using System;
using System.Collections.Generic;

using UnityEngine;

namespace Framework.Geometry.Lines.Fitting {

  /// <summary>Fits 2D line segments to geometric data</summary>
  public static class Segment2Fitter {

		/// <summary>Fits a line segment to an arbitrary set of points</summary>
		/// <param name="points">Points to which a line segment will be fitted</param>
		/// <returns>The line segment fitted to the points</returns>
		public static Segment2 Fit(IList<Vector2> points) {

			// Special logic for point sets with no or just a single point
			int pointCount = points.Count;
			switch (pointCount) {
				case 0: { return new Segment2(); }
				case 1: { return new Segment2(points[0], points[0]); }
			}

			// Fit an infinite line to the point set
			Line2 fittedLine = Line2Fitter.Fit(points);

			// Now look for the points furthest to the negative direction of the line and
			// to the positive direction of the line, also sum the intervals so the direction
			// of the line segment can be matched to the direction of the point set.
			float minInterval, maxInterval, intervalSum;
			{
				float lastInterval = Vector2.Dot(points[0] - fittedLine.Offset, fittedLine.Direction);
				intervalSum = 0.0f;
				minInterval = lastInterval;
				maxInterval = lastInterval;

				for (int index = 1; index < pointCount; ++index) {
					float interval = Vector2.Dot(points[index] - fittedLine.Offset, fittedLine.Direction);

					if (interval < minInterval) {
						minInterval = interval;
					}
					if (interval > maxInterval) {
						maxInterval = interval;
					}

					intervalSum += (interval - lastInterval);
					lastInterval = interval;
				}
			}

			// If the interval sum was negative, the points are sorted in reverse to
			// the positive direction of the line, so flip it around
			if(intervalSum >= 0) {
				return new Segment2(
					fittedLine.Offset + (minInterval * fittedLine.Direction),
					fittedLine.Offset + (maxInterval * fittedLine.Direction)
				);
			} else {
				return new Segment2(
					fittedLine.Offset + (maxInterval * fittedLine.Direction),
					fittedLine.Offset + (minInterval * fittedLine.Direction)
				);
			}
		}

	}

} // namespace Framework.Geometry.Lines.Fitting