/******************************************************************************
 * Spine Runtimes Software License
 * Version 2.3
 * 
 * Copyright (c) 2013-2015, Esoteric Software
 * All rights reserved.
 * 
 * You are granted a perpetual, non-exclusive, non-sublicensable and
 * non-transferable license to use, install, execute and perform the Spine
 * Runtimes Software (the "Software") and derivative works solely for personal
 * or internal use. Without the written permission of Esoteric Software (see
 * Section 2 of the Spine Software License Agreement), you may not (a) modify,
 * translate, adapt or otherwise create derivative works, improvements of the
 * Software or develop new applications using the Software or (b) remove,
 * delete, alter or obscure any trademarks or any copyright, trademark, patent
 * or other intellectual property or proprietary rights notices on or in the
 * Software, including any copy thereof. Redistributions in binary or source
 * form must include this license and terms.
 * 
 * THIS SOFTWARE IS PROVIDED BY ESOTERIC SOFTWARE "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 BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) 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 THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *****************************************************************************/

using System;
using System.Collections.Generic;

namespace Spine {
	public class IkConstraint : IUpdatable {
		internal IkConstraintData data;
		internal ExposedList<Bone> bones = new ExposedList<Bone>();
		internal Bone target;
		internal int bendDirection;
		internal float mix;

		public IkConstraintData Data { get { return data; } }
		public ExposedList<Bone> Bones { get { return bones; } }
		public Bone Target { get { return target; } set { target = value; } }
		public int BendDirection { get { return bendDirection; } set { bendDirection = value; } }
		public float Mix { get { return mix; } set { mix = value; } }

		public IkConstraint (IkConstraintData data, Skeleton skeleton) {
			if (data == null) throw new ArgumentNullException("data cannot be null.");
			if (skeleton == null) throw new ArgumentNullException("skeleton cannot be null.");
			this.data = data;
			mix = data.mix;
			bendDirection = data.bendDirection;

			bones = new ExposedList<Bone>(data.bones.Count);
			foreach (BoneData boneData in data.bones)
				bones.Add(skeleton.FindBone(boneData.name));
			target = skeleton.FindBone(data.target.name);
		}

		public void Update () {
			Apply();
		}

		public void Apply () {
			Bone target = this.target;
			ExposedList<Bone> bones = this.bones;
			switch (bones.Count) {
			case 1:
				Apply(bones.Items[0], target.worldX, target.worldY, mix);
				break;
			case 2:
				Apply(bones.Items[0], bones.Items[1], target.worldX, target.worldY, bendDirection, mix);
				break;
			}
		}

		override public String ToString () {
			return data.name;
		}

		/// <summary>Adjusts the bone rotation so the tip is as close to the target position as possible. The target is specified
		/// in the world coordinate system.</summary>
		static public void Apply (Bone bone, float targetX, float targetY, float alpha) {
			float parentRotation = bone.parent == null ? 0 : bone.parent.WorldRotationX;
			float rotation = bone.rotation;
			float rotationIK = MathUtils.Atan2(targetY - bone.worldY, targetX - bone.worldX) * MathUtils.radDeg - parentRotation;
			if ((bone.worldSignX != bone.worldSignY) != (bone.skeleton.flipX != (bone.skeleton.flipY != Bone.yDown)))
				rotationIK = 360 - rotationIK;
			if (rotationIK > 180) rotationIK -= 360;
			else if (rotationIK < -180) rotationIK += 360;
			bone.UpdateWorldTransform(bone.x, bone.y, rotation + (rotationIK - rotation) * alpha, bone.appliedScaleX, bone.appliedScaleY);
		}

		/// <summary>Adjusts the parent and child bone rotations so the tip of the child is as close to the target position as
		/// possible. The target is specified in the world coordinate system.</summary>
		/// <param name="child">A direct descendant of the parent bone.</param>
		static public void Apply (Bone parent, Bone child, float targetX, float targetY, int bendDir, float alpha) {
			if (alpha == 0) return;
			float px = parent.x, py = parent.y, psx = parent.appliedScaleX, psy = parent.appliedScaleY;
			int os1, os2, s2;
			if (psx < 0) {
				psx = -psx;
				os1 = 180;
				s2 = -1;
			} else {
				os1 = 0;
				s2 = 1;
			}
			if (psy < 0) {
				psy = -psy;
				s2 = -s2;
			}
			float cx = child.x, cy = child.y, csx = child.appliedScaleX;
			bool u = Math.Abs(psx - psy) <= 0.0001f;
			if (!u && cy != 0) {
				child.worldX = parent.a * cx + parent.worldX;
				child.worldY = parent.c * cx + parent.worldY;
				cy = 0;
			}
			if (csx < 0) {
				csx = -csx;
				os2 = 180;
			} else
				os2 = 0;
			Bone pp = parent.parent;
			float tx, ty, dx, dy;
			if (pp == null) {
				tx = targetX - px;
				ty = targetY - py;
				dx = child.worldX - px;
				dy = child.worldY - py;
			} else {
				float a = pp.a, b = pp.b, c = pp.c, d = pp.d, invDet = 1 / (a * d - b * c);
				float wx = pp.worldX, wy = pp.worldY, x = targetX - wx, y = targetY - wy;
				tx = (x * d - y * b) * invDet - px;
				ty = (y * a - x * c) * invDet - py;
				x = child.worldX - wx;
				y = child.worldY - wy;
				dx = (x * d - y * b) * invDet - px;
				dy = (y * a - x * c) * invDet - py;
			}
			float l1 = (float)Math.Sqrt(dx * dx + dy * dy), l2 = child.data.length * csx, a1, a2;
			if (u) {
				l2 *= psx;
				float cos = (tx * tx + ty * ty - l1 * l1 - l2 * l2) / (2 * l1 * l2);
				if (cos < -1) cos = -1;
				else if (cos > 1) cos = 1;
				a2 = (float)Math.Acos(cos) * bendDir;
				float a = l1 + l2 * cos, o = l2 * MathUtils.Sin(a2);
				a1 = MathUtils.Atan2(ty * a - tx * o, tx * a + ty * o);
			} else {
				float a = psx * l2, b = psy * l2, ta = MathUtils.Atan2(ty, tx);
				float aa = a * a, bb = b * b, ll = l1 * l1, dd = tx * tx + ty * ty;
				float c0 = bb * ll + aa * dd - aa * bb, c1 = -2 * bb * l1, c2 = bb - aa;
				float d = c1 * c1 - 4 * c2 * c0;
				if (d >= 0) {
					float q = (float)Math.Sqrt(d);
					if (c1 < 0) q = -q;
					q = -(c1 + q) / 2;
					float r0 = q / c2, r1 = c0 / q;
					float r = Math.Abs(r0) < Math.Abs(r1) ? r0 : r1;
					if (r * r <= dd) {
						float y1 = (float)Math.Sqrt(dd - r * r) * bendDir;
						a1 = ta - MathUtils.Atan2(y1, r);
						a2 = MathUtils.Atan2(y1 / psy, (r - l1) / psx);
						goto outer;
					}
				}
				float minAngle = 0, minDist = float.MaxValue, minX = 0, minY = 0;
				float maxAngle = 0, maxDist = 0, maxX = 0, maxY = 0;
				float x = l1 + a, dist = x * x;
				if (dist > maxDist) {
					maxAngle = 0;
					maxDist = dist;
					maxX = x;
				}
				x = l1 - a;
				dist = x * x;
				if (dist < minDist) {
					minAngle = MathUtils.PI;
					minDist = dist;
					minX = x;
				}
				float angle = (float)Math.Acos(-a * l1 / (aa - bb));
				x = a * MathUtils.Cos(angle) + l1;
				float y = b * MathUtils.Sin(angle);
				dist = x * x + y * y;
				if (dist < minDist) {
					minAngle = angle;
					minDist = dist;
					minX = x;
					minY = y;
				}
				if (dist > maxDist) {
					maxAngle = angle;
					maxDist = dist;
					maxX = x;
					maxY = y;
				}
				if (dd <= (minDist + maxDist) / 2) {
					a1 = ta - MathUtils.Atan2(minY * bendDir, minX);
					a2 = minAngle * bendDir;
				} else {
					a1 = ta - MathUtils.Atan2(maxY * bendDir, maxX);
					a2 = maxAngle * bendDir;
				}
			}
		outer:
			float os = MathUtils.Atan2(cy, cx) * s2;
			a1 = (a1 - os) * MathUtils.radDeg + os1;
			a2 = (a2 + os) * MathUtils.radDeg * s2 + os2;
			if (a1 > 180) a1 -= 360;
			else if (a1 < -180) a1 += 360;
			if (a2 > 180) a2 -= 360;
			else if (a2 < -180) a2 += 360;
			float rotation = parent.rotation;
			parent.UpdateWorldTransform(px, py, rotation + (a1 - rotation) * alpha, parent.appliedScaleX, parent.appliedScaleY);
			rotation = child.rotation;
			child.UpdateWorldTransform(cx, cy, rotation + (a2 - rotation) * alpha, child.appliedScaleX, child.appliedScaleY);
		}
	}
}