//Copyright Paul Reiche, Fred Ford. 1992-2002

/*
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include "collide.h"
#include "element.h"
#include "races.h"
#include "units.h"
#include "libs/mathlib.h"
#include "libs/log.h"


//#define DEBUG_COLLIDE

void
collide (ELEMENT *ElementPtr0, ELEMENT *ElementPtr1)
{
	SIZE speed;
	SIZE dx0, dy0, dx1, dy1, dx_rel, dy_rel;
	SIZE TravelAngle0, TravelAngle1, ImpactAngle0, ImpactAngle1;
	SIZE RelTravelAngle, Directness;

	dx_rel = ElementPtr0->next.location.x
			- ElementPtr1->next.location.x;
	dy_rel = ElementPtr0->next.location.y
			- ElementPtr1->next.location.y;
	ImpactAngle0 = ARCTAN (dx_rel, dy_rel);
	ImpactAngle1 = NORMALIZE_ANGLE (ImpactAngle0 + HALF_CIRCLE);

	GetCurrentVelocityComponents (&ElementPtr0->velocity, &dx0, &dy0);
	TravelAngle0 = GetVelocityTravelAngle (&ElementPtr0->velocity);
	GetCurrentVelocityComponents (&ElementPtr1->velocity, &dx1, &dy1);
	TravelAngle1 = GetVelocityTravelAngle (&ElementPtr1->velocity);
	dx_rel = dx0 - dx1;
	dy_rel = dy0 - dy1;
	RelTravelAngle = ARCTAN (dx_rel, dy_rel);
	speed = square_root ((long)dx_rel * dx_rel + (long)dy_rel * dy_rel);

	Directness = NORMALIZE_ANGLE (RelTravelAngle - ImpactAngle0);
	if (Directness <= QUADRANT || Directness >= HALF_CIRCLE + QUADRANT)
			/* shapes just scraped each other but still collided,
			 * they will collide again unless we fudge it.
			 */
	{
		Directness = HALF_CIRCLE;
		ImpactAngle0 = TravelAngle0 + HALF_CIRCLE;
		ImpactAngle1 = TravelAngle1 + HALF_CIRCLE;
	}

#ifdef DEBUG_COLLIDE
	log_add (log_Debug, "Centers: <%d, %d> <%d, %d>",
			ElementPtr0->next.location.x, ElementPtr0->next.location.y,
			ElementPtr1->next.location.x, ElementPtr1->next.location.y);
	log_add (log_Debug, "RelTravelAngle : %d, ImpactAngles <%d, %d>",
			RelTravelAngle, ImpactAngle0, ImpactAngle1);
#endif /* DEBUG_COLLIDE */

	if (ElementPtr0->next.location.x == ElementPtr0->current.location.x
			&& ElementPtr0->next.location.y == ElementPtr0->current.location.y
			&& ElementPtr1->next.location.x == ElementPtr1->current.location.x
			&& ElementPtr1->next.location.y == ElementPtr1->current.location.y)
	{
		if (ElementPtr0->state_flags & ElementPtr1->state_flags & DEFY_PHYSICS)
		{
			ImpactAngle0 = TravelAngle0 + (HALF_CIRCLE - OCTANT);
			ImpactAngle1 = TravelAngle1 + (HALF_CIRCLE - OCTANT);
			ZeroVelocityComponents (&ElementPtr0->velocity);
			ZeroVelocityComponents (&ElementPtr1->velocity);
		}
		ElementPtr0->state_flags |= (DEFY_PHYSICS | COLLISION);
		ElementPtr1->state_flags |= (DEFY_PHYSICS | COLLISION);
#ifdef DEBUG_COLLIDE
		log_add (log_Debug, "No movement before collision -- "
				"<(%d, %d) = %d, (%d, %d) = %d>",
				dx0, dy0, ImpactAngle0 - OCTANT, dx1, dy1,
				ImpactAngle1 - OCTANT);
#endif /* DEBUG_COLLIDE */
	}

	{
		SIZE mass0, mass1;
		long scalar;

		mass0 = ElementPtr0->mass_points /* << 2 */;
		mass1 = ElementPtr1->mass_points /* << 2 */;
		scalar = (long)SINE (Directness, speed << 1) * (mass0 * mass1);

		if (!GRAVITY_MASS (ElementPtr0->mass_points + 1))
		{
			if (ElementPtr0->state_flags & PLAYER_SHIP)
			{
				STARSHIP *StarShipPtr;

				GetElementStarShip (ElementPtr0, &StarShipPtr);
				StarShipPtr->cur_status_flags &=
						~(SHIP_AT_MAX_SPEED | SHIP_BEYOND_MAX_SPEED);
				if (!(ElementPtr0->state_flags & DEFY_PHYSICS))
				{
					if (ElementPtr0->turn_wait < COLLISION_TURN_WAIT)
						ElementPtr0->turn_wait += COLLISION_TURN_WAIT;
					if (ElementPtr0->thrust_wait < COLLISION_THRUST_WAIT)
						ElementPtr0->thrust_wait += COLLISION_THRUST_WAIT;
				}
			}

			speed = (SIZE)(scalar / ((long)mass0 * (mass0 + mass1)));
			DeltaVelocityComponents (&ElementPtr0->velocity,
					COSINE (ImpactAngle0, speed),
					SINE (ImpactAngle0, speed));

			GetCurrentVelocityComponents (&ElementPtr0->velocity, &dx0, &dy0);
			if (dx0 < 0)
				dx0 = -dx0;
			if (dy0 < 0)
				dy0 = -dy0;

			if (VELOCITY_TO_WORLD (dx0 + dy0) < SCALED_ONE)
				SetVelocityComponents (&ElementPtr0->velocity,
						COSINE (ImpactAngle0,
						WORLD_TO_VELOCITY (SCALED_ONE) - 1),
						SINE (ImpactAngle0,
						WORLD_TO_VELOCITY (SCALED_ONE) - 1));
		}

		if (!GRAVITY_MASS (ElementPtr1->mass_points + 1))
		{
			if (ElementPtr1->state_flags & PLAYER_SHIP)
			{
				STARSHIP *StarShipPtr;

				GetElementStarShip (ElementPtr1, &StarShipPtr);
				StarShipPtr->cur_status_flags &=
						~(SHIP_AT_MAX_SPEED | SHIP_BEYOND_MAX_SPEED);
				if (!(ElementPtr1->state_flags & DEFY_PHYSICS))
				{
					if (ElementPtr1->turn_wait < COLLISION_TURN_WAIT)
						ElementPtr1->turn_wait += COLLISION_TURN_WAIT;
					if (ElementPtr1->thrust_wait < COLLISION_THRUST_WAIT)
						ElementPtr1->thrust_wait += COLLISION_THRUST_WAIT;
				}
			}

			speed = (SIZE)(scalar / ((long)mass1 * (mass0 + mass1)));
			DeltaVelocityComponents (&ElementPtr1->velocity,
					COSINE (ImpactAngle1, speed),
					SINE (ImpactAngle1, speed));

			GetCurrentVelocityComponents (&ElementPtr1->velocity, &dx1, &dy1);
			if (dx1 < 0)
				dx1 = -dx1;
			if (dy1 < 0)
				dy1 = -dy1;

			if (VELOCITY_TO_WORLD (dx1 + dy1) < SCALED_ONE)
				SetVelocityComponents (&ElementPtr1->velocity,
						COSINE (ImpactAngle1,
						WORLD_TO_VELOCITY (SCALED_ONE) - 1),
						SINE (ImpactAngle1,
						WORLD_TO_VELOCITY (SCALED_ONE) - 1));
		}
#ifdef DEBUG_COLLIDE
		GetCurrentVelocityComponents (&ElementPtr0->velocity, &dx0, &dy0);
		GetCurrentVelocityComponents (&ElementPtr1->velocity, &dx1, &dy1);
		log_add (log_Debug, "After: <%d, %d> <%d, %d>\n",
				dx0, dy0, dx1, dy1);
#endif /* DEBUG_COLLIDE */
	}
}