#pragma once

// Easy window creation in C++.
//
// This header-only library uses SDL; therefore, on a Linux system, you need to
// add something to the effect of the following to your build system:
//   CXXFLAGS += $(shell pkg-config --cflags sdl2)
//   LDFLAGS += $(shell pkg-config --libs sdl2)

#include <string>
#include <vector>
#include <array>
#include <functional>
#include <stdexcept>
#include <SDL.h>


class Window {
public:
	class Opts {
	public:
		inline Opts() = default;

		inline Opts& fullscreen(bool f) { _fullscreen = f; return *this; }
		inline Opts& resizable(bool r) { _resizable = r; return *this; }

		inline bool fullscreen() const { return _fullscreen; }
		inline bool resizable() const { return _resizable; }

	private:
		bool _fullscreen = false;
		bool _resizable = false;
	};

	/// The width and height passed to this function are _suggestions_.
	/// The window manager may decide to use some other size instead, and this
	/// size may also change during execution (especially if resizable, but
	/// perhaps also otherwise).
	inline Window(const std::string &title, int wid_sugg, int hei_sugg);
	inline Window(const std::string &title, int wid_sugg, int hei_sugg, Opts opts);

	inline ~Window();

	class Buffer {
	public:
		using Clr = std::array<uint8_t, 3>;

		inline Buffer(int width, int height, std::vector<uint8_t> &arr);

		inline std::vector<uint8_t>& raw() { return arr; }
		inline int width() { return wid; }
		inline int height() { return hei; }

		inline void clear(Clr clr);
		inline void plot(int x, int y, Clr clr, float alpha = 1.0);
		inline void plotf(float x, float y, Clr clr, float alpha = 1.0);

	private:
		int wid, hei;
		std::vector<uint8_t> &arr;
	};

	enum Action {
		ACT_REDRAW,
		ACT_STOP,
		ACT_OK,
	};

	/// The draw buffer will be of size 3 * width * height; row-major order,
	/// RGB pixels. The draw handler will be invoked if the event handler
	/// returns ACT_REDRAW, but also possibly in other circumstances (e.g.
	/// window resize).
	using DrawHandler = std::function<void(Buffer &buffer)>;
	using EventHandler = std::function<Action(const SDL_Event&)>;

	inline void event_loop(EventHandler eventfunc, DrawHandler drawfunc);

private:
	SDL_Window *win = nullptr;
	std::vector<uint8_t> drawbuf;
	SDL_Surface *surface = nullptr;
	int surf_wid = -1, surf_hei = -1;
};

inline Window::Window(const std::string &title, int wid_sugg, int hei_sugg)
	: Window(title, wid_sugg, hei_sugg, Opts{})
{}

inline Window::Window(const std::string &title, int wid_sugg, int hei_sugg, Opts opts) {
	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
		throw std::runtime_error(std::string{"SDL init error: "} + SDL_GetError());
	}

	Uint32 flags = 0;
	if (opts.fullscreen()) flags |= SDL_WINDOW_FULLSCREEN_DESKTOP;
	if (opts.resizable()) flags |= SDL_WINDOW_RESIZABLE;

	win = SDL_CreateWindow(
		title.data(), SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
		wid_sugg, hei_sugg, flags
	);
	if (!win) {
		throw std::runtime_error(std::string{"SDL window creation error: "} + SDL_GetError());
	}

	SDL_GetWindowSize(win, &surf_wid, &surf_hei);
	drawbuf.resize(3 * surf_wid * surf_hei);
	surface = SDL_CreateRGBSurfaceFrom(
		drawbuf.data(), surf_wid, surf_hei, 24, 3 * surf_wid,
		255, 255 << 8, 255 << 16, 0
	);

	SDL_BlitSurface(surface, nullptr, SDL_GetWindowSurface(win), nullptr);
	SDL_UpdateWindowSurface(win);
}

inline Window::~Window() {
	if (surface) SDL_FreeSurface(surface);
	SDL_DestroyWindow(win);
	SDL_Quit();
}

inline void Window::event_loop(EventHandler eventfunc, DrawHandler drawfunc) {
	SDL_Event e;
	while (true) {
		if (SDL_WaitEvent(&e) == 0) {
			throw std::runtime_error(std::string{"SDL event wait error: "} + SDL_GetError());
		}

		if (e.type == SDL_QUIT) break;

		bool need_redraw = false;
		bool need_refresh = false;

		if (e.type == SDL_WINDOWEVENT) {
			if (e.window.event == SDL_WINDOWEVENT_FOCUS_GAINED) {
				need_refresh = true;
			}
		}

		Action act = eventfunc(e);
		switch (act) {
			case ACT_STOP: return;
			case ACT_REDRAW: need_redraw = true; break;
			case ACT_OK: break;
			default:
				throw std::logic_error("Invalid Action from EventHandler");
		}

		int width, height;
		SDL_GetWindowSize(win, &width, &height);

		if (width != surf_wid || height != surf_hei) {
			SDL_FreeSurface(surface);

			surf_wid = width;
			surf_hei = height;
			drawbuf.resize(3 * surf_wid * surf_hei);
			surface = SDL_CreateRGBSurfaceFrom(
				drawbuf.data(), surf_wid, surf_hei, 24, 3 * surf_wid,
				255, 255 << 8, 255 << 16, 0
			);
			need_redraw = true;
		}

		if (need_redraw) {
			Buffer buffer{width, height, drawbuf};
			drawfunc(buffer);
		}

		if (need_redraw || need_refresh) {
			SDL_Surface *winsurf = SDL_GetWindowSurface(win);
			if (SDL_MUSTLOCK(winsurf)) SDL_LockSurface(winsurf);
			SDL_BlitSurface(surface, nullptr, winsurf, nullptr);
			if (SDL_MUSTLOCK(winsurf)) SDL_UnlockSurface(winsurf);

			SDL_UpdateWindowSurface(win);
		}
	}
}

inline Window::Buffer::Buffer(int width, int height, std::vector<uint8_t> &arr)
	: wid{width}, hei{height}, arr{arr}
{}

inline void Window::Buffer::clear(Clr clr) {
	if (clr[0] == clr[1] && clr[1] == clr[2]) {
		memset(arr.data(), clr[0], 3 * wid * hei);
	} else {
		for (int i = 0; i < wid * hei; i++) {
			for (int j = 0; j < 3; j++) {
				arr[3 * i + j] = clr[j];
			}
		}
	}
}

inline void Window::Buffer::plot(int x, int y, Clr clr, float alpha) {
	for (int i = 0; i < 3; i++) {
		uint8_t &orig = arr[3 * (wid * y + x) + i];
		orig = alpha * clr[i] + (1 - alpha) * orig;
	}
}

inline void Window::Buffer::plotf(float x, float y, Clr clr, float alpha) {
	const int x0 = x, y0 = y;
	const float xal = x - x0, yal = y - y0;
	plot(x0    , y0    , clr, (1 - xal) * (1 - yal) * alpha);
	plot(x0 + 1, y0    , clr, xal       * (1 - yal) * alpha);
	plot(x0    , y0 + 1, clr, (1 - xal) * yal       * alpha);
	plot(x0 + 1, y0 + 1, clr, xal       * yal       * alpha);
}