using System;
using System.Drawing;
using System.Drawing.Drawing2D;

namespace DrawLines
{
	/// <summary>
	/// Line 表示一條線段。
	/// </summary>
	public class Line
	{
		#region 構造函數
		/// <summary>
		/// 構造函數。根據給出的點構造一個Line對象。
		/// </summary>
		/// <param name="begin">線條的起始點。</param>
		/// <param name="end">線條的終止點。</param>
		public Line(Point begin, Point end)
		{
			this.Begin = begin;
			this.End = end;
			pralDistnc = 5;
		}
		#endregion

		#region 線段的端點
		/// <summary>
		/// 線段的起始點。
		/// </summary>
		public Point Begin
		{
			get
			{
				return begin;
			}
			set
			{
				begin = value;
			}
		}
		private Point begin;	
		/// <summary>
		/// 線段的終止點。
		/// </summary>
		public Point End
		{
			get
			{
				return end;
			}
			set
			{
				end = value;
			}
		}
		private Point end;
		private int pralDistnc;	//平行線的距離。
		#endregion

		#region 相關數據計算
		/// <summary>
		/// 返回線段的斜率。
		/// </summary>
		public float Slope
		{
			get
			{
				if (Begin.X == End.X)
					return Int32.MaxValue;
				return (float)(Begin.Y - End.Y) / (Begin.X - End.X);
			}
		}
		/// <summary>
		/// 本線段與線段line是否相交。
		/// </summary>
		/// <param name="line">檢查是否與本線段相交的線段。</param>
		/// <returns>若相交，返回真，否則返回假。</returns>
		public bool IsCutWithLine(Line line)
		{
			if (this.Slope == line.Slope)	
				return false;		//兩條線段平行。
			if (this.Begin == this.End || line.Begin == line.End)
				return false;		//有一條線段是點。
			// 計算兩線段所在直線的交點的橫坐標。
			float CutPointX = (this.Slope * this.Begin.X - line.Slope * line.Begin.X
				- this.Begin.Y + line.Begin.Y) / (this.Slope - line.Slope);
			if (CutPointX < this.Begin.X && CutPointX < this.End.X)
				return false;	//交點在本線段的左側。
			if (CutPointX > this.Begin.X && CutPointX > this.End.X)
				return false;	//交點在本線段的右側。
			if (CutPointX < line.Begin.X && CutPointX < line.End.X)
				return false;	//交點在line的左側。
			if (CutPointX > line.Begin.X && CutPointX > line.End.X)
				return false;	//交點在line的右側。
			return true;		//交點在本線段和line上，說明兩線段相交。
		}

		#endregion

		#region 繪制線段
		/// <summary>
		/// 繪制線段以及兩條平行線。
		/// </summary>
		/// <param name="dc">繪制的圖片對象。</param>
		/// <param name="pen">繪制使用的鋼筆。</param>
		public void Draw(Graphics dc, Pen pen)
		{
			//繪制本條線段。
			dc.DrawLine(pen, Begin, End);

			//繪制兩條平行線。
			float tanCida = -1 / this.Slope;
			//繪制第一條平行線。
			float sinCida = (float)Math.Sin(Math.Atan(tanCida));
			float cosCida = sinCida / tanCida;
			float x = Begin.X + pralDistnc * cosCida;
			float y = Begin.Y + pralDistnc * sinCida;
			Point pralBegin = new Point((int)(x + 0.5), (int)(y + 0.5));
			x = End.X + pralDistnc * cosCida;
			y = End.Y + pralDistnc * sinCida;
			Point pralEnd = new Point((int)(x + 0.5), (int)(y + 0.5));
			Pen pralPen = new Pen(pen.Color, pen.Width);
			pralPen.DashStyle = DashStyle.Dot;
			dc.DrawLine(pralPen, pralBegin, pralEnd);
			//繪制第二條平行線
			sinCida = (float)Math.Sin(Math.Atan(tanCida)) * -1;
			cosCida = sinCida / tanCida;
			x = Begin.X + pralDistnc * cosCida;
			y = Begin.Y + pralDistnc * sinCida;
			pralBegin = new Point((int)(x + 0.5), (int)(y + 0.5));
			x = End.X + pralDistnc * cosCida;
			y = End.Y + pralDistnc * sinCida;
			pralEnd = new Point((int)(x + 0.5), (int)(y + 0.5));
			dc.DrawLine(pralPen, pralBegin, pralEnd);
		}
		#endregion
	}
}