// Link statically with GLEW
#define GLEW_STATIC

// Headers
#include <GL/glew.h>
#include <SFML/Window.hpp>

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

// Vertex shader
const GLchar* vertexShaderSrc = GLSL(
    in vec2 pos;
    in vec3 color;
    in float sides;

    out vec3 vColor;
    out float vSides;

    void main()
    {
        gl_Position = vec4(pos, 0.0, 1.0);
        vColor = color;
        vSides = sides;
    }
);

// Geometry shader
const GLchar* geometryShaderSrc = GLSL(
    layout(points) in;
    layout(line_strip, max_vertices = 64) out;

    in vec3 vColor[];
    in float vSides[];
    out vec3 fColor;

    const float PI = 3.1415926;

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

        // Safe, GLfloats can represent small integers exactly
        for (int i = 0; i <= vSides[0]; i++) {
            // Angle between each side in radians
            float ang = PI * 2.0 / vSides[0] * i;

            // Offset from center of point (0.3 to accomodate for aspect ratio)
            vec4 offset = vec4(cos(ang) * 0.3, -sin(ang) * 0.4, 0.0, 0.0);
            gl_Position = gl_in[0].gl_Position + offset;

            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()
{
    sf::ContextSettings settings;
    settings.depthBits = 24;
    settings.stencilBits = 8;

    sf::Window window(sf::VideoMode(800, 600, 32), "Circles", 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             Sides
        -0.45f,  0.45f, 1.0f, 0.0f, 0.0f,  4.0f,
         0.45f,  0.45f, 0.0f, 1.0f, 0.0f,  8.0f,
         0.45f, -0.45f, 0.0f, 0.0f, 1.0f, 16.0f,
        -0.45f, -0.45f, 1.0f, 1.0f, 0.0f, 32.0f
    };

    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 the layout of the vertex data
    GLint posAttrib = glGetAttribLocation(shaderProgram, "pos");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 2, 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*) (2 * sizeof(GLfloat)));

    GLint sidesAttrib = glGetAttribLocation(shaderProgram, "sides");
    glEnableVertexAttribArray(sidesAttrib);
    glVertexAttribPointer(sidesAttrib, 1, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (void*) (5 * sizeof(GLfloat)));

    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);

        // Render frame
        glDrawArrays(GL_POINTS, 0, 4);

        // Swap buffers
        window.display();
    }

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

    glDeleteBuffers(1, &vbo);

    glDeleteVertexArrays(1, &vao);

    window.close();

    return 0;
}