/*
 * physics.c
 *
 * Calculate what happens
 *
 * (c) 2008 Thomas White <taw27@cam.ac.uk>
 *
 *  thrust3d - a silly game
 *
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <SDL.h>
#include <math.h>

#include "types.h"
#include "model.h"
#include "game.h"
#include "utils.h"

/* Acceleration due to gravity in metres per millisecond per millisecond */
#define GRAVITY (9.81e-6)

/* Acceleration due to booster rocket, metres per ms per ms */
#define THRUST (GRAVITY*2)

/* Acceleration due to forwards/backwards thrusters, m per ms per ms */
#define FTHRUST (GRAVITY*0.5)

/* Air friction in (m per ms per ms) per (m per ms) */
#define FRICTION 0.0008

/* Lander craft turning speed in radians per ms per ms */
#define YAWTHRUST (M_PI/3000000)

/* Conversion factor between friction and 'yawthrust' */
#define TORQUE 1

static void physics_process(ModelInstance *obj, Uint32 dt) {

	/* Air friction */
	if ( obj->vx > 0.0 ) {
		obj->vx -= FRICTION * dt * obj->vx;
		if ( obj->vx < 0.0 ) obj->vx = 0.0;
	} else {
		obj->vx += FRICTION * dt * -obj->vx;
		if ( obj->vx > 0.0 ) obj->vx = 0.0;
	}
	
	if ( obj->vy > 0.0 ) {
		obj->vy -= FRICTION * dt * obj->vy;
		if ( obj->vy < 0.0 ) obj->vy = 0.0;
	} else {
		obj->vy += FRICTION * dt * -obj->vy;
		if ( obj->vy > 0.0 ) obj->vy = 0.0;
	}
	
	if ( obj->vz > 0.0 ) {
		obj->vz -= FRICTION * dt * obj->vz;
		if ( obj->vz < 0.0 ) obj->vz = 0.0;
	} else {
		obj->vz += FRICTION * dt * -obj->vz;
		if ( obj->vz > 0.0 ) obj->vz = 0.0;
	}
	
	if ( obj->yawspeed > 0.0 ) {
		obj->yawspeed -= FRICTION * dt * obj->yawspeed * TORQUE;
		if ( obj->yawspeed < 0.0 ) obj->yawspeed = 0.0;
	} else {
		obj->yawspeed += FRICTION * dt * -obj->yawspeed * TORQUE;
		if ( obj->yawspeed > 0.0 ) obj->yawspeed = 0.0;
	}
	
	/* Gravity */
	if ( obj->attribs & OBJ_GRAVITY ) obj->vz -= GRAVITY * dt;
	
	/* Take a step */
	obj->x += obj->vx * dt;
	obj->y += obj->vy * dt;
	obj->z += obj->vz * dt;
	obj->yaw += obj->yawspeed * dt;
	
	if ( obj->yaw < -M_PI ) obj->yaw += 2*M_PI;
	if ( obj->yaw > M_PI ) obj->yaw -= 2*M_PI;

}

void physics_step(Game *game) {

	int i, j;
	Uint32 dt, t;
	
	t = SDL_GetTicks();
	dt = t - game->tlast;
	
	/* Handle things specific to the lander craft */
	if ( game->thrusting ) {
		game->lander->vz += THRUST * dt;
	}
	if ( game->forward ) {
		game->lander->vx += sinf(game->lander->yaw) * FTHRUST * dt;
		game->lander->vy += cosf(game->lander->yaw) * FTHRUST * dt;
	} else if ( game->reverse ) {
		game->lander->vx -= sinf(game->lander->yaw) * FTHRUST * dt;
		game->lander->vy -= cosf(game->lander->yaw) * FTHRUST * dt;
	}
	if ( game->turn_left ) {
		game->lander->yawspeed -= YAWTHRUST * dt;	/* -ve yaw is "left" */
	}
	if ( game->turn_right ) {
		game->lander->yawspeed += YAWTHRUST *dt;	/* +ve yaw is "right" */
	}
	physics_process(game->lander, dt);
	game_check_handoff(game);
	
	for ( j=0; j<game->num_rooms; j++ ) {
	
		Room *room;
		
		room = game->rooms[j];
		if ( room == NULL ) return;
		for ( i=0; i<room->num_objects; i++ ) {
			
			ModelInstance *obj;
			
			obj = room->objects[i];
			if ( obj == NULL ) continue;
			
			physics_process(obj, dt);
			
		}
	
	}
	
	//game->view_angle = deg2rad(30.0 - 30.0 * game->lander->vz/0.015);
	
	game->tlast = t;

}