arc.ElementAt(1).Position,
                "The second arc point is not the point that was expected.");
        }

        [Test, Description("A test to ensure that the IArc places " +
            "the points in the proper order even if it is given line " +
            "segments that are out of order.")]
        public void OrderedPointsGivenOutOfOrderLineSegments()
        {
            const int uniquePointCount = 4;

            ITransform point1 = new MatrixTransform();
            point1.Position = new Vector3(0, 0, 0);

            ITransform point2 = new MatrixTransform();
            point2.Position = new Vector3(5, 0, 0);

            ITransform point3 = new MatrixTransform();
            point3.Position = new Vector3(5, 0, 0);

            ITransform point4 = new MatrixTransform();
            point4.Position = new Vector3(10, 0, 0);

            ITransform point5 = new MatrixTransform();
            point5.Position = new Vector3(10, 0, 0);

            ITransform point6 = new MatrixTransform();
            point6.Position = new Vector3(15, 0, 0);

            ILineSegment[] lines = {
                new LineSegment(point1, point2),
                new LineSegment(point5, point6),
                new LineSegment(point3, point4),
            };

            IArc arc = CreateArc((IEnumerable<ILineSegment>)lines);

            // Compare the points. Remember that although we used 6 points to
            // compose the line segments above, only 4 of those points are unique
            // so only 4 points should be in the arc.
            Assert.AreEqual(uniquePointCount, arc.Count(),
                "The are too few or too many points in the arc.");

            Assert.AreEqual(point1.Position, arc.ElementAt(0).Position,
                "The first arc point is not the point that was expected.");
            Assert.AreEqual(point3.Position, arc.ElementAt(1).Position,
                "The second arc point is not the point that was expected.");
            Assert.AreEqual(point5.Position, arc.ElementAt(2).Position,
                "The third arc point is not the point that was expected.");
            Assert.AreEqual(point6.Position, arc.ElementAt(3).Position,
                "The fourth arc point is not the point that was expected.");
        }

        [Test, Description("A test to ensure that the IArc places " +
            "the points in the proper order even if it is given line " +
            "segments that are arranged in a loop.")]
        public void OrderedPointsGivenLoopedLineSegments()
        {
            const int uniquePointCount = 5;

            const float top = 10;
            const float bottom = 0;
            const float left = 0;
            const float right = 10;

            ITransform topLeft = new MatrixTransform();
            topLeft.Position = new Vector3(left, top, 0);

            ITransform topRight = new MatrixTransform();
            topRight.Position = new Vector3(right, top, 0);

            ITransform bottomRight = new MatrixTransform();
            bottomRight.Position = new Vector3(right, bottom, 0);

            ITransform bottomLeft = new MatrixTransform();
            bottomLeft.Position = new Vector3(left, bottom, 0);

            ILineSegment[] lines = {
                new LineSegment(topLeft, topRight),      // top
                new LineSegment(topRight, bottomRight),  // right
                new LineSegment(topLeft, bottomLeft),    // left
                new LineSegment(bottomLeft, bottomRight) // bottom
            };

            IArc arc = CreateArc((IEnumerable<ILineSegment>)lines);

            // Compare the points. Remember that although we used 4 points to
            // compose the line segments above, the segments looped around so
            // there should be 5 to show this.
            Assert.AreEqual(uniquePointCount, arc.Count(),
                "The are too few or too many points in the arc.");

            Assert.AreEqual(topLeft.Position, arc.ElementAt(0).Position,
                "The first arc point is not the point that was expected.");
            Assert.AreEqual(topRight.Position, arc.ElementAt(1).Position,
                "The second arc point is not the point that was expected.");
            Assert.AreEqual(bottomRight.Position, arc.ElementAt(2).Position,
                "The third arc point is not the point that was expected.");
            Assert.AreEqual(bottomLeft.Position, arc.ElementAt(3).Position,
                "The fourth arc point is not the point that was expected.");
            Assert.AreEqual(topLeft.Position, arc.ElementAt(4).Position,
                "The fifth arc point is not the point that was expected.");
        }

        /// <summary>
        /// Creates the <see cref="IArc"/> instance that is to be tested. This
        /// method should not return the same <see cref="IArc"/> instance more
        /// than once.
        /// </summary>
        /// <param name="points">The points that make up the arc.</param>
        /// <returns>The <see cref="IArc"/> instance that is to be tested.</returns>
        protected abstract IArc CreateArc(IEnumerable<ITransform> points);

        /// <summary>
        /// Creates the <see cref="IArc"/> instance that is to be tested. This
        /// method should not return the same <see cref="IArc"/> instance more
        /// than once.
        /// </summary>
        /// <param name="lines">The <see cref="ILineSegment"/> instances that
        /// make up the arc.</param>
        /// <returns>The <see cref="IArc"/> instance that is to be tested.</returns>
        protected abstract IArc CreateArc(IEnumerable<ILineSegment> lines);
    }
}