using System.Collections.Generic;
using Chernobyl.DesignPatterns.Extension;
using Chernobyl.Mathematics.Movement;

namespace Chernobyl.Mathematics.Geometry
{
    /// <summary>
    /// A representation of a part of a curve that is bounded by two distinct 
    /// end points and contains every point on the curve between its end points.
    /// The <see cref="IArc"/> holds several <see cref="ITransform"/> instances
    /// that represent points along the arc. The first <see cref="ITransform"/> 
    /// is the first end point and the last <see cref="ITransform"/> is the last 
    /// end point. <see cref="ITransform"/> instances are ordered in this
    /// <see cref="IEnumerable{T}"/> so that drawing an arc through these
    /// points in the order specified by this <see cref="IEnumerable{T}"/>
    /// represents the actual arc. If an <see cref="ITransform"/> is stored at
    /// the beginning of the <see cref="IEnumerable{T}"/> and at the end of it
    /// then the arc is a loop. If this <see cref="IEnumerable{T}"/> has only
    /// two <see cref="ITransform"/> points then it is a straight line segment.
    /// </summary>
    public interface IArc : IEnumerable<ITransform>, IExtendable
    {}

    /// <summary>
    /// Utility methods for types implementing <see cref="IArc"/>.
    /// </summary>
    public static class ArcExtensions
    {
        /// <summary>
        /// Breaks the <see cref="IArc"/> instance down into the line segments
        /// that make up its length.
        /// </summary>
        /// <param name="arc">The instance that is to be broken down into 
        /// <see cref="ILineSegment"/> instances.</param>
        /// <returns>The <see cref="ILineSegment"/> instances that define the
        /// <see cref="IArc"/> passed in.</returns>
        public static IEnumerable<ILineSegment> ToLineSegments(this IArc arc)
        {
            using(IEnumerator<ITransform> arcEnumerator = arc.GetEnumerator())
            {
                if(arcEnumerator.MoveNext() == true)
                {
                    // First we must obtain the first line segment to start us off
                    // with.
                    ITransform previous = arcEnumerator.Current;

                    while (arcEnumerator.MoveNext() == true)
                    {
                        yield return new LineSegment(previous, arcEnumerator.Current);
                        previous = arcEnumerator.Current;
                    }
                }
            }
        }
    }
}