#include "lodepng.h"
#include <SDL2/SDL.h>
#include <cmath>
#include <cstdint>
#include <cstdlib>
#include <cstdio>
#include <array>
#include <utility>


constexpr int cellWidth = 8, cellHeight = 16;

enum class EColour : unsigned char
{
	BLACK, BLUE, GREEN, CYAN, RED, MEGENTA, BROWN, LTGREY,
	DKGREY, LTBLUE, LTGREEN, LTCYAN, LTRED, LTMEGENTA, YELLOW, WHITE
};

static constexpr std::array<SDL_Colour, 16> colourTable =
{
	/* EColour::BLACK     */ SDL_Colour{ 0x00, 0x00, 0x00, 0xFF },
	/* EColour::BLUE      */ SDL_Colour{ 0x00, 0x00, 0xAA, 0xFF },
	/* EColour::GREEN     */ SDL_Colour{ 0x00, 0xAA, 0x00, 0xFF },
	/* EColour::CYAN      */ SDL_Colour{ 0x00, 0xAA, 0xAA, 0xFF },
	/* EColour::RED       */ SDL_Colour{ 0xAA, 0x00, 0x00, 0xFF },
	/* EColour::MEGENTA   */ SDL_Colour{ 0xAA, 0x00, 0xAA, 0xFF },
	/* EColour::BROWN     */ SDL_Colour{ 0xAA, 0x55, 0x00, 0xFF },
	/* EColour::LTGREY    */ SDL_Colour{ 0xAA, 0xAA, 0xAA, 0xFF },
	/* EColour::DKGREY    */ SDL_Colour{ 0x55, 0x55, 0x55, 0xFF },
	/* EColour::LTBLUE    */ SDL_Colour{ 0x55, 0x55, 0xFF, 0xFF },
	/* EColour::LTGREEN   */ SDL_Colour{ 0x55, 0xFF, 0x55, 0xFF },
	/* EColour::LTCYAN    */ SDL_Colour{ 0x55, 0xFF, 0xFF, 0xFF },
	/* EColour::LTRED     */ SDL_Colour{ 0xFF, 0x55, 0x55, 0xFF },
	/* EColour::LTMEGENTA */ SDL_Colour{ 0xFF, 0x55, 0xFF, 0xFF },
	/* EColour::YELLOW    */ SDL_Colour{ 0xFF, 0xFF, 0x55, 0xFF },
	/* EColour::WHITE     */ SDL_Colour{ 0xFF, 0xFF, 0xFF, 0xFF }
};

struct Cell
{
	unsigned char character;
	EColour bgColour, fgColour;
	bool blinking;
};

template <typename T> constexpr T clamp(T x, T min, T max)
{
	return x < min ? min : (x > max ? max : x);
}

class Application final
{
	int argc;
	const char** argv;

	SDL_Window* window;
	SDL_Renderer* renderer;
	SDL_Texture* codepage;
	SDL_TimerID blinkTimer;

	bool needRepaint;

	bool mouseLeft, mouseRight;
	int mousePrevX, mousePrevY, mouseX, mouseY;
	bool mouseInWindow;

	bool drawing, blinkState;

	std::array<Cell, 2000> display;

	int create();
	int handleEvent(const SDL_Event& event) noexcept;
	int update();
	int repaint();

	static Uint32 timerCallback(Uint32 interval, void* param);

	inline void damage() noexcept { needRepaint = true; }
	SDL_Texture* loadTexture(const std::string& path);

public:
	Application(int argc, const char* argv[]);
	~Application();

	int run();
};

Uint32 Application::timerCallback(Uint32 interval, void* param)
{
	SDL_Event event =
	{
		.type = SDL_USEREVENT,
		.user =
		{
			.type      = SDL_USEREVENT,
			.timestamp = SDL_GetTicks(),
			.code      = 0,
			.data1     = nullptr,
			.data2     = nullptr
		}
	};
	SDL_PushEvent(&event);
	return interval;
}


Application::Application(int aArgc, const char* aArgv[]) :
	argc(aArgc), argv(aArgv),
	window(nullptr), renderer(nullptr), codepage(nullptr), blinkTimer(0),
	needRepaint(true),
	mouseLeft(false), mouseRight(false),
	mousePrevX(0), mousePrevY(0), mouseX(0), mouseY(0),
	mouseInWindow(false),
	drawing(false), blinkState(true) {}

Application::~Application()
{
	SDL_RemoveTimer(blinkTimer);
	SDL_DestroyTexture(codepage);
	SDL_DestroyRenderer(renderer);
	SDL_DestroyWindow(window);
	SDL_Quit();
}

SDL_Texture* Application::loadTexture(const std::string& path)
{
	unsigned pixelWidth, pixelHeight;
	std::vector<unsigned char> pixels;
	if (lodepng::decode(pixels, pixelWidth, pixelHeight, path, LCT_RGBA, 8) != 0)
	{
		return nullptr;
	}

	constexpr Uint32 format = SDL_PIXELFORMAT_RGBA8888;
	constexpr int access = SDL_TEXTUREACCESS_STATIC;
	const int textureWidth = static_cast<int>(pixelWidth), textureHeight = static_cast<int>(pixelHeight);
	SDL_Texture* texture = SDL_CreateTexture(renderer, format, access, textureWidth, textureHeight);
	if (texture == nullptr)
	{
		return nullptr;
	}

	if (SDL_UpdateTexture(texture, nullptr, pixels.data(), 4 * static_cast<int>(pixelWidth)) != 0 ||
		SDL_SetTextureBlendMode(texture, SDL_BLENDMODE_BLEND) != 0)
	{
		SDL_DestroyTexture(texture);
	}

	return texture;
}


int Application::create()
{
	if (SDL_Init(SDL_INIT_VIDEO) < 0)
	{
		return -1;
	}

	constexpr int screenWidth = cellWidth * 80;
	constexpr int screenHeight = cellHeight * 25;

	constexpr Uint32 winFlags = SDL_WINDOW_ALLOW_HIGHDPI | SDL_WINDOW_RESIZABLE;
	if (SDL_CreateWindowAndRenderer(screenWidth * 2, screenHeight * 2, winFlags, &window, &renderer) < 0)
	{
		return -1;
	}

	SDL_SetWindowTitle(window, "EnDOOMed");
	SDL_RenderSetLogicalSize(renderer, screenWidth, screenHeight);

	if ((codepage = Application::loadTexture("codepage.png")) == nullptr)
	{
		return -1;
	}

	std::memset(display.data(), 0, sizeof(Cell) * display.size());

	FILE* file = fopen("ENDOOM.bin", "rb");
	if (file == nullptr)
	{
		return -1;
	}

	for (Cell& currentCharacter : display)
	{
		unsigned char character[2];
		fread(character, sizeof(unsigned char), 2, file);

		currentCharacter =
		{
			.character = character[0],
			.bgColour = EColour((character[1] & 0x70) >> 4),
			.fgColour = EColour( character[1] & 0x0F),
			.blinking =         (character[1] & (0x80 > 1)) ? true : false
		};
	}

	fclose(file);

	blinkTimer = SDL_AddTimer(400, Application::timerCallback, nullptr);
	if (blinkTimer == 0)
	{
		return -1;
	}

	return 0;
}

int Application::handleEvent(const SDL_Event& event) noexcept
{
	switch (event.type)
	{
	case SDL_QUIT:
		return 1;
	case SDL_USEREVENT:
		blinkState = !blinkState;
		damage();
		return 0;
	case SDL_MOUSEBUTTONDOWN:
		switch (event.button.button)
		{
		case SDL_BUTTON_LEFT:
			mouseLeft = true;
			break;
		case SDL_BUTTON_RIGHT:
			mouseRight = true;
			break;
		}
		return 0;
	case SDL_MOUSEBUTTONUP:
		switch (event.button.button)
		{
		case SDL_BUTTON_LEFT:
			mouseLeft = false;
			break;
		case SDL_BUTTON_RIGHT:
			mouseRight = false;
			break;
		}
		return 0;
	case SDL_MOUSEMOTION:
		mouseX = event.motion.x;
		mouseY = event.motion.y;
		return 0;
	case SDL_WINDOWEVENT:
		switch (event.window.event)
		{
		case SDL_WINDOWEVENT_LEAVE:
			mouseInWindow = false;
			break;
		case SDL_WINDOWEVENT_ENTER:
			mouseInWindow = true;
			break;
		};
		return 0;
	default:
		return 0;
	}
}

int Application::update()
{
	Cell leftBrush =
	{
		.character = 219,
		.bgColour = EColour::BLACK,
		.fgColour = EColour::LTGREY,
		.blinking = false
	};
	Cell rightBrush =
	{
		.character = ' ',
		.bgColour = EColour::BLACK,
		.fgColour = EColour::LTGREY,
		.blinking = false
	};

	if (mouseInWindow && (mouseLeft || mouseRight))
	{
		if (!drawing)
		{
			mousePrevX = mouseX;
			mousePrevY = mouseY;
			drawing = true;
		}
		int fromX = clamp(mouseX / cellWidth, 0, 79);
		int fromY = clamp(mouseY / cellHeight, 0, 24);
		int toX = clamp(mousePrevX / cellWidth, 0, 79);
		int toY = clamp(mousePrevY / cellHeight, 0, 24);

		auto srcChar = mouseLeft ? leftBrush : rightBrush;
		if (toX == fromX && toY == fromY)
		{
			display[toX + toY * 80] = srcChar;
		}
		else
		{
			bool steep = std::abs(toY - fromY) > std::abs(toX - fromX);
			if (steep)
			{
				std::swap(fromY, fromX);
				std::swap(toY, toX);
			}
			if (fromX > toX)
			{
				std::swap(toX, fromX);
				std::swap(toY, fromY);
			}

			int deltaX = toX - fromX;
			int deltaY = std::abs(toY - fromY);
			int error = deltaX / 2;
			int y = fromY;
			int yStep = (fromY < toY) ? 1 : -1;
			for (int x = fromX; x <= toX; ++x)
			{
				int idx = steep
					? y + x * 80
					: x + y * 80;
				display[idx] = srcChar;

				error -= deltaY;
				if (error < 0)
				{
					y += yStep;
					error += deltaX;
				}
			}
		}

		mousePrevX = mouseX;
		mousePrevY = mouseY;

		damage();
	}
	else if (drawing && !mouseLeft && !mouseRight)
	{
		drawing = false;
	}
	return 0;
}

int Application::repaint()
{
	SDL_SetRenderDrawColor(renderer, 48, 48, 48, 255);
	SDL_RenderClear(renderer);

	SDL_Rect src, dst;
	src.w = cellWidth;
	src.h = cellHeight;
	dst.w = cellWidth;
	dst.h = cellHeight;

	int x = 0, y = 0;
	for (const auto& currentCharacter : display)
	{
		auto currentBgColour = colourTable[static_cast<unsigned char>(currentCharacter.bgColour)];
		auto currentFgColour = colourTable[static_cast<unsigned char>(currentCharacter.fgColour)];

		src.x = (currentCharacter.character % 32) * cellWidth;
		src.y = (currentCharacter.character / 32) * cellHeight;
		dst.x = x * cellWidth;
		dst.y = y * cellHeight;

		SDL_SetRenderDrawColor(renderer, currentBgColour.r, currentBgColour.g, currentBgColour.b, currentBgColour.a);
		SDL_RenderFillRect(renderer, &dst);
		SDL_SetRenderDrawColor(renderer, 0, 0, 0, currentFgColour.a);

		if (blinkState || !currentCharacter.blinking)
		{
			SDL_SetTextureColorMod(codepage, currentFgColour.r, currentFgColour.g, currentFgColour.b);
			SDL_RenderCopy(renderer, codepage, &src, &dst);
		}

		if (++x >= 80)
		{
			x = 0;
			++y;
		}
	}

	SDL_RenderPresent(renderer);
	return 0;
}

int Application::run()
{
	int res = create();
	while (res == 0)
	{
		SDL_Event event;
		if (SDL_WaitEvent(&event))
		{
			do
			{
				res = handleEvent(event);
			} while (res == 0 && SDL_PollEvent(&event) > 0);
		}
		if (res == 0)
		{
			res = update();
		}
		if (res == 0 && needRepaint)
		{
			res = repaint();
			needRepaint = false;
		}
	}
	return res < 0 ? 1 : 0;
};


int main(int argc, char* argv[])
{
	Application app(argc, const_cast<const char**>(argv));
	return app.run();
}