#include "stdafx.h"
#include "Shaders.h"


PFNGLCREATESHADERPROC glCreateShader = NULL;
PFNGLSHADERSOURCEPROC glShaderSource = NULL;
PFNGLCOMPILESHADERPROC glCompileShader = NULL;
PFNGLGETSHADERIVPROC glGetShaderiv = NULL;
PFNGLGETPROGRAMIVPROC glGetProgramiv = NULL;
PFNGLCREATEPROGRAMPROC glCreateProgram = NULL;
PFNGLATTACHSHADERPROC glAttachShader = NULL;
PFNGLLINKPROGRAMPROC glLinkProgram = NULL;
PFNGLUSEPROGRAMPROC glUseProgram = NULL;
PFNGLGETSHADERINFOLOGPROC glGetShaderInfoLog = NULL;
PFNGLGETPROGRAMINFOLOGPROC glGetProgramInfoLog = NULL;


void useProgram(GLhandleARB ah_Program)
{
	glUseProgram(ah_Program);
}


void initShaders()
{
	glCreateShader = (PFNGLCREATESHADERPROC)myGetProcAddress("glCreateShader");
	glShaderSource = (PFNGLSHADERSOURCEPROC)myGetProcAddress("glShaderSource");
	glCompileShader = (PFNGLCOMPILESHADERPROC)myGetProcAddress("glCompileShader");
	glGetShaderiv =	(PFNGLGETSHADERIVPROC)myGetProcAddress("glGetShaderiv");
	glGetProgramiv = (PFNGLGETPROGRAMIVPROC)myGetProcAddress("glGetProgramiv");
	glCreateProgram = (PFNGLCREATEPROGRAMPROC)myGetProcAddress("glCreateProgram");
	glAttachShader = (PFNGLATTACHSHADERPROC)myGetProcAddress("glAttachShader");
	glLinkProgram = (PFNGLLINKPROGRAMPROC)myGetProcAddress("glLinkProgram");
	glUseProgram = (PFNGLUSEPROGRAMPROC)myGetProcAddress("glUseProgram");
	glGetShaderInfoLog = (PFNGLGETSHADERINFOLOGPROC)myGetProcAddress("glGetShaderInfoLog");
	glGetProgramInfoLog = (PFNGLGETPROGRAMINFOLOGPROC)myGetProcAddress("glGetProgramInfoLog");
	
	if (!(glCreateShader && glShaderSource && glCompileShader && glGetShaderiv && glGetProgramiv && glCreateProgram && glAttachShader && glLinkProgram && glUseProgram && glGetShaderInfoLog && glGetProgramInfoLog))
	{
		std::cerr <<  "Some shader functions are not available!" << std::endl;
	}
}


GLhandleARB createVertexShader(const char* as_FileName)
{
	GLhandleARB lh_Shader = 0;
	
	char* ls_ShaderSource = textFileRead(as_FileName);

	if (ls_ShaderSource == NULL)
	{
		std::cerr << "Error reading file: " << as_FileName << std::endl;
		return lh_Shader;
	}

	lh_Shader = glCreateShader(GL_VERTEX_SHADER);

	glShaderSource(lh_Shader, 1, (const char**)&ls_ShaderSource, NULL);
	glCompileShader(lh_Shader);

	free(ls_ShaderSource);

	int li_Status = 0;
	glGetShaderiv(lh_Shader, GL_COMPILE_STATUS, &li_Status);

	if (li_Status == GL_FALSE)
	{
		std::cerr << "Error compiling vertex shader: " << as_FileName << std::endl;
	}

	return lh_Shader;
}


GLhandleARB createFragmentShader(const char* as_FileName)
{
	GLhandleARB lh_Shader = 0;

	char* ls_ShaderSource = textFileRead(as_FileName);
	if (ls_ShaderSource == NULL)
	{
		std::cerr << "Error reading file: " << as_FileName << std::endl;
		return lh_Shader;
	}

	lh_Shader = glCreateShader(GL_FRAGMENT_SHADER);

	glShaderSource(lh_Shader, 1, (const char**)&ls_ShaderSource, NULL);
	glCompileShader(lh_Shader);

	int li_Status = 0;

	glGetShaderiv(lh_Shader, GL_COMPILE_STATUS, &li_Status);

	if (li_Status == GL_FALSE)
	{
		std::cerr << "Error compiling fragment shader: " << as_FileName << std::endl;
	}

	free(ls_ShaderSource);

	return lh_Shader;
}


GLhandleARB createProgram(GLhandleARB ah_VertexShader, GLhandleARB ah_FragmentShader)
{
	GLhandleARB lh_Program = 0;
	
	if (ah_VertexShader + ah_FragmentShader <= 1)
	{
		std::cerr << "Cannot create program." << std::endl;
		return lh_Program;
	}

	lh_Program = glCreateProgram();

	glAttachShader(lh_Program, ah_VertexShader);
	glAttachShader(lh_Program, ah_FragmentShader);
	glLinkProgram(lh_Program);

	int li_Status = 0;

	glGetProgramiv(lh_Program, GL_LINK_STATUS, &li_Status);

	if (li_Status == GL_FALSE)
	{
		std::cerr << "Error linking shaders." << std::endl;
	}

	return lh_Program;
}


char* textFileRead(const char* as_FileName) 
{
	FILE* lh_File;
	char* ls_Content = NULL;
	size_t li_Count = 0;

	if (as_FileName != NULL) 
	{
		fopen_s(&lh_File, as_FileName, "rt");

		if (lh_File != NULL) 
		{
			fseek(lh_File, 0, SEEK_END);
			li_Count = ftell(lh_File);
			rewind(lh_File);

			if (li_Count > 0) 
			{
				ls_Content = (char*) malloc(sizeof(char) * (li_Count + 1));
				li_Count = fread(ls_Content, sizeof(char), li_Count, lh_File);
				ls_Content[li_Count] = '\0';
			}

			fclose(lh_File);
		}
	}

	return ls_Content;
}