#region Copyright & License Information
/*
 * Copyright 2007-2015 The OpenRA Developers (see AUTHORS)
 * This file is part of OpenRA, which is free software. It is made
 * available to you under the terms of the GNU General Public License
 * as published by the Free Software Foundation. For more information,
 * see COPYING.
 */
#endregion

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;

namespace OpenRA.Graphics
{
	public class RgbaColorRenderer : Renderer.IBatchRenderer
	{
		static readonly float2 Offset = new float2(0.5f, 0.5f);

		readonly Renderer renderer;
		readonly IShader shader;
		readonly Action renderAction;

		readonly Vertex[] vertices;
		int nv = 0;

		public RgbaColorRenderer(Renderer renderer, IShader shader)
		{
			this.renderer = renderer;
			this.shader = shader;
			vertices = new Vertex[renderer.TempBufferSize];
			renderAction = () => renderer.DrawBatch(vertices, nv, PrimitiveType.TriangleList);
		}

		public void Flush()
		{
			if (nv > 0)
			{
				renderer.Device.SetBlendMode(BlendMode.Alpha);
				shader.Render(renderAction);
				renderer.Device.SetBlendMode(BlendMode.None);

				nv = 0;
			}
		}

		public void DrawLine(float2 start, float2 end, float width, Color startColor, Color endColor)
		{
			renderer.CurrentBatchRenderer = this;

			if (nv + 6 > renderer.TempBufferSize)
				Flush();

			var delta = (end - start) / (end - start).Length;
			var corner = width / 2 * new float2(-delta.Y, delta.X);

			startColor = Util.PremultiplyAlpha(startColor);
			var sr = startColor.R / 255.0f;
			var sg = startColor.G / 255.0f;
			var sb = startColor.B / 255.0f;
			var sa = startColor.A / 255.0f;

			endColor = Util.PremultiplyAlpha(endColor);
			var er = endColor.R / 255.0f;
			var eg = endColor.G / 255.0f;
			var eb = endColor.B / 255.0f;
			var ea = endColor.A / 255.0f;

			vertices[nv++] = new Vertex(start - corner + Offset, sr, sg, sb, sa);
			vertices[nv++] = new Vertex(start + corner + Offset, sr, sg, sb, sa);
			vertices[nv++] = new Vertex(end + corner + Offset, er, eg, eb, ea);
			vertices[nv++] = new Vertex(end + corner + Offset, er, eg, eb, ea);
			vertices[nv++] = new Vertex(end - corner + Offset, er, eg, eb, ea);
			vertices[nv++] = new Vertex(start - corner + Offset, sr, sg, sb, sa);
		}

		public void DrawLine(float2 start, float2 end, float width, Color color)
		{
			renderer.CurrentBatchRenderer = this;

			if (nv + 6 > renderer.TempBufferSize)
				Flush();

			var delta = (end - start) / (end - start).Length;
			var corner = width / 2 * new float2(-delta.Y, delta.X);

			color = Util.PremultiplyAlpha(color);
			var r = color.R / 255.0f;
			var g = color.G / 255.0f;
			var b = color.B / 255.0f;
			var a = color.A / 255.0f;

			vertices[nv++] = new Vertex(start - corner + Offset, r, g, b, a);
			vertices[nv++] = new Vertex(start + corner + Offset, r, g, b, a);
			vertices[nv++] = new Vertex(end + corner + Offset, r, g, b, a);
			vertices[nv++] = new Vertex(end + corner + Offset, r, g, b, a);
			vertices[nv++] = new Vertex(end - corner + Offset, r, g, b, a);
			vertices[nv++] = new Vertex(start - corner + Offset, r, g, b, a);
		}

		/// <summary>
		/// Calculate the intersection of two lines.
		/// Will behave badly if the lines are parallel
		/// </summary>
		float2 IntersectionOf(float2 a, float2 da, float2 b, float2 db)
		{
			var crossA = a.X * (a.Y + da.Y) - a.Y * (a.X + da.X);
			var crossB = b.X * (b.Y + db.Y) - b.Y * (b.X + db.X);
			var x = da.X * crossB - db.X * crossA;
			var y = da.Y * crossB - db.Y * crossA;
			var d = da.X * db.Y - da.Y * db.X;
			return new float2(x, y) / d;
		}

		void DrawDisconnectedLine(IEnumerable<float2> points, float width, Color color)
		{
			using (var e = points.GetEnumerator())
			{
				if (!e.MoveNext())
					return;

				var lastPoint = e.Current;
				while (e.MoveNext())
				{
					var point = e.Current;
					DrawLine(lastPoint, point, width, color);
					lastPoint = point;
				}
			}
		}

		void DrawConnectedLine(float2[] points, float width, Color color, bool closed)
		{
			// Not a line
			if (points.Length < 2)
				return;

			// Single segment
			if (points.Length == 2)
			{
				DrawLine(points[0], points[1], width, color);
				return;
			}

			renderer.CurrentBatchRenderer = this;
			color = Util.PremultiplyAlpha(color);
			var r = color.R / 255.0f;
			var g = color.G / 255.0f;
			var b = color.B / 255.0f;
			var a = color.A / 255.0f;

			var start = points[0];
			var end = points[1];
			var dir = (end - start) / (end - start).Length;
			var corner = width / 2 * new float2(-dir.Y, dir.X);

			// Corners for start of line segment
			var ca = start - corner;
			var cb = start + corner;

			// Segment is part of closed loop
			if (closed)
			{
				var prev = points[points.Length - 1];
				var prevDir = (start - prev) / (start - prev).Length;
				var prevCorner = width / 2 * new float2(-prevDir.Y, prevDir.X);
				ca = IntersectionOf(start - prevCorner, prevDir, start - corner, dir);
				cb = IntersectionOf(start + prevCorner, prevDir, start + corner, dir);
			}

			var limit = closed ? points.Length : points.Length - 1;
			for (var i = 0; i < limit; i++)
			{
				var next = points[(i + 2) % points.Length];
				var nextDir = (next - end) / (next - end).Length;
				var nextCorner = width / 2 * new float2(-nextDir.Y, nextDir.X);

				// Vertices for the corners joining start-end to end-next
				var cc = closed || i < limit ? IntersectionOf(end + corner, dir, end + nextCorner, nextDir) : end + corner;
				var cd = closed || i < limit ? IntersectionOf(end - corner, dir, end - nextCorner, nextDir) : end - corner;

				// Fill segment
				if (nv + 6 > renderer.TempBufferSize)
					Flush();

				vertices[nv++] = new Vertex(ca + Offset, r, g, b, a);
				vertices[nv++] = new Vertex(cb + Offset, r, g, b, a);
				vertices[nv++] = new Vertex(cc + Offset, r, g, b, a);
				vertices[nv++] = new Vertex(cc + Offset, r, g, b, a);
				vertices[nv++] = new Vertex(cd + Offset, r, g, b, a);
				vertices[nv++] = new Vertex(ca + Offset, r, g, b, a);

				// Advance line segment
				end = next;
				dir = nextDir;
				corner = nextCorner;

				ca = cd;
				cb = cc;
			}
		}

		public void DrawLine(IEnumerable<float2> points, float width, Color color, bool connectSegments = false)
		{
			if (!connectSegments)
				DrawDisconnectedLine(points, width, color);
			else
				DrawConnectedLine(points as float2[] ?? points.ToArray(), width, color, false);
		}

		public void DrawPolygon(float2[] vertices, float width, Color color)
		{
			DrawConnectedLine(vertices, width, color, true);
		}

		public void DrawRect(float2 tl, float2 br, float width, Color color)
		{
			var tr = new float2(br.X, tl.Y);
			var bl = new float2(tl.X, br.Y);
			DrawPolygon(new[] { tl, tr, br, bl }, width, color);
		}

		public void FillRect(float2 tl, float2 br, Color color)
		{
			var tr = new float2(br.X, tl.Y);
			var bl = new float2(tl.X, br.Y);
			FillRect(tl, tr, br, bl, color);
		}

		public void FillRect(float2 a, float2 b, float2 c, float2 d, Color color)
		{
			renderer.CurrentBatchRenderer = this;

			if (nv + 6 > renderer.TempBufferSize)
				Flush();

			color = Util.PremultiplyAlpha(color);
			var cr = color.R / 255.0f;
			var cg = color.G / 255.0f;
			var cb = color.B / 255.0f;
			var ca = color.A / 255.0f;

			vertices[nv++] = new Vertex(a + Offset, cr, cg, cb, ca);
			vertices[nv++] = new Vertex(b + Offset, cr, cg, cb, ca);
			vertices[nv++] = new Vertex(c + Offset, cr, cg, cb, ca);
			vertices[nv++] = new Vertex(c + Offset, cr, cg, cb, ca);
			vertices[nv++] = new Vertex(d + Offset, cr, cg, cb, ca);
			vertices[nv++] = new Vertex(a + Offset, cr, cg, cb, ca);
		}

		public void FillEllipse(RectangleF r, Color color, int vertices = 32)
		{
			// TODO: Create an ellipse polygon instead
			var a = (r.Right - r.Left) / 2;
			var b = (r.Bottom - r.Top) / 2;
			var xc = (r.Right + r.Left) / 2;
			var yc = (r.Bottom + r.Top) / 2;
			for (var y = r.Top; y <= r.Bottom; y++)
			{
				var dx = a * (float)Math.Sqrt(1 - (y - yc) * (y - yc) / b / b);
				DrawLine(new float2(xc - dx, y), new float2(xc + dx, y), 1, color);
			}
		}

		public void SetViewportParams(Size screen, float zoom, int2 scroll)
		{
			shader.SetVec("Scroll", scroll.X, scroll.Y);
			shader.SetVec("r1", zoom * 2f / screen.Width, -zoom * 2f / screen.Height);
			shader.SetVec("r2", -1, 1);
		}
	}
}