#include <SDL2/SDL.h>

#include <assert.h>
#include <stdbool.h>
#include <math.h>

#include "game.h"

#define SPEED      (0.0005 / TICK)
#define ROTATE     (0.03 / TICK)
#define BULL_SPEED (0.4  / TICK)

#define MAX_SPEED  (0.1 / TICK)
#define MAX_ROTATE (0.3 / TICK)

// Цифры взяты с потолка, но вроде неплохо подобраны
#define G      6.6719199e-11
#define M_STAR 3e8
#define M_SHIP 0.001

Player g_player[MAX_PLAYERS];
Bullet g_bullet[MAX_BULLETS];

static bool svmode;

void g_player_set(unsigned int id, bool live, float x, float y, float r, float vx, float vy, float vr, int shoot) {
	assert(id < MAX_PLAYERS);
	g_player[id] = (Player) {
		.updated = true,
		.live    = live,
		.x       = x,
		.y       = y,
		.r       = r,
		.vx      = vx,
		.vy      = vy,
		.vr      = vr,
	};
}

void g_bullet_set(unsigned int id, unsigned int owner, bool live, float x, float y, float vx, float vy, int tick) {
	assert(id < MAX_BULLETS);
	assert(owner < MAX_PLAYERS);
	g_bullet[id] = (Bullet) {
		.live  = live,
		.owner = owner,
		.x     = x,
		.y     = y,
		.vx    = vx,
		.vy    = vy,
		.tick  = tick,
	};
}

static int freebullet() {
	for(int i = 0; i < MAX_BULLETS; i++)
		if(!g_bullet[i].live)
			return i;
	return -1;
}

static void moveplayer(int id, float speed) {
	if(fabs(g_player[id].vx) < MAX_SPEED)
		g_player[id].vx += speed * cos(g_player[id].r * 2 * M_PI);
	if(fabs(g_player[id].vy) < MAX_SPEED)
		g_player[id].vy += speed * sin(g_player[id].r * 2 * M_PI);
}

static void roteplayer(int id, float speed) {
	g_player[id].vr += speed;
	if(fabs(g_player[id].vr) > MAX_ROTATE)
		g_player[id].vr = copysignf(MAX_ROTATE, g_player[id].vr);
}

static void fireplayer(int id) {
	int j = freebullet();
	if(j < 0)
		return;

	if(g_player[id].shoot < PLAYER_SHOOT)
		return;

	g_player[id].shoot = 0;

	if(svmode) {
		float vx = BULL_SPEED * cos(g_player[id].r * 2 * M_PI);
		float vy = BULL_SPEED * sin(g_player[id].r * 2 * M_PI);
		g_bullet_set(j, id, true, g_player[id].x, g_player[id].y, vx, vy, 0);
	}
}

static void checkspacebound(float * a) {
	float x = *a;
	if(x < -1 || x > 1)
		x = copysign(fmodf(x, 1) + 1, -1 * x);
	*a = x;
}

static float length(float x1, float y1, float x2, float y2) {
	return sqrtf(powf(x1 - x2, 2) + powf(y1 - y2, 2));
}

static bool collide(float x1, float y1, float r1, float x2, float y2, float r2) {
	return ((length(x1, y1, x2, y2) - r1 - r2) <= 0);
}

static void gravity(float * vx, float * vy, float x, float y) {
	*vx += copysign(G * M_STAR * M_SHIP / length(0, 0, x, y), x * -1);
	*vy += copysign(G * M_STAR * M_SHIP / length(0, 0, x, y), y * -1);
}

void g_player_does(unsigned int id, DoesBits code) {
	assert(id < MAX_PLAYERS);

	if(code.up)
		moveplayer(id, SPEED);
	if(code.down)
		moveplayer(id, -SPEED);
	if(code.left)
		roteplayer(id, -ROTATE);
	if(code.right)
		roteplayer(id, ROTATE);
	if(code.fire)
		fireplayer(id);
}

void g_update() {
	for(int i = 0; i < MAX_PLAYERS; i++) {
		if(g_player[i].live) {
			g_player[i].updated = true;
			g_player[i].x += g_player[i].vx;
			g_player[i].y += g_player[i].vy;
			g_player[i].r += g_player[i].vr;

			gravity(&g_player[i].vx, &g_player[i].vy, g_player[i].x, g_player[i].y);

			checkspacebound(&g_player[i].x);
			checkspacebound(&g_player[i].y);

			++g_player[i].shoot;
			if(g_player[i].shoot > PLAYER_SHOOT)
				g_player[i].shoot = PLAYER_SHOOT;

			if(collide(g_player[i].x, g_player[i].y, PLAYER_SIZE, 0, 0, STAR_SIZE))
				g_player[i].live = false;
		}
	}

	for(int i = 0; i < MAX_BULLETS; i++) {
		if(g_bullet[i].live) {
			g_bullet[i].updated = true;
			g_bullet[i].tick += 1;
			g_bullet[i].x += g_bullet[i].vx;
			g_bullet[i].y += g_bullet[i].vy;

			checkspacebound(&g_bullet[i].x);
			checkspacebound(&g_bullet[i].y);

			gravity(&g_bullet[i].vx, &g_bullet[i].vy, g_bullet[i].x, g_bullet[i].y);

			for(int j = 0; j < MAX_PLAYERS; j++)
				if(g_player[j].live)
					if(collide(g_bullet[i].x, g_bullet[i].y, 0.0001, g_player[j].x, g_player[j].y, PLAYER_SIZE))
						if(j != g_bullet[i].owner)
							g_player[j].live = false;

			if(g_bullet[i].tick > BULLET_TIME)
				g_bullet[i].live = false;
		}
	}
}

void g_init(bool server_mode) {
	svmode = server_mode;
	// TODO memset & co
}