#include "esUtil.h"
typedef struct
{
    // Handle to a program object
   GLuint programObject;
} UserData;
///
// Create a shader object, load the shader source, and
// compile the shader.
//
GLuint LoadShader(const char *shaderSrc, GLenum type)
{
   GLuint shader;
   GLint compiled;
   // Create the shader object
    shader = glCreateShader(type);
   if(shader == 0)
       return 0;
   // Load the shader source
   glShaderSource(shader, 1, &shaderSrc, NULL);
    // Compile the shader
   glCompileShader(shader);
    // Check the compile status
   glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
   if(!compiled)
   {
       GLint infoLen = 0;
       glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);
       if(infoLen > 1)
       {
          char* infoLog = malloc(sizeof(char) * infoLen);
          glGetShaderInfoLog(shader, infoLen, NULL, infoLog);
          esLogMessage("Error compiling shader:\n%s\n", infoLog);
          free(infoLog);
       }
       glDeleteShader(shader);
       return 0;
   }
   return shader;
}
///
// Initialize the shader and program object
//
int Init(ESContext *esContext)
{
    UserData *userData = esContext->userData;
   GLbyte vShaderStr[] =
       "attribute vec4 vPosition;   \n"
       "void main()                 \n"
       "{                           \n"
       "   gl_Position = vPosition; \n"
       "}                           \n";
   GLbyte fShaderStr[] =
       "precision mediump float;                   \n"
       "void main()                                \n"
       "{                                          \n"
       " gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); \n"
       "}                                          \n";
   GLuint vertexShader;
   GLuint fragmentShader;
   GLuint programObject;
   GLint linked;
  // Load the vertex/fragment shaders
  vertexShader = LoadShader(GL_VERTEX_SHADER, vShaderStr);
  fragmentShader = LoadShader(GL_FRAGMENT_SHADER, fShaderStr);
  // Create the program object
  programObject = glCreateProgram();
  if(programObject == 0)
     return 0;
  glAttachShader(programObject, vertexShader);
  glAttachShader(programObject, fragmentShader);
  // Bind vPosition to attribute 0
  glBindAttribLocation(programObject, 0, "vPosition");
  // Link the program
  glLinkProgram(programObject);
  // Check the link status
  glGetProgramiv(programObject, GL_LINK_STATUS, &linked);
  if(!linked)
  {
     GLint infoLen = 0;
     glGetProgramiv(programObject, GL_INFO_LOG_LENGTH, &infoLen);
     if(infoLen > 1)
     {
        char* infoLog = malloc(sizeof(char) * infoLen);
        glGetProgramInfoLog(programObject, infoLen, NULL, infoLog);
        esLogMessage("Error linking program:\n%s\n", infoLog);
        free(infoLog);
     }
     glDeleteProgram(programObject);
     return FALSE;
  }
  // Store the program object
  userData->programObject = programObject;
  glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
  return TRUE;
}
///
// Draw a triangle using the shader pair created in Init()
//
void Draw(ESContext *esContext)
{
    UserData *userData = esContext->userData;
   GLfloat vVertices[] = {0.0f, 0.5f, 0.0f,
                           -0.5f, -0.5f, 0.0f,
                           0.5f, -0.5f, 0.0f};
    // Set the viewport
   glViewport(0, 0, esContext->width, esContext->height);
    // Clear the color buffer
   glClear(GL_COLOR_BUFFER_BIT);
    // Use the program object
   glUseProgram(userData->programObject);
   // Load the vertex data
   glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vVertices);
   glEnableVertexAttribArray(0);
   glDrawArrays(GL_TRIANGLES, 0, 3);
   eglSwapBuffers(esContext->eglDisplay, esContext->eglSurface);
}
int main(int argc, char *argv[])
{
   ESContext esContext;
   UserData userData;
   esInitialize(&esContext);
    esContext.userData = &userData;
   esCreateWindow(&esContext, "Hello Triangle", 320, 240,
                   ES_WINDOW_RGB);
   if(!Init(&esContext))
       return 0;
   esRegisterDrawFunc(&esContext, Draw);
   esMainLoop(&esContext);
}