#include <glm/gtc/matrix_transform.hpp>

#include "dumbLog.h"
#include "render_object.h"


// forward declarations

bool initGLFloatBuffer(glm::vec3* buffer, uint count, GLuint& buffer_id);
bool initGLIndexBuffer(uint* buffer, uint num_indices, GLuint& buffer_id);
bool initGLTexture(const util_image image, GLuint& tex_id);


// interface

bool
roInit(meMeshInfo* mi_in, render_object& ro_out)
{
	if (initGLFloatBuffer(mi_in->vertices,
			mi_in->num_vertices,
			ro_out.vertex_buffer_id) &&
		initGLFloatBuffer(mi_in->normals,
			mi_in->num_vertices,
			ro_out.normal_buffer_id) &&
		initGLFloatBuffer(mi_in->texture_coords,
			mi_in->num_vertices,
			ro_out.uv_buffer_id) &&
		initGLIndexBuffer(mi_in->indices,
			mi_in->num_indices,
			ro_out.index_buffer_id) &&
		initGLTexture(mi_in->diffuse_texture, ro_out.tex_id))
	{
		ro_out.node_xform = mi_in->model_transform;
		ro_out.index_buffer_count = mi_in->num_indices;
		return true;
	}

	LOG(Error) << "Failed to initialize render_object\n";
	roFree(ro_out);
	return false;
}

void
roFree(render_object& ro)
{
	LOG(Debug) << "TODO: release GL buffers from render_object\n";
}

//----------- WIP --------------

// TODO: really only need to update the view and projection matrices once per
// 	frame, maybe add another interface function in render_object to call from
// 	renRenderFrame
inline void
updateMatrices(shader_program& shader, camera& cam, glm::mat4 node_xform)
{
	glUniformMatrix4fv(shader.model_matrix_id, 1, GL_FALSE, &node_xform[0][0]);
	glUniformMatrix4fv(shader.view_matrix_id, 1, GL_FALSE, &cam.view[0][0]);
	glUniformMatrix4fv(shader.projection_matrix_id, 1, GL_FALSE, &cam.projection[0][0]);

	glm::mat3 normal_matrix = glm::transpose(glm::inverse(glm::mat3(cam.model)));
	glUniformMatrix3fv(shader.normal_matrix_id, 1, GL_FALSE, &normal_matrix[0][0]);
}

inline void
enableGLFloatBuffer(uint buffer_id, uint location)
{
	glEnableVertexAttribArray(location);
	glBindBuffer(GL_ARRAY_BUFFER, buffer_id);
	glVertexAttribPointer(location, 3, GL_FLOAT, GL_FALSE, 0, (void*) 0);
}

#include <sstream> // TODO: remove this and make something in util.h

inline void
updateLights(shader_program& shader, point_light* lights, uint num_lights)
{
	// TODO: use Uniform Buffer Objects to update light data
	// 	https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_uniform_buffer_object.txt
	// 	https://www.khronos.org/opengl/wiki/Uniform_Buffer_Objects

	glUniform1ui(shader.num_lights_id, num_lights);

	for (uint i = 0; i < num_lights; i++) {
		// TODO: don't do this every frame * every render_group
		std::stringstream ss;
		ss << "lights[" << i << "].position";
		int light_pos_loc = glGetUniformLocation(shader.program_id, ss.str().c_str());
		glUniform3fv(light_pos_loc, 1, &lights[i].position[0]);
	}
}

//----------- WIP --------------

void
roDraw(render_object& ro,
	camera& cam,
	shader_program& shader,
	point_light* lights,
	uint num_lights)
{
	glUseProgram(shader.program_id);
	updateMatrices(shader, cam, ro.node_xform);
	enableGLFloatBuffer(ro.vertex_buffer_id, 0);
	enableGLFloatBuffer(ro.normal_buffer_id, 1);
	updateLights(shader, lights, num_lights);
	// TODO: could pass in a stride parameter here to enableGLFloatBuffer()
	// 	could then use a 2d buffer for uv coords
	enableGLFloatBuffer(ro.uv_buffer_id, 2);

	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ro.index_buffer_id);
	glDrawElements(GL_TRIANGLES, ro.index_buffer_count, GL_UNSIGNED_INT, 0);

	glDisableVertexAttribArray(0);
	glDisableVertexAttribArray(1);
	glDisableVertexAttribArray(2);
	glUseProgram(0);
}

// internal

bool
initGLFloatBuffer(glm::vec3* buffer, uint count, GLuint& buffer_id)
{
	glGenBuffers(1, &buffer_id);
	glBindBuffer(GL_ARRAY_BUFFER, buffer_id);
	glBufferData(GL_ARRAY_BUFFER,
		count * sizeof(GLfloat),
		buffer,
		GL_STATIC_DRAW);

	return (glGetError() == GL_NO_ERROR);
}

bool
initGLIndexBuffer(uint* buffer, uint num_indices, GLuint& buffer_id)
{
	glGenBuffers(1, &buffer_id);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, buffer_id);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER,
		num_indices * sizeof(uint),
		buffer,
		GL_STATIC_DRAW);

	return (glGetError() == GL_NO_ERROR);
}

bool
initGLTexture(const util_image image, GLuint& tex_id)
{
	glGenTextures(1, &tex_id);
	glBindTexture(GL_TEXTURE_2D, tex_id);
	glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
	GLenum pixel_format = (image.num_channels == 3) ? GL_RGB : GL_RGBA;
	glTexImage2D(GL_TEXTURE_2D, 0, pixel_format, image.w, image.h, 0,
			pixel_format, GL_UNSIGNED_BYTE, image.pixels);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

	return (glGetError() == GL_NO_ERROR);
}