// Link statically with GLEW
#define GLEW_STATIC

// Headers
#include <GL/glew.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <SFML/Window.hpp>
#include <chrono>

// Shader macro
#define GLSL(src) "#version 150 core\n" #src

// Vertex shader
const GLchar* vertexShaderSrc = GLSL(
    in vec3 pos;
    in vec3 color;

    out vec3 vColor;

    void main()
    {
        gl_Position = vec4(pos, 1.0);
        vColor = color;
    }
);

// Geometry shader
const GLchar* geometryShaderSrc = GLSL(
    layout(points) in;
    layout(line_strip, max_vertices = 16) out;

    in vec3 vColor[];
    out vec3 fColor;

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

    void main()
    {
        fColor = vColor[0];

        gl_in[0].gl_Position = proj * view * model * gl_in[0].gl_Position;

        // +X direction is "North", -X direction is "South"
        // +Y direction is "Up",    -Y direction is "Down"
        // +Z direction is "East",  -Z direction is "West"
        //                                     N/S   U/D   E/W
        vec4 NEU = proj * view * model * vec4( 0.1,  0.1,  0.1, 0.0);
        vec4 NED = proj * view * model * vec4( 0.1, -0.1,  0.1, 0.0);
        vec4 NWU = proj * view * model * vec4( 0.1,  0.1, -0.1, 0.0);
        vec4 NWD = proj * view * model * vec4( 0.1, -0.1, -0.1, 0.0);
        vec4 SEU = proj * view * model * vec4(-0.1,  0.1,  0.1, 0.0);
        vec4 SED = proj * view * model * vec4(-0.1, -0.1,  0.1, 0.0);
        vec4 SWU = proj * view * model * vec4(-0.1,  0.1, -0.1, 0.0);
        vec4 SWD = proj * view * model * vec4(-0.1, -0.1, -0.1, 0.0);

        // Create a cube centered on the given point.
        gl_Position = gl_in[0].gl_Position + NED;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + NWD;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + SWD;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + SED;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + SEU;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + SWU;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + NWU;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + NEU;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + NED;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + SED;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + SEU;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + NEU;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + NWU;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + NWD;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + SWD;
        EmitVertex();

        gl_Position = gl_in[0].gl_Position + SWU;
        EmitVertex();

        EndPrimitive();
    }
);

// Fragment shader
const GLchar* fragmentShaderSrc = GLSL(
    in vec3 fColor;

    out vec4 outColor;

    void main()
    {
        outColor = vec4(fColor, 1.0);
    }
);

// Shader creation helper
GLuint createShader(GLenum type, const GLchar* src) {
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &src, nullptr);
    glCompileShader(shader);
    return shader;
}

int main()
{
    auto t_start = std::chrono::high_resolution_clock::now();

    sf::ContextSettings settings;
    settings.depthBits = 24;
    settings.stencilBits = 8;

    sf::Window window(sf::VideoMode(800, 600, 32), "Cubes", sf::Style::Titlebar | sf::Style::Close, settings);

    // Initialize GLEW
    glewExperimental = GL_TRUE;
    glewInit();

    // Compile and activate shaders
    GLuint vertexShader = createShader(GL_VERTEX_SHADER, vertexShaderSrc);
    GLuint geometryShader = createShader(GL_GEOMETRY_SHADER, geometryShaderSrc);
    GLuint fragmentShader = createShader(GL_FRAGMENT_SHADER, fragmentShaderSrc);

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, geometryShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

    // Create VBO with point coordinates
    GLuint vbo;
    glGenBuffers(1, &vbo);

    GLfloat points[] = {
    //  Coordinates             Color
        -0.45f,  0.45f, -0.45f, 1.0f, 0.0f, 0.0f,
         0.45f,  0.45f, -0.45f, 0.0f, 1.0f, 0.0f,
         0.45f, -0.45f, -0.45f, 0.0f, 0.0f, 1.0f,
        -0.45f, -0.45f, -0.45f, 1.0f, 1.0f, 0.0f,
        -0.45f,  0.45f,  0.45f, 0.0f, 1.0f, 1.0f,
         0.45f,  0.45f,  0.45f, 1.0f, 0.0f, 1.0f,
         0.45f, -0.45f,  0.45f, 1.0f, 0.5f, 0.5f,
        -0.45f, -0.45f,  0.45f, 0.5f, 1.0f, 0.5f,
    };

    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW);

    // Create VAO
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    // Specify layout of point data
    GLint posAttrib = glGetAttribLocation(shaderProgram, "pos");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), 0);

    GLint colAttrib = glGetAttribLocation(shaderProgram, "color");
    glEnableVertexAttribArray(colAttrib);
    glVertexAttribPointer(colAttrib, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (void*)(3 * sizeof(GLfloat)));

    // Set up transformation matrices
    GLint uniModel = glGetUniformLocation(shaderProgram, "model");

    glm::mat4 view = glm::lookAt(
        glm::vec3(1.5f, 1.5f, 2.0f),
        glm::vec3(0.0f, 0.0f, 0.0f),
        glm::vec3(0.0f, 0.0f, 1.0f)
    );
    GLint uniView = glGetUniformLocation(shaderProgram, "view");
    glUniformMatrix4fv(uniView, 1, GL_FALSE, glm::value_ptr(view));

    glm::mat4 proj = glm::perspective(glm::radians(45.0f), 800.0f / 600.0f, 1.0f, 10.0f);
    GLint uniProj = glGetUniformLocation(shaderProgram, "proj");
    glUniformMatrix4fv(uniProj, 1, GL_FALSE, glm::value_ptr(proj));

    bool running = true;
    while (running)
    {
        sf::Event windowEvent;
        while (window.pollEvent(windowEvent))
        {
            switch (windowEvent.type)
            {
            case sf::Event::Closed:
                running = false;
                break;
            }
        }

        // Clear the screen to black
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        
        // Calculate transformation
        auto t_now = std::chrono::high_resolution_clock::now();
        float time = std::chrono::duration_cast<std::chrono::duration<float>>(t_now - t_start).count();

        glm::mat4 model;
        model = glm::rotate(
            model,
            0.25f * time * glm::radians(180.0f),
            glm::vec3(0.0f, 0.0f, 1.0f)
        );
        glUniformMatrix4fv(uniModel, 1, GL_FALSE, glm::value_ptr(model));

        // Render frame
        glDrawArrays(GL_POINTS, 0, 8);

        // Swap buffers
        window.display();
    }

    glDeleteProgram(shaderProgram);
    glDeleteShader(fragmentShader);
    glDeleteShader(geometryShader);
    glDeleteShader(vertexShader);

    glDeleteBuffers(1, &vbo);

    glDeleteVertexArrays(1, &vao);

    window.close();

    return 0;
}