#include "imgui.h"
#include "imgui_impl_sdl.h"

static double g_Time = 0.0f;
static bool g_MousePressed[3] = {false, false, false};
static float g_MouseWheel = 0.0f;
static GLuint g_FontTexture = 0;

void ImGui_ImplSdl_RenderDrawLists(ImDrawData* draw_data) {
	ImGuiIO& io = ImGui::GetIO();
	
	int fb_width = (int)(io.DisplaySize.x * io.DisplayFramebufferScale.x);
	int fb_height = (int)(io.DisplaySize.y * io.DisplayFramebufferScale.y);
	
	if (fb_width == 0 || fb_height == 0)
		return;
	
	draw_data->ScaleClipRects(io.DisplayFramebufferScale);

	GLint last_texture;
	glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
	
	GLint last_viewport[4];
	glGetIntegerv(GL_VIEWPORT, last_viewport);
	
	GLint last_scissor_box[4];
	glGetIntegerv(GL_SCISSOR_BOX, last_scissor_box);

	glPushAttrib(GL_ENABLE_BIT | GL_COLOR_BUFFER_BIT | GL_TRANSFORM_BIT);
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glDisable(GL_CULL_FACE);
	glDisable(GL_DEPTH_TEST);
	glEnable(GL_SCISSOR_TEST);
	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_TEXTURE_COORD_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY);
	glEnable(GL_TEXTURE_2D);
	
	glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
	glMatrixMode(GL_PROJECTION);
	glPushMatrix();
	glLoadIdentity();
	glOrtho(0.0f, io.DisplaySize.x, io.DisplaySize.y, 0.0f, -1.0f, +1.0f);
	glMatrixMode(GL_MODELVIEW);
	glPushMatrix();
	glLoadIdentity();

	#define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))
	for (int n = 0; n < draw_data->CmdListsCount; n++) {
		const ImDrawList* cmd_list = draw_data->CmdLists[n];
		const ImDrawVert* vtx_buffer = cmd_list->VtxBuffer.Data;
		const ImDrawIdx* idx_buffer = cmd_list->IdxBuffer.Data;
		glVertexPointer(2, GL_FLOAT, sizeof(ImDrawVert), (const GLvoid*)((const char*)vtx_buffer + OFFSETOF(ImDrawVert, pos)));
		glTexCoordPointer(2, GL_FLOAT, sizeof(ImDrawVert), (const GLvoid*)((const char*)vtx_buffer + OFFSETOF(ImDrawVert, uv)));
		glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(ImDrawVert), (const GLvoid*)((const char*)vtx_buffer + OFFSETOF(ImDrawVert, col)));

		for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++) {
			const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
			if (pcmd->UserCallback) {
				pcmd->UserCallback(cmd_list, pcmd);
			} else {
				glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
				glScissor((int)pcmd->ClipRect.x, (int)(fb_height - pcmd->ClipRect.w), (int)(pcmd->ClipRect.z - pcmd->ClipRect.x), (int)(pcmd->ClipRect.w - pcmd->ClipRect.y));
				glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer);
			}
			idx_buffer += pcmd->ElemCount;
		}
	}
	#undef OFFSETOF

	glDisableClientState(GL_COLOR_ARRAY);
	glDisableClientState(GL_TEXTURE_COORD_ARRAY);
	glDisableClientState(GL_VERTEX_ARRAY);
	glBindTexture(GL_TEXTURE_2D, (GLuint)last_texture);
	glMatrixMode(GL_MODELVIEW);
	glPopMatrix();
	glMatrixMode(GL_PROJECTION);
	glPopMatrix();
	glPopAttrib();
	glViewport(last_viewport[0], last_viewport[1], (GLsizei)last_viewport[2], (GLsizei)last_viewport[3]);
	glScissor(last_scissor_box[0], last_scissor_box[1], (GLsizei)last_scissor_box[2], (GLsizei)last_scissor_box[3]);
}

static const char* ImGui_ImplSdl_GetClipboardText(void*) {
	return SDL_GetClipboardText();
}

static void ImGui_ImplSdl_SetClipboardText(void*, const char* text) {
	SDL_SetClipboardText(text);
}

bool ImGui_ImplSdl_ProcessEvent(SDL_Event* event) {
	ImGuiIO& io = ImGui::GetIO();

	switch (event->type) {
		case SDL_MOUSEWHEEL:
		{
			if (!io.WantCaptureMouse)
				return false;

			if (event->wheel.y > 0)
				g_MouseWheel = 1;
			if (event->wheel.y < 0)
				g_MouseWheel = -1;
			return true;
		}
		case SDL_MOUSEBUTTONDOWN:
		{
			if (!io.WantCaptureMouse)
				return false;

			if (event->button.button == SDL_BUTTON_LEFT) g_MousePressed[0] = true;
			if (event->button.button == SDL_BUTTON_RIGHT) g_MousePressed[1] = true;
			if (event->button.button == SDL_BUTTON_MIDDLE) g_MousePressed[2] = true;
			return true;
		}
		case SDL_TEXTINPUT:
		{
			if (!io.WantCaptureKeyboard)
				return false;

			io.AddInputCharactersUTF8(event->text.text);
			return true;
		}
		case SDL_KEYDOWN:
		case SDL_KEYUP:
		{
			if (!io.WantCaptureKeyboard)
				return false;

			int key = event->key.keysym.sym & ~SDLK_SCANCODE_MASK;
			io.KeysDown[key] = (event->type == SDL_KEYDOWN);
			io.KeyShift = ((SDL_GetModState() & KMOD_SHIFT) != 0);
			io.KeyCtrl = ((SDL_GetModState() & KMOD_CTRL) != 0);
			io.KeyAlt = ((SDL_GetModState() & KMOD_ALT) != 0);
			io.KeySuper = ((SDL_GetModState() & KMOD_GUI) != 0);
			return true;
		}
	}

	return false;
}

bool ImGui_ImplSdl_CreateDeviceObjects() {
	ImGuiIO& io = ImGui::GetIO();
	
	unsigned char* pixels;
	int width, height;
	io.Fonts->GetTexDataAsAlpha8(&pixels, &width, &height);

	GLint last_texture;
	glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
	glGenTextures(1, &g_FontTexture);
	glBindTexture(GL_TEXTURE_2D, g_FontTexture);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_UNSIGNED_BYTE, pixels);

	io.Fonts->TexID = (void *)(intptr_t)g_FontTexture;

	glBindTexture(GL_TEXTURE_2D, last_texture);

	return true;
}

void ImGui_ImplSdl_InvalidateDeviceObjects() {
	if (g_FontTexture) {
		glDeleteTextures(1, &g_FontTexture);
		ImGui::GetIO().Fonts->TexID = 0;
		g_FontTexture = 0;
	}
}

bool ImGui_ImplSdl_Init(SDL_Window* window) {
	ImGuiIO& io = ImGui::GetIO();
	io.KeyMap[ImGuiKey_Tab] = SDLK_TAB;
	io.KeyMap[ImGuiKey_LeftArrow] = SDL_SCANCODE_LEFT;
	io.KeyMap[ImGuiKey_RightArrow] = SDL_SCANCODE_RIGHT;
	io.KeyMap[ImGuiKey_UpArrow] = SDL_SCANCODE_UP;
	io.KeyMap[ImGuiKey_DownArrow] = SDL_SCANCODE_DOWN;
	io.KeyMap[ImGuiKey_PageUp] = SDL_SCANCODE_PAGEUP;
	io.KeyMap[ImGuiKey_PageDown] = SDL_SCANCODE_PAGEDOWN;
	io.KeyMap[ImGuiKey_Home] = SDL_SCANCODE_HOME;
	io.KeyMap[ImGuiKey_End] = SDL_SCANCODE_END;
	io.KeyMap[ImGuiKey_Delete] = SDLK_DELETE;
	io.KeyMap[ImGuiKey_Backspace] = SDLK_BACKSPACE;
	io.KeyMap[ImGuiKey_Enter] = SDLK_RETURN;
	io.KeyMap[ImGuiKey_Escape] = SDLK_ESCAPE;
	io.KeyMap[ImGuiKey_A] = SDLK_a;
	io.KeyMap[ImGuiKey_C] = SDLK_c;
	io.KeyMap[ImGuiKey_V] = SDLK_v;
	io.KeyMap[ImGuiKey_X] = SDLK_x;
	io.KeyMap[ImGuiKey_Y] = SDLK_y;
	io.KeyMap[ImGuiKey_Z] = SDLK_z;

	io.RenderDrawListsFn = ImGui_ImplSdl_RenderDrawLists;
	io.SetClipboardTextFn = ImGui_ImplSdl_SetClipboardText;
	io.GetClipboardTextFn = ImGui_ImplSdl_GetClipboardText;
	io.ClipboardUserData = NULL;

	(void)window;
	
	return true;
}

void ImGui_ImplSdl_Shutdown() {
	ImGui_ImplSdl_InvalidateDeviceObjects();
	ImGui::Shutdown();
}

void ImGui_ImplSdl_NewFrame(SDL_Window *window) {
	if (!g_FontTexture)
		ImGui_ImplSdl_CreateDeviceObjects();

	ImGuiIO& io = ImGui::GetIO();

	int w, h, display_w, display_h;

	SDL_GetWindowSize(window, &w, &h);
	SDL_GL_GetDrawableSize(window, &display_w, &display_h);
	
	io.DisplaySize = ImVec2((float)w, (float)h);
	io.DisplayFramebufferScale = ImVec2(w > 0 ? ((float)display_w / w) : 0, h > 0 ? ((float)display_h / h) : 0);

	Uint32	time = SDL_GetTicks();
	double current_time = time / 1000.0;
	io.DeltaTime = g_Time > 0.0 ? (float)(current_time - g_Time) : (float)(1.0f / 60.0f);
	g_Time = current_time;

	if (io.WantCaptureMouse)
	{
		int mx, my;
		Uint32 mouseMask = SDL_GetMouseState(&mx, &my);

		if (SDL_GetWindowFlags(window) & SDL_WINDOW_MOUSE_FOCUS)
			io.MousePos = ImVec2((float)mx, (float)my);
		else
			io.MousePos = ImVec2(-1, -1);

		io.MouseDown[0] = g_MousePressed[0] || (mouseMask & SDL_BUTTON(SDL_BUTTON_LEFT)) != 0;
		io.MouseDown[1] = g_MousePressed[1] || (mouseMask & SDL_BUTTON(SDL_BUTTON_RIGHT)) != 0;
		io.MouseDown[2] = g_MousePressed[2] || (mouseMask & SDL_BUTTON(SDL_BUTTON_MIDDLE)) != 0;
		g_MousePressed[0] = g_MousePressed[1] = g_MousePressed[2] = false;

		io.MouseWheel = g_MouseWheel;
		g_MouseWheel = 0.0f;

		SDL_ShowCursor(io.MouseDrawCursor ? 0: 1);
	}

	ImGui::NewFrame();
}