/*
 * Copyright (C) 2021  P. J. McDermott
 *
 * This file is part of Dodge Balls
 *
 * Dodge Balls 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 3 of the License, or
 * (at your option) any later version.
 *
 * Dodge Balls 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 Dodge Balls.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <SDL.h>
#include "collision.h"

int
db_pt_in_rect(int x, int y, SDL_Rect *rect)
{
	if (x < rect->x) {
		return 0;
	}
	if (y < rect->y) {
		return 0;
	}
	if (x > rect->x + rect->w) {
		return 0;
	}
	if (y > rect->y + rect->h) {
		return 0;
	}
	return 1;
}

int
db_col_cir_line(double cir_x, double cir_y, double cir_r,
		int line_x1, int line_y1, int line_x2, int line_y2,
		double *col_x, double *col_y)
{
	int line_min;
	int line_max;

	if (line_y1 == line_y2) {
		/* Horizontal line */
		if (line_x1 < line_x2) {
			line_min = line_x1;
			line_max = line_x2;
		} else {
			line_min = line_x2;
			line_max = line_x1;
		}
		if (cir_x < line_min) {
			*col_x = line_min;
		} else if (cir_x > line_max) {
			*col_x = line_max;
		} else {
			*col_x = cir_x;
		}
		*col_y = line_y1;
	} else if (line_x1 == line_x2) {
		/* Vertical line */
		if (line_y1 < line_y2) {
			line_min = line_y1;
			line_max = line_y2;
		} else {
			line_min = line_y2;
			line_max = line_y1;
		}
		if (cir_y < line_min) {
			*col_y = line_min;
		} else if (cir_y > line_max) {
			*col_y = line_max;
		} else {
			*col_y = cir_y;
		}
		*col_x = line_x1;
	} else {
		return -1;
	}
	return (cir_r * cir_r) >=
		((*col_x - cir_x) * (*col_x - cir_x) +
		 (*col_y - cir_y) * (*col_y - cir_y));
}

void
db_closest_pt_on_rect(int x, int y, SDL_Rect *rect,
		double *close_x, double *close_y)
{
	*close_x = x;
	if (x < rect->x) {
		*close_x = rect->x;
	} else if (x > rect->x + rect->w) {
		*close_x = rect->x + rect->w;
	}
	*close_y = y;
	if (y < rect->y) {
		*close_y = rect->y;
	} else if (y > rect->y + rect->h) {
		*close_y = rect->y + rect->h;
	}
}

int
db_col_cir_rect(int x, int y, int r, SDL_Rect *rect,
		double *col_x, double *col_y)
{
	db_closest_pt_on_rect(x, y, rect, col_x, col_y);
	return (r * r) >=
		((*col_x - x) * (*col_x - x) + (*col_y - y) * (*col_y - y));
}

int
db_col_cir_cir(double x1, double y1, double r1, double x2, double y2, double r2)
{
	return ((r1 + r2) * (r1 + r2)) >=
		((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}

/*
 * This function will be called after moving the two balls being checked.  A
 * more accurate way to handle collisions would be to microstep through
 * movements to find the exact point of collision.
 */
int
db_col_pt_cir_cir(double x1, double y1, double r1,
		double x2, double y2, double r2, double *col_x, double *col_y)
{
	if (db_col_cir_cir(x1, y1, r1, x2, y2, r2)) {
		*col_x = (x1 + x2) / 2.0;
		*col_y = (y1 + y2) / 2.0;
		return 1;
	} else {
		return 0;
	}
}