// This code example is created for educational purpose
// by Thorsten Thormaehlen (contact: www.thormae.de).
// It is distributed without any warranty.

#include <GL/glew.h>
#include <GL/freeglut.h> // we use glut here as window manager
#define _USE_MATH_DEFINES
#include <math.h>

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <vector>
using namespace std;

class Renderer {

private:
  struct Vertex {
    float position[3];
    float color[4];
  };

public:
  float t;

private:
  enum {Triangle, numVAOs};
  enum {TriangleAll, numVBOs};
  GLuint vaoID[numVAOs];
  GLuint bufID[numVBOs];
  int triangleVertNo;
  GLuint progID;
  GLuint vertID;
  GLuint fragID;
  GLint vertexLoc;
  GLint colorLoc;
  GLint projectionLoc;
  GLint modelviewLoc;
  float projection[16];  // projection matrix
  float modelview[16];  // modelview matrix

public:
  // constructor
  Renderer() : t(0.0f), triangleVertNo(0), progID(0), vertID(0), fragID(0),
               vertexLoc(-1), colorLoc(-1), projectionLoc(-1), modelviewLoc(-1)
               {}

public:
  void init() {
    glEnable(GL_DEPTH_TEST);

    setupShaders();

    // create a Vertex Array Objects (VAO)
    glGenVertexArrays(numVAOs, vaoID);

    // generate a Vertex Buffer Object (VBO)
    glGenBuffers(numVBOs, bufID);

    // binding the Triangle VAO
    glBindVertexArray(vaoID[Triangle]);

    float triangleVertexData[] = {
       0.0f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f,
      -0.5f,-0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f,
       0.5f,-0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 1.0f,
    };
    triangleVertNo = 3;

    glBindBuffer(GL_ARRAY_BUFFER, bufID[TriangleAll]);
    glBufferData(GL_ARRAY_BUFFER, triangleVertNo*sizeof(Vertex),
                 triangleVertexData, GL_STATIC_DRAW);

    int stride = sizeof(Vertex); // stride in bytes
    int offset = 0; // offset in bytes

    // position
    if(vertexLoc != -1) {
      glVertexAttribPointer(vertexLoc, 3, GL_FLOAT, GL_FALSE, stride, (const void*)(intptr_t)offset);
      glEnableVertexAttribArray(vertexLoc);
    }

    // color
    if(colorLoc != -1) {
      offset = 3 * sizeof(float);
      glVertexAttribPointer(colorLoc, 4, GL_FLOAT, GL_FALSE, stride, (const void*)(intptr_t)offset);
      glEnableVertexAttribArray(colorLoc);
    }
  }

  void resize(int w, int h) {
    glViewport(0, 0, w, h);

    // this function replaces gluPerspective
    mat4Perspective(projection, 45.0f, (float)w/(float)h, 0.5f, 4.0f);
    // mat4Print(projection);
  }

  void display() {
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // camera orbits in the y=2 plane
    // and looks at the origin
    // mat4LookAt replaces gluLookAt
    double rad = M_PI / 180.0f * t;
    mat4LookAt(modelview,
               2.0f*float(cos(rad)), 2.0f, 2.0f*float(sin(rad)), // eye
               0.0f, 0.0f, 0.0f, // look at
               0.0f, 1.0f, 0.0f); // up
  
    //mat4Print(modelview);

    glUseProgram(progID);

    // load the current projection and modelview matrix into the
    // corresponding UNIFORM variables of the shader
    glUniformMatrix4fv(projectionLoc, 1, false, projection);
    glUniformMatrix4fv(modelviewLoc, 1, false, modelview);

    // bind Triangle VAO
    glBindVertexArray(vaoID[Triangle]);
    // render data
    glDrawArrays(GL_TRIANGLES, 0, triangleVertNo);
  }

  void dispose() {
    glDeleteVertexArrays(numVAOs, vaoID);
    glDeleteBuffers(numVBOs, bufID);
    glDeleteProgram(progID);
    glDeleteShader(vertID);
    glDeleteShader(fragID);
  }

private:
  void setupShaders() {

    // create shader
    vertID = glCreateShader(GL_VERTEX_SHADER);
    fragID = glCreateShader(GL_FRAGMENT_SHADER);

    // load shader source from file
    std::string vs = loadShaderSrc("./uniform.vert");
    const char* vss = vs.c_str();
    std::string fs = loadShaderSrc("./uniform.frag");
    const char* fss = fs.c_str();

    // specify shader source
    glShaderSource(vertID, 1, &(vss), NULL);
    glShaderSource(fragID, 1, &(fss), NULL);

    // compile the shader
    glCompileShader(vertID);
    glCompileShader(fragID);

    // check for errors
    printShaderInfoLog(vertID);
    printShaderInfoLog(fragID);

    // create program and attach shaders
    progID = glCreateProgram();
    glAttachShader(progID, vertID);
    glAttachShader(progID, fragID);

    // "outColor" is a user-provided OUT variable
    // of the fragment shader.
    // Its output is bound to the first color buffer
    // in the framebuffer
    glBindFragDataLocation(progID, 0, "outputColor");

    // link the program
    glLinkProgram(progID);
    // output error messages
    printProgramInfoLog(progID);

    // "inputPosition" and "inputColor" are user-provided
    // IN variables of the vertex shader.
    // Their locations are stored to be used later with
    // glEnableVertexAttribArray()
    vertexLoc = glGetAttribLocation(progID, "inputPosition");
    colorLoc = glGetAttribLocation(progID, "inputColor");

    // "projection" and "modelview" are user-provided
    // UNIFORM variables of the vertex shader.
    // Their locations are stored for later use.
    projectionLoc = glGetUniformLocation(progID, "projection");
    modelviewLoc = glGetUniformLocation(progID, "modelview");

  }

  void printShaderInfoLog(GLuint obj) {
    int infoLogLength = 0;
    int returnLength  = 0;
    char *infoLog;
    glGetShaderiv(obj, GL_INFO_LOG_LENGTH,&infoLogLength);
    if (infoLogLength > 0) {
      infoLog = (char *)malloc(infoLogLength);
      glGetShaderInfoLog(obj, infoLogLength, &returnLength, infoLog);
      printf("%s\n",infoLog);
      free(infoLog);
    }
  }

  void printProgramInfoLog(GLuint obj) {
    int infoLogLength = 0;
    int returnLength  = 0;
    char *infoLog;
    glGetProgramiv(obj, GL_INFO_LOG_LENGTH,&infoLogLength);
    if (infoLogLength > 0) {
      infoLog = (char *)malloc(infoLogLength);
      glGetProgramInfoLog(obj, infoLogLength, &returnLength, infoLog);
      printf("%s\n",infoLog);
      free(infoLog);
    }
  }

  std::string loadShaderSrc(const std::string& filename) {
    std::ifstream is(filename);
    if (is.is_open()) {
      std::stringstream buffer;
      buffer << is.rdbuf();
      return buffer.str();
    }
    cerr << "Unable to open file " << filename << endl;
    exit(1);
  }

  // the following functions are some matrix and vector helpers
  // they work for this demo but in general it is recommended
  // to use more advanced matrix libraries,
  // e.g. OpenGL Mathematics (GLM)
  float vec3Dot( float *a, float *b) {
    return a[0]*b[0] + a[1]*b[1] + a[2]*b[2];
  }

  void vec3Cross( float *a, float *b, float *res) {
    res[0] = a[1] * b[2]  -  b[1] * a[2];
    res[1] = a[2] * b[0]  -  b[2] * a[0];
    res[2] = a[0] * b[1]  -  b[0] * a[1];
  }

  void vec3Normalize(float *a) {
    float mag = sqrt(a[0] * a[0]  +  a[1] * a[1]  +  a[2] * a[2]);
    a[0] /= mag; a[1] /= mag; a[2] /= mag;
  }

  void mat4Identity( float *a) {
    for (int i = 0; i < 16; ++i) a[i] = 0.0f;
    for (int i = 0; i < 4; ++i) a[i + i * 4] = 1.0f;
  }

  void mat4Multiply(float *a, float *b, float *res) {
    for (int i = 0; i < 4; ++i) {
      for (int j = 0; j < 4; ++j) {
        res[j*4 + i] = 0.0f;
        for (int k = 0; k < 4; ++k) {
          res[j*4 + i] += a[k*4 + i] * b[j*4 + k];
        }
      }
    }
  }

  void mat4Perspective(float *a, float fov, float aspect, float zNear, float zFar) {
    float f = 1.0f / float(tan (fov/2.0f * (M_PI / 180.0f)));
    mat4Identity(a);
    a[0] = f / aspect;
    a[1 * 4 + 1] = f;
    a[2 * 4 + 2] = (zFar + zNear)  / (zNear - zFar);
    a[3 * 4 + 2] = (2.0f * zFar * zNear) / (zNear - zFar);
    a[2 * 4 + 3] = -1.0f;
    a[3 * 4 + 3] = 0.0f;
  }

  void mat4LookAt(float *viewMatrix,
                  float eyeX, float eyeY, float eyeZ,
                  float centerX, float centerY, float centerZ,
                  float upX, float upY, float upZ) {

    float dir[3], right[3], up[3], eye[3];
    up[0]=upX; up[1]=upY; up[2]=upZ;
    eye[0]=eyeX; eye[1]=eyeY; eye[2]=eyeZ;

    dir[0]=centerX-eyeX; dir[1]=centerY-eyeY; dir[2]=centerZ-eyeZ;
    vec3Normalize(dir);
    vec3Cross(dir,up,right);
    vec3Normalize(right);
    vec3Cross(right,dir,up);
    vec3Normalize(up);
    // first row
    viewMatrix[0]  = right[0];
    viewMatrix[4]  = right[1];
    viewMatrix[8]  = right[2];
    viewMatrix[12] = -vec3Dot(right, eye);
    // second row
    viewMatrix[1]  = up[0];
    viewMatrix[5]  = up[1];
    viewMatrix[9]  = up[2];
    viewMatrix[13] = -vec3Dot(up, eye);
    // third row
    viewMatrix[2]  = -dir[0];
    viewMatrix[6]  = -dir[1];
    viewMatrix[10] = -dir[2];
    viewMatrix[14] =  vec3Dot(dir, eye);
    // forth row
    viewMatrix[3]  = 0.0f;
    viewMatrix[7]  = 0.0f;
    viewMatrix[11] = 0.0f;
    viewMatrix[15] = 1.0f;
  }
  void mat4Print(float* a) {
    // opengl uses column major order
    for (int i = 0; i < 4; ++i) {
      for (int j = 0; j < 4; ++j) {
        cout << a[j * 4 + i] << " ";
      }
      cout << endl;
    }
  }
};


//this is a static pointer to a Renderer used in the glut callback functions
static Renderer *renderer;

//glut static callbacks start
static void glutResize(int w, int h) 
{
  renderer->resize(w,h);
}

static void glutDisplay() 
{
  renderer->display();
  glutSwapBuffers();
  glutReportErrors();
}

static void glutClose()
{
  renderer->dispose();
}

static void timer(int v) 
{
  float offset = 1.0f;
  renderer->t += offset;
  glutDisplay();
  glutTimerFunc(unsigned(20), timer, ++v);
}

int main(int argc, char **argv) 
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
  glutInitWindowPosition(100,100);
  glutInitWindowSize(320, 320);

  glutCreateWindow("Shader-based gluLookAt simulation");
  GLenum err = glewInit();
  if (GLEW_OK != err) {
    fprintf(stderr, "Glew error: %s\n", glewGetErrorString(err));
  }
  glutDisplayFunc(glutDisplay);
  //glutIdleFunc(glutDisplay);
  glutReshapeFunc(glutResize);
  glutCloseFunc(glutClose);

  renderer = new Renderer;
  renderer->init();

  glutTimerFunc(unsigned(20), timer, 0);

  glutMainLoop();
}