#include "opengl_widget.hh"

#include <QMouseEvent>


static const GLchar *vertex_shader_source = R"glsl(
#version 330 core

layout(location = 0) in vec3 in_pos;
layout(location = 1) in vec2 in_uv;

out vec2 uv;

uniform mat4 proj;
uniform mat4 view;
uniform mat4 model;

void main() {
	gl_Position = proj * view * model * vec4(in_pos, 1.0);
	uv = in_uv;
}
)glsl";

static const GLchar *fragment_shader_source = R"glsl(
#version 330 core

in vec2 uv;
out vec4 final_col;

uniform sampler2D tex;

void main() {
	final_col = texture(tex, uv);
}
)glsl";


static void GLAPIENTRY opengl_debug_cb(GLenum source, GLenum type, GLuint id,
									   GLenum severity, GLsizei length,
									   const GLchar* message,
									   const void* userParam) {
	(void) source; (void) type; (void) id; (void) severity; (void) length;
	(void) userParam;
	qDebug() << "OpenGL debug output:" << message;
}


OpenGLWidget *OpenGLWidget::instance = nullptr;


OpenGLWidget::OpenGLWidget(QWidget *parent)
	:QOpenGLWidget(parent) {
	OpenGLWidget::instance = this;
}


OpenGLWidget::~OpenGLWidget() {
	OpenGLWidget::instance = nullptr;
}


void OpenGLWidget::initializeGL() {
	initializeOpenGLFunctions();
	GLint major, minor;
	glGetIntegerv(GL_MAJOR_VERSION, &major);
	glGetIntegerv(GL_MINOR_VERSION, &minor);
	qDebug("OpenGL version %d.%d", major, minor);

	glEnable(GL_DEBUG_OUTPUT);
	glDebugMessageCallback(opengl_debug_cb, 0);

	/* Compile the vertex shader. */
	GLuint vertex_shader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vertex_shader, 1, &vertex_shader_source, NULL);
	glCompileShader(vertex_shader);
	GLint status;
	glGetShaderiv(vertex_shader, GL_COMPILE_STATUS, &status);
	if (status != GL_TRUE) {
		char log[1024];
		glGetShaderInfoLog(vertex_shader, sizeof log, NULL, log);
		fprintf(stderr, "Failed to compile the vertex shader: %s\n", log);
		exit(1);
	}

	/* Compile the fragment shader. */
	GLuint fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragment_shader, 1, &fragment_shader_source, NULL);
	glCompileShader(fragment_shader);
	glGetShaderiv(fragment_shader, GL_COMPILE_STATUS, &status);
	if (status != GL_TRUE) {
		char log[1024];
		glGetShaderInfoLog(fragment_shader, sizeof log, NULL, log);
		fprintf(stderr, "Failed to compile the fragment shader: %s\n", log);
		exit(1);
	}

	/* Link the shader program. */
	GLuint shader_program = glCreateProgram();
	glAttachShader(shader_program, vertex_shader);
	glAttachShader(shader_program, fragment_shader);
	glBindFragDataLocation(shader_program, 0, "final_col");
	glLinkProgram(shader_program);
	glGetProgramiv(shader_program, GL_LINK_STATUS, &status);
	if (status != GL_TRUE) {
		char log[1024];
		glGetProgramInfoLog(shader_program, sizeof log, NULL, log);
		fprintf(stderr, "Failed to link the shader program: %s\n", log);
		exit(1);
	}

	/* Use it. */
	glUseProgram(shader_program);

	/* Get the position attribute. */
	pos_attr = glGetAttribLocation(shader_program, "pos");

	proj_attr = glGetUniformLocation(shader_program, "proj");
	view_attr = glGetUniformLocation(shader_program, "view");
	model_attr = glGetUniformLocation(shader_program, "model");

	QMatrix4x4 view;
	view.translate(0, 0, 5);
	glUniformMatrix4fv(view_attr, 1, GL_FALSE, view.data());

	QMatrix4x4 trans;
	trans.translate(0, 0, -5);
	glUniformMatrix4fv(view_attr, 1, GL_FALSE, trans.data());

	glUniform1i(glGetUniformLocation(shader_program, "tex"), 0);

	glClearColor(1, 1, 1, 0);

	glEnable(GL_DEPTH_TEST);
	glEnable(GL_MULTISAMPLE);

	emit initialized();
}


void OpenGLWidget::resizeGL(int w, int h) {
	QMatrix4x4 projection;
	projection.perspective(FOV, (float) w/h, .1, 1000);
	glUniformMatrix4fv(proj_attr, 1, GL_FALSE, projection.data());
}


void OpenGLWidget::paintGL() {
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	QMatrix4x4 trans;
	trans.translate(0, 0, -cam_dist);
	QMatrix4x4 view = trans * rot;
	glUniformMatrix4fv(view_attr, 1, GL_FALSE, view.data());
	glActiveTexture(GL_TEXTURE0);
	for (const OpenGLMesh &mesh : meshes) {
		glUniformMatrix4fv(model_attr, 1, GL_FALSE, mesh.mat.data());
		glBindVertexArray(mesh.vao);
		mesh.tex->bind();
		glDrawArrays(GL_TRIANGLES, 0, mesh.nverts);
	}
}


void OpenGLWidget::mousePressEvent(QMouseEvent *e) {
	if (e->button() == Qt::LeftButton) {
		mouse_pos = e->pos();
	}
}


void OpenGLWidget::mouseReleaseEvent(QMouseEvent *e) {
	(void) e;
	rot_start = rot;
}


void OpenGLWidget::mouseMoveEvent(QMouseEvent *e) {
	if (e->buttons() & Qt::LeftButton) {
		QPoint delta = e->pos() - mouse_pos;
		rot = rot_start;
		rot.rotate(delta.x() / 5., 0, 1, 0);
		rot.rotate(delta.y() / 5., QVector3D(1, 0, 0) * rot);
		update();
	}
}


void OpenGLWidget::wheelEvent(QWheelEvent *e) {
	cam_dist -= e->angleDelta().y() / 1000. * cam_dist;
	update();
}