#ifdef _WIN32 // грубый способ определения; на деле разница не в ОС, а в компиляторe
	#include <SDL.h>
	#include <SDL_image.h>
	#include <SDL_timer.h>
#else
	#include <SDL2/SDL.h>
	#include <SDL2/SDL_image.h>
	#include <SDL2/SDL_timer.h>
#endif
#include <time.h>
#include <math.h>

#define SCALE 	1
#define BOIDNUM 30
#define SPEED	1
#define CRANGE 	30
#define WIDTH	1280
#define HEIGHT 	640
#define PI 		3.1415926535

struct boid { double x, y, dx, dy, th; };
typedef struct vec { float x, y; } vector;
struct boid B[BOIDNUM];
char color[3] = {0, 255, 0};

int init() 
{
	srand(time(NULL));

	for(int i = 0; i<BOIDNUM; i++) {
		B[i].x =  WIDTH/2  + rand() % 128 - 64; 
		B[i].y =  HEIGHT/2 + rand() % 128 - 64;
		B[i].th = rand() / (float)RAND_MAX * (PI/3) - PI/6;
		B[i].dx = SPEED * cos(B[i].th); 
		B[i].dy = SPEED * sin(B[i].th);
		// printf("%f",B[i].th);
	}

	return 0;
}

int processEvents(SDL_Window *window) 
{
	SDL_Event event;

	while(SDL_PollEvent(&event))
	{
		switch(event.type)
		{	
			case SDL_WINDOWEVENT_CLOSE:
				if(window)
				{
					SDL_DestroyWindow(window);
					window = NULL;
					return 1;
				}
				break;
			
			case SDL_KEYDOWN:
				switch(event.key.keysym.sym) {
					case SDLK_ESCAPE:
						return 1;
				}
		}
	}
	return 0;
}

void render(SDL_Renderer *renderer) 
{
	SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255); // фон
	SDL_RenderClear(renderer);

	SDL_Vertex arrow[BOIDNUM][3];
	for(int i = 0; i<BOIDNUM; i++) {
		arrow[i][0].position.x = (B[i].x+7 *cos(B[i].th-PI/2))/SCALE;
		arrow[i][0].position.y = (B[i].y+7 *sin(B[i].th-PI/2))/SCALE;
		arrow[i][1].position.x = (B[i].x+7 *cos(B[i].th+PI/2))/SCALE;
		arrow[i][1].position.y = (B[i].y+7 *sin(B[i].th+PI/2))/SCALE;
		arrow[i][2].position.x = (B[i].x+20*cos(B[i].th))	  /SCALE;
		arrow[i][2].position.y = (B[i].y+20*sin(B[i].th))	  /SCALE;
	
		for(int j = 0; j<3; j++) {
			arrow[i][j].color.r = color[0];
			arrow[i][j].color.g = color[1]+j*25;
			arrow[i][j].color.b = color[2];
			arrow[i][j].color.a = 255;
		}
	SDL_RenderGeometry(renderer, NULL, arrow[i], 3, NULL, 0);
	}

	SDL_RenderPresent(renderer);
}

float geomdist(int i, int j)
{
	return sqrt(pow( B[i].x - B[j].x, 2 ) + pow( B[i].y - B[j].y, 2 ));
}

vector cohesion(int n, int factor) 
{
	vector sum = {0, 0};
	for(int b = 0; b < BOIDNUM; b++) {
		if(geomdist(n, b) > CRANGE) {continue;}
		if(b == n) {continue;}
		sum.x += B[b].x;
		sum.y += B[b].y;
	}

	sum.x /= BOIDNUM - 1;
	sum.y /= BOIDNUM - 1;

	sum.x -= B[n].x;
	sum.y -= B[n].y;
	sum.x /= factor;
	sum.y /= factor;

	return sum;
}

vector separation(int n, float dist, int factor)
{
	vector c = {0, 0};
	c.x = 0;
	c.y = 0;

	for(int b = 0; b < BOIDNUM; b++) {
		if(geomdist(n, b) > CRANGE) {continue;}
		if(b == n) {continue;}
		if(geomdist(n, b) < dist) {
			c.x -= B[b].x - B[n].x;
			c.y -= B[b].y - B[n].y;
		}
	}

	c.x /= factor;
	c.y /= factor;

	return c;
}

vector alignment(int n, int factor)
{
	vector pv = {0, 0};

	for(int b = 0; b < BOIDNUM; b++) {
		if(geomdist(n, b) > CRANGE) {continue;}
		if(b == n) {continue;}
		pv.x += B[b].dx;
		pv.y += B[b].dy;
	}

	pv.x /= BOIDNUM - 1;
	pv.y /= BOIDNUM - 1;

	pv.x -= B[n].dx;
	pv.y -= B[n].dy;
	pv.x /= factor;
	pv.y /= factor;

	return pv;
}

int updatePos(SDL_Renderer *renderer) {
	vector v[3];
	for(int i = 0; i<BOIDNUM; i++) {
		B[i].x += B[i].dx;
		B[i].y += B[i].dy;
		// B[i].th += PI/72;
		if(B[i].x > WIDTH)
			B[i].x -= WIDTH;
			// B[i].dx = 0;
		if(B[i].y > HEIGHT)
			B[i].y -= HEIGHT;
			// B[i].dy = 0;
		if(B[i].x < 0)
			B[i].x += WIDTH;
			// B[i].dx = 0;
		if(B[i].y < 0)
			B[i].y += HEIGHT;
			// B[i].dy = 0;

		v[0] = cohesion(i, 40);
		v[1] = separation(i, 20, 200);
		// v[0].x = 0;
		// v[0].y = 0;
		v[2] = alignment(i, 80);
		// v[2].x = 0;
		// v[2].y = 0;

		for(int j = 0; j<3; j++) {
			if(i == 0) {
				SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
				SDL_RenderDrawLine(renderer, B[i].x, B[i].y, B[i].x-v[j].x, B[i].y - v[j].y);
				SDL_RenderPresent(renderer);
				printf("|vx = %f, vy = %f", v[j].x, v[j].y);
			}

			B[i].dx += v[j].x / 1000;
			B[i].dy += v[j].y / 1000;
		}
		// if (B[i].dx > sqrt(50)) B[i].dx = sqrt(50);
		// if (B[i].dy > sqrt(50)) B[i].dy = sqrt(50);
		B[i].th = acos(B[i].dx / sqrt(B[i].dx * B[i].dx + B[i].dy * B[i].dy) + 0.0001);
		// if(i == 0) {
			// printf("%f|", B[i].th);
		// }
	}
	return 0;
}

int main(int argc, char *argv[]) 
{
	SDL_Window *window = NULL;
	SDL_Renderer *renderer = NULL;

	init();
	SDL_Init(SDL_INIT_VIDEO);

	window = SDL_CreateWindow("Boids",
				  SDL_WINDOWPOS_CENTERED,
				  SDL_WINDOWPOS_CENTERED,
				  WIDTH,
				  HEIGHT,
				  0);
	renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);

	while(1) {
		if(processEvents(window) == 1)
			break;
		render(renderer);
		updatePos(renderer);
		SDL_Delay(10);
	}

	return 0;
}