#include <iostream>
#include <fstream>
#include <cstring>
#include <GL/glut.h>
#include <GL/glext.h>

using namespace std; 

// This is a basic program to initiate a shader
// The textFileRead function reads in a filename into a string
// programerrors and shadererrors output compilation errors
// initshaders initiates a vertex or fragment shader
// initprogram initiates a program with vertex and fragment shaders

string textFileRead (const char * filename) {
	string str,ret = ""; 
	ifstream in; 
	in.open(filename); 
	if (in.is_open()) {
		getline (in,str); 
		while (in) {
			ret += str + "\n"; 
			getline (in,str); 
		}
		//    cout << "Shader below\n" << ret << "\n"; 
		return ret; 
	}
	else {
		cerr << "Unable to Open File " << filename << "\n"; 
		throw 2; 
	}
}

void programerrors (const GLint program) {
	GLint length; 
	GLchar * log; 
	glGetProgramiv(program,GL_INFO_LOG_LENGTH,&length); 
	log = new GLchar[length+1];
	glGetProgramInfoLog(program,length,&length,log); 
	cout << "Compile Error,Log Below\n" << log << "\n"; 
	delete [] log; 
}
void shadererrors (const GLint shader) {
	GLint length; 
	GLchar * log; 
	glGetShaderiv(shader,GL_INFO_LOG_LENGTH,&length); 
	log = new GLchar[length+1];
	glGetShaderInfoLog(shader,length,&length,log); 
	cout << "Compile Error,Log Below\n" << log << "\n"; 
	delete [] log; 
}

GLuint initshaders (GLenum type,const char *filename) 
{
	// Using GLSL shaders,OpenGL book,page 679 

	GLuint shader = glCreateShader(type); 
	GLint compiled; 
	string str = textFileRead (filename); 
	GLchar * cstr = new GLchar[str.size()+1]; 
	const GLchar * cstr2 = cstr; // Weirdness to get a const char
	strcpy(cstr,str.c_str()); 
	glShaderSource (shader,1,&cstr2,NULL); 
	glCompileShader (shader); 
	glGetShaderiv (shader,GL_COMPILE_STATUS,&compiled); 
	if (!compiled) { 
		shadererrors (shader); 
		throw 3; 
	}
	return shader; 
}

GLuint initprogram (GLuint vertexshader,GLuint fragmentshader) 
{
	GLuint program = glCreateProgram(); 
	GLint linked; 
	glAttachShader(program,vertexshader); 
	glAttachShader(program,fragmentshader); 
	glLinkProgram(program); 
	glGetProgramiv(program,GL_LINK_STATUS,&linked); 
	if (linked) glUseProgram(program); 
	else { 
		programerrors(program); 
		throw 4; 
	}
	return program; 
}
