/*
* Copyright (c) 2006-2009 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#ifndef B2_COLLISION_H
#define B2_COLLISION_H

#include <Box2D/Common/b2Math.h>
#include <climits>

/// @file
/// Structures and functions used for computing contact points, distance
/// queries, and TOI queries.

class b2Shape;
class b2CircleShape;
class b2EdgeShape;
class b2PolygonShape;

const uint8 b2_nullFeature = UCHAR_MAX;

/// The features that intersect to form the contact point
/// This must be 4 bytes or less.
struct b2ContactFeature
{
    enum Type
    {
        e_vertex = 0,
        e_face = 1
    };

    uint8 indexA;        ///< Feature index on shapeA
    uint8 indexB;        ///< Feature index on shapeB
    uint8 typeA;        ///< The feature type on shapeA
    uint8 typeB;        ///< The feature type on shapeB
};

/// Contact ids to facilitate warm starting.
union b2ContactID
{
    b2ContactFeature cf;
    uint32 key;                    ///< Used to quickly compare contact ids.
};

/// A manifold point is a contact point belonging to a contact
/// manifold. It holds details related to the geometry and dynamics
/// of the contact points.
/// The local point usage depends on the manifold type:
/// -e_circles: the local center of circleB
/// -e_faceA: the local center of cirlceB or the clip point of polygonB
/// -e_faceB: the clip point of polygonA
/// This structure is stored across time steps, so we keep it small.
/// Note: the impulses are used for internal caching and may not
/// provide reliable contact forces, especially for high speed collisions.
struct b2ManifoldPoint
{
    b2Vec2 localPoint;        ///< usage depends on manifold type
    float32 normalImpulse;    ///< the non-penetration impulse
    float32 tangentImpulse;    ///< the friction impulse
    b2ContactID id;            ///< uniquely identifies a contact point between two shapes
};

/// A manifold for two touching convex shapes.
/// Box2D supports multiple types of contact:
/// - clip point versus plane with radius
/// - point versus point with radius (circles)
/// The local point usage depends on the manifold type:
/// -e_circles: the local center of circleA
/// -e_faceA: the center of faceA
/// -e_faceB: the center of faceB
/// Similarly the local normal usage:
/// -e_circles: not used
/// -e_faceA: the normal on polygonA
/// -e_faceB: the normal on polygonB
/// We store contacts in this way so that position correction can
/// account for movement, which is critical for continuous physics.
/// All contact scenarios must be expressed in one of these types.
/// This structure is stored across time steps, so we keep it small.
struct b2Manifold
{
    enum Type
    {
        e_circles,
        e_faceA,
        e_faceB
    };

    b2ManifoldPoint points[b2_maxManifoldPoints];    ///< the points of contact
    b2Vec2 localNormal;                                ///< not use for Type::e_points
    b2Vec2 localPoint;                                ///< usage depends on manifold type
    Type type;
    int32 pointCount;                                ///< the number of manifold points
};

/// This is used to compute the current state of a contact manifold.
struct b2WorldManifold
{
    /// Evaluate the manifold with supplied transforms. This assumes
    /// modest motion from the original state. This does not change the
    /// point count, impulses, etc. The radii must come from the shapes
    /// that generated the manifold.
    void Initialize(const b2Manifold* manifold,
                    const b2Transform& xfA, float32 radiusA,
                    const b2Transform& xfB, float32 radiusB);

    b2Vec2 normal;                            ///< world vector pointing from A to B
    b2Vec2 points[b2_maxManifoldPoints];    ///< world contact point (point of intersection)
};

/// This is used for determining the state of contact points.
enum b2PointState
{
    b2_nullState,        ///< point does not exist
    b2_addState,        ///< point was added in the update
    b2_persistState,    ///< point persisted across the update
    b2_removeState        ///< point was removed in the update
};

/// Compute the point states given two manifolds. The states pertain to the transition from manifold1
/// to manifold2. So state1 is either persist or remove while state2 is either add or persist.
void b2GetPointStates(b2PointState state1[b2_maxManifoldPoints], b2PointState state2[b2_maxManifoldPoints],
                      const b2Manifold* manifold1, const b2Manifold* manifold2);

/// Used for computing contact manifolds.
struct b2ClipVertex
{
    b2Vec2 v;
    b2ContactID id;
};

/// Ray-cast input data. The ray extends from p1 to p1 + maxFraction * (p2 - p1).
struct b2RayCastInput
{
    b2Vec2 p1, p2;
    float32 maxFraction;
};

/// Ray-cast output data. The ray hits at p1 + fraction * (p2 - p1), where p1 and p2
/// come from b2RayCastInput.
struct b2RayCastOutput
{
    b2Vec2 normal;
    float32 fraction;
};

/// An axis aligned bounding box.
struct b2AABB
{
    /// Verify that the bounds are sorted.
    bool IsValid() const;

    /// Get the center of the AABB.
    b2Vec2 GetCenter() const
    {
        return 0.5f * (lowerBound + upperBound);
    }

    /// Get the extents of the AABB (half-widths).
    b2Vec2 GetExtents() const
    {
        return 0.5f * (upperBound - lowerBound);
    }

    /// Get the perimeter length
    float32 GetPerimeter() const
    {
        float32 wx = upperBound.x - lowerBound.x;
        float32 wy = upperBound.y - lowerBound.y;
        return 2.0f * (wx + wy);
    }

    /// Combine an AABB into this one.
    void Combine(const b2AABB& aabb)
    {
        lowerBound = b2Min(lowerBound, aabb.lowerBound);
        upperBound = b2Max(upperBound, aabb.upperBound);
    }

    /// Combine two AABBs into this one.
    void Combine(const b2AABB& aabb1, const b2AABB& aabb2)
    {
        lowerBound = b2Min(aabb1.lowerBound, aabb2.lowerBound);
        upperBound = b2Max(aabb1.upperBound, aabb2.upperBound);
    }

    /// Does this aabb contain the provided AABB.
    bool Contains(const b2AABB& aabb) const
    {
        bool result = true;
        result = result && lowerBound.x <= aabb.lowerBound.x;
        result = result && lowerBound.y <= aabb.lowerBound.y;
        result = result && aabb.upperBound.x <= upperBound.x;
        result = result && aabb.upperBound.y <= upperBound.y;
        return result;
    }

    bool RayCast(b2RayCastOutput* output, const b2RayCastInput& input) const;

    b2Vec2 lowerBound;    ///< the lower vertex
    b2Vec2 upperBound;    ///< the upper vertex
};

/// Compute the collision manifold between two circles.
void b2CollideCircles(b2Manifold* manifold,
                      const b2CircleShape* circleA, const b2Transform& xfA,
                      const b2CircleShape* circleB, const b2Transform& xfB);

/// Compute the collision manifold between a polygon and a circle.
void b2CollidePolygonAndCircle(b2Manifold* manifold,
                               const b2PolygonShape* polygonA, const b2Transform& xfA,
                               const b2CircleShape* circleB, const b2Transform& xfB);

/// Compute the collision manifold between two polygons.
void b2CollidePolygons(b2Manifold* manifold,
                       const b2PolygonShape* polygonA, const b2Transform& xfA,
                       const b2PolygonShape* polygonB, const b2Transform& xfB);

/// Compute the collision manifold between an edge and a circle.
void b2CollideEdgeAndCircle(b2Manifold* manifold,
                               const b2EdgeShape* polygonA, const b2Transform& xfA,
                               const b2CircleShape* circleB, const b2Transform& xfB);

/// Compute the collision manifold between an edge and a circle.
void b2CollideEdgeAndPolygon(b2Manifold* manifold,
                               const b2EdgeShape* edgeA, const b2Transform& xfA,
                               const b2PolygonShape* circleB, const b2Transform& xfB);

/// Clipping for contact manifolds.
int32 b2ClipSegmentToLine(b2ClipVertex vOut[2], const b2ClipVertex vIn[2],
                            const b2Vec2& normal, float32 offset, int32 vertexIndexA);

/// Determine if two generic shapes overlap.
bool b2TestOverlap(    const b2Shape* shapeA, int32 indexA,
                    const b2Shape* shapeB, int32 indexB,
                    const b2Transform& xfA, const b2Transform& xfB);

// ---------------- Inline Functions ------------------------------------------

inline bool b2AABB::IsValid() const
{
    b2Vec2 d = upperBound - lowerBound;
    bool valid = d.x >= 0.0f && d.y >= 0.0f;
    valid = valid && lowerBound.IsValid() && upperBound.IsValid();
    return valid;
}

inline bool b2TestOverlap(const b2AABB& a, const b2AABB& b)
{
    b2Vec2 d1, d2;
    d1 = b.lowerBound - a.upperBound;
    d2 = a.lowerBound - b.upperBound;

    if (d1.x > 0.0f || d1.y > 0.0f)
        return false;

    if (d2.x > 0.0f || d2.y > 0.0f)
        return false;

    return true;
}

#endif