#include <cstdio>

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <cstdlib>
#include <cstring>
#include <vector>

GLuint loadShader(const char *source, GLenum shader_type) {
  GLuint shaderId = glCreateShader(shader_type);
  GLint result = GL_FALSE;
  int infoLogLength;
  // Compile Vertex Shader
  glShaderSource(shaderId, 1, &source, nullptr);
  glCompileShader(shaderId);
  glGetShaderiv(shaderId, GL_COMPILE_STATUS, &result);
  glGetShaderiv(shaderId, GL_INFO_LOG_LENGTH, &infoLogLength);
  if (infoLogLength > 0) {
    std::vector<char> VertexShaderErrorMessage(infoLogLength + 1);
    glGetShaderInfoLog(shaderId, infoLogLength, nullptr,
                       &VertexShaderErrorMessage[0]);
    printf("%s\n", &VertexShaderErrorMessage[0]);
    exit(-1);
  }
  return shaderId;
}

GLuint loadProgram(const std::vector<GLuint> &shaders) {
  GLuint programId = glCreateProgram();
  for (const auto &item : shaders) {
    glAttachShader(programId, item);
  }
  glLinkProgram(programId);

  GLint result = GL_FALSE;
  int infoLogLength;

  glGetProgramiv(programId, GL_LINK_STATUS, &result);
  glGetProgramiv(programId, GL_INFO_LOG_LENGTH, &infoLogLength);
  if (infoLogLength > 0) {
    std::vector<char> ProgramErrorMessage(infoLogLength + 1);
    glGetProgramInfoLog(programId, infoLogLength, nullptr,
                        &ProgramErrorMessage[0]);
    printf("%s\n", &ProgramErrorMessage[0]);
  }
  return programId;
}

static const char *vertex_shader =
    "#version 460\n"
    "layout(location = 0) in vec3 vertexPosition_modelspace;\n"
    "out vec2 coord;\n"
    "void main(){\n"
    "  gl_Position.xyz = vertexPosition_modelspace;\n"
    "  gl_Position.w = 1.0;\n"
    "  coord.xy = vertexPosition_modelspace.xy;\n"
    "}";

static const char *fragment_shader = "#version 460\n"
                                     "out vec3 color;\n"
                                     "in vec2 coord;\n"
                                     "layout (std430, binding = 2) restrict readonly buffer shader_data\n"
                                     "{\n"
                                     "  int c[];\n"
                                     "};\n"

                                     "void main(){\n"
                                     "  int x = int(255. * (coord.x + 1.) / 2.);"
                                     "  color = vec3(c[x]/255., 0.5,0.5);\n"
                                     "}";

int main() {
  glewExperimental = true;
  if (!glfwInit()) {
    fprintf(stderr, "Failed to initialize GLFW\n");
    return -1;
  }

  glfwWindowHint(GLFW_SAMPLES, 0);
  glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
  glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 6);
  glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
  glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

  GLFWwindow *window =
      glfwCreateWindow(1024, 768, "Tutorial 01", nullptr, nullptr);
  if (window == nullptr) {
    fprintf(stderr,
            "Failed to open GLFW window. If you have an Intel GPU, they are "
            "not 3.3 compatible. Try the 2.1 version of the tutorials.\n");
    glfwTerminate();
    return -1;
  }
  glfwMakeContextCurrent(window); // Initialize GLEW
  glewExperimental = true;        // Needed in core profile
  if (glewInit() != GLEW_OK) {
    fprintf(stderr, "Failed to initialize GLEW\n");
    return -1;
  }

  glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);

  GLuint VertexArrayID;
  glGenVertexArrays(1, &VertexArrayID);
  glBindVertexArray(VertexArrayID);
  const GLfloat g_vertex_buffer_data[] = {
      -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f,
  };
  GLuint vertexbuffer;
  glGenBuffers(1, &vertexbuffer);
  glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
  glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data),
               g_vertex_buffer_data, GL_STATIC_DRAW);

  GLuint programId = loadProgram({
      loadShader(vertex_shader, GL_VERTEX_SHADER),
      loadShader(fragment_shader, GL_FRAGMENT_SHADER),
  });

  int c[256];

  for (size_t i = 0; i < 256; ++i) {
    c[i] = i;
  }

  GLuint ssbo = 0;
  glGenBuffers(1, &ssbo);
  glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
  glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(int)*256, &c,GL_DYNAMIC_COPY);
  glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);

  unsigned int block_index = glGetProgramResourceIndex(programId, GL_SHADER_STORAGE_BLOCK, "shader_data");
  GLuint ssbo_binding_point_index = 2;
  glBindBufferBase(GL_SHADER_STORAGE_BUFFER, ssbo_binding_point_index, ssbo);
  glShaderStorageBlockBinding(programId, block_index, ssbo_binding_point_index);

  do {
    glClear(GL_COLOR_BUFFER_BIT);
    glUseProgram(programId);

    for (int & i : c) {
      i = (i + 1) % 256;
    }

    glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
    GLvoid *p = glMapBuffer(GL_SHADER_STORAGE_BUFFER, GL_WRITE_ONLY);
    std::memcpy(p, &c, sizeof(int) * 256);
    glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);

    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
    glDrawArrays(GL_TRIANGLES, 0,3);
    glDisableVertexAttribArray(0);

    glfwSwapBuffers(window);
    glfwPollEvents();

  } // Check if the ESC key was pressed or the window was closed
  while (glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS &&
         glfwWindowShouldClose(window) == 0);
}