# The LearningOnline Network with CAPA
#
# Page flip handler
#
# $Id: lonpageflip.pm,v 1.80.8.13 2021/12/14 21:34:45 raeburn Exp $
#
# Copyright Michigan State University Board of Trustees
#
# This file is part of the LearningOnline Network with CAPA (LON-CAPA).
#
# LON-CAPA 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 2 of the License, or
# (at your option) any later version.
#
# LON-CAPA 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 LON-CAPA; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# /home/httpd/html/adm/gpl.txt
#
# http://www.lon-capa.org/
#



package Apache::lonpageflip;

use strict;
use LONCAPA;
use Apache::Constants qw(:common :http REDIRECT);
use Apache::lonnet;
use Apache::loncommon();
use Apache::lonuserstate;
use Apache::lonlocal;
use HTML::TokeParser;
use GDBM_File;

# ========================================================== Module Global Hash
  
my %hash;

sub cleanup {
    if (tied(%hash)){
	&Apache::lonnet::logthis('Cleanup pageflip: hash');
        unless (untie(%hash)) {
	    &Apache::lonnet::logthis('Failed cleanup pageflip: hash');
        }
    }
    return OK;
}

sub addrid {
    my ($current,$new,$condid)=@_;
    unless ($condid) { $condid=0; }

	if ($current) {
	    $current.=','.$new;
        } else {
            $current=''.$new;
        }

    return $current;
}

sub fullmove {
    my ($rid,$mapurl,$direction)=@_;
    if (tie(%hash,'GDBM_File',$env{'request.course.fn'}.'.db',
                        &GDBM_READER(),0640)) {
	($rid,$mapurl)=&move($rid,$mapurl,$direction);
        untie(%hash);
    }
    return($rid,$mapurl);
}

sub hash_src {
    my ($id)=@_;
    my ($mapid,$resid)=split(/\./,$id);
    my $symb=&Apache::lonnet::encode_symb($hash{'map_id_'.$mapid},
					  $resid,$hash{'src_'.$id});
    my $anchor;
    if ($hash{'ext_'.$id} eq 'true:') {
        if ($hash{'src_'.$id} =~ /(\#.+)$/) {
            $anchor = $1;
        }
    }
    if ($hash{'encrypted_'.$id}) {
	return (&Apache::lonenc::encrypted($hash{'src_'.$id}),
		&Apache::lonenc::encrypted($symb),
                $hash{'encrypted_'.$id},$anchor);
    }
    return ($hash{'src_'.$id},$symb,$hash{'encrypted_'.$id},$anchor);
}

sub move {
    my ($next,$endupmap,$direction) = @_;
    my $safecount=0;
    my $allowed=0;
    do {
	($next,$endupmap)=&get_next_possible_move($next,$endupmap,$direction);

	my $url = $hash{'src_'.$next};
	my ($mapid,$resid)=split(/\./,$next);
	my $symb = &Apache::lonnet::encode_symb($hash{'map_id_'.$mapid},
						$resid,$url);
	if ($url eq '' || $symb eq '') {
	    $allowed = 0;
	} else {
	    my $priv = &Apache::lonnet::allowed('bre',$url,$symb);
	    $allowed = (($priv eq 'F') || ($priv eq '2'));
	}
	$safecount++;
    } while (   ($next)
	     && ($next!~/\,/)
	     && (
		    (!$hash{'src_'.$next})
		 || (
		        (!$env{'request.role.adv'})
		     &&  $hash{'randomout_'.$next}
		    )
		 || (!$allowed)
		)
	     && ($safecount<10000));

    return ($next,$endupmap);
}

sub get_next_possible_move {
    my ($rid,$mapurl,$direction)=@_;
    my $startoutrid=$rid;

    my $next='';

              my $mincond=1;
              my $posnext='';
              if ($direction eq 'forward') {
# --------------------------------------------------------------------- Forward
                  while ($hash{'type_'.$rid} eq 'finish') {
	             $rid=$hash{'ids_'.$hash{'map_id_'.(split(/\./,$rid))[0]}};
                  }
		  foreach my $id (split(/\,/,$hash{'to_'.$rid})) {
		     my $condition= $hash{'conditions_'.$hash{'goesto_'.$id}};
		     my $rescond  = &Apache::lonnet::docondval($condition);
		     my $linkcond = &Apache::lonnet::directcondval($hash{'condid_'.$hash{'undercond_'.$id}});
		     my $thiscond = ($rescond<$linkcond)?$rescond:$linkcond;
		     if ($thiscond>=$mincond) {
		          if ($posnext) {
		             $posnext.=','.$id.':'.$thiscond;
                          } else {
                             $posnext=$id.':'.$thiscond;
		          }
                          if ($thiscond>$mincond) { $mincond=$thiscond; }
	              }
                  } 
		  foreach my $id (split(/\,/,$posnext))  {
                      my ($linkid,$condval)=split(/\:/,$id);
                      if ($condval>=$mincond) {
		          $next=&addrid($next,$hash{'goesto_'.$linkid},
                                $hash{'condid_'.$hash{'undercond_'.$linkid}});
                      }
                  }
                  if ($hash{'is_map_'.$next}) {
# This jumps to the beginning of a new map (going down level)
                      if (
      $hash{'map_type_'.$hash{'map_pc_'.$hash{'src_'.$next}}} eq 'sequence') {
			  $mapurl=$hash{'src_'.$next};
			  $next=$hash{'map_start_'.$hash{'src_'.$next}};
                     } elsif (
# This jumps back up from an empty sequence, to a page up one level
                         $hash{'map_type_'.$hash{'map_pc_'.$hash{'src_'.$next}}} eq 'page') {
                         $mapurl=$hash{'map_id_'.(split(/\./,$next))[0]};
                     }
                  } elsif 
                    ((split(/\./,$startoutrid))[0]!=(split(/\./,$next))[0]) {
# This comes up from a map (coming up one level);
		      $mapurl=$hash{'map_id_'.(split(/\./,$next))[0]};
		  }
              } elsif ($direction eq 'back') {
# ------------------------------------------------------------------- Backwards
                 while ($hash{'type_'.$rid} eq 'start') {
	             $rid=$hash{'ids_'.$hash{'map_id_'.(split(/\./,$rid))[0]}};
		 }
		 foreach my $id (split(/\,/,$hash{'from_'.$rid})) {
		     my $condition= $hash{'conditions_'.$hash{'comesfrom_'.$id}};
		     my $rescond  = &Apache::lonnet::docondval($condition);
		     my $linkcond = &Apache::lonnet::directcondval($hash{'condid_'.$hash{'undercond_'.$id}});
		     my $thiscond = ($rescond<$linkcond)?$rescond:$linkcond;
		     if ($thiscond>=$mincond) {
			 if ($posnext) {
		             $posnext.=','.$id.':'.$thiscond;
			 } else {
                             $posnext=$id.':'.$thiscond;
			 }
			 if ($thiscond>$mincond) { $mincond=$thiscond; }
		     }
		 } 
		 foreach my $id (split(/\,/,$posnext)) {
		     my ($linkid,$condval)=split(/\:/,$id);
		     if ($condval>=$mincond) {
			 $next=&addrid($next,$hash{'comesfrom_'.$linkid},
				       $hash{'condid_'.$hash{'undercond_'.$linkid}});
		     }
		 }
                  if ($hash{'is_map_'.$next}) {
# This jumps to the end of a new map (going down one level)
                      if (
      $hash{'map_type_'.$hash{'map_pc_'.$hash{'src_'.$next}}} eq 'sequence') {
			  $mapurl=$hash{'src_'.$next};
			  $next=$hash{'map_finish_'.$hash{'src_'.$next}};
                      } elsif (
      $hash{'map_type_'.$hash{'map_pc_'.$hash{'src_'.$next}}} eq 'page') {
# This jumps back up from an empty sequence, to a page up one level
                          $mapurl=$hash{'map_id_'.(split(/\./,$next))[0]};
                      }
                  } elsif 
                    ((split(/\./,$startoutrid))[0]!=(split(/\./,$next))[0]) {
# This comes back up from a map (going up one level);
		      $mapurl=$hash{'map_id_'.(split(/\./,$next))[0]};
                  }
	      }
              return ($next,$mapurl);
}

sub first_accessible_resource {
    my $furl;
    if (tie(%hash,'GDBM_File',$env{'request.course.fn'}.'.db',
	    &GDBM_READER(),0640)) {
	$furl=$hash{'first_url'};
	my (%args,$url,$argstr);
	if ($furl =~ m{^/enc/}) {
	    ($url,$argstr) = split(/\?/,&Apache::lonenc::unencrypted($furl));
	} else {
	    ($url,$argstr) = split(/\?/,$furl);
	}
	foreach my $pair (split(/\&/,$argstr)) {
	    my ($name,$value) = split(/=/,$pair);
	    $args{&unescape($name)} = &unescape($value);
	}
        if (!&Apache::lonnet::allowed('bre',$url,$args{'symb'})) {
# Wow, we cannot see this ... move forward to the next one that we can see
	    my ($newrid,$newmap)=&move($hash{'first_rid'},$hash{'first_mapurl'},'forward');
# Build the new URL
            if ($newrid eq '') {
                $furl = '/adm/navmaps';
            } else {
	        my ($newmapid,$newresid)=split(/\./,$newrid);
	        my $symb=&Apache::lonnet::encode_symb($newmap,$newresid,$hash{'src_'.$newrid});
	        $furl=&add_get_param($hash{'src_'.$newrid},{ 'symb' => $symb });
	        if ($hash{'encrypted_'.$newrid}) {
		    $furl=&Apache::lonenc::encrypted($furl);
	        }
	    }
        }
	untie(%hash);
	return $furl;
    } else {
	return '/adm/navmaps';
    }
}

sub check_http_req {
    my ($srcref,$hostname) = @_;
    return unless (ref($srcref) eq 'SCALAR');
    my $usehttp;
    if ($env{'request.course.id'}) {
        my $cnum = $env{'course.'.$env{'request.course.id'}.'.num'};
        my $cdom = $env{'course.'.$env{'request.course.id'}.'.domain'};
        if (($$srcref =~ m{^\Q/public/$cdom/$cnum/syllabus\E($|\?)}) &&
            ($ENV{'SERVER_PORT'} == 443) &&
            ($env{'course.'.$env{'request.course.id'}.'.externalsyllabus'} =~ m{^http://})) {
            unless ((&Apache::lonnet::uses_sts()) ||
                    (&Apache::lonnet::waf_allssl($hostname))) {
                $$srcref .= (($$srcref =~/\?/)? '&':'?') . 'usehttp=1';
                $usehttp = 1;
            }
        } elsif (($$srcref =~ m{^\Q/adm/wrapper/ext/\E(?!https:)}) &&
                 ($ENV{'SERVER_PORT'} == 443)) {
            unless ((&Apache::lonnet::uses_sts()) ||
                    (&Apache::lonnet::waf_allssl($hostname))) {
                my ($url,$anchor) = ($$srcref =~ /^([^\#]+)(?:|(\#[^\#]+))$/);
                $$srcref = $url . (($$srcref =~/\?/)? '&':'?') . 'usehttp=1' .$anchor;
                $usehttp = 1;
            }
        }
    }
    return $usehttp;
}

sub reinited_js {
    my ($url,$cid,$timeout) = @_;
    if (!$timeout) {
        $timeout = 0;
    }
    return <<"END";
<script type="text/javascript">
// <![CDATA[
setTimeout(function() {
    var newurl = '$url';
    if (document.getElementById('LC_update_$cid')) {
        document.getElementById('LC_update_$cid').style.display = 'none';
    }
    if ((newurl !== null) && (newurl !== '') && (newurl !== 'undefined')) {
        window.location.href = "$url";
    }
}, $timeout);
// ]]>
</script>
END
}

# ================================================================ Main Handler

sub handler {
   my $r=shift;

# ------------------------------------------- Set document type for header only

  if ($r->header_only) {
      &Apache::loncommon::content_type($r,'text/html');
      $r->send_http_header;
      return OK;
  }

  my %cachehash=(); 
  my $multichoice=0;
  my %multichoicehash=();
  my %prog_state=(); 
  my ($redirecturl,$redirectsymb,$enc,$anchor);
  my $next='';
  my $hostname = $r->hostname();
  my @possibilities=();
   &Apache::loncommon::get_unprocessed_cgi($ENV{'QUERY_STRING'},['postdata']);
  if (($env{'form.postdata'})&&($env{'request.course.fn'})) {
      my ($direction,$currenturl) = ($env{'form.postdata'}=~/(\w+)\:(.*)/);
      if ($currenturl=~m|^/enc/|) {
          $currenturl=&Apache::lonenc::unencrypted($currenturl);
      }
      $currenturl=~s/\.\d+\.(\w+)$/\.$1/;
      $currenturl=~s/^https?\:\/\///;
      $currenturl=~s/^[^\/]+//;
      my ($preupdatepos,$last,$reinitcheck);
      if ($direction eq 'return') {
          if (tie(%hash,'GDBM_File',$env{'request.course.fn'}.'_symb.db',
                    &GDBM_READER(),0640)) {
              $last=$hash{'last_known'};
              untie(%hash);
          }
      }
      if ($env{'request.course.id'}) {
          # Check if course needs to be re-initialized
          my $loncaparev = $r->dir_config('lonVersion');
          ($reinitcheck,my @reinit) = &Apache::loncommon::needs_coursereinit($loncaparev);
          if ($reinitcheck eq 'switch') {
              &Apache::loncommon::content_type($r,'text/html');
              $r->send_http_header;
              $r->print(&Apache::loncommon::check_release_result(@reinit));
              return OK;
          } elsif ($reinitcheck eq 'update') {
              my $cnum = $env{'course.'.$env{'request.course.id'}.'.num'};
              my $cdom = $env{'course.'.$env{'request.course.id'}.'.domain'};
              $preupdatepos = &Apache::lonnet::symbread($currenturl);
              unless ($direction eq 'return') {
                  if (tie(%hash,'GDBM_File',$env{'request.course.fn'}.'_symb.db',
                                &GDBM_READER(),0640)) {
                      $last=$hash{'last_known'};
                      untie(%hash);
                  }
              }
              &Apache::loncommon::content_type($r,'text/html');
              $r->send_http_header;
              $r->print(&Apache::loncommon::start_page('Content Changed'));
              my $preamble = '<div id="LC_update_'.$env{'request.course.id'}.'" class="LC_info">'.
                             '<br />'.
                             &mt('Your course session is being updated because of recent changes by course personnel.').
                             ' '.&mt('Please be patient').'.<br /></div>'.
                             '<div style="padding:0;clear:both;margin:0;border:0"></div>';
              %prog_state = &Apache::lonhtmlcommon::Create_PrgWin($r,undef,$preamble);
              &Apache::lonhtmlcommon::Update_PrgWin($r,\%prog_state,&mt('Updating course'));
              my ($furl,$ferr) = &Apache::lonuserstate::readmap("$cdom/$cnum");
              &Apache::lonhtmlcommon::Update_PrgWin($r,\%prog_state,&mt('Finished!'));
              if ($ferr) {
                  &Apache::lonhtmlcommon::Close_PrgWin($r,\%prog_state);
                  my $requrl = $r->uri;
                  $env{'user.error.msg'}="$requrl:bre:0:0:Course not initialized";
                  $env{'user.reinit'} = 1;
                  return HTTP_NOT_ACCEPTABLE;
              } else {
                  if ($last) {
                      my ($murl,$id,$fn)=&Apache::lonnet::decode_symb($last);
                      unless (&Apache::lonnet::symbverify($last,$fn)) {
                          undef($last);
                      }
                  }
              }
          }
      }
      if ($direction eq 'firstres') {
	  my $furl=&first_accessible_resource();
          my $usehttp = &check_http_req(\$furl,$hostname);
          if (($usehttp) && ($hostname ne '')) {
              $furl='http://'.$hostname.$furl;
          } else {
              $furl=&Apache::lonnet::absolute_url().$furl;
          }
          if ($reinitcheck eq 'update') {
              &Apache::lonhtmlcommon::Close_PrgWin($r,\%prog_state);
              $r->print(&reinited_js($furl,$env{'request.course.id'},100));
              $r->print(&Apache::loncommon::end_page());
              return OK;
          } else {
	      &Apache::loncommon::content_type($r,'text/html');
	      $r->header_out(Location => $furl);
	      return REDIRECT;
          }
      }
      if ($direction eq 'return') {
# -------------------------------------------------------- Return to last known
         my ($newloc,$usehttp);
         if (($last) && (tie(%hash,'GDBM_File',$env{'request.course.fn'}.'.db',
                        &GDBM_READER(),0640))) {
            my ($murl,$id,$fn)=&Apache::lonnet::decode_symb($last);
	    $id=$hash{'map_pc_'.&Apache::lonnet::clutter($murl)}.'.'.$id;
	    $newloc=$hash{'src_'.$id};
	    if ($newloc) {
                $usehttp = &check_http_req(\$newloc,$hostname);
                if ($hash{'encrypted_'.$id}) {
                    $newloc=&Apache::lonenc::encrypted($newloc);
                }
                if ($newloc =~ m{^(/adm/wrapper/ext/[^\#]+)(?:|(\#[^\#]+))$}) {
                    my ($url,$anchor) = ($1,$2);
                    if ($anchor) {
                        $newloc = $url.(($url=~/\?/)?'&':'?').'symb='.&escape($last).$anchor;
                    }
                }
	    } else {
		$newloc='/adm/navmaps';
	    }
            untie %hash;
         } else {
	    $newloc='/adm/navmaps';
         }
         if (($usehttp) && ($hostname ne '')) {
             $newloc='http://'.$hostname.$newloc;
         } else {
             $newloc=&Apache::lonnet::absolute_url().$newloc
         }
         if ($reinitcheck eq 'update') {
             $r->print(&reinited_js($newloc,$env{'request.course.id'},100));
             $r->print(&Apache::loncommon::end_page());
             return OK;
         } else {
             &Apache::loncommon::content_type($r,'text/html');
             $r->header_out(Location => $newloc);
             return REDIRECT;
         }
      }
#
# Is the current URL on the map? If not, start with last known URL
#

      unless (&Apache::lonnet::is_on_map($currenturl)) {
         if ($preupdatepos) {
             undef($preupdatepos);
         } elsif (tie(%hash,'GDBM_File',$env{'request.course.fn'}.'_symb.db',
                            &GDBM_READER(),0640)) {
             $last=$hash{'last_known'};
             untie(%hash);
         }
         if ($last) {
	     $currenturl=&Apache::lonnet::clutter((&Apache::lonnet::decode_symb($last))[2]);
	 } else {
             my $newloc = &Apache::lonnet::absolute_url().
                          '/adm/navmaps';
             if ($reinitcheck eq 'update') {
                 &Apache::lonhtmlcommon::Close_PrgWin($r,\%prog_state);
                 $r->print(&reinited_js($newloc,$env{'request.course.id'},100));
                 $r->print(&Apache::loncommon::end_page());
                 return OK;
             } else {
                 &Apache::loncommon::content_type($r,'text/html');
	         $r->header_out(Location => $newloc);
	         return REDIRECT;
             }
         }
      }
# ------------------------------------------- Do we have any idea where we are?
      my $position;
      if ($preupdatepos) {
          $position = $preupdatepos;
      } else {
          $position=Apache::lonnet::symbread($currenturl);
      }
      if ($position) {
# ------------------------------------------------------------------------- Yes
	  my ($startoutmap,$mapnum,$thisurl)=&Apache::lonnet::decode_symb($position);
          $cachehash{$startoutmap}{$thisurl}=[$thisurl,$mapnum];
          $cachehash{$startoutmap}{'last_known'}=
                             [&Apache::lonnet::declutter($currenturl),$mapnum];

# ============================================================ Tie the big hash
          if (tie(%hash,'GDBM_File',$env{'request.course.fn'}.'.db',
                        &GDBM_READER(),0640)) {
              my $rid=$hash{'map_pc_'.&Apache::lonnet::clutter($startoutmap)}.
                      '.'.$mapnum;

# ------------------------------------------------- Move forward, backward, etc
              my $endupmap;
              ($next,$endupmap)=&move($rid,$startoutmap,$direction);
# -------------------------------------- Do we have one and only one empty URL?
# We are now at at least one non-empty URL
# ----------------------------------------------------- Check out possibilities
              if ($next) {
                  @possibilities=split(/\,/,$next);
                  if ($#possibilities==0) {
# ---------------------------------------------- Only one possibility, redirect
	              ($redirecturl,$redirectsymb,$enc,$anchor)=&hash_src($next);
                      $cachehash{$endupmap}{$redirecturl}=
			  [$redirecturl,(split(/\./,$next))[1]];
                  } else {
# ------------------------ There are multiple possibilities for a next resource
                      $multichoice=1;
		      foreach my $id (@possibilities) {
			  $multichoicehash{'src_'.$id}=$hash{'src_'.$id};
                          $multichoicehash{'title_'.$id}=$hash{'title_'.$id};
                          $multichoicehash{'type_'.$id}=$hash{'type_'.$id};
                          (my $first, my $second) = $id =~ /(\d+).(\d+)/;
                          my $symbSrc = Apache::lonnet::declutter($hash{'src_'.$id});
                          $multichoicehash{'symb_'.$id} = 
                              Apache::lonnet::declutter($hash{'map_id_'.$first}.'___'.
                                                        $second.'___'.$symbSrc);
                                                         
                          my ($choicemap,$choiceres)=split(/\./,$id);
			  my $map=&Apache::lonnet::declutter($hash{'src_'.$choicemap});
			  my $url=$multichoicehash{'src_'.$id};
                          $cachehash{$map}{$url}=[$url,$choiceres];
                      }
                  }
	      } else {
# -------------------------------------------------------------- No place to go
                  $multichoice=-1;
              }
# ----------------- The program must come past this point to untie the big hash
	      untie(%hash);
# --------------------------------------------------------- Store position info
              $cachehash{$startoutmap}{'last_direction'}=[$direction,'notasymb'];
              foreach my $thismap (keys(%cachehash)) {
		  my $mapnum=$cachehash{$thismap}->{'mapnum'};
		  delete($cachehash{$thismap}->{'mapnum'});
		  &Apache::lonnet::symblist($thismap,
					    %{$cachehash{$thismap}});
	      }
# ============================================== Do not return before this line
              if ($redirecturl) {
# ----------------------------------------------------- There is a URL to go to
		  if ($direction eq 'forward') {
                     &Apache::lonnet::linklog($currenturl,$redirecturl);
		  }
		  if ($direction eq 'back') {
                     &Apache::lonnet::linklog($redirecturl,$currenturl);
		  }
# ------------------------------------- Check for and display critical messages
                  my ($redirect, $url) = &Apache::loncommon::critical_redirect(300);
                  unless ($redirect) {
                      my $usehttp = &check_http_req(\$redirecturl,$hostname);
                      if (($usehttp) && ($hostname ne '')) {
                          $url='http://'.$hostname.$redirecturl;
                      } else {
                          $url=&Apache::lonnet::absolute_url().$redirecturl;
                      }
                      my $addanchor;
                      if (($anchor ne '') && (!$enc || $env{'request.role.adv'})) {
                          $addanchor = 1;
                          $url =~ s/\#.+$//;
                      }
                      $url = &add_get_param($url, { 'symb' => $redirectsymb});
                      if ($addanchor) {
                          $url .= $anchor;
                      }
                  }
                  if ($reinitcheck eq 'update') {
                      &Apache::lonhtmlcommon::Close_PrgWin($r,\%prog_state);
                      $r->print(&reinited_js($url,$env{'request.course.id'},100));
                      $r->print(&Apache::loncommon::end_page());
                      return OK;
                  } else {
                      &Apache::loncommon::content_type($r,'text/html');
                      $r->header_out(Location => $url);
                      return REDIRECT;
                  }
	      } else {
# --------------------------------------------------------- There was a problem
                  &Apache::loncommon::content_type($r,'text/html');
                  $r->send_http_header;
		  my %lt=&Apache::lonlocal::texthash('title' => 'End of Sequence',
						     'explain' =>
						     'You have reached the end of the sequence of materials.',
						     'back' => 'Go Back',
						     'nav' => 'Course Contents',
						     'wherenext' =>
						     'There are several possibilities of where to go next',
						     'pick' =>
						     'Please click on the the resource you intend to access',
						     'titleheader' => 'Title',
						     'type' => 'Type',
                                                     'update' => 'Content updated',
                                                     'expupdate' => 'As a result of a recent update to the sequence of materials, it is not possible to complete the page flip.',
                                                     'gonav' => 'Go to the Contents page to select a resource to display.');
                  if (&Apache::loncommon::course_type() eq 'Community') {
                      $lt{'nav'} = &mt('Community Contents');
                  }
                  if ($#possibilities>0) {
		      my $start_page=
			  &Apache::loncommon::start_page('Multiple Resources');
                     $r->print(<<ENDSTART);
$start_page
<h3>$lt{'wherenext'}</h3>
<p>
$lt{'pick'}:
<p>
<table border="2">
<tr><th>$lt{'titleheader'}</th><th>$lt{'type'}</th></tr>
ENDSTART
                     foreach my $id (@possibilities) {
                        my $src = $multichoicehash{'src_'.$id};
                        my $usehttp = &check_http_req(\$src,$hostname);
                        if (($usehttp) && ($hostname ne '')) {
                            $src = 'http://'.$hostname.$src;
                        }
                        $r->print(
                              '<tr><td><a href="'.
				  &add_get_param($src,
						 {'symb' =>
						      $multichoicehash{'symb_'.$id},
						  }).'">'.
                              $multichoicehash{'title_'.$id}.
                              '</a></td><td>'.$multichoicehash{'type_'.$id}.
			      '</td></tr>');
                     }
                     $r->print('</table>');
                  } else {
                      if ($reinitcheck) {
                          if (&Apache::loncommon::course_type() eq 'Community') {
                              $r->print(
                                  &Apache::loncommon::start_page('Community Contents Updated'));
                          } else { 
                              $r->print(
                                  &Apache::loncommon::start_page('Course Contents Updated'));
                          }
                          $r->print('<h2>'.$lt{'update'}.'</h2>'
                                  .'<p>'.$lt{'expupdate'}.'<br />'
                                  .$lt{'gonav'}.'</p>');
                      } else {
                          $r->print(
                              &Apache::loncommon::start_page('No Resource')
                             .'<h2>'.$lt{'title'}.'</h2>'
                             .'<p>'.$lt{'explain'}.'</p>');
                      }
		  }
                  if ((!@possibilities) && ($reinitcheck))  {
                      $r->print(
                          &Apache::lonhtmlcommon::actionbox(
                              ['<a href="/adm/navmaps">'.$lt{'nav'}.'</a></li>'
                              ]));
                  } else {
                      $r->print(
                          &Apache::lonhtmlcommon::actionbox(
                              ['<a href="/adm/flip?postdata=return:">'.$lt{'back'}.'</a></li>',
                               '<a href="/adm/navmaps">'.$lt{'nav'}.'</a></li>'
                              ]));
                  }
                  $r->print(&Apache::loncommon::end_page());
      
                  return OK;
	      }
	  } else {
# ------------------------------------------------- Problem, could not tie hash
              if ($reinitcheck eq 'update') {
                  &Apache::lonhtmlcommon::Close_PrgWin($r,\%prog_state);
                  $r->print(&Apache::loncommon::end_page());
              }
              $env{'user.error.msg'}="/adm/flip:bre:0:1:Course Data Missing";
              return HTTP_NOT_ACCEPTABLE; 
          }
      } else {
# ---------------------------------------- No, could not determine where we are
          my $newloc = '/adm/ambiguous';
          if ($reinitcheck eq 'update') {
              &Apache::lonhtmlcommon::Close_PrgWin($r,\%prog_state);
              $r->print(&reinited_js($newloc,$env{'request.course.id'},100));
              $r->print(&Apache::loncommon::end_page());
          } else {
	      $r->internal_redirect($newloc);
          }
          return OK;
      }
  } else {
# -------------------------- Class was not initialized or page fliped strangely
      $env{'user.error.msg'}="/adm/flip:bre:0:0:Choose Course";
      return HTTP_NOT_ACCEPTABLE; 
  } 
}

1;
__END__

=pod

=head1 NAME

Apache::lonpageflip

=head1 SYNOPSIS

Deals with forward, backward, and other page flips.

This is part of the LearningOnline Network with CAPA project
described at http://www.lon-capa.org.

=head1 OVERVIEW

(empty)

=head1 SUBROUTINES

=over cleanup()

=item addrid()

=item fullmove()

=item hash_src()

=item move()

=item get_next_possible_move()

=item first_accessible_resource()

=item handler()

=back

=cut






<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>500 Internal Server Error</title>
</head><body>
<h1>Internal Server Error</h1>
<p>The server encountered an internal error or
misconfiguration and was unable to complete
your request.</p>
<p>Please contact the server administrator at 
 root@localhost to inform them of the time this error occurred,
 and the actions you performed just before this error.</p>
<p>More information about this error may be available
in the server error log.</p>
</body></html>