#include <GL/glew.h>
#include <GLFW/glfw3.h>

#include <iostream>
#include <string>

static unsigned int CompileShader(unsigned int type, const std::string &source)
{
    unsigned int id = glCreateShader(type);
    const char *src = source.c_str();
    glShaderSource(id, 1, &src, nullptr);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE)
    {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        char *message = (char * ) alloca(sizeof(char) * length);
        glGetShaderInfoLog(id, length, &length, message);
        std::cout << "Failed to compile " << (type == GL_VERTEX_SHADER ? "vertex" : "fragment")
                    << " shader\n";
        std::cout << message << "\n";
        glDeleteShader(id);
        return 0;
    }

    return id;
}

static unsigned int CreateShader(const std::string &vertexShader, const std::string &fragmentShader) {
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);

    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);

    glDeleteShader(vs);
    glDeleteShader(fs);

    return program;
}

int main(void)
{
    GLFWwindow* window;

    if (!glfwInit())
        return -1;

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    if (glewInit() != GLEW_OK)
        return 0;

    float positions[6] = {
        -0.5f, -0.5f,
         0.0f,  0.5f,
         0.5f, -0.5f
    };

    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), positions, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
    glEnableVertexAttribArray(0);

    std::string vertexShader =
        "#version 330 core\n"
        "\n"
        "layout(location = 0) in vec4 position;\n"
        "\n"
        "void main()\n"
        "{\n"
        "   gl_Position = position;\n"
        "}\n";

    std::string fragmentShader =
        "#version 330 core\n"
        "\n"
        "layout(location = 0) out vec4 color;\n"
        "\n"
        "void main()\n"
        "{\n"
        "   color = vec4(1.0, 0.0, 0.0, 1.0);\n"
        "}\n";

    unsigned int shader = CreateShader(vertexShader, fragmentShader);
    glUseProgram(shader);

    while (!glfwWindowShouldClose(window))
    {

        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);

        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}