/*
Transformation matrices.
*/

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#define GLEW_STATIC
#include <GL/glew.h>

#include <GLFW/glfw3.h>

#include "common.h"

static const GLuint WIDTH = 800;
static const GLuint HEIGHT = 600;
/* ourColor is passed on to the fragment shader. */
static const GLchar* vertex_shader_source =
    "#version 330 core\n"
    "layout (location = 0) in vec3 position;\n"
    "layout (location = 1) in vec3 color;\n"
    "out vec3 ourColor;\n"
    "uniform mat4 transform;\n"
    "void main() {\n"
    "    gl_Position = transform * vec4(position, 1.0f);\n"
    "    ourColor = color;\n"
    "}\n";
static const GLchar* fragment_shader_source =
    "#version 330 core\n"
    "in vec3 ourColor;\n"
    "out vec4 color;\n"
    "void main() {\n"
    "    color = vec4(ourColor, 1.0f);\n"
    "}\n";
static GLfloat vertices[] = {
/*   Positions          Colors */
     0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 0.0f,
    -0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f,
     0.0f,  0.5f, 0.0f, 0.0f, 0.0f, 1.0f
};

int main(void) {
    GLint shader_program;
    GLint transform_location;
    GLuint vbo;
    GLuint vao;
    GLFWwindow* window;
    double time;

    glfwInit();
    window = glfwCreateWindow(WIDTH, HEIGHT, __FILE__, NULL, NULL);
    glfwMakeContextCurrent(window);
    glewExperimental = GL_TRUE;
    glewInit();
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glViewport(0, 0, WIDTH, HEIGHT);

    shader_program = common_get_shader_program(vertex_shader_source, fragment_shader_source);

    glGenVertexArrays(1, &vao);
    glGenBuffers(1, &vbo);
    glBindVertexArray(vao);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    /* Position attribute */
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);
    /* Color attribute */
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(1);
    glBindVertexArray(0);

    while (!glfwWindowShouldClose(window)) {
        glfwPollEvents();
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shader_program);
        transform_location = glGetUniformLocation(shader_program, "transform");
        /* To do serious things, we'd need a math library like glm here. */
        GLfloat transform[] = {
            0.0f, 0.0f, 0.0f, 0.0f,
            0.0f, 0.0f, 0.0f, 0.0f,
            0.0f, 0.0f, 1.0f, 0.0f,
            0.0f, 0.0f, 0.0f, 1.0f,
        };
        time = glfwGetTime();
        transform[0] = 2.0f * sin(time);
        transform[5] = 2.0f * cos(time);
        glUniformMatrix4fv(transform_location, 1, GL_FALSE, transform);

        glBindVertexArray(vao);
        glDrawArrays(GL_TRIANGLES, 0, 3);
        glBindVertexArray(0);
        glfwSwapBuffers(window);
    }
    glDeleteVertexArrays(1, &vao);
    glDeleteBuffers(1, &vbo);
    glfwTerminate();
    return EXIT_SUCCESS;
}