#include <cassert>
#include <cstdlib> // calloc

#include <glm/glm.hpp>
#include <glm/geometric.hpp>
#include <glm/gtc/matrix_transform.hpp>

#include "aixlog.hpp"

#include "render_group.h"
#include "mesh.h"
#include "util.h"

#define INFO_LOG_MAX_LENGTH 312;


// forward declarations

render_object * allocateRenderObject(uint buffer_len, uint index_len = 0);
void freeRenderObject(render_object* ro);
bool convertMeshInfo(meMeshInfo* mesh, render_object* ro, bool use_normals);
void sendIndexBufferToGL(gl_index_buffer* index_buffer, GLenum usage, GLenum target);
void drawRenderObject(render_group* rg, render_object* ro,
		glm::mat4 model_matrix, glm::mat4 view_matrix, glm::mat4 projection_matrix,
		glm::vec3 light_position, GLuint light_id, bool update_vertex_data);


// interface

render_group*
rgInitSingle(rg_shader_program& sp, uint vertex_buffer_len,
			bool use_normals, uint index_buffer_len,
			GLenum draw_mode)
{
	render_group* rg = UTIL_ALLOC(1, render_group);
	rg->shader = sp;
	rg->use_normals = use_normals;
	rg->draw_indexed = (index_buffer_len > 0);
	rg->draw_mode = draw_mode;

	rg->render_objects = UTIL_ALLOC(1, render_object*);
	rg->render_objects[0] = allocateRenderObject(vertex_buffer_len, index_buffer_len);
	rg->num_objects = 1;

	if (rg->render_objects[0] == nullptr) {
		LOG(ERROR) << "Allocation Error\n";
		rgFree(rg);
	}

	return rg;
}

bool
rgInitShaderProgram(rg_shader_program& sp, const char * vertex_code, const char * frag_code)
{
	glGenVertexArrays(1, &sp.vertex_array_id);
	glBindVertexArray(sp.vertex_array_id);
	GLuint vertex_shader_id = glCreateShader(GL_VERTEX_SHADER);
	GLuint fragment_shader_id = glCreateShader(GL_FRAGMENT_SHADER);

	glShaderSource(vertex_shader_id, 1, &vertex_code, NULL);
	glShaderSource(fragment_shader_id, 1, &frag_code, NULL);
	glCompileShader(vertex_shader_id);
	glCompileShader(fragment_shader_id);

	sp.program_id = glCreateProgram();
	glAttachShader(sp.program_id, vertex_shader_id);
	glAttachShader(sp.program_id, fragment_shader_id);
	glLinkProgram(sp.program_id);

	sp.model_matrix_id = glGetUniformLocation(sp.program_id, "model");
	sp.view_matrix_id = glGetUniformLocation(sp.program_id, "view");
	sp.projection_matrix_id = glGetUniformLocation(sp.program_id, "projection");
	sp.normal_matrix_id = glGetUniformLocation(sp.program_id, "normal_matrix");

	glDetachShader(sp.program_id, vertex_shader_id);
	glDetachShader(sp.program_id, fragment_shader_id);
	glDeleteShader(vertex_shader_id);
	glDeleteShader(fragment_shader_id);

	// TODO: quick hack to allow 'dynamic' stack allocation for msvc
	// 	also remove INFO_LOG_MAX_LENGTH define
	GLint isLinked = 0;
	glGetProgramiv(sp.program_id, GL_LINK_STATUS, &isLinked);
	if (isLinked == GL_FALSE) {
		GLint maxLength = INFO_LOG_MAX_LENGTH;
		glGetProgramiv(sp.program_id, GL_INFO_LOG_LENGTH, &maxLength);
#ifdef _WIN32
		GLchar infoLog[312] = { 0 };
#else
		GLchar infoLog[maxLength] = { 0 };
#endif
		glGetProgramInfoLog(sp.program_id, maxLength, &maxLength, &infoLog[0]);
		LOG(ERROR) << infoLog << "\n";
		glDeleteProgram(sp.program_id);

		return false;
	}

	return true;
}

// TODO: move Entity initialization to Entity.h/.cpp to fix circular dependancy
// 	then just call into convertMeshInfo directly
bool
rgInitEntity(Entity* e)
{
	render_group* rg = UTIL_ALLOC(1, render_group);
	e->ren_group = rg;
	rg->draw_indexed = true;
	rg->draw_mode = GL_TRIANGLES;
	rg->use_normals = e->mesh_group.use_normals;
	uint num_meshes = rg->num_objects = e->mesh_group.num_meshes;

	// apply translation/rotation/scaling
	e->world_transform = glm::mat4(1.0);
	e->world_transform = glm::translate(e->world_transform, e->translation);
	e->world_transform = glm::scale(e->world_transform, e->scale);

	rg->render_objects = (render_object**) std::calloc(num_meshes, sizeof(render_object*));

	for (uint i = 0; i < num_meshes; i++)
	{
		uint buffer_len =  e->mesh_group.meshes[i]->num_vertices * 3;
		uint index_len = e->mesh_group.meshes[i]->num_indices;
		rg->render_objects[i] = allocateRenderObject(buffer_len, index_len);

		if (rg->render_objects[i] == nullptr)
			return false;

		// TODO: safely free memory here when convertMeshInfo returns false
		if (!convertMeshInfo(e->mesh_group.meshes[i], rg->render_objects[i], rg->use_normals))
			return false;
	}

	return true;
}

void
rgBufferData(gl_buffer* buffer, GLenum usage, GLenum target)
{
	glGenBuffers(1, &buffer->buffer_id);
	glBindBuffer(target, buffer->buffer_id);
	glBufferData(target, buffer->buffer_len * sizeof(GLfloat), buffer->buffer, usage);
}

void
rgDraw(render_group* rg, glm::mat4 model_matrix, glm::mat4 view_matrix, glm::mat4 projection_matrix,
		glm::vec3 light_position, GLuint light_id, bool update_vertex_data)
{
	for (uint i = 0; i < rg->num_objects; i++) {
		drawRenderObject(rg, rg->render_objects[i], model_matrix, view_matrix, projection_matrix,
				light_position, light_id, update_vertex_data);
	}
}

void
rgFree(render_group* rg)
{
	if (rg == nullptr) {
		LOG(ERROR) << "tried to free nullptr\n";
		return;
	}

	for (uint i = 0; i < rg->num_objects; i++)
		freeRenderObject(rg->render_objects[i]);

	utilSafeFree(rg->render_objects);
	utilSafeFree(rg);
}


// internal

render_object *
allocateRenderObject(uint buffer_len, uint index_len)
{
	render_object* ro = UTIL_ALLOC(1, render_object);

	if (ro == nullptr)
		return nullptr;

	ro->vertex_buffer.buffer = UTIL_ALLOC(buffer_len, GLfloat);
	ro->vertex_buffer.buffer_len = buffer_len;
	ro->normal_buffer.buffer = UTIL_ALLOC(buffer_len, GLfloat);
	ro->normal_buffer.buffer_len = buffer_len;
	ro->color_buffer.buffer = UTIL_ALLOC(buffer_len, GLfloat);
	ro->color_buffer.buffer_len = buffer_len;

	if (index_len > 0) {
		ro->index_buffer.buffer = UTIL_ALLOC(index_len, uint);
		ro->index_buffer.buffer_len = index_len;
	}

	if (ro->vertex_buffer.buffer == nullptr ||
		ro->normal_buffer.buffer == nullptr ||
		ro->color_buffer.buffer == nullptr ||
		((index_len > 0) && (ro->vertex_buffer.buffer == nullptr)))
	{
		freeRenderObject(ro);
		return nullptr;
	}

	return ro;
}

void
freeRenderObject(render_object* ro)
{
	utilSafeFree(ro->vertex_buffer.buffer);
	utilSafeFree(ro->normal_buffer.buffer);
	utilSafeFree(ro->color_buffer.buffer);
	utilSafeFree(ro->index_buffer.buffer);
	utilSafeFree(ro);
}

void
sendIndexBufferToGL(gl_index_buffer* index_buffer, GLenum usage, GLenum target)
{
	glGenBuffers(1, &index_buffer->buffer_id);
	glBindBuffer(target, index_buffer->buffer_id);
	glBufferData(target, index_buffer->buffer_len * sizeof(uint), index_buffer->buffer, usage);
}

bool
convertMeshInfo(meMeshInfo* mesh, render_object* ro, bool use_normals)
{
	uint vertex_buf_len = mesh->num_vertices * 3;
	GLfloat* vertex_buf = ro->vertex_buffer.buffer;
	GLfloat* color_buf = ro->color_buffer.buffer;
	GLfloat* normal_buf = ro->normal_buffer.buffer;
	uint* index_buf = ro->index_buffer.buffer;

	if (!vertex_buf || !color_buf || !normal_buf || !index_buf)
		return false;

	// dump vertices, colors, and normals into render_group buffers
	uint vertex_index = 0;
	uint vertex_prop_index = 0;

	for (uint i = 0; i < vertex_buf_len; i++) {
		const glm::vec3& vertex = mesh->vertices[vertex_index];
		const glm::vec3& normal = mesh->normals[vertex_index];

		switch (vertex_prop_index) {
			case 0:	vertex_buf[i] = vertex.x; break;
			case 1: vertex_buf[i] = vertex.y; break;
			case 2: vertex_buf[i] = vertex.z; break;
		}

		if (use_normals) {
			switch (vertex_prop_index) {
				case 0:	normal_buf[i] = normal.x; break;
				case 1: normal_buf[i] = normal.y; break;
				case 2: normal_buf[i] = normal.z; break;
			}
		}

		color_buf[i] = mesh->diffuse_color[vertex_prop_index];
		vertex_prop_index++;

		if (vertex_prop_index == 3) {
			vertex_prop_index = 0;
			vertex_index++;
		}
	}

	// dump indices
	for (uint i = 0; i < mesh->num_indices; i++)
		index_buf[i] = mesh->indices[i];

	rgBufferData(&ro->vertex_buffer, GL_DYNAMIC_DRAW, GL_ARRAY_BUFFER);
	rgBufferData(&ro->color_buffer, GL_STATIC_DRAW, GL_ARRAY_BUFFER);
	if (use_normals)
		rgBufferData(&ro->normal_buffer, GL_STATIC_DRAW, GL_ARRAY_BUFFER);
	sendIndexBufferToGL(&ro->index_buffer, GL_STATIC_DRAW, GL_ELEMENT_ARRAY_BUFFER);

	return true;
}

void
drawRenderObject(render_group* rg, render_object* ro,
		glm::mat4 model_matrix, glm::mat4 view_matrix, glm::mat4 projection_matrix,
		glm::vec3 light_position, GLuint light_id, bool update_vertex_data)
{
	glUseProgram(rg->shader.program_id);
	glUniformMatrix4fv(rg->shader.model_matrix_id, 1, GL_FALSE, &model_matrix[0][0]);
	glUniformMatrix4fv(rg->shader.view_matrix_id, 1, GL_FALSE, &view_matrix[0][0]);
	glUniformMatrix4fv(rg->shader.projection_matrix_id, 1, GL_FALSE, &projection_matrix[0][0]);

	// 1st attribute buffer : vertices
	glEnableVertexAttribArray(0);
	glBindBuffer(GL_ARRAY_BUFFER, ro->vertex_buffer.buffer_id);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*) 0);

	if (update_vertex_data)
	{
		glBufferSubData(GL_ARRAY_BUFFER, 0, ro->vertex_buffer.buffer_len * sizeof(GLfloat),
			ro->vertex_buffer.buffer);
	}

	// 2nd attribute buffer : colors
	if (ro->color_buffer.buffer)
	{
		glEnableVertexAttribArray(1);
		glBindBuffer(GL_ARRAY_BUFFER, ro->color_buffer.buffer_id);
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, (void*) 0);

		// TODO: maybe add an option to not send color data every frame?
		glBufferSubData(GL_ARRAY_BUFFER, 0, ro->color_buffer.buffer_len * sizeof(GLfloat),
				ro->color_buffer.buffer);
	}

	// 3rd attribute buffer: normals
	if (rg->use_normals) {
		glEnableVertexAttribArray(2);
		glBindBuffer(GL_ARRAY_BUFFER, ro->normal_buffer.buffer_id);
		glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, 0, (void*) 0);

		// TODO: testing lighting
		glUniform3f(light_id, light_position.x, light_position.y, light_position.z);
		glm::mat3 normal_matrix = glm::transpose(glm::inverse(glm::mat3(model_matrix)));
		glUniformMatrix3fv(rg->shader.normal_matrix_id, 1, GL_FALSE, &normal_matrix[0][0]);
	}

	// draw
	if (rg->draw_indexed) {
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ro->index_buffer.buffer_id);
		glDrawElements(rg->draw_mode, ro->index_buffer.buffer_len, GL_UNSIGNED_INT, 0);
	} else {
		glDrawArrays(rg->draw_mode, 0, ro->vertex_buffer.buffer_len / 3);
	}

	// cleanup
	glDisableVertexAttribArray(0);
	if (ro->color_buffer.buffer)
		glDisableVertexAttribArray(1);
	if (rg->use_normals)
		glDisableVertexAttribArray(2);
}