// ImGui SDL2 binding with OpenGL3
// https://github.com/ocornut/imgui

#include <SDL.h>
#include <SDL_syswm.h>
#include <GL/glew.h>
#include "imgui.h"
#include "imgui_impl_sdlogl3.h"

// Data
static SDL_Window*  g_Window = NULL;
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;
static int          g_ShaderHandle = 0, g_VertHandle = 0, g_FragHandle = 0;
static int          g_AttribLocationTex = 0, g_AttribLocationProjMtx = 0;
static int          g_AttribLocationPosition = 0, g_AttribLocationUV = 0, g_AttribLocationColor = 0;
static unsigned int g_VboHandle = 0, g_VaoHandle = 0, g_ElementsHandle = 0;

// This is the main rendering function that you have to implement and provide to ImGui (via setting up 'RenderDrawListsFn' in the ImGuiIO structure)
// If text or lines are blurry when integrating ImGui in your engine:
// - in your Render function, try translating your projection matrix by (0.5f,0.5f) or (0.375f,0.375f)
void ImGui_ImplSdlOgl3_RenderDrawLists(ImDrawData* draw_data)
{
	// Backup GL state
	GLint last_program; glGetIntegerv(GL_CURRENT_PROGRAM, &last_program);
	GLint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
	GLint last_array_buffer; glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
	GLint last_element_array_buffer; glGetIntegerv(GL_ELEMENT_ARRAY_BUFFER_BINDING, &last_element_array_buffer);
	GLint last_vertex_array; glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
	GLint last_blend_src; glGetIntegerv(GL_BLEND_SRC, &last_blend_src);
	GLint last_blend_dst; glGetIntegerv(GL_BLEND_DST, &last_blend_dst);
	GLint last_blend_equation_rgb; glGetIntegerv(GL_BLEND_EQUATION_RGB, &last_blend_equation_rgb);
	GLint last_blend_equation_alpha; glGetIntegerv(GL_BLEND_EQUATION_ALPHA, &last_blend_equation_alpha);
	GLboolean last_enable_blend = glIsEnabled(GL_BLEND);
	GLboolean last_enable_cull_face = glIsEnabled(GL_CULL_FACE);
	GLboolean last_enable_depth_test = glIsEnabled(GL_DEPTH_TEST);
	GLboolean last_enable_scissor_test = glIsEnabled(GL_SCISSOR_TEST);

	// Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled
	glEnable(GL_BLEND);
	glBlendEquation(GL_FUNC_ADD);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glDisable(GL_CULL_FACE);
	glDisable(GL_DEPTH_TEST);
	glEnable(GL_SCISSOR_TEST);
	glActiveTexture(GL_TEXTURE0);

	// Handle cases of screen coordinates != from framebuffer coordinates (e.g. retina displays)
	ImGuiIO& io = ImGui::GetIO();
	float fb_height = io.DisplaySize.y * io.DisplayFramebufferScale.y;
	draw_data->ScaleClipRects(io.DisplayFramebufferScale);

	// Setup orthographic projection matrix
	const float ortho_projection[4][4] =
	{
		{ 2.0f / io.DisplaySize.x, 0.0f,                   0.0f, 0.0f },
		{ 0.0f,                  2.0f / -io.DisplaySize.y, 0.0f, 0.0f },
		{ 0.0f,                  0.0f,                  -1.0f, 0.0f },
		{ -1.0f,                  1.0f,                   0.0f, 1.0f },
	};
	glUseProgram(g_ShaderHandle);
	glUniform1i(g_AttribLocationTex, 0);
	glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
	glBindVertexArray(g_VaoHandle);

	for (int n = 0; n < draw_data->CmdListsCount; n++)
	{
		const ImDrawList* cmd_list = draw_data->CmdLists[n];
		const ImDrawIdx* idx_buffer_offset = 0;

		glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
		glBufferData(GL_ARRAY_BUFFER, (GLsizeiptr)cmd_list->VtxBuffer.size() * sizeof(ImDrawVert), (GLvoid*)&cmd_list->VtxBuffer.front(), GL_STREAM_DRAW);

		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, (GLsizeiptr)cmd_list->IdxBuffer.size() * sizeof(ImDrawIdx), (GLvoid*)&cmd_list->IdxBuffer.front(), GL_STREAM_DRAW);

		for (const ImDrawCmd* pcmd = cmd_list->CmdBuffer.begin(); pcmd != cmd_list->CmdBuffer.end(); pcmd++)
		{
			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, GL_UNSIGNED_SHORT, idx_buffer_offset);
			}
			idx_buffer_offset += pcmd->ElemCount;
		}
	}

	// Restore modified GL state
	glUseProgram(last_program);
	glBindTexture(GL_TEXTURE_2D, last_texture);
	glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, last_element_array_buffer);
	glBindVertexArray(last_vertex_array);
	glBlendEquationSeparate(last_blend_equation_rgb, last_blend_equation_alpha);
	glBlendFunc(last_blend_src, last_blend_dst);
	if (last_enable_blend) glEnable(GL_BLEND); else glDisable(GL_BLEND);
	if (last_enable_cull_face) glEnable(GL_CULL_FACE); else glDisable(GL_CULL_FACE);
	if (last_enable_depth_test) glEnable(GL_DEPTH_TEST); else glDisable(GL_DEPTH_TEST);
	if (last_enable_scissor_test) glEnable(GL_SCISSOR_TEST); else glDisable(GL_SCISSOR_TEST);
}

static const char* ImGui_ImplSdlOgl3_GetClipboardText()
{
	return SDL_GetClipboardText();
}

static void ImGui_ImplSdlOgl3_SetClipboardText(const char* text)
{
	SDL_SetClipboardText(text);
}

bool ImGui_ImplSdlOgl3_ProcessEvent(SDL_Event* event)
{
	ImGuiIO& io = ImGui::GetIO();
	switch (event->type)
	{
	case SDL_MOUSEWHEEL:
	{
		if (event->wheel.y > 0)
			g_MouseWheel = 1;
		if (event->wheel.y < 0)
			g_MouseWheel = -1;
		return true;
	}
	case SDL_MOUSEBUTTONDOWN:
	{
		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:
	{
		ImGuiIO& io = ImGui::GetIO();
		io.AddInputCharactersUTF8(event->text.text);
		return true;
	}
	case SDL_KEYDOWN:
	case SDL_KEYUP:
	{
		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);
		return true;
	}
	}
	return false;
}

void ImGui_ImplSdlOgl3_CreateFontsTexture()
{
	ImGuiIO& io = ImGui::GetIO();

	// Build texture atlas
	unsigned char* pixels;
	int width, height;
	io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);   // Load as RGBA 32-bits for OpenGL3 demo because it is more likely to be compatible with user's existing shader.

															  // Create OpenGL 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);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);

	// Store our identifier
	io.Fonts->TexID = (void *)(intptr_t)g_FontTexture;

	// Cleanup (don't clear the input data if you want to append new fonts later)
	io.Fonts->ClearInputData();
	io.Fonts->ClearTexData();
}

bool ImGui_ImplSdlOgl3_CreateDeviceObjects()
{
	// Backup GL state
	GLint last_texture, last_array_buffer, last_vertex_array;
	glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
	glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
	glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);

	const GLchar *vertex_shader =
		"#version 330\n"
		"uniform mat4 ProjMtx;\n"
		"in vec2 Position;\n"
		"in vec2 UV;\n"
		"in vec4 Color;\n"
		"out vec2 Frag_UV;\n"
		"out vec4 Frag_Color;\n"
		"void main()\n"
		"{\n"
		"	Frag_UV = UV;\n"
		"	Frag_Color = Color;\n"
		"	gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
		"}\n";

	const GLchar* fragment_shader =
		"#version 330\n"
		"uniform sampler2D Texture;\n"
		"in vec2 Frag_UV;\n"
		"in vec4 Frag_Color;\n"
		"out vec4 Out_Color;\n"
		"void main()\n"
		"{\n"
		"	Out_Color = Frag_Color * texture( Texture, Frag_UV.st);\n"
		"}\n";

	g_ShaderHandle = glCreateProgram();
	g_VertHandle = glCreateShader(GL_VERTEX_SHADER);
	g_FragHandle = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(g_VertHandle, 1, &vertex_shader, 0);
	glShaderSource(g_FragHandle, 1, &fragment_shader, 0);
	glCompileShader(g_VertHandle);
	glCompileShader(g_FragHandle);
	glAttachShader(g_ShaderHandle, g_VertHandle);
	glAttachShader(g_ShaderHandle, g_FragHandle);
	glLinkProgram(g_ShaderHandle);

	g_AttribLocationTex = glGetUniformLocation(g_ShaderHandle, "Texture");
	g_AttribLocationProjMtx = glGetUniformLocation(g_ShaderHandle, "ProjMtx");
	g_AttribLocationPosition = glGetAttribLocation(g_ShaderHandle, "Position");
	g_AttribLocationUV = glGetAttribLocation(g_ShaderHandle, "UV");
	g_AttribLocationColor = glGetAttribLocation(g_ShaderHandle, "Color");

	glGenBuffers(1, &g_VboHandle);
	glGenBuffers(1, &g_ElementsHandle);

	glGenVertexArrays(1, &g_VaoHandle);
	glBindVertexArray(g_VaoHandle);
	glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
	glEnableVertexAttribArray(g_AttribLocationPosition);
	glEnableVertexAttribArray(g_AttribLocationUV);
	glEnableVertexAttribArray(g_AttribLocationColor);

#define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))
	glVertexAttribPointer(g_AttribLocationPosition, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, pos));
	glVertexAttribPointer(g_AttribLocationUV, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, uv));
	glVertexAttribPointer(g_AttribLocationColor, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, col));
#undef OFFSETOF

	ImGui_ImplSdlOgl3_CreateFontsTexture();

	// Restore modified GL state
	glBindTexture(GL_TEXTURE_2D, last_texture);
	glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
	glBindVertexArray(last_vertex_array);

	return true;
}

void    ImGui_ImplSdlOgl3_InvalidateDeviceObjects()
{
	if (g_FontTexture)
	{
		glDeleteTextures(1, &g_FontTexture);
		ImGui::GetIO().Fonts->TexID = 0;
		g_FontTexture = 0;
	}
}

bool    ImGui_ImplSdlOgl3_Init(SDL_Window *window)
{
	g_Window = window;
	
	ImGuiIO& io = ImGui::GetIO();
	io.KeyMap[ImGuiKey_Tab] = SDLK_TAB;                     // Keyboard mapping. ImGui will use those indices to peek into the io.KeyDown[] array.
	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_ImplSdlOgl3_RenderDrawLists;   // Alternatively you can set this to NULL and call ImGui::GetDrawData() after ImGui::Render() to get the same ImDrawData pointer.
	io.SetClipboardTextFn = ImGui_ImplSdlOgl3_SetClipboardText;
	io.GetClipboardTextFn = ImGui_ImplSdlOgl3_GetClipboardText;

#ifdef _WIN32
	SDL_SysWMinfo wmInfo;
	SDL_VERSION(&wmInfo.version);
	SDL_GetWindowWMInfo(window, &wmInfo);
	io.ImeWindowHandle = wmInfo.info.win.window;
#endif

	return true;
}

void ImGui_ImplSdlOgl3_Shutdown()
{
	if (g_VaoHandle) glDeleteVertexArrays(1, &g_VaoHandle);
	if (g_VboHandle) glDeleteBuffers(1, &g_VboHandle);
	if (g_ElementsHandle) glDeleteBuffers(1, &g_ElementsHandle);
	g_VaoHandle = g_VboHandle = g_ElementsHandle = 0;

	glDetachShader(g_ShaderHandle, g_VertHandle);
	glDeleteShader(g_VertHandle);
	g_VertHandle = 0;

	glDetachShader(g_ShaderHandle, g_FragHandle);
	glDeleteShader(g_FragHandle);
	g_FragHandle = 0;

	glDeleteProgram(g_ShaderHandle);
	g_ShaderHandle = 0;

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

void ImGui_ImplSdlOgl3_NewFrame(SDL_Window *window)
{
	if (!g_FontTexture)
		ImGui_ImplSdlOgl3_CreateDeviceObjects();

	ImGuiIO& io = ImGui::GetIO();

	// Setup display size (every frame to accommodate for window resizing)
	int w, h;
	int display_w, display_h;
	SDL_GetWindowSize(window, &w, &h);
	SDL_GetWindowSize(window, &display_w, &display_h);
	io.DisplaySize = ImVec2((float)w, (float)h);
	io.DisplayFramebufferScale = ImVec2((float)display_w / w, (float)display_h / h);

	// Setup time step
	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;

	// Setup inputs
	// (we already got mouse wheel, keyboard keys & characters from glfw callbacks polled in glfwPollEvents())
	int mx, my;
	Uint32 mouseMask = SDL_GetMouseState(&mx, &my);
	if (SDL_GetWindowFlags(window) & SDL_WINDOW_MOUSE_FOCUS)
		io.MousePos = ImVec2((float)mx, (float)my);   // Mouse position, in pixels (set to -1,-1 if no mouse / on another screen, etc.)
	else
		io.MousePos = ImVec2(-1, -1);

	io.MouseDown[0] = g_MousePressed[0] || (mouseMask & SDL_BUTTON(SDL_BUTTON_LEFT)) != 0;		// If a mouse press event came, always pass it as "mouse held this frame", so we don't miss click-release events that are shorter than 1 frame.
	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;

	// Hide OS mouse cursor if ImGui is drawing it
	SDL_ShowCursor(io.MouseDrawCursor ? 0 : 1);

	// Start the frame
	ImGui::NewFrame();
}