// MIT License

// Copyright (c) 2019 Erin Catto

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#include "box2d/b2_collision.h"
#include "box2d/b2_circle_shape.h"
#include "box2d/b2_polygon_shape.h"

void b2CollideCircles(
	b2Manifold* manifold,
	const b2CircleShape* circleA, const b2Transform& xfA,
	const b2CircleShape* circleB, const b2Transform& xfB)
{
	manifold->pointCount = 0;

	b2Vec2 pA = b2Mul(xfA, circleA->m_p);
	b2Vec2 pB = b2Mul(xfB, circleB->m_p);

	b2Vec2 d = pB - pA;
	float distSqr = b2Dot(d, d);
	float rA = circleA->m_radius, rB = circleB->m_radius;
	float radius = rA + rB;
	if (distSqr > radius * radius)
	{
		return;
	}

	manifold->type = b2Manifold::e_circles;
	manifold->localPoint = circleA->m_p;
	manifold->localNormal.SetZero();
	manifold->pointCount = 1;

	manifold->points[0].localPoint = circleB->m_p;
	manifold->points[0].id.key = 0;
}

void b2CollidePolygonAndCircle(
	b2Manifold* manifold,
	const b2PolygonShape* polygonA, const b2Transform& xfA,
	const b2CircleShape* circleB, const b2Transform& xfB)
{
	manifold->pointCount = 0;

	// Compute circle position in the frame of the polygon.
	b2Vec2 c = b2Mul(xfB, circleB->m_p);
	b2Vec2 cLocal = b2MulT(xfA, c);

	// Find the min separating edge.
	int32 normalIndex = 0;
	float separation = -b2_maxFloat;
	float radius = polygonA->m_radius + circleB->m_radius;
	int32 vertexCount = polygonA->m_count;
	const b2Vec2* vertices = polygonA->m_vertices;
	const b2Vec2* normals = polygonA->m_normals;

	for (int32 i = 0; i < vertexCount; ++i)
	{
		float s = b2Dot(normals[i], cLocal - vertices[i]);

		if (s > radius)
		{
			// Early out.
			return;
		}

		if (s > separation)
		{
			separation = s;
			normalIndex = i;
		}
	}

	// Vertices that subtend the incident face.
	int32 vertIndex1 = normalIndex;
	int32 vertIndex2 = vertIndex1 + 1 < vertexCount ? vertIndex1 + 1 : 0;
	b2Vec2 v1 = vertices[vertIndex1];
	b2Vec2 v2 = vertices[vertIndex2];

	// If the center is inside the polygon ...
	if (separation < b2_epsilon)
	{
		manifold->pointCount = 1;
		manifold->type = b2Manifold::e_faceA;
		manifold->localNormal = normals[normalIndex];
		manifold->localPoint = 0.5f * (v1 + v2);
		manifold->points[0].localPoint = circleB->m_p;
		manifold->points[0].id.key = 0;
		return;
	}

	// Compute barycentric coordinates
	float u1 = b2Dot(cLocal - v1, v2 - v1);
	float u2 = b2Dot(cLocal - v2, v1 - v2);
	if (u1 <= 0.0f)
	{
		if (b2DistanceSquared(cLocal, v1) > radius * radius)
		{
			return;
		}

		manifold->pointCount = 1;
		manifold->type = b2Manifold::e_faceA;
		manifold->localNormal = cLocal - v1;
		manifold->localNormal.Normalize();
		manifold->localPoint = v1;
		manifold->points[0].localPoint = circleB->m_p;
		manifold->points[0].id.key = 0;
	}
	else if (u2 <= 0.0f)
	{
		if (b2DistanceSquared(cLocal, v2) > radius * radius)
		{
			return;
		}

		manifold->pointCount = 1;
		manifold->type = b2Manifold::e_faceA;
		manifold->localNormal = cLocal - v2;
		manifold->localNormal.Normalize();
		manifold->localPoint = v2;
		manifold->points[0].localPoint = circleB->m_p;
		manifold->points[0].id.key = 0;
	}
	else
	{
		b2Vec2 faceCenter = 0.5f * (v1 + v2);
		float s = b2Dot(cLocal - faceCenter, normals[vertIndex1]);
		if (s > radius)
		{
			return;
		}

		manifold->pointCount = 1;
		manifold->type = b2Manifold::e_faceA;
		manifold->localNormal = normals[vertIndex1];
		manifold->localPoint = faceCenter;
		manifold->points[0].localPoint = circleB->m_p;
		manifold->points[0].id.key = 0;
	}
}