/*
 * initShader.c
 *
 *  Created on: Aug 28, 2017
 *      Author: Thumrongsak Kosiyatrakul
 */

#include "initShader.h"
#include <stdio.h>
#include <stdlib.h>

// Create a NULL-terminated string by reading the provided file
static char* readShaderSource(const char* shaderFile)
{
    FILE* fp = fopen(shaderFile, "r");

    if (fp == NULL)
	return NULL;

    fseek(fp, 0L, SEEK_END);
    long size = ftell(fp);

    fseek(fp, 0L, SEEK_SET);
    char *buf = (char *) malloc(size + 1);
    fread(buf, 1, size, fp);

    buf[size] = '\0';
    fclose(fp);

    return buf;
}


// Create a GLSL program object from vertex and fragment shader files
GLuint initShader(const char* vShaderFile, const char* fShaderFile)
{
    int i;

    struct Shader shaders[2] = {
	{ vShaderFile, GL_VERTEX_SHADER, NULL },
	{ fShaderFile, GL_FRAGMENT_SHADER, NULL }
    };

    GLuint program = glCreateProgram();

    for (i = 0; i < 2; ++i)
    {
	struct Shader s = shaders[i];
	s.source = readShaderSource(s.filename);
	if(s.source == NULL)
	{
	    fprintf(stderr, "Failed to read %s\n", s.filename);
	    exit(EXIT_FAILURE);
	}

	GLuint shader = glCreateShader(s.type);
	glShaderSource(shader, 1, (const GLchar**) &s.source, NULL);
	glCompileShader(shader);

	GLint  compiled;
	glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
	if ( !compiled )
	{
	    fprintf(stderr, "%s failed to compile:\n", s.filename);
	    GLint  logSize;
	    glGetShaderiv( shader, GL_INFO_LOG_LENGTH, &logSize );
	    char* logMsg = (char *) malloc(logSize);
	    glGetShaderInfoLog( shader, logSize, NULL, logMsg );
	    fprintf(stderr, "%s\n", logMsg);
	    free(logMsg);

	    exit( EXIT_FAILURE );
	}

	free(s.source);

	glAttachShader(program, shader);
    }

    /* link  and error check */
    glLinkProgram(program);

    GLint  linked;
    glGetProgramiv(program, GL_LINK_STATUS, &linked);
    if ( !linked )
    {
	fprintf(stderr, "Shader program failed to link\n");
	GLint  logSize;
	glGetProgramiv( program, GL_INFO_LOG_LENGTH, &logSize);
	char *logMsg = (char *) malloc(logSize);
	glGetProgramInfoLog( program, logSize, NULL, logMsg );
	fprintf(stderr, "%s\n", logMsg);
	free(logMsg);

	exit(EXIT_FAILURE);
    }

    /* use program object */
    glUseProgram(program);

    return program;
}