#include <cassert>

#define GLM_FORCE_XYZW_ONLY
#include <glm/gtc/matrix_transform.hpp>

#include "tangerine.h"
#define UTIL_IMPLEMENTATION
#include "util.h"
#define GL_DEBUG_IMPLEMENTATION
#include "GLDebug.h"


// forward declarations

bool initGraphics(SDLHandles* handles, const char* title, uvec2 dims);

LightsBuffer* initLights(RenderState* rs, u32 max_lights, vec4 ambient_color);


// interface

RenderState*
initRenderState(const char* window_title,
	uvec2 window_dims,
	u32 SDL_flags,
	GLClearColor clear_col,
	vec4 ambient_color,
	u32 max_models,
	u32 max_textures,
	u32 max_shaders,
	u32 max_render_groups,
	u32 max_ubos,
	u32 max_lights)
{
	LOGF(Info, "Initializing Renderer\n");
	RenderState* rs = UTIL_ALLOC(1, RenderState);

	if (rs) {
		rs->clear_col = clear_col;
		rs->assets.arena = arenaInit(DEFAULT_ARENA_SIZE);
		rs->assets.max_models = max_models;
		rs->assets.models = ARENA_ALLOC(rs->assets.arena, Model, max_models);
		rs->assets.max_textures = max_textures;
		rs->assets.textures =
			ARENA_ALLOC(rs->assets.arena, Texture, max_textures);

		rs->rg_arena = arenaInit(DEFAULT_ARENA_SIZE);
		rs->max_render_groups = DEFAULT_RENDER_GROUP_COUNT;
		rs->render_groups = ARENA_ALLOC(rs->rg_arena, RenderGroup,
				DEFAULT_RENDER_GROUP_COUNT);
		rs->window_dims = window_dims;
		rs->handles.SDL_flags = SDL_flags;

		if (!initGraphics(&rs->handles, window_title, window_dims)) {
			LOGF(Error, "error initializing renderer\n");
			return nullptr;
		}

		rs->gl_ctx = initGLContext(rs->assets.arena,
				max_shaders,
				max_textures,
				max_ubos);

		rs->camera = UTIL_ALLOC(1, Camera);
		GLBuffer* xforms_ubo = initGLBackingBuffer(rs->gl_ctx,
													rs->assets.arena,
													"matrices",
													GL_FLOAT,
													sizeof(Transforms),
													&rs->camera->xforms);
		assert(xforms_ubo);

		// FIXME: should this be an interface function?
		rs->lights_buf = initLights(rs, max_lights, ambient_color);

		// FIXME: should have an error message instead of assert here, and
		// 	clean up arenas/allocations before returning
		bool ret = loadDefaultShaders(rs);
		assert(ret);
	}

	return rs;
}

void
freeRenderState(RenderState*& rs)
{
	if (rs) {
		SDL_GL_DeleteContext(rs->handles.sdl_gl_ctx);
		SDL_DestroyWindow(rs->handles.window);
		arenaFree(rs->assets.arena);
		arenaFree(rs->rg_arena);
		utilSafeFree(rs);
		rs = nullptr;
	}

	SDL_Quit();
}

void
initRenderGroup(RenderGroup* rg,
		MemoryArena* arena,
		ShaderProgram* shader,
		u32 num_entities,
		const char* name)
{
	rg->max_entities = num_entities;
	rg->shader = shader;
	rg->name = arenaCopyCStr(arena, name);
	rg->entities = ARENA_ALLOC(arena, Entity, num_entities);
}

void
freeRenderGroup(RenderGroup* rg, MemoryArena* arena)
{
	LOGF(Info, "should probably look into freeing arena memory?\n");
	assert(0);
}

RenderGroup*
getFreeRenderGroup(RenderState* rs)
{
	if (rs->num_render_groups < rs->max_render_groups)
		return &rs->render_groups[rs->num_render_groups++];

	LOGF(Error, "no free render group\n");
	return nullptr;
}

RenderGroup*
getRenderGroupByName(RenderState* rs, const char* name)
{
	RenderGroup* rg_out = nullptr;

	for (u32 i = 0; i < rs->num_render_groups; i++) {
		RenderGroup* rg = &rs->render_groups[i];

		if (utilCStrMatch(name, rg->name))
			rg_out = rg;
	}

	if (rg_out == nullptr)
		LOGF(Error, "render group with name, \"%s\", not found\n", name);

	return rg_out;
}

Entity*
getFreeEntity(RenderGroup* rg)
{
	if (rg->num_entities < rg->max_entities)
		return &rg->entities[rg->num_entities++];

	LOGF(Error, "render group full\n");
	return nullptr;
}

Entity*
getEntityByName(RenderGroup* rg, const char* name)
{
	Entity* e_out = nullptr;

	for (u32 i = 0; i < rg->num_entities; i++) {
		Entity* e = &rg->entities[i];

		if (utilCStrMatch(name, e->name))
			e_out = e;
	}

	if (e_out == nullptr)
		LOGF(Error, "Entity with name, \"%s\", not found\n", name);

	return e_out;
}

void
doRenderLoop(RenderState* rs,
	u32 framerate,
	frame_callback_fn cb_func_pre,
	frame_callback_fn cb_func_post,
	void* user_data)
{
	u32 delay = (framerate > 0) ? 1 / framerate : 0;
	u32 frameStart, frameTime;
	rs->running = true;
	SDL_Event e;

	while (rs->running) {
		frameStart = SDL_GetTicks();

		if (cb_func_pre != nullptr) {
			cb_func_pre(rs, user_data);
		} else {
			while (SDL_PollEvent(&e)) {
				if (e.type == SDL_QUIT ||
					(e.type == SDL_KEYDOWN && e.key.keysym.sym == SDLK_ESCAPE))
				{
					rs->running = false;
					break;
				}
			}
		}

		renderFrame(rs, rs->clear_col);

		if (cb_func_post != nullptr)
			cb_func_post(rs, user_data);

		SDL_GL_SwapWindow(rs->handles.window);
		frameTime = SDL_GetTicks() - frameStart;

		if (delay > frameTime)
			SDL_Delay(delay - frameTime);
	}
}

void
renderFrame(RenderState* rs, const GLClearColor& clear_col)
{
	glClearColor(clear_col.R,
		clear_col.G,
		clear_col.B,
		clear_col.A);
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

	for (u32 i = 0; i < rs->num_render_groups; i++) {
		RenderGroup* rg = &rs->render_groups[i];

		for (u32 j = 0; j < rg->num_entities; j++) {
			Entity* e = &rg->entities[j];

			for (u32 k = 0; k < e->num_meshes; k++) {
				GLMesh& glm = e->meshes[k];
				renderVAO(&glm, e->model_xform, rg->shader,
							e->diffuse_texture, e->draw_mode);
			}
		}
	}
}

bool
loadDefaultShaders(RenderState* rs,
	u32 num_shaders,
	const ShaderInit shaders[])
{
	for (u32 i = 0; i < num_shaders; i++) {
		const ShaderInit& si = shaders[i];

		if (!addShaderProgram(rs->assets.arena,
								rs->gl_ctx,
								si.vert_path,
								si.frag_path,
								si.name))
		{
			LOG(Error) << "failed to load shader " << si.name << "\n";
			return false;
		}

		ShaderProgram* shader = getShaderByName(si.name, rs->gl_ctx);
		assert(shader);

		// NOTE: not every buffer will be available for every shader, so we
		// 	enumerate them all, and store the ones that are present
		u32 attrib_idx = 0;

		for (u32 i = 0; i < MESH_BUFFER_TYPE_COUNT; i++) {
			MeshBufferType buf_type = (MeshBufferType) i;
			GLVertexAttrib* attrib = getVertexAttribByType(shader, buf_type);

			if (attrib)
				shader->attrib_mappings[attrib_idx++] = { attrib, buf_type };
		}
	}

	return true;
}

GLVertexAttrib*
getVertexAttribByType(ShaderProgram* shader, MeshBufferType buf_type)
{
	switch (buf_type) {
		case VERTEX: return getVertexAttribByName(shader, "position");
		case NORMAL: return getVertexAttribByName(shader, "normal");
		case UV: return getVertexAttribByName(shader, "uv");
		case COLOR: return getVertexAttribByName(shader, "color");
		default: return nullptr;
	}
}


// internal

bool
initGraphics(SDLHandles* handles, const char* title, uvec2 dims)
{
	handles->window = SDL_CreateWindow(
		title,
		SDL_WINDOWPOS_CENTERED_DISPLAY(0),
		SDL_WINDOWPOS_CENTERED_DISPLAY(0),
		dims.x,
		dims.y,
		SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);

	if (SDL_Init(handles->SDL_flags) != 0) {
		std::cout << "error, sdl init: " << SDL_GetError() << "\n";
		return false;
	}

	SDL_GL_SetSwapInterval(1);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS,
		SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK,
		SDL_GL_CONTEXT_PROFILE_CORE);
	SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
	SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
	SDL_GetCurrentDisplayMode(0, &handles->display_mode);

	handles->sdl_gl_ctx = SDL_GL_CreateContext(handles->window);

	if (!handles->sdl_gl_ctx) {
		std::cout << "error creating context\n";
		return false;
	}

	if (glewInit()) {
		std::cout << "error initializing opengl\n";
		return false;
	}

	std::cout << "opengl vendor: " << glGetString(GL_VENDOR) << "\n";
	std::cout << "opengl renderer: " << glGetString(GL_RENDERER) << "\n";
	std::cout << "opengl version: " << glGetString(GL_VERSION) << "\n";

	glEnable(GL_DEPTH_TEST);
	glEnable(GL_LINE_SMOOTH);
	glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

	glEnable (GL_DEBUG_OUTPUT);
	glDebugMessageCallback((GLDEBUGPROC) openglDebugCallback, 0);

	return handles->window != nullptr;
}

LightsBuffer*
initLights(RenderState* rs,
	u32 max_lights,
	vec4 ambient_color)
{
	// FIXME: revisit for 'Scene' abstraction
	// FIXME: see if we can simplify this with the use of offsetof()
	// 	https://en.cppreference.com/w/cpp/types/offsetof

	LightsBuffer* lb = ARENA_ALLOC(rs->assets.arena, LightsBuffer, 1);
	lb->buf_size = 8 * sizeof(u32) // NOTE: 'header'
				+ sizeof(vec4) // NOTE: ambient color
				+ 6 * max_lights * sizeof(vec4); // NOTE: vector arrays
	LOGF(Debug, "buf_size: %d\n", lb->buf_size);
	lb->buffer = ARENA_ALLOC(rs->assets.arena, u8, lb->buf_size);

	lb->max_p_lights = (u32*) lb->buffer;
	lb->active_p_lights =
		(u32*) arenaGetAddressOffset(lb->max_p_lights, sizeof(u32));
	lb->max_d_lights =
		(u32*) arenaGetAddressOffset(lb->active_p_lights, sizeof(u32));
	lb->active_d_lights =
		(u32*) arenaGetAddressOffset(lb->max_d_lights, sizeof(u32));

	*lb->max_p_lights = max_lights;
	*lb->max_d_lights = max_lights;

	// NOTE: add padding, we're not actually using  this since 4 * u32 is on a
	// 	16 byte boundary, but will be helpful if we need to add more 'headers'
	// 	in the future
	void* arr_start = arenaGetAddressOffset(lb->buffer, 8 * sizeof(u32));

	// NOTE: ambient color
	lb->ambient_color = (vec4*) arr_start;
	*lb->ambient_color = ambient_color;

	// NOTE: set offsets for array pointers
	u32 arr_size = max_lights * sizeof(vec4);
	lb->pl_positions = //(vec4*) arr_start;
		(vec4*) arenaGetAddressOffset(arr_start, sizeof(vec4));
	lb->pl_colors =
		(vec4*) arenaGetAddressOffset(lb->pl_positions, arr_size);
	lb->pl_intensities =
		(uvec4*) arenaGetAddressOffset(lb->pl_colors, arr_size);
	lb->dl_directions =
		(vec4*) arenaGetAddressOffset(lb->pl_intensities, arr_size);
	lb->dl_colors =
		(vec4*) arenaGetAddressOffset(lb->dl_directions, arr_size);
	lb->dl_intensities =
		(uvec4*) arenaGetAddressOffset(lb->dl_colors, arr_size);

	initGLBackingBuffer(rs->gl_ctx,
						rs->assets.arena,
						"lights",
						GL_BYTE,
						lb->buf_size,
						lb->buffer);

	return lb;
}