/******************************************************************************
 * Spine Runtimes License Agreement
 * Last updated January 1, 2020. Replaces all prior versions.
 *
 * Copyright (c) 2013-2020, Esoteric Software LLC
 *
 * Integration of the Spine Runtimes into software or otherwise creating
 * derivative works of the Spine Runtimes is permitted under the terms and
 * conditions of Section 2 of the Spine Editor License Agreement:
 * http://esotericsoftware.com/spine-editor-license
 *
 * Otherwise, it is permitted to integrate the Spine Runtimes into software
 * or otherwise create derivative works of the Spine Runtimes (collectively,
 * "Products"), provided that each user of the Products must obtain their own
 * Spine Editor license and redistribution of the Products in any form must
 * include this license and copyright notice.
 *
 * THE SPINE RUNTIMES ARE PROVIDED BY ESOTERIC SOFTWARE LLC "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL ESOTERIC SOFTWARE LLC BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES,
 * BUSINESS INTERRUPTION, OR LOSS OF USE, DATA, OR PROFITS) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THE SPINE RUNTIMES, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *****************************************************************************/

using System;
using UnityEngine;

namespace Spine {
	public class SkeletonClipping {
		internal readonly Triangulator triangulator = new Triangulator();
		internal readonly ExposedList<float> clippingPolygon = new ExposedList<float>();
		internal readonly ExposedList<float> clipOutput = new ExposedList<float>(128);
		internal readonly ExposedList<float> clippedVertices = new ExposedList<float>(128);
		internal readonly ExposedList<int> clippedTriangles = new ExposedList<int>(128);
		internal readonly ExposedList<float> clippedUVs = new ExposedList<float>(128);
		internal readonly ExposedList<float> scratch = new ExposedList<float>();

		internal ClippingAttachment clipAttachment;
		internal ExposedList<ExposedList<float>> clippingPolygons;

		public ExposedList<float> ClippedVertices { get { return clippedVertices; } }
		public ExposedList<int> ClippedTriangles { get { return clippedTriangles; } }
		public ExposedList<float> ClippedUVs { get { return clippedUVs; } }

		public bool IsClipping { get { return clipAttachment != null; } }

		public int ClipStart (Slot slot, ClippingAttachment clip) {
			if (clipAttachment != null) return 0;
			clipAttachment = clip;
			Debug.LogError($"SkeletonClipping.ClipStart.");
			int n = clip.worldVerticesLength;
			float[] vertices = clippingPolygon.Resize(n).Items;
			clip.ComputeWorldVertices(slot, 0, n, vertices, 0, 2);
			MakeClockwise(clippingPolygon);
			clippingPolygons = triangulator.Decompose(clippingPolygon, triangulator.Triangulate(clippingPolygon));
			foreach (var polygon in clippingPolygons) {
				MakeClockwise(polygon);
				polygon.Add(polygon.Items[0]);
				polygon.Add(polygon.Items[1]);
			}
			return clippingPolygons.Count;
		}

		public void ClipEnd (Slot slot) {
			if (clipAttachment != null && clipAttachment.endSlot == slot.data) ClipEnd();
		}

		public void ClipEnd () {
			if (clipAttachment == null) return;
			clipAttachment = null;
			clippingPolygons = null;
			clippedVertices.Clear();
			clippedTriangles.Clear();
			clippingPolygon.Clear();
		}

		public void ClipTriangles (float[] vertices, int verticesLength, int[] triangles, int trianglesLength, float[] uvs) {
			ExposedList<float> clipOutput = this.clipOutput, clippedVertices = this.clippedVertices;
			var clippedTriangles = this.clippedTriangles;
			var polygons = clippingPolygons.Items;
			int polygonsCount = clippingPolygons.Count;

			int index = 0;
			clippedVertices.Clear();
			clippedUVs.Clear();
			clippedTriangles.Clear();
			//outer:
			for (int i = 0; i < trianglesLength; i += 3) {
				int vertexOffset = triangles[i] << 1;
				float x1 = vertices[vertexOffset], y1 = vertices[vertexOffset + 1];
				float u1 = uvs[vertexOffset], v1 = uvs[vertexOffset + 1];

				vertexOffset = triangles[i + 1] << 1;
				float x2 = vertices[vertexOffset], y2 = vertices[vertexOffset + 1];
				float u2 = uvs[vertexOffset], v2 = uvs[vertexOffset + 1];

				vertexOffset = triangles[i + 2] << 1;
				float x3 = vertices[vertexOffset], y3 = vertices[vertexOffset + 1];
				float u3 = uvs[vertexOffset], v3 = uvs[vertexOffset + 1];

				for (int p = 0; p < polygonsCount; p++) {
					int s = clippedVertices.Count;
					if (Clip(x1, y1, x2, y2, x3, y3, polygons[p], clipOutput)) {
						int clipOutputLength = clipOutput.Count;
						if (clipOutputLength == 0) continue;
						float d0 = y2 - y3, d1 = x3 - x2, d2 = x1 - x3, d4 = y3 - y1;
						float d = 1 / (d0 * d2 + d1 * (y1 - y3));

						int clipOutputCount = clipOutputLength >> 1;
						float[] clipOutputItems = clipOutput.Items;
						float[] clippedVerticesItems = clippedVertices.Resize(s + clipOutputCount * 2).Items;
						float[] clippedUVsItems = clippedUVs.Resize(s + clipOutputCount * 2).Items;
						for (int ii = 0; ii < clipOutputLength; ii += 2) {
							float x = clipOutputItems[ii], y = clipOutputItems[ii + 1];
							clippedVerticesItems[s] = x;
							clippedVerticesItems[s + 1] = y;
							float c0 = x - x3, c1 = y - y3;
							float a = (d0 * c0 + d1 * c1) * d;
							float b = (d4 * c0 + d2 * c1) * d;
							float c = 1 - a - b;
							clippedUVsItems[s] = u1 * a + u2 * b + u3 * c;
							clippedUVsItems[s + 1] = v1 * a + v2 * b + v3 * c;
							s += 2;
						}

						s = clippedTriangles.Count;
						int[] clippedTrianglesItems = clippedTriangles.Resize(s + 3 * (clipOutputCount - 2)).Items;
						clipOutputCount--;
						for (int ii = 1; ii < clipOutputCount; ii++) {
							clippedTrianglesItems[s] = index;
							clippedTrianglesItems[s + 1] = index + ii;
							clippedTrianglesItems[s + 2] = index + ii + 1;
							s += 3;
						}
						index += clipOutputCount + 1;
					}
					else {
						float[] clippedVerticesItems = clippedVertices.Resize(s + 3 * 2).Items;
						float[] clippedUVsItems = clippedUVs.Resize(s + 3 * 2).Items;
						clippedVerticesItems[s] = x1;
						clippedVerticesItems[s + 1] = y1;
						clippedVerticesItems[s + 2] = x2;
						clippedVerticesItems[s + 3] = y2;
						clippedVerticesItems[s + 4] = x3;
						clippedVerticesItems[s + 5] = y3;

						clippedUVsItems[s] = u1;
						clippedUVsItems[s + 1] = v1;
						clippedUVsItems[s + 2] = u2;
						clippedUVsItems[s + 3] = v2;
						clippedUVsItems[s + 4] = u3;
						clippedUVsItems[s + 5] = v3;

						s = clippedTriangles.Count;
						int[] clippedTrianglesItems = clippedTriangles.Resize(s + 3).Items;
						clippedTrianglesItems[s] = index;
						clippedTrianglesItems[s + 1] = index + 1;
						clippedTrianglesItems[s + 2] = index + 2;
						index += 3;
						break; //continue outer;
					}
				}
			}

		}

		/** Clips the input triangle against the convex, clockwise clipping area. If the triangle lies entirely within the clipping
		 * area, false is returned. The clipping area must duplicate the first vertex at the end of the vertices list. */
		internal bool Clip (float x1, float y1, float x2, float y2, float x3, float y3, ExposedList<float> clippingArea, ExposedList<float> output) {
			var originalOutput = output;
			var clipped = false;

			// Avoid copy at the end.
			ExposedList<float> input = null;
			if (clippingArea.Count % 4 >= 2) {
				input = output;
				output = scratch;
			} else {
				input = scratch;
			}

			input.Clear();
			input.Add(x1);
			input.Add(y1);
			input.Add(x2);
			input.Add(y2);
			input.Add(x3);
			input.Add(y3);
			input.Add(x1);
			input.Add(y1);
			output.Clear();

			float[] clippingVertices = clippingArea.Items;
			int clippingVerticesLast = clippingArea.Count - 4;
			for (int i = 0; ; i += 2) {
				float edgeX = clippingVertices[i], edgeY = clippingVertices[i + 1];
				float edgeX2 = clippingVertices[i + 2], edgeY2 = clippingVertices[i + 3];
				float deltaX = edgeX - edgeX2, deltaY = edgeY - edgeY2;

				float[] inputVertices = input.Items;
				int inputVerticesLength = input.Count - 2, outputStart = output.Count;
				for (int ii = 0; ii < inputVerticesLength; ii += 2) {
					float inputX = inputVertices[ii], inputY = inputVertices[ii + 1];
					float inputX2 = inputVertices[ii + 2], inputY2 = inputVertices[ii + 3];
					bool side2 = deltaX * (inputY2 - edgeY2) - deltaY * (inputX2 - edgeX2) > 0;
					if (deltaX * (inputY - edgeY2) - deltaY * (inputX - edgeX2) > 0) {
						if (side2) { // v1 inside, v2 inside
							output.Add(inputX2);
							output.Add(inputY2);
							continue;
						}
						// v1 inside, v2 outside
						float c0 = inputY2 - inputY, c2 = inputX2 - inputX;
						float s = c0 * (edgeX2 - edgeX) - c2 * (edgeY2 - edgeY);
						if (Math.Abs(s) > 0.000001f) {
							float ua = (c2 * (edgeY - inputY) - c0 * (edgeX - inputX)) / s;
							output.Add(edgeX + (edgeX2 - edgeX) * ua);
							output.Add(edgeY + (edgeY2 - edgeY) * ua);
						} else {
							output.Add(edgeX);
							output.Add(edgeY);
						}
					}
					else if (side2) { // v1 outside, v2 inside
						float c0 = inputY2 - inputY, c2 = inputX2 - inputX;
						float s = c0 * (edgeX2 - edgeX) - c2 * (edgeY2 - edgeY);
						if (Math.Abs(s) > 0.000001f) {
							float ua = (c2 * (edgeY - inputY) - c0 * (edgeX - inputX)) / s;
							output.Add(edgeX + (edgeX2 - edgeX) * ua);
							output.Add(edgeY + (edgeY2 - edgeY) * ua);
						} else {
							output.Add(edgeX);
							output.Add(edgeY);
						}
						output.Add(inputX2);
						output.Add(inputY2);
					}
					clipped = true;
				}

				if (outputStart == output.Count) { // All edges outside.
					originalOutput.Clear();
					return true;
				}

				output.Add(output.Items[0]);
				output.Add(output.Items[1]);

				if (i == clippingVerticesLast) break;
				var temp = output;
				output = input;
				output.Clear();
				input = temp;
			}

			if (originalOutput != output) {
				originalOutput.Clear();
				for (int i = 0, n = output.Count - 2; i < n; i++) {
					originalOutput.Add(output.Items[i]);
				}
			} else {
				originalOutput.Resize(originalOutput.Count - 2);
			}

			return clipped;
		}

		public static void MakeClockwise (ExposedList<float> polygon) {
			float[] vertices = polygon.Items;
			int verticeslength = polygon.Count;

			float area = vertices[verticeslength - 2] * vertices[1] - vertices[0] * vertices[verticeslength - 1], p1x, p1y, p2x, p2y;
			for (int i = 0, n = verticeslength - 3; i < n; i += 2) {
				p1x = vertices[i];
				p1y = vertices[i + 1];
				p2x = vertices[i + 2];
				p2y = vertices[i + 3];
				area += p1x * p2y - p2x * p1y;
			}
			if (area < 0) return;

			for (int i = 0, lastX = verticeslength - 2, n = verticeslength >> 1; i < n; i += 2) {
				float x = vertices[i], y = vertices[i + 1];
				int other = lastX - i;
				vertices[i] = vertices[other];
				vertices[i + 1] = vertices[other + 1];
				vertices[other] = x;
				vertices[other + 1] = y;
			}
		}
	}
}