/**
 * libgamma -- Display server abstraction layer for gamma ramp adjustments
 * Copyright (C) 2014, 2015  Mattias Andrée (maandree@member.fsf.org)
 * 
 * This library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this library.  If not, see <http://www.gnu.org/licenses/>.
 */
#include "edid.h"

#include "libgamma-method.h"
#include "libgamma-error.h"

#include <stdint.h>


/*
 * EDID structure revision 1.1:
 *   http://en.wikipedia.org/w/index.php?title=Extended_display_identification_data&oldid=46295569
 * 
 * EDID structure revision 1.3:
 *   http://en.wikipedia.org/wiki/Extended_display_identification_data
 */


/**
 * Parse the EDID of a monitor.
 * 
 * @param   this    Instance of a data structure to fill with the information about the EDID.
 *                  It must contain the EDID and its length.
 * @param   feilds  OR:ed identifiers for the information about the EDID that should be parsed.
 *                  Fields that do not have to do with EDID are ignored.
 * @return          Non-zero on error.
 */
int libgamma_parse_edid(libgamma_crtc_information_t* restrict this, int32_t fields)
{
#define __test_version(edid, major, minor_min, minor_max)  \
  (((edid)[18] == major) && (minor_min <= (edid)[19]) && ((edid)[19] <= minor_max))
#define __m(value)  (this->edid[index++] != value)
  
  int error = 0;
  int checksum = 0;
  size_t i, index = 0;
  
  /* If the length of the EDID is not 128 bytes, we know that it is not of EDID
     structure revision 1.0–1.3, and thus we do not support it. Additionally
     this make sure we do not do segmentation violation on the next test. */
  if (this->edid_length != 128)
    error = LIBGAMMA_EDID_LENGTH_UNSUPPORTED;
  /* Check that the magic number of that of the EDID structure. */
  else if (__m(0x00) || __m(0xFF) || __m(0xFF) || __m(0xFF) || __m(0xFF) || __m(0xFF) || __m(0xFF) || __m(0x00))
    error = LIBGAMMA_EDID_WRONG_MAGIC_NUMBER;
  /* Check that EDID structure revision 1.1–1.3 is used, those are the only
     version we support. EDID structure revision 1.3 is also by far the most
     commonly use revision and it is currently the newest revision. We know
     that parsing works for both revision 1.1 and revision 1.3, because of
     this we assume it is also correct for revision 1.2. However, we are not
     assuming this for revision 1.0 which appeared in August 1994 and was
     replaced by revision 1.1 in April 1996. */
  else if (__test_version(this->edid, 1, 1, 3) == 0)
    error = LIBGAMMA_EDID_REVISION_UNSUPPORTED;
  
  /* If we have encountered an error, report it for the fields that require
     the EDID to be parsed. Note that it is not stored for the EDID field
     itself because it is not considered an error just because we do not
     support the used version. */
  this->width_mm_edid_error = this->height_mm_edid_error = this->gamma_error = error;
  
  /* Retrieve the size of the viewport. This is done even if it is not
     requested because it is not worth it branch. */
  this->width_mm_edid = (size_t)(this->edid[21]) * 10;
  this->height_mm_edid = (size_t)(this->edid[22]) * 10;
  
  /* Retrieve the monitor's gamma characteristics. */
  if ((fields & LIBGAMMA_CRTC_INFO_GAMMA) && (error == 0))
    {
      if (this->edid[23] == 0xFF)
	/* If the gamma charactistics is FFh (3,55) it should be interpreted as not specified. */
	this->gamma_error = LIBGAMMA_GAMMA_NOT_SPECIFIED;
      else
	this->gamma_red = this->gamma_green = this->gamma_blue = (float)((int)(this->edid[23]) + 100) / 100.f;
    }
  
  /* If not error has occurred, calculate and test the checksum.
     It is not considered an error that the gamma characteristics
     is left unspecified in the EDID. */
  if (error == 0)
    for (i = 0; i < this->edid_length; i++)
      checksum += (int)(this->edid[i]);
  /* The checksum should be zero. */
  if ((checksum & 255))
    {
      /* Store the error in all fields that require the EDID to be parsed,
         as well as the EDID field itself. */
      error = LIBGAMMA_EDID_CHECKSUM_ERROR;
      this->edid_error = this->width_mm_edid_error = this->height_mm_edid_error = error;
      /* If the gamma characteristics is not specified, that is kept,
         and the checksum error is augmented. */
      this->gamma_error = this->gamma_error == LIBGAMMA_GAMMA_NOT_SPECIFIED
	? LIBGAMMA_GAMMA_NOT_SPECIFIED_AND_EDID_CHECKSUM_ERROR : error;
    }
  
  /* Return whether or not we encountered an error or if
     the gamma characteristics was requested but is not
     specified in the monitor's EDID. */
  return error | this->gamma_error;
  
#undef __m
#undef __test_version
}