#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

#include <SDL3/SDL.h>

#define BULLET_SIZE  2
#define ENTITY_SIZE 16

static void render(void);
static void update(float delta);
static void process_events(void);

typedef struct {
	float x, y;
} Player;

typedef struct {
	float x, y;
	float vx, vy;
	bool active;
} Ghost;

typedef struct {
	float x, y;
	float vx, vy;
	float time;
	bool active;
} Bullet;

static SDL_Window *window;
static SDL_Renderer *renderer;
static bool running;
static Uint64 old_ticks, new_ticks;

static Player player;
static Ghost ghosts[1024];
static Bullet bullet[1024];

static float camera_x, camera_y;

static bool shot;
static int shotx, shoty;

int
main()
{
	if(!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO)) {
		fprintf(stderr, "SDL_Init(): %s\n", SDL_GetError());
		return 1;
	}

	if(!SDL_CreateWindowAndRenderer("window", 800, 600, SDL_WINDOW_OPENGL, &window, &renderer)) {
		fprintf(stderr, "SDL_CreateWindowAndRenderer: %s\n", SDL_GetError());
		return -1;
	}

	for(int i = 0; i < 10; i++) {
		ghosts[i].active = 1;
		ghosts[i].x = rand() % 800;
		ghosts[i].y = rand() % 600;
	}

	running = true;
	old_ticks = SDL_GetTicksNS();
	while(running) {
		double delta;
		process_events();

		new_ticks = SDL_GetTicksNS();
	    delta = (new_ticks - old_ticks) / 1000000000.0;
		old_ticks = new_ticks;
		update(delta);

		render();
		SDL_RenderPresent(renderer);
	}
	
	SDL_DestroyWindow(window);
	SDL_Quit();
	return 0;
}

void
render(void)
{
	{
		float plx, ply, minx, miny, maxx, maxy;

		plx = player.x - camera_x;
		ply = player.y - camera_y;

		minx = plx - 80;
		miny = ply - 80;
		maxx = plx + 80;
		maxy = ply + 80;
		
		if(minx < 0)
			camera_x += minx;

		if(miny < 0)
			camera_y += miny;

		if(maxx > 800)
			camera_x += (maxx - 800);

		if(maxy > 600)
			camera_y += (maxy - 600);
	}

	SDL_SetRenderDrawColor(renderer, 0x00, 0x00, 0x00, 0xFF);
	SDL_RenderClear(renderer);

	SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0xFF, 0xFF);
	SDL_RenderRect(renderer, &(SDL_FRect){
		.x = player.x - ENTITY_SIZE - camera_x,
		.y = player.y - ENTITY_SIZE - camera_y, 
		.w = ENTITY_SIZE * 2.0,
		.h = ENTITY_SIZE * 2.0
	});

	for(int i = 0; i < 1024; i++) {
		if(!ghosts[i].active)
			continue;

		SDL_SetRenderDrawColor(renderer, 0xAA, 0xAA, 0xAA, 0xFF);
		SDL_RenderRect(renderer, &(SDL_FRect){
			.x = ghosts[i].x - ENTITY_SIZE - camera_x,
			.y = ghosts[i].y - ENTITY_SIZE - camera_y, 
			.w = ENTITY_SIZE * 2.0,
			.h = ENTITY_SIZE * 2.0
		});
	}

	for(int i = 0; i < 1024; i++) {
		if(!bullet[i].active)
			continue;

		SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0x00, 0xFF);
		SDL_RenderRect(renderer, &(SDL_FRect){
			.x = bullet[i].x - BULLET_SIZE - camera_x,
			.y = bullet[i].y - BULLET_SIZE - camera_y, 
			.w = BULLET_SIZE * 2.0,
			.h = BULLET_SIZE * 2.0
		});
	}
}

void
update(float delta)
{
#	define SPEED 100
	const _Bool *kstate = SDL_GetKeyboardState(NULL);

	if(kstate[SDL_SCANCODE_W])
		player.y -= delta * SPEED;
	if(kstate[SDL_SCANCODE_A])
		player.x -= delta * SPEED;
	if(kstate[SDL_SCANCODE_S])
		player.y += delta * SPEED;
	if(kstate[SDL_SCANCODE_D])
		player.x += delta * SPEED;

	if(shot) {
		shot = false;
		int i;

		float dx = shotx - player.x;
		float dy = shoty - player.y;
		float dd = sqrtf(dx * dx + dy * dy);

		dx /= dd; 
		dy /= dd;
	
		for(i = 0; i < 1024 && bullet[i].active; i++)
			;

		if(i < 1024) {
			bullet[i].time = 0.5;
			bullet[i].vx = dx * SPEED * 5.0;
			bullet[i].vy = dy * SPEED * 5.0;
			bullet[i].x = player.x;
			bullet[i].y = player.y;
			bullet[i].active = true;
		}
	}

	for(int i = 0; i < 1024; i++) {
		if(!bullet[i].active)
			continue;

		for(int j = 0; j < 1024; j++) {
			if(!ghosts[j].active)
				continue;
 
			float dx = bullet[i].x - ghosts[j].x;
			float dy = bullet[i].y - ghosts[j].y;

			float hs = (ENTITY_SIZE + BULLET_SIZE);

			float minx = dx - hs;
			float miny = dy - hs;
			float maxx = dx + hs;
			float maxy = dy + hs;

			bool contains_x = minx < 0 && maxx > 0;
			bool contains_y = miny < 0 && maxy > 0;

			if(contains_x && contains_y) {
				ghosts[j].active = false;
				bullet[i].active = false;
			}
		}
	}

	for(int i = 0; i < 1024; i++) {
		if(!ghosts[i].active)
			continue;

		float vx = 0, vy = 0;

		float dx = player.x - ghosts[i].x;
		float dy = player.y - ghosts[i].y;
		float dd = sqrtf(dx * dx + dy * dy);

		dx /= dd;
		dy /= dd;

		vx += dx * SPEED;
		vy += dy * SPEED;

		for(int j = 0; j < 1024; j++) {
			if(!ghosts[j].active || i == j)
				continue;

			float dx = ghosts[j].x - ghosts[i].x;
			float dy = ghosts[j].y - ghosts[i].y;
			float dd = sqrtf(dx * dx + dy * dy);

			dx /= dd;
			dy /= dd;

			if(dd < 40) {
				vx -= dx * 100;
				vy -= dy * 100;
			}
		}

		ghosts[i].vx = vx;
		ghosts[i].vy = vy;
	}

	for(int i = 0; i < 1024; i++) {
		if(!ghosts[i].active)
			continue;
		
		ghosts[i].x += ghosts[i].vx * delta;
		ghosts[i].y += ghosts[i].vy * delta;
	}

	for(int i = 0; i < 1024; i++) {
		if(!bullet[i].active)
			continue;

		bullet[i].time -= delta;
		if(bullet[i].time <= 0.0) {
			bullet[i].active = false;
			continue;
		}

		bullet[i].x += delta * bullet[i].vx;
		bullet[i].y += delta * bullet[i].vy;
	}
}
void
process_events()
{
	SDL_Event event;

	while(SDL_PollEvent(&event)) {
		switch(event.type) {
			case SDL_EVENT_QUIT:
				running = false;
				break;
			case SDL_EVENT_MOUSE_BUTTON_DOWN:
				shot = true;
				shotx = event.button.x + camera_x;
				shoty = event.button.y + camera_y;
				break;
		}
	}
}