#include "shader.h"

static void checkShaderError(GLuint shader, GLuint flag, bool isProgram, const std::string &errorMessage);
static std::string loadShader(const std::string &fileName);
static GLuint createShader(const std::string &text, GLenum shaderType);

Shader::Shader(const std::string &fileName)
{
	m_program = glCreateProgram();
	m_shaders[0] = createShader(loadShader(fileName + ".vs"), GL_VERTEX_SHADER);
	m_shaders[1] = createShader(loadShader(fileName + ".fs"), GL_FRAGMENT_SHADER);

	for (unsigned int i = 0; i < NUM_SHADERS; i++)
		glAttachShader(m_program, m_shaders[i]);

	glBindAttribLocation(m_program, 0, "position");

	glLinkProgram(m_program);
	checkShaderError(m_program, GL_LINK_STATUS, true, "Error: Shader linking failed: ");

	glValidateProgram(m_program);
	checkShaderError(m_program, GL_VALIDATE_STATUS, true, "Error: Shader validation failed: ");
}

Shader::~Shader()
{
	for (unsigned int i = 0; i < NUM_SHADERS; i++)
	{
		glDetachShader(m_program, m_shaders[i]);
		glDeleteShader(m_shaders[i]);
	}
	glDeleteProgram(m_program);
}

void Shader::bind()
{
	glUseProgram(m_program);
}

static GLuint createShader(const std::string &text, GLenum shaderType)
{
	GLuint shader = glCreateShader(shaderType);

	if (shader == 0)
		std::cerr << "Error: Shader creation failed!" << std::endl;

	const GLchar *p[1];
	GLint pLengths[1];

	p[0] = text.c_str();
	pLengths[0] = text.length();

	glShaderSource(shader, 1, p, pLengths);
	glCompileShader(shader);

	checkShaderError(shader, GL_COMPILE_STATUS, false, "Error: Shader compilation failed: ");

	return shader;
}

static std::string loadShader(const std::string &fileName)
{

	std::ifstream file;
	file.open((fileName).c_str());

	std::string output;
	std::string line;

	if (file.is_open())
	{
		while (file.good())
		{
			getline(file, line);
			output.append(line + "/n");
		}
	}

	else
	{
		std::cerr << "Unable to load shader: " + fileName << std::endl;
	}

	return output;
}

static void checkShaderError(GLuint shader, GLuint flag, bool isProgram, const std::string &errorMessage)
{
	GLint success = 1;
	GLchar error[1024] = { 0 };

	if (isProgram)
		glGetProgramiv(shader, flag, &success);
	else
		glGetShaderiv(shader, flag, &success);

	if (success == GL_FALSE)
	{
		if (isProgram)
			glGetProgramInfoLog(shader, sizeof(error), NULL, error);
		else
			glGetShaderInfoLog(shader, sizeof(error), NULL, error);

		std::cerr << errorMessage + ": '" + error + "'" << std::endl;
	}
}