// Physac - https://github.com/raysan5/raylib/blob/master/src/physac.h

using System;
using System.Runtime.InteropServices;

namespace Raylib
{
    #region Raylib-cs Enums

    public enum PhysicsShapeType
    {
        PHYSICS_CIRCLE,
        PHYSICS_POLYGON
    }

    #endregion

    #region Raylib-cs Types

    // Mat2 type (used for polygon shape rotation matrix)
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public struct Mat2
    {      
        public float m00;
        public float m01;
        public float m10;
        public float m11;
    }

    // [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    [StructLayout(LayoutKind.Explicit, Size = 388)]
    public unsafe struct PolygonData
    {
        [FieldOffset(0)]
        public uint vertexCount;                           // Current used vertex and normals count       
        [FieldOffset(4)]
        public unsafe Vector2* positions;
        [FieldOffset(196)]
        public unsafe Vector2* normals;
    }

    // [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    [StructLayout(LayoutKind.Explicit, Size = 424)]
    public struct PhysicsShape
    {
        [FieldOffset(0)]
        public PhysicsShapeType type;                      // Physics shape type (circle or polygon)  
        [FieldOffset(8)]
        public IntPtr body;                                // Shape physics body reference      
        [FieldOffset(16)]
        public float radius;                               // Circle shape radius (used for circle shapes)      
        [FieldOffset(20)]
        public Mat2 transform;                             // Vertices transform matrix 2x2     
        [FieldOffset(36)]
        public PolygonData vertexData;                     // Polygon shape vertices position and normals data (just used for polygon shapes)
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public partial struct PhysicsBodyData
    {      
        public uint id;    
        public bool enabled;
        public Vector2 position;    
        public Vector2 velocity;    
        public Vector2 force;
        public float angularVelocity;  
        public float torque;
        public float orient;
        public float inertia;
        public float inverseInertia;
        public float mass;
        public float inverseMass;
        public float staticFriction;
        public float dynamicFriction;
        public float restitution;
        public bool useGravity;
        public bool isGrounded; 
        public bool freezeOrient;
        public PhysicsShape shape;
    
        // convert c bool(stored as byte) to bool
        /*public bool enabled
        {
            get { return Convert.ToBoolean(bEnabled); }
            set {
                bEnabled = Convert.ToByte(value); }
        }

        public bool useGravity
        {
            get { return Convert.ToBoolean(bUseGravity); }
            set { bUseGravity = Convert.ToByte(value); }
        }

        public bool isGrounded
        {
            get { return bIsGrounded != 0; }
            set { bIsGrounded = (byte)(value ? 1 : 0); }
        }

        public bool freezeOrient
        {
            get { return Convert.ToBoolean(bFreezeOrient); }
            set { bFreezeOrient = Convert.ToByte(value); }
        }*/
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public unsafe struct PhysicsManifoldData
    {        
        public uint id;                            // Reference unique identifier  
        public IntPtr bodyA;                          // Manifold first physics body reference   
        public IntPtr bodyB;                          // Manifold second physics body reference
        public float penetration;                          // Depth of penetration from collision
        public Vector2 normal;                             // Normal direction vector from 'a' to 'b'
        public unsafe Vector2* contacts;       // Points of contact during collision
        public uint contactsCount;                 // Current collision number of contacts
        public float restitution;                          // Mixed restitution during collision
        public float dynamicFriction;                      // Mixed dynamic friction during collision
        public float staticFriction;                       // Mixed static friction during collision
    }

    #endregion

    public static partial class Raylib
    {
        #region Raylib-cs Variables

        public const int PHYSAC_MAX_BODIES = 64;
        public const int PHYSAC_MAX_MANIFOLDS = 4096;
        public const int PHYSAC_MAX_VERTICES = 24;
        public const int PHYSAC_CIRCLE_VERTICES = 24;

        public const float PHYSAC_DESIRED_DELTATIME = 1.0f / 60.0f;
        public const float PHYSAC_MAX_TIMESTEP = 0.02f;
        public const int PHYSAC_COLLISION_ITERATIONS = 100;
        public const float PHYSAC_PENETRATION_ALLOWANCE = 0.05f;
        public const float PHYSAC_PENETRATION_CORRECTION = 0.4f;

        public const float PHYSAC_PI = 3.14159265358979323846f;
        public const float PHYSAC_DEG2RAD = (PHYSAC_PI / 180.0f);

        #endregion

        #region Raylib-cs Functions

        // Initializes physics values, pointers and creates physics loop thread
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void InitPhysics();

        // Run physics step, to be used if PHYSICS_NO_THREADS is set in your main loop
        [DllImport(nativeLibName, CallingConvention = CallingConvention.Cdecl)]
        public static extern void RunPhysicsStep();

        // Returns true if physics thread is currently enabled
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern bool IsPhysicsEnabled();

        // Sets physics global gravity force
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void SetPhysicsGravity(float x, float y);

        // Creates a new circle physics body with generic parameters
        [DllImport(nativeLibName, EntryPoint = "CreatePhysicsBodyCircle")]
        private static extern IntPtr CreatePhysicsBodyCircleImport(Vector2 pos, float radius, float density);
        public static PhysicsBodyData CreatePhysicsBodyCircle(Vector2 pos, float radius, float density)
        {
            var body = CreatePhysicsBodyCircleImport(pos, radius, density);
            var data = (PhysicsBodyData)Marshal.PtrToStructure(body, typeof(PhysicsBodyData));
            return data;
        }

        // Creates a new rectangle physics body with generic parameters
        [DllImport(nativeLibName, EntryPoint = "CreatePhysicsBodyRectangle")]
        private static extern IntPtr CreatePhysicsBodyRectangleImport(Vector2 pos, float width, float height, float density);
        public static PhysicsBodyData CreatePhysicsBodyRectangle(Vector2 pos, float width, float height, float density)
        {
            var body = CreatePhysicsBodyRectangleImport(pos, width, height, density);
            var data = (PhysicsBodyData)Marshal.PtrToStructure(body, typeof(PhysicsBodyData));
            return data;
        }

        // Creates a new polygon physics body with generic parameters
        [DllImport(nativeLibName, EntryPoint = "CreatePhysicsBodyPolygon")]
        private static extern IntPtr CreatePhysicsBodyPolygonImport(Vector2 pos, float radius, int sides, float density);
        public static PhysicsBodyData CreatePhysicsBodyPolygon(Vector2 pos, float radius, int sides, float density)
        {
            var body = CreatePhysicsBodyPolygonImport(pos, radius, sides, density);
            var data = (PhysicsBodyData)Marshal.PtrToStructure(body, typeof(PhysicsBodyData));
            return data;
        }

        // Adds a force to a physics body
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void PhysicsAddForce(PhysicsBodyData body, Vector2 force);

        // Adds an angular force to a physics body
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void PhysicsAddTorque(PhysicsBodyData body, float amount);

        // Shatters a polygon shape physics body to little physics bodies with explosion force
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void PhysicsShatter(PhysicsBodyData body, Vector2 position, float force);

        // Returns the current amount of created physics bodies
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern int GetPhysicsBodiesCount();

        // Returns a physics body of the bodies pool at a specific index
        [DllImport(nativeLibName, EntryPoint = "GetPhysicsBody")]
        public static extern IntPtr GetPhysicsBodyImport(int index);
        public static PhysicsBodyData GetPhysicsBody(int index)
        {
            var body = GetPhysicsBodyImport(index);
            var data = (PhysicsBodyData)Marshal.PtrToStructure(body, typeof(PhysicsBodyData));
            return data;
        }

        // Returns the physics body shape type (PHYSICS_CIRCLE or PHYSICS_POLYGON)
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern int GetPhysicsShapeType(int index);

        // Returns the amount of vertices of a physics body shape
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern int GetPhysicsShapeVerticesCount(int index);

        // Returns transformed position of a body shape (body position + vertex transformed position)
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern Vector2 GetPhysicsShapeVertex(PhysicsBodyData body, int vertex);

        // Sets physics body shape transform based on radians parameter
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void SetPhysicsBodyRotation(PhysicsBodyData body, float radians);

        // Unitializes and destroy a physics body
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void DestroyPhysicsBody(PhysicsBodyData body);

        // Destroys created physics bodies and manifolds and resets global values
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void ResetPhysics();

        // Unitializes physics pointers and closes physics loop thread
        [DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
        public static extern void ClosePhysics();

        #endregion
    }
}