using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Microsoft.Xna.Framework;

namespace TalkingIsAFreeAction
{
    public static class Physics
    {
        public const float GRAVITY = 50;
        public const float MINIMUM_VELOCITY = 10;
        public const float SLOWDOWN_RATE = 0.75f;
        public const float EDGE_SLOWDOWN_RATE = 0.99f;

        private static float lastFrameLength = 0.1f;

        public static List<PhysicsObject> activePhysicsBodies = new List<PhysicsObject>();
        public static List<PhysicsObject> passivePhysicsBodies = new List<PhysicsObject>();

        public static void CapSpeed(PhysicsObject current)
        {
            if (current.velocityX > -MINIMUM_VELOCITY && current.velocityX < MINIMUM_VELOCITY) current.velocityX = 0;
            if (current.velocityY > -MINIMUM_VELOCITY && current.velocityY < MINIMUM_VELOCITY) current.velocityY = 0;
        }

        public static void TryAccelerateX(PhysicsObject current, float amount)
        {
            current.velocityX += amount; //This method got a lot less complicated all of a sudden
        }

        public static void ApplyPhysics(float seconds)
        {
            lastFrameLength = seconds;
            for (int i = 0; i < activePhysicsBodies.Count; i++)
            {
                PhysicsObject current = activePhysicsBodies[i];

                if (current.velocityX > current.maxVelocityX) current.velocityX = current.maxVelocityX;
                if (current.velocityX < -current.maxVelocityX) current.velocityX = -current.maxVelocityX;
                if (current.velocityY > current.maxVelocityY) current.velocityY = current.maxVelocityY;

                float targetX = current.x + current.velocityX * seconds;
                float targetY = current.y + current.velocityY * seconds;

                float reductionFactor = 0.9f;

                //Check for collisions
                for (int ii = 0; ii < passivePhysicsBodies.Count; ii++)
                {
                    PhysicsObject other = passivePhysicsBodies[ii];

                    Vector2 collision;
                    bool colliding = true;

                    while (colliding)
                    {
                        colliding = false;

                        //Horizontal
                        collision = Util.CalculateCollision(targetX, current.y, current.width, current.height, other.x, other.y, other.width, other.height);
                        if (collision.X > 0 && collision.Y > 0)
                        {
                            current.velocityX *= reductionFactor;
                            colliding = true;
                        }

                        //Vertical
                        collision = Util.CalculateCollision(current.x, targetY, current.width, current.height, other.x, other.y, other.width, other.height);
                        if (collision.X > 0 && collision.Y > 0)
                        {
                            current.velocityY *= reductionFactor;
                            colliding = true;
                        }

                        //Recalculate if velocity was modified
                        if (colliding)
                        {
                            CapSpeed(current);

                            targetX = current.x + current.velocityX * seconds;
                            targetY = current.y + current.velocityY * seconds;
                        }
                    }
                }

                current.ApplyNewPosition(targetX, targetY);

                //Apply gravity
                if (!Main.climbing)
                {
                    if (current.velocityY <= GRAVITY) current.velocityY += GRAVITY;
                    else current.velocityY *= 1f + (5f * seconds);

                    //Check if standing on ground
                    for (int ii = 0; ii < passivePhysicsBodies.Count; ii++)
                    {
                        PhysicsObject other = passivePhysicsBodies[ii];

                        if (Util.CheckCollision(current.x, (current.y + 1), current.width, current.height, other.x, other.y, other.width, other.height))
                        {
                            current.onGroundTimer += seconds;
                        }
                    }
                }
            }
        }

        public static bool CheckIfPassable(float x, float y, float width, float height)
        {
            for (int i = 0; i < passivePhysicsBodies.Count; i++)
            {
                PhysicsObject other = passivePhysicsBodies[i];
                //If it collides...
                if (Util.CheckCollision(x, y, width, height, other.x, other.y, other.width, other.height))
                {
                    return false;
                }
            }

            return true;
        }
    }
}