#include <SDL2/SDL.h>
#include <stdio.h>
#include <math.h>

/* 
Copyright (c) 2020 Devine Lu Linvega

Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE.
*/

/* 

cc -std=c89 -DDEBUG -Wall -Wno-unknown-pragmas -Wpedantic -Wshadow -Wextra -Werror=implicit-int -Werror=incompatible-pointer-types -Werror=int-conversion -Wvla -g -Og -fsanitize=address -fsanitize=undefined main.c -L/usr/local/lib -lSDL2 -lm -o main

*/

typedef unsigned char Uint8;
typedef signed char Sint8;
typedef unsigned short Uint16;
typedef signed short Sint16;

#define PI 3.14159265358979323846

Uint16 WIDTH = 320;
Uint16 HEIGHT = 240;
Uint16 FPS = 30, ZOOM = 2;

typedef struct {
	int x, y;
} Point2d;

SDL_Window *gWindow;
SDL_Renderer *gRenderer;
SDL_Texture *gTexture;
Uint32 *pixels;

#pragma mark - HELPERS

Point2d
Pt2d(int x, int y)
{
	Point2d p;
	p.x = x;
	p.y = y;
	return p;
}

Point2d
PtCircle2d(Point2d c, double r, double angle)
{
	return Pt2d(
		c.x + r * cos(angle),
		c.y + r * sin(angle));
}

double
distance(Point2d a, Point2d b)
{
	return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

double
angle(Point2d a, Point2d b)
{
	return atan2(b.y - a.y, b.x - a.x);
}

#pragma mark - DRAW

void
clear(Uint32 *dst)
{
	int v, h;
	for(v = 0; v < HEIGHT; v++)
		for(h = 0; h < WIDTH; h++)
			dst[v * WIDTH + h] = 0xFFFFFF;
}

void
pixel(Point2d p, Uint32 color)
{
	if(p.x >= 0 && p.x < WIDTH - 8 && p.y >= 0 && p.y < HEIGHT - 8)
		pixels[(Uint32)(p.y * WIDTH + p.x)] = color;
}

void
drawCircle(int xc, int yc, int x, int y, Uint32 color)
{
	pixel(Pt2d(xc + x, yc + y), color);
	pixel(Pt2d(xc - x, yc + y), color);
	pixel(Pt2d(xc + x, yc - y), color);
	pixel(Pt2d(xc - x, yc - y), color);
	pixel(Pt2d(xc + y, yc + x), color);
	pixel(Pt2d(xc - y, yc + x), color);
	pixel(Pt2d(xc + y, yc - x), color);
	pixel(Pt2d(xc - y, yc - x), color);
}

void
circle(int xc, int yc, int r, Uint32 color)
{
	int x = 0, y = r;
	int d = 3 - 2 * r;
	drawCircle(xc, yc, x, y, color);
	while(y >= x) {
		x++;
		if(d > 0) {
			y--;
			d = d + 4 * (x - y) + 10;
		} else
			d = d + 4 * x + 6;
		drawCircle(xc, yc, x, y, color);
	}
}

void
line(Point2d a, Point2d b, Uint32 color)
{
	int dx = abs(b.x - a.x), sx = a.x < b.x ? 1 : -1;
	int dy = -abs(b.y - a.y), sy = a.y < b.y ? 1 : -1;
	int err = dx + dy, e2;
	for(;;) {
		pixel(a, color);
		if((int)a.x == (int)b.x && (int)a.y == (int)b.y)
			break;
		e2 = 2 * err;
		if(e2 >= dy) {
			err += dy;
			a.x += sx;
		}
		if(e2 <= dx) {
			err += dx;
			a.y += sy;
		}
	}
}

void
mark(Point2d p, double r, Uint32 color)
{
	line(Pt2d(p.x - r, p.y), Pt2d(p.x, p.y - r), color);
	line(Pt2d(p.x, p.y - r), Pt2d(p.x + r, p.y), color);
	line(Pt2d(p.x + r, p.y), Pt2d(p.x, p.y + r), color);
	line(Pt2d(p.x, p.y + r), Pt2d(p.x - r, p.y), color);
}

void
redraw(Uint32 *dst)
{
	Point2d pta = Pt2d(WIDTH / 2, HEIGHT / 2);
	Point2d ptb = Pt2d(pta.x + 53, pta.y - 64);
	Point2d ptc = Pt2d(ptb.x, pta.y);
	Point2d ptd = PtCircle2d(pta, distance(pta, ptb) / 2, angle(ptb, pta) * 2);

	line(pta, ptb, 0);
	line(ptb, ptc, 0xFF0000);
	line(ptc, pta, 0x72DEC2);
	line(ptb, ptd, 0);
	mark(pta, 2, 0);
	mark(ptb, 2, 0);
	mark(ptc, 2, 0);
	mark(ptd, 2, 0);

	circle(pta.x, pta.y, distance(pta, ptb), 0);
	circle(ptb.x, ptb.y, distance(pta, ptb) / 2, 0);
	circle(ptd.x, ptd.y, distance(pta, ptb) / 2, 0);

	SDL_UpdateTexture(gTexture, NULL, dst, WIDTH * sizeof(Uint32));
	SDL_RenderClear(gRenderer);
	SDL_RenderCopy(gRenderer, gTexture, NULL, NULL);
	SDL_RenderPresent(gRenderer);
}

#pragma mark - OPTIONS

int
error(char *msg, const char *err)
{
	printf("Error %s: %s\n", msg, err);
	return 0;
}

void
quit(void)
{
	free(pixels);
	SDL_DestroyTexture(gTexture);
	gTexture = NULL;
	SDL_DestroyRenderer(gRenderer);
	gRenderer = NULL;
	SDL_DestroyWindow(gWindow);
	gWindow = NULL;
	SDL_Quit();
	exit(0);
}

#pragma mark - TRIGGERS

int
init(void)
{
	if(SDL_Init(SDL_INIT_VIDEO) < 0)
		return error("Init", SDL_GetError());
	gWindow = SDL_CreateWindow("Nasu",
		SDL_WINDOWPOS_UNDEFINED,
		SDL_WINDOWPOS_UNDEFINED,
		WIDTH * ZOOM,
		HEIGHT * ZOOM,
		SDL_WINDOW_SHOWN);
	if(gWindow == NULL)
		return error("Window", SDL_GetError());
	gRenderer = SDL_CreateRenderer(gWindow, -1, 0);
	if(gRenderer == NULL)
		return error("Renderer", SDL_GetError());
	gTexture = SDL_CreateTexture(gRenderer,
		SDL_PIXELFORMAT_ARGB8888,
		SDL_TEXTUREACCESS_STATIC,
		WIDTH,
		HEIGHT);
	if(gTexture == NULL)
		return error("Texture", SDL_GetError());
	pixels = (Uint32 *)malloc(WIDTH * HEIGHT * sizeof(Uint32));
	if(pixels == NULL)
		return error("Pixels", "Failed to allocate memory");
	clear(pixels);
	return 1;
}

int
main(int argc, char **argv)
{
	int ticknext = 0;
	if(!init())
		return error("Init", "Failure");
	redraw(pixels);
	while(1) {
		int tick = SDL_GetTicks();
		SDL_Event event;
		if(tick < ticknext)
			SDL_Delay(ticknext - tick);
		ticknext = tick + (1000 / FPS);
		while(SDL_PollEvent(&event) != 0) {
			switch(event.type) {
			case SDL_QUIT: quit(); break;
			case SDL_WINDOWEVENT:
				if(event.window.event == SDL_WINDOWEVENT_EXPOSED)
					redraw(pixels);
				break;
			}
		}
	}
	quit();
	return 0;
}