#include <math.h>

#include "random.h"
#include "planet.h"
#include "utils.h"

static void putpixel(struct SDL_Surface *screen, const int x, const int y,
		     const unsigned char r, const unsigned char g,
		     const unsigned char b)
{
	int offset = y * screen->pitch + x * 4;
	unsigned char *buf = screen->pixels;

	buf[offset++] = b;
	buf[offset++] = g;
	buf[offset]   = r;
}

static void reshape_planet(struct planet *p)
{
	p->radius = pow(p->mass / 100, 1 / 3.0);
}

void init_planet(struct planet *p)
{
	p->speed.x = 0;
	p->speed.y = 0;
	p->pos.x = 0;
	p->pos.y = 0;
	p->mass = 0;
	reshape_planet(p);
	p->r = get_random() % 256;
	p->g = get_random() % 256;
	p->b = get_random() % 256;

	INIT_LIST_HEAD(&p->list);
}

/**
 * setup_planet - set the planet on a "solarsystem"
 * @p:		pointer to struct planet to set up
 * @mass:	mass of the planet to set up
 * @total_mass: total mass of the system
 * @radius:	maximum radius of the system
 */

static void setup_planet(struct planet *p, double mass, double total_mass,
			 double radius)
{
	double angle = M_PI * 2 * get_random_double();
	double velocity;
	double distance;

	distance = radius * pow(get_random_double(), 2);
	velocity = sqrt(total_mass / radius);

	velocity *= pow(distance / radius, 0.2);

	p->pos.x = cos(angle) * distance;
	p->pos.y = sin(angle) * distance;

	p->speed.x = -sin(angle) * velocity;
	p->speed.y = cos(angle) * velocity;

	p->mass = mass;

	reshape_planet(p);
}

void create_planets(struct planet *p, int num, double total_mass, double radius)
{
	int i;
	double sum = 0;
	struct planet *new_planet;

	setup_planet(p,
		     total_mass / num * 2 * get_random_double(),
		     total_mass,
		     radius);

	for (i = 0; i < num; i++) {
		new_planet = malloc(sizeof(*new_planet));
		init_planet(new_planet);
		list_add(&new_planet->list, &p->list);
		setup_planet(new_planet,
			     total_mass / num * 2 * get_random_double(),
			     total_mass,
			     radius);

		sum += new_planet->mass;
	}
}

void draw_planet(SDL_Surface *screen, struct planet *p,
		 const struct camera *cam)
{
	struct vector pos;
	float radius = p->radius * cam->zoom;
	float r2 = radius * radius;
	int x, x_start, y, x_end;

	vector_sub(&p->pos, &cam->pos, &pos);
	vector_scale(&pos, cam->zoom, &pos);
	pos.x += screen->w / 2;
	pos.y += screen->h / 2;

	y = MAX(pos.y - radius, 0);

	if (radius * 2 <= 1) {
		if (pos.x >= 0 && pos.x < screen->w &&
		    pos.y >= 0 && pos.y < screen->h)
			putpixel(screen, (int)pos.x, (int)pos.y,
				 p->r, p->g, p->b);
		return;
	}

	for (; y < MIN(pos.y + radius, screen->h); y++) {
		int offset;
		unsigned char *buf = screen->pixels;
		float y2 = (y - pos.y);

		y2 = sqrt(r2 - y2 * y2);
		x_start = pos.x - y2;
		x_end = pos.x + y2;
		x_start = MAX(0, x_start);
		x_end = MIN(x_end, screen->w);

		offset = y * screen->pitch + x_start * 4;
		for (x = x_start; x < x_end; x++) {
			buf[offset++] = p->b;
			buf[offset++] = p->g;
			buf[offset++] = p->r;
			offset++;
		}
	}
}

int gravitize_planets(struct planet *a, struct planet *b, const double time)
{
	struct vector distance, sum;
	double dist, f, acc;

	vector_sub(&a->pos, &b->pos, &distance);

	dist = vector_abs(&distance);

	/* Return true in case of a collision */
	if (dist < (a->radius + b->radius))
		return 1;

	vector_div(&distance, dist, &distance);

	f = a->mass * b->mass / (dist * dist) * time;

	acc = f / b->mass;
	vector_scale(&distance, acc, &sum);
	vector_add(&b->speed, &sum, &b->speed);

	acc = f / a->mass;
	vector_scale(&distance, acc, &sum);
	vector_sub(&a->speed, &sum, &a->speed);

	return 0;
}

/*
 * Merge planets a and b into planet a
 *
 * It is left for the caller to deal with the scrap planet b
 */
static void _merge_planets(struct planet *a, struct planet *b)
{
	struct vector pa, pb, p;

	vector_scale(&a->speed, a->mass, &pa);
	vector_scale(&b->speed, b->mass, &pb);
	vector_add(&pa, &pb, &p);

	if (a->mass < b->mass)
		a->pos = b->pos;

	a->mass += b->mass;
	reshape_planet(a);
	vector_div(&p, a->mass, &a->speed);
}

/*
 * Merge planets a and b into a the new planet a, which pointer is
 * returned to the caller. Planet b is removed from the linked list
 * and it's memory is freed. The merged planet will retain in the
 * list.
 */
struct planet *merge_planets(struct planet *a, struct planet *b)
{
	_merge_planets(a, b);

	list_del(&b->list);
	free(b);
	return a;
}

void move_planet(struct planet *p, const double time)
{
	struct vector tmp;
	vector_scale(&p->speed, time, &tmp);
	vector_add(&p->pos, &tmp, &p->pos);
}

void print_planet(const struct planet *p)
{
	printf("pos: (%f,%f), speed: (%f,%f), mass: %f, radius %f\n",
	       p->pos.x, p->pos.y, p->speed.x, p->speed.y, p->mass, p->radius);
}