argument to check if the node's author is the logged in user

I think there is something wrong with the user access of "edit own availability calendars"
When you grant a role user access "edit own availability calendars" they can not only edit their own calendars but every users calendar and I would like to change that. Users should only be permitted to edit calendars on nodes that they created.

the full code is this

<?php
// $Id: availability_calendars.module,v 1.1.4.4 2009/01/11 15:59:45 geodan Exp $

/**
 * Availability Calendars Module
 *
 * @file
 * Allows for availability information to be displayed using calendars on specified content types. Originally based on the Availability Module.
 * @author Dan Karran (geodaniel) <dan at karran dot net>
 */

/**
 * A callback function to see if allowed to edit the calendar.
 */
function availability_can_edit() {

  return user_access('edit availability calendars') || user_access('edit own availability calendars');

}

/**
 * Implementation of hook_menu().
 */
function availability_calendars_menu() {
  $items = array();

  $items['admin/settings/availability-calendars'] = array(
    'title' => 'Availability Calendars',
    'description' => 'Configure global settings for availability calendars module.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('availability_calendars_admin_settings'),
    'access arguments' => array('edit availability calendars')
  );

  $items['availability-calendars'] = array(
    'title' => 'Availability calendar',
    'page callback' => 'availability_calendars_page',
    'access callback' => 'availability_can_edit',
    'type' => MENU_CALLBACK,
  );

  return $items;
}

/**
 * Implementation of hook_perm().
 */
function availability_calendars_perm() {
  return array('edit own availability calendars', 'edit availability calendars');
}

/**
 * Settings page callback.
 */
function availability_calendars_admin_settings() {
  $form = array();

  $form['display'] = array(
    '#type' => 'fieldset',
    '#title' => t('View settings'),
    '#description' => t('Check where you want availability calendars to be displayed. If you choose none of the suggested places below you will need to output it manually using %func function.', array('%func' => 'theme_availability_calendars_node()'))
  );
  $form['display']['availability_calendars_display_nodeview'] = array(
    '#type' => 'checkbox',
    '#title' => t('Node view page'),
    '#default_value' => variable_get('availability_calendars_display_nodeview', TRUE)
  );
  $form['display']['availability_calendars_display_monthcount'] = array(
    '#type' => 'textfield',
    '#title' => t('Number of months to display'),
    '#default_value' => variable_get('availability_calendars_display_monthcount', 12),
    '#description' => t("Your calendars will show this number of months to all users except those with the 'edit own availability calendars' or 'edit availability calendars' who will always see 3 extra months on the calendars they can edit. This is to allow them to enter information into future calendars before it is made publicly available.")
  );

  //TODO: add status codes and css classes in here

  return system_settings_form($form);
}

/**
 * Create tab to show node availability
 */
function availability_calendars_menu_callback() {
  $node = menu_get_object();

  if (availability_calendars_enabled($node->type)) {
    return theme('availability_calendars_node', $node);
  }
  else {
    return FALSE;
  }
}

/**
 * Availability calendars page
 */
function availability_calendars_page($nid = NULL, $year = NULL, $month = NULL, $edit = FALSE) {
  if (is_numeric($nid)) {
    $node = node_load($nid);
    drupal_set_title(t('Availability for %name', array('%name' => $node->title)));

    if (is_numeric($year) && is_numeric($month)) {
      drupal_set_title(t('Availability for %name in %date', array('%name' => $node->title, '%date' => date('M Y', strtotime("$year-$month-01")))));
      if ($edit == 'edit') {
        // Display the edit form for the availability calendar on the node
        return availability_calendars_node_edit($node, $year, $month);
      }
      else {
        // Display availability calendar for single month
        $monthstodisplay = 1;
        return theme('availability_calendars_node', $node, $year, $month, $monthstodisplay);
      }
    }
    elseif (is_numeric($year)) {
      // Display availability calendar for a whole year
      $month = 1;
      $monthstodisplay = 12;
      return theme('availability_calendars_node', $node, $year, $month, $monthstodisplay);
    }
    else {
      // Display rolling availability calendar from this point onwards
      $year = date('Y');
      $month = date('m');
      $monthstodisplay = variable_get('availability_display_monthcount', 12);
      return theme('availability_calendars_node', $node, $year, $month, $monthstodisplay);
    }
  }
  else {
    print drupal_not_found();
  }
}

function availability_calendars_node_edit() {
  return drupal_get_form('availability_calendars_node_edit_form');
}

function availability_calendars_node_edit_form() {
  $nid = check_plain(arg(1));
  $year = check_plain(arg(2));
  $month = check_plain(arg(3));
  $form['nid'] = array(
    '#type' => 'hidden',
    '#default_value' => $nid,
  );
  $form['year'] = array(
    '#type' => 'hidden',
    '#default_value' => $year,
  );
  $form['month'] = array(
    '#type' => 'hidden',
    '#default_value' => $month,
  );

  $startofweek = variable_get('availability_calendars_'. $nid .'_startofweek', 1);
  $month_meta = availability_calendars_month_meta($year, $month, $startofweek);

  // find all entries in database for this month ($availability, $notes) and pre-populate
  $notes_result = db_query('SELECT week, note FROM {availability_calendars_week} WHERE nid = %d AND year = %d and month = %d', $nid, $year, $month);
  while ($note = db_fetch_array($notes_result)) {
    $notes[$note['week']] = $note['note'];
  }

  $status_result = db_query('SELECT day, status FROM {availability_calendars_day} WHERE nid = %d AND year = %d AND month = %d', $nid, $year, $month);
  while ($status = db_fetch_array($status_result)) {
    $day_status[$status['day']] = $status['status'];
  }

  $day = 1;
  for ($week = 1; $week <= $month_meta['weeksinmonth']; $week++) {
    $form['week-'. $week] = array(
      '#type' => 'fieldset',
      '#title' => 'Week '. $week,
    );
    $form['week-'. $week]['note-'. $week] = array(
      '#type' => 'textfield',
      '#title' => 'Note',
      '#default_value' => $notes[$week],
      '#description' => 'This will be displayed beside the week in the calendar. It could include, for example, a weekly price.',
    );
    if ($week == 1) {
      $daysinweekremaining = 7 - $month_meta['firstday'];
    }
    else {
      $daysinweekremaining = 7;
    }
    while ($daysinweekremaining > 0 && $day <= $month_meta['daysinmonth']) {
      $form['week-'. $week]['day-'. $day] = array(
        '#type' => 'select',
        '#title' => date('l d F', strtotime("$year-$month-$day")),
        '#options' => availability_calendars_options(),
        '#default_value' => $day_status[$day]
      );
      $day++;
      $daysinweekremaining--;
    }
  }

  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Submit'),
  );

  return $form;
}

function availability_calendars_node_edit_form_submit($form, &$form_state) {
  $nid = check_plain($form_state['values']['nid']);
  $year = check_plain($form_state['values']['year']);
  $month = check_plain($form_state['values']['month']);

  // save weekly notes
  $week = 1;
  $nomoreweeks = FALSE;
  while (!$nomoreweeks) {
    if (isset($form_state['values']['note-'. $week])) {
      $notes[$week] = check_plain($form_state['values']['note-'. $week]);
      $week++;
    }
    else {
      $nomoreweeks = TRUE;
    }
  }

  // save $days
  $day = 1;
  $nomoredays = FALSE;
  while (!$nomoredays) {
    if (isset($form_state['values']['day-'. $day])) {
      $days[$day] = $form_state['values']['day-'. $day];
      $day++;
    }
    else {
      $nomoredays = TRUE;
    }
  }

  db_query('DELETE FROM {availability_calendars_week} WHERE nid = %d AND year = %d AND month = %d', $nid, $year, $month);
  foreach ($notes as $week => $note) {
    db_query('INSERT INTO {availability_calendars_week} (nid, year, month, week, note) VALUES (%d, %d, %d, %d, "%s")', $nid, $year, $month, $week, $note);
  }

  db_query('DELETE FROM {availability_calendars_day} WHERE nid = %d AND year = %d AND month = %d', $nid, $year, $month);
  foreach ($days as $day => $status) {
    db_query('INSERT INTO {availability_calendars_day} (nid, year, month, day, status) VALUES (%d, %d, %d, %d, %d)', $nid, $year, $month, $day, $status);
  }

  drupal_set_message('Availability information saved.');
}

/**
 * Implementation of hook_theme().
 */
function availability_calendars_theme() {

  return array('availability_calendars_node' => array(
                 'arguments' => array('node' => NULL, 'year' => 2008, 'month' => 01, 'monthstodisplay' => 12)
	       ),
	       'availability_calendars_month' => array(
                 'arguments' => array('node' => NULL, 'year' => 2008, 'month' => 01, 'startofweek' => NULL, 'booked' => NULL)
	       )
	 );

}
//function theme_availability_calendars_month($node, $year, $month, $startofweek, $booked) {

/**
 * Themed output to display a lits of node dates.
 *
 * @param $node
 * @return HTML output.
 */
function theme_availability_calendars_node($node, $year = 2008, $month = 01, $monthstodisplay = 12) {

  drupal_add_css(drupal_get_path('module', 'availability_calendars') .'/availability_calendars.css');
  $rows = array();

  // Fill availability array
  /* foreach ($node->availability_dates as $k => $v) {
    foreach ($v as $i) {
      $booked[date("Y", $i['date'])][date("m", $i['date'])][date("d", $i['date'])] = 1;
    }
  } */



  // Calendar code based on example at http://evolt.org/node/60673 :
  $day = 1;

  $startofweek = variable_get('availability_calendars_'. $node->nid .'_startofweek', 1);

  $monthsremaining = $monthstodisplay;
  while ($monthsremaining > 0) {
    $output .= theme('availability_calendars_month', $node, $year, $month, $startofweek, $booked);
    $monthsremaining--;
    $month++;
    if ($month > 12) {
      $month = 1;
      $year++;
    }
  }

  // add an extra three months for editors only
  if (user_access('edit availability calendars')) {
    $monthsremaining = 1;
    while ($monthsremaining > 0) {
      $output .= theme('availability_calendars_month', $node, $year, $month, $startofweek, $booked);
      $monthsremaining--; 
      $month++;
      if ($month > 12) {
        $month = 1;
        $year++; 
      }
    } 
  }

  return $output;
  
}

function availability_calendars_month_meta($year, $month, $startofweek) {
  $month_meta['daysinmonth'] = date("t", mktime(0, 0, 0, $month, 1, $year));
  $month_meta['firstday'] = date("w", mktime(0, 0, 0, $month, 1, $year)) + $startofweek;
  $tempDays = $month_meta['firstday'] + $month_meta['daysinmonth']; // padding
  $month_meta['weeksinmonth'] = ceil($tempDays / 7);

  // Stop empty weeks occuring at start of month
  if ($month_meta['firstday'] > 6) { 
    $month_meta['firstday'] = $month_meta['firstday'] - 7; 
    $month_meta['weeksinmonth'] --;  
  }
  return $month_meta;
}

function theme_availability_calendars_month($node, $year, $month, $startofweek, $booked) {
global $user;
  
  $month_meta = availability_calendars_month_meta($year, $month, $startofweek);
  
  for ($j=0;$j<$month_meta['weeksinmonth'];$j++) {
    for ($i=0;$i<7;$i++) {
      $counter++;
      $week[$j][$i] = $counter;
      // offset the days
      $week[$j][$i] -= $month_meta['firstday'];
      if (($week[$j][$i] < 1) || ($week[$j][$i] > $month_meta['daysinmonth'])) {    
        $week[$j][$i] = "";
      }
    }
  }
  
  $output  = "<table class='cal'>\n";
  $output .= "<tr class='calmonth'>\n";
  $output .= "<th colspan='8'>". t("@date", array('@date' => format_date(mktime(12, 0, 0, $month, 1, $year), 'custom', 'F Y')));
  if ($user->uid != $node->uid && $user->uid != 1) {
    $output .= ' '. l('edit', 'availability-calendars/'. $node->nid .'/'. date('Y/m', mktime(0, 0, 0, $month, 1, $year)) .'/edit',
                      array('query' => 'destination=node/'. $node->nid));
  }
  $output .= "</th>\n";
  $output .= "</tr>\n";


  
/*  $days = array(
      6 => array("M", "Mon", "Monday"),
      5 => array("T", "Tue", "Tuesday"),
      4 => array("W", "Wed", "Wednesday"),
      3 => array("T", "Thu", "Thursday"),
      2 => array("F", "Fri", "Friday"),
      1 => array("S", "Sat", "Saturday"),
      0 => array("S", "Sun", "Sunday"),
    );

 // Figure out how to generate the header - see archive.module in 4.7
  $output .= "<tr class='caldays'>\n";
  $output .= "<th></th>\n";
  $output .= "<th>S</th>\n";
  $output .= "<th>S</th>\n";
  $output .= "<th>M</th>\n";
  $output .= "<th>T</th>\n";
  $output .= "<th>W</th>\n";
  $output .= "<th>T</th>\n";
  $output .= "<th>F</th>\n";
  $output .= "</tr>\n";
 */

  // find all entries in database for this month ($availability, $notes) and pre-populate
  $notes_result = db_query('SELECT week, note FROM {availability_calendars_week} WHERE nid = %d AND year = %d AND month = %d', $node->nid, $year, $month);
  while ($note = db_fetch_array($notes_result)) {
    $notes[$note['week']] = $note['note'];
  }

  $status_result = db_query('SELECT day, status FROM {availability_calendars_day} WHERE nid = %d AND year = %d AND month = %d', $node->nid, $year, $month);
  while ($status = db_fetch_array($status_result)) {
    $day_status[$status['day']] = $status['status'];
  }

  $availability_calendars_options = availability_calendars_options();

  foreach ($week as $key => $val) {
    $weeknumber = $key + 1;

    $output .= "<tr class='calweek'>\n";
    $output .= "<td class='calnote'>". $notes[$weeknumber] ."</td>\n";
    for ($i=0; $i<7; $i++) {

      // if there's a date, it's part of this month
      if ($week[$key][$i]) {
        if ($day_status[$week[$key][$i]] == 1) {
        // booked
          $output .= " <td class='calnotavailable'>". $week[$key][$i] ."</td>\n";
        }
        elseif ($day_status[$week[$key][$i]] == 2) {
          // provisionally booked
          $output .= " <td class='calnotavailableprov'>". $week[$key][$i] ."</td>\n";
        }
        else {
          // available
          $output .= " <td class='calavailable'>". $week[$key][$i] ."</td>\n";
        }
      }
      else {
        $output .= " <td class='calothermonth'>". $number ."</td>\n";
      }
    }

  $output .= "</tr>\n";

  }

  if ($weeknumber == 5) {
    $output .= "<tr>\n";
    $output .= "<td colspan='8'>&nbsp;</td>\n";
    $output .= "</tr>\n";
  }

  $output .= "</table>";

  return $output;
}

function availability_calendars_options() {
  // TODO: make these configurable
  return array(
    0 => t('Available'),
    1 => t('Fully booked'),
    2 => t('Provisionally booked')
  );
}

/**
 * Implementation of hook_form_alter();
 */
function availability_calendars_form_alter(&$form, &$form_state, $form_id) {
  global $user;

  // Alter node type form to allow availability support to be enabled/disabled
  if ($form_id == 'node_type_form') {
    $form['availability_calendars'] = array(
      '#type' => 'fieldset',
      '#title' => t('Availability calendars'),
      '#collapsible' => TRUE,
      '#collapsed' => !variable_get('availability_calendars_'. $form['#node_type']->type, 0),
    );
    $form['availability_calendars']['availability_calendars'] = array(
      '#type' => 'radios',
      '#title' => t('Availability calendar support'),
      '#default_value' => variable_get('availability_calendars_'. $form['#node_type']->type, 0),
      '#options' => array(
        0 => t('Disabled'),
        1 => t('Enabled')
      ),
      '#description' => t('Enable or disable availability support for this content type. If enabled, node owner will be able to specify node availability.'),
    );
  }

  // Alter node edit form if availability support is enabled for that content type
  elseif (isset($form['type']) && $form['type']['#value'] .'_node_form' == $form_id &&
      availability_calendars_enabled($form['type']['#value'])) {

    $form['availability_calendars'] = array(
      '#type' => 'fieldset',
      '#title' => t('Availability calendar settings'),
    );
    $form['availability_calendars']['startofweek'] = array(
      '#type' => 'select',
      '#title' => t('First day of week'),
      '#default_value' => variable_get('availability_calendars_'. $form['nid']['#value'] .'_startofweek', 1),
      '#options' => array(
        6 => t('Monday'),
        5 => t('Tuesday'),
        4 => t('Wednesday'),
        3 => t('Thursday'),
        2 => t('Friday'),
        1 => t('Saturday'),
        0 => t('Sunday'),
      ),
    );

  }
}

/**
 * Implementation hook node_nodeapi();
 */
function availability_calendars_nodeapi(&$node, $op, $a3 = NULL, $a4 = NULL) {
  global $user;

  if (!availability_calendars_enabled($node->type)) return;

  switch ($op) {
    case 'view':
      if (variable_get('availability_calendars_display_nodeview', TRUE)) {
        $year = date('Y');
        $month = date('m');
        $monthstodisplay = variable_get('availability_calendars_display_monthcount', 12);
        $calendar_node = $node;
        if ($node->tnid) {
          // if Content Translation module is enabled and this is a translated node, use calendar of original node
          if ($node->tnid != $node->nid) {
            $calendar_node = node_load($node->tnid);
          }
        }
        $node->content['availability_calendars'] = array(
          '#value' => theme('availability_calendars_node', $calendar_node, $year, $month, $monthstodisplay),
          '#weight' => 10,
        );
      }
      break;
    case 'insert':
    case 'update':
      availability_calendars_save($node);
      break;
    case 'delete':
      break;
  }
}

/**
 * Saves a set of dates associated with the node after editing it.
 *
 * @param object $node Node information to save into the database.
 */
function availability_calendars_save(&$node) {
  variable_set('availability_calendars_'. $node->nid .'_startofweek', $node->startofweek);
}

/**
 * Checks if availability is enabled for specified content type.
 *
 * @param string $node_type
 */
function availability_calendars_enabled($node_type) {
  return variable_get('availability_calendars_'. $node_type, 0);
}

If someone could fix this problem you'd be doing me a huge favour
thanks