# The LearningOnline Network with CAPA
#
# $Id: lonstathelpers.pm,v 1.24 2004/09/23 14:35:25 matthew 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/
#
####################################################
####################################################

=pod

=head1 NAME

Apache::lonstathelpers - helper routines used by statistics

=head1 SYNOPSIS

This module provides a place to consolidate much of the statistics 
routines that are needed across multiple statistics functions.

=head1 OVERVIEW

=over 4

=cut

####################################################
####################################################
package Apache::lonstathelpers;

use strict;
use Apache::lonnet();
use Apache::loncommon();
use Apache::lonhtmlcommon();
use Apache::loncoursedata();
use Apache::lonstatistics;
use Apache::lonlocal;
use HTML::Entities();
use Time::Local();
use Spreadsheet::WriteExcel();
use GDBM_File;
use Storable qw(freeze thaw);

####################################################
####################################################

=pod

=item &render_resource($resource)

Input: a resource generated from 
&Apache::loncoursedata::get_sequence_assessment_data().

Retunrs: a scalar containing html for a rendering of the problem
within a table.

=cut

####################################################
####################################################
sub render_resource {
    my ($resource) = @_;
    ##
    ## Render the problem
    my $base;
    ($base,undef) = ($resource->{'src'} =~ m|(.*/)[^/]*$|);
    $base = "http://".$ENV{'SERVER_NAME'}.$base;
    my $rendered_problem = 
        &Apache::lonnet::ssi_body($resource->{'src'});
    $rendered_problem =~ s/<\s*form\s*/<nop /g;
    $rendered_problem =~ s|(<\s*/form\s*>)|<\/nop>|g;
    return '<table bgcolor="ffffff"><tr><td>'.
        '<base href="'.$base.'" />'.
        $rendered_problem.
        '</td></tr></table>';
}

####################################################
####################################################

=pod

=item &ProblemSelector($AcceptedResponseTypes)

Input: scalar containing regular expression which matches response
types to show.  '.' will yield all, '(option|radiobutton)' will match
all option response and radiobutton problems.

Returns: A string containing html for a table which lists the sequences
and their contents.  A radiobutton is provided for each problem.
Skips 'survey' problems.

=cut

####################################################
####################################################
sub ProblemSelector {
    my ($AcceptedResponseTypes) = @_;
    my $Str;
    $Str = "\n<table>\n";
    foreach my $seq (&Apache::lonstatistics::Sequences_with_Assess('all')) {
        next if ($seq->{'num_assess'}<1);
        my $seq_str = '';
        foreach my $res (@{$seq->{'contents'}}) {
            next if ($res->{'type'} ne 'assessment');
            foreach my $part (@{$res->{'parts'}}) {
                my $partdata = $res->{'partdata'}->{$part};
                for (my $i=0;$i<scalar(@{$partdata->{'ResponseTypes'}});$i++){
                    my $respid = $partdata->{'ResponseIds'}->[$i];
                    my $resptype = $partdata->{'ResponseTypes'}->[$i];
                    if ($resptype =~ m/$AcceptedResponseTypes/) {
                        my $value = &make_target_id({symb=>$res->{'symb'},
                                                     part=>$part,
                                                     respid=>$respid,
                                                     resptype=>$resptype});
                        my $checked = '';
                        if ($ENV{'form.problemchoice'} eq $value) {
                            $checked = 'checked ';
                        }
                        my $title = $res->{'title'};
                        if (! defined($title) || $title eq '') {
                            ($title) = ($res->{'src'} =~ m:/([^/]*)$:);
                        }
                        $seq_str .= '<tr><td>'.
  '<input type="radio" name="problemchoice" value="'.$value.'" '.$checked.'/>'.
  '</td><td>'.          
  $resptype.'</td><td>'.
  '<a href="'.$res->{'src'}.'">'.$title.'</a> ';
#  '<a href="'.$res->{'src'}.'">'.$resptype.' '.$res->{'title'}.'</a> ';
                        if (scalar(@{$partdata->{'ResponseIds'}}) > 1) {
                            $seq_str .= &mt('response').' '.$respid;
                        }
                        $seq_str .= "</td></tr>\n";
                    }
                }
            }
        }
        if ($seq_str ne '') {
            $Str .= '<tr><td>&nbsp</td><td colspan="2"><b>'.$seq->{'title'}.'</b></td>'.
                "</tr>\n".$seq_str;
        }
    }
    $Str .= "</table>\n";
    return $Str;
}

####################################################
####################################################

=pod

=item &MultipleProblemSelector($navmap,$selected,$inputname)

Generate HTML with checkboxes for problem selection.

Input: 

$navmap: a navmap object.  If undef, navmaps will be called to create a
new object.

$selected: Scalar, Array, or hash reference of currently selected items.

$inputname: The name of the form elements to use for the checkboxs.

Returns: A string containing html for a table which lists the sequences
and their contents.  A checkbox is provided for each problem.

=cut

####################################################
####################################################
sub MultipleProblemSelector {
    my ($navmap,$inputname,$formname)=@_;
    my $cid = $ENV{'request.course.id'};
    my $Str;
    # Massage the input as needed.
    if (! defined($navmap)) {
        $navmap = Apache::lonnavmaps::navmap->new();
        if (! defined($navmap)) {
            $Str .= 
                '<h1>'.&mt('Error: cannot process course structure').'</h1>';
            return $Str;
        }
    }
    my $selected = {map { ($_,1) } (&get_selected_symbs($inputname))};
    # Header
    $Str .= <<"END";
<script>
    function checkall(value) {
        for (i=0; i<document.forms.$formname.elements.length; i++) {
            ele = document.forms.$formname.elements[i];
            if (ele.name == '$inputname') {
                document.forms.$formname.elements[i].checked=value;
            }
        }
    }
</script>
END
    $Str .= 
        '<a href="javascript:checkall(true)">'.&mt('Select All').'</a>'.
        ('&nbsp;'x4).
        '<a href="javascript:checkall(false)">'.&mt('Unselect All').'</a>';
    $Str .= $/.'<table>'.$/;
    my $iterator = $navmap->getIterator(undef, undef, undef, 1);
    my $sequence_string;
    my @Accumulator = (&new_accumulator($ENV{'course.'.$cid.'.description'},
                                        '',
                                        '',
                                        $inputname));
    my @Sequence_Data;
    while (my $curRes = $iterator->next()) {
        if ($curRes == $iterator->END_MAP) {
            if (ref($Accumulator[-1]) eq 'CODE') {
                my $old_accumulator = pop(@Accumulator);
                push(@Sequence_Data,&{$old_accumulator}());
            }
        } elsif ($curRes == $iterator->BEGIN_MAP) {
            # Not much to do here.
        }
        next if (! ref($curRes));
        if ($curRes->is_map) {
            push(@Accumulator,&new_accumulator($curRes->compTitle,
                                               $curRes->src,
                                               $curRes->symb,
                                               $inputname));
        } elsif ($curRes->is_problem) {
            if (@Accumulator && $Accumulator[-1] ne '') {
                &{$Accumulator[-1]}($curRes,
                                    exists($selected->{$curRes->symb}));
            }
        }
    }
    my $course_seq = pop(@Sequence_Data);
    foreach my $seq ($course_seq,@Sequence_Data) {
        #my $seq = pop(@Sequence_Data);
        next if (! defined($seq) || ref($seq) ne 'HASH');
        $Str.= '<tr><td colspan="2">'.
            '<b>'.$seq->{'title'}.'</b>'.
            '</td></tr>'.$/;
        $Str.= $seq->{'html'};
    }
    $Str .= '</table>'.$/;
    return $Str;
}

sub get_title {
    my ($title,$src) = @_;
    if ($title eq '') {
        ($title) = ($src =~ m|/([^/]+)$|);
    } else {
        $title =~ s/\&colon;/:/g;
    }
    return $title;
}

sub new_accumulator {
    my ($title,$src,$symb,$inputname) = @_;
    my $target;
    return 
        sub {
            if (@_) { 
                my ($res,$checked) = @_;
                $target.='<tr><td><label>'.
                    '<input type="checkbox" name="'.$inputname.'" ';
                if ($checked) {
                    $target .= 'checked ';
                }
                $target.= 
                    'value="'.&Apache::lonnet::escape($res->symb).'" />'.
                    '&nbsp;'.$res->compTitle.'</label></td>'.
                    '</tr>'.$/;
            } else { 
                if (defined($target)) {
                    return { title => $title,
                             symb  => $symb,
                             src   => $src,
                             html  => $target, }; 
                }
                return undef;
            }
        };
}

sub get_selected_symbs {
    my ($inputfield) = @_;
    my $field = 'form.'.$inputfield;
    my @Symbs;
    if (exists($ENV{$field})) {
        if (! ref($ENV{$field})) {
            @Symbs = (&Apache::lonnet::unescape($ENV{$field}));
        } else {
            @Symbs = (map {&Apache::lonnet::unescape($_);} @{$ENV{$field}});
        }
    }
    return @Symbs;
}

####################################################
####################################################

=pod

=item &make_target_id($target)

Inputs: Hash ref with the following entries:
    $target->{'symb'}, $target->{'part'}, $target->{'respid'}, 
    $target->{'resptype'}.

Returns: A string, suitable for a form parameter, which uniquely identifies
the problem, part, and response to do statistical analysis on.

Used by Apache::lonstathelpers::ProblemSelector().

=cut

####################################################
####################################################
sub make_target_id {
    my ($target) = @_;
    my $id = &Apache::lonnet::escape($target->{'symb'}).':'.
             &Apache::lonnet::escape($target->{'part'}).':'.
             &Apache::lonnet::escape($target->{'respid'}).':'.
             &Apache::lonnet::escape($target->{'resptype'});
    return $id;
}

####################################################
####################################################

=pod

=item &get_target_from_id($id)

Inputs: $id, a scalar string from Apache::lonstathelpers::make_target_id().

Returns: A hash reference, $target, containing the following keys:
    $target->{'symb'}, $target->{'part'}, $target->{'respid'}, 
    $target->{'resptype'}.

=cut

####################################################
####################################################
sub get_target_from_id {
    my ($id) = @_;
    if (! ref($id)) {
        my ($symb,$part,$respid,$resptype) = split(':',$id);
        return ({ symb     => &Apache::lonnet::unescape($symb),
                  part     => &Apache::lonnet::unescape($part),
                  respid   => &Apache::lonnet::unescape($respid),
                  resptype => &Apache::lonnet::unescape($resptype)});
    } elsif (ref($id) eq 'ARRAY') {
        my @Return;
        foreach my $selected (@$id) {
            my ($symb,$part,$respid,$resptype) = split(':',$selected);
            push(@Return,{ symb     => &Apache::lonnet::unescape($symb),
                           part     => &Apache::lonnet::unescape($part),
                           respid   => &Apache::lonnet::unescape($respid),
                           resptype => &Apache::lonnet::unescape($resptype)});
        }
        return \@Return;
    }
}

####################################################
####################################################

=pod

=item &get_prev_curr_next($target,$AcceptableResponseTypes,$granularity)

Determine the problem parts or responses preceeding and following the
current resource.

Inputs: $target (see &Apache::lonstathelpers::get_target_from_id())
  $AcceptableResponseTypes, regular expression matching acceptable
                            response types,
  $granularity, either 'part', 'response', or 'part_survey'

Returns: three hash references, $prev, $curr, $next, which refer to the
preceeding, current, or following problem parts or responses, depending
on the value of $granularity.  Values of undef indicate there is no
previous or next part/response.  A value of undef for all three indicates
there was no match found to the current part/resource.

The hash references contain the following keys:
    symb, part, resource

If $granularity eq 'response', the following ADDITIONAL keys will be present:
    respid, resptype

=cut

####################################################
####################################################
sub get_prev_curr_next {
    my ($target,$AcceptableResponseTypes,$granularity) = @_;
    #
    # Build an array with the data we need to search through
    my @Resource;
    foreach my $seq (&Apache::lonstatistics::Sequences_with_Assess('all')) {
        foreach my $res (@{$seq->{'contents'}}) {
            next if ($res->{'type'} ne 'assessment');
            foreach my $part (@{$res->{'parts'}}) {
                my $partdata = $res->{'partdata'}->{$part};
                if ($partdata->{'Survey'} && ($granularity eq 'part_survey')){
                    push (@Resource,
                          { symb     => $res->{symb},
                            part     => $part,
                            resource => $res,
                        } );
                } elsif ($granularity eq 'part') {
                    push (@Resource,
                          { symb     => $res->{symb},
                            part     => $part,
                            resource => $res,
                        } );
                } elsif ($granularity eq 'response') {
                    for (my $i=0;
                         $i<scalar(@{$partdata->{'ResponseTypes'}});
                         $i++){
                        my $respid = $partdata->{'ResponseIds'}->[$i];
                        my $resptype = $partdata->{'ResponseTypes'}->[$i];
                        next if ($resptype !~ m/$AcceptableResponseTypes/);
                        push (@Resource,
                              { symb     => $res->{symb},
                                part     => $part,
                                respid   => $partdata->{'ResponseIds'}->[$i],
                                resource => $res,
                                resptype => $resptype
                                } );
                    }
                }
            }
        }
    }
    #
    # Get the index of the current situation
    my $curr_idx;
    for ($curr_idx=0;$curr_idx<$#Resource;$curr_idx++) {
        my $curr_item = $Resource[$curr_idx];
        if ($granularity eq 'part' || $granularity eq 'part_survey') {
            if ($curr_item->{'symb'} eq $target->{'symb'} &&
                $curr_item->{'part'} eq $target->{'part'}) {
                last;
            }
        } elsif ($granularity eq 'response') {
            if ($curr_item->{'symb'} eq $target->{'symb'} &&
                $curr_item->{'part'} eq $target->{'part'} &&
                $curr_item->{'respid'} eq $target->{'respid'} &&
                $curr_item->{'resptype'} eq $target->{'resptype'}) {
                last;
            }
        }
    }
    my $curr_item = $Resource[$curr_idx];
    if ($granularity eq 'part' || $granularity eq 'part_survey') {
        if ($curr_item->{'symb'}     ne $target->{'symb'} ||
            $curr_item->{'part'}     ne $target->{'part'}) {
            # bogus symb - return nothing
            return (undef,undef,undef);
        }
    } elsif ($granularity eq 'response') {
        if ($curr_item->{'symb'}     ne $target->{'symb'} ||
            $curr_item->{'part'}     ne $target->{'part'} ||
            $curr_item->{'respid'}   ne $target->{'respid'} ||
            $curr_item->{'resptype'} ne $target->{'resptype'}){
            # bogus symb - return nothing
            return (undef,undef,undef);
        }
    }
    #
    # Now just pick up the data we need
    my ($prev,$curr,$next);
    if ($curr_idx == 0) {
        $prev = undef;
        $curr = $Resource[$curr_idx  ];
        $next = $Resource[$curr_idx+1];
    } elsif ($curr_idx == $#Resource) {
        $prev = $Resource[$curr_idx-1];
        $curr = $Resource[$curr_idx  ];
        $next = undef;
    } else {
        $prev = $Resource[$curr_idx-1];
        $curr = $Resource[$curr_idx  ];
        $next = $Resource[$curr_idx+1];
    }
    return ($prev,$curr,$next);
}


#####################################################
#####################################################

=pod

=item GetStudentAnswers($r,$problem,$Students)

Determines the correct answer for a set of students on a given problem.
The students answers are stored in the student hashes pointed to by the
array @$Students under the key 'answer'.

Inputs: $r
$problem: hash reference containing the keys 'resource', 'part', and 'respid'.
$Students: reference to array containing student hashes (need 'username', 
    'domain').  

Returns: nothing 

=cut

#####################################################
#####################################################
sub GetStudentAnswers {
    my ($r,$problem,$Students,$formname,$inputname) = @_;
    my $status_type;
    if (defined($formname)) {
        $status_type = 'inline';
    } else {
        $status_type = 'popup';
    }    
    my $c = $r->connection();
    my %Answers;
    my ($resource,$partid,$respid) = ($problem->{'resource'},
                                      $problem->{'part'},
                                      $problem->{'respid'});
    # Read in the cache (if it exists) before we start timing things.
    &Apache::lonstathelpers::ensure_proper_cache($resource->{'symb'});
    # Open progress window
    my %prog_state=&Apache::lonhtmlcommon::Create_PrgWin
        ($r,'Student Answer Compilation Status',
         'Student Answer Compilation Progress', scalar(@$Students),
         $status_type,undef,$formname,$inputname);
    $r->rflush();
    foreach my $student (@$Students) {
        last if ($c->aborted());
        my $sname = $student->{'username'};
        my $sdom = $student->{'domain'};
        my $answer = &Apache::lonstathelpers::analyze_problem_as_student
            ($resource,$sname,$sdom,$partid,$respid);
        &Apache::lonhtmlcommon::Increment_PrgWin($r,\%prog_state,
                                                 &mt('last student'));
        $student->{'answer'} = $answer;
    }
    &Apache::lonstathelpers::write_answer_cache();
    return if ($c->aborted());
    $r->rflush();
    # close progress window
    &Apache::lonhtmlcommon::Close_PrgWin($r,\%prog_state);
    return;
}

#####################################################
#####################################################

=pod

=item analyze_problem_as_student

Analyzes a homework problem for a student and returns the correct answer
for the student.  Attempts to put together an answer for problem types 
that do not natively support it.

Inputs: $resource: a resource object
        $sname, $sdom, $partid, $respid

Returns: $answer

If $partid and $respid are specified, $answer is simply a scalar containing
the correct answer for the response.

If $partid or $respid are undefined, $answer will be a hash reference with
keys $partid.'.'.$respid.'.answer'.

=cut

#####################################################
#####################################################
sub analyze_problem_as_student {
    my ($resource,$sname,$sdom,$partid,$respid) = @_;
    if (ref($resource) ne 'HASH') {
        my $res = $resource;
        $resource = { 'src' => $res->src,
                      'symb' => $res->symb,
                      'parts' => $res->parts };
        foreach my $part (@{$resource->{'parts'}}) {
            $resource->{'partdata'}->{$part}->{'ResponseIds'}=
                [$res->responseIds($part)];
        }
    }
    my $returnvalue;
    my $url = $resource->{'src'};
    my $symb = $resource->{'symb'};
    my $answer = &get_from_answer_cache($sname,$sdom,$symb,$partid,$respid);
    if (defined($answer)) {
        return($answer);
    }
    my $courseid = $ENV{'request.course.id'};
    my $Answ=&Apache::lonnet::ssi($url,('grade_target' => 'analyze',
                                        'grade_domain' => $sdom,
                                        'grade_username' => $sname,
                                        'grade_symb' => $symb,
                                        'grade_courseid' => $courseid));
    (my $garbage,$Answ)=split(/_HASH_REF__/,$Answ,2);
    my %Answer=&Apache::lonnet::str2hash($Answ);
    #
    undef($answer);
    foreach my $partid (@{$resource->{'parts'}}) {
        my $partdata = $resource->{'partdata'}->{$partid};
        foreach my $respid (@{$partdata->{'ResponseIds'}}) {
            my $prefix = $partid.'.'.$respid;
            my $key = $prefix.'.answer';
            $answer->{$partid}->{$respid} = &get_answer($prefix,$key,%Answer);
        }
    }
    &store_answer($sname,$sdom,$symb,undef,undef,$answer);
    if (! defined($partid)) {
        $returnvalue = $answer;
    } elsif (! defined($respid)) {
        $returnvalue = $answer->{$partid};
    } else {
        $returnvalue = $answer->{$partid}->{$respid};
    }
    return $returnvalue;
}

sub get_answer {
    my ($prefix,$key,%Answer) = @_;
    my $returnvalue;
    if (exists($Answer{$key})) {
        my $student_answer = $Answer{$key}->[0];
        if (! defined($student_answer)) {
            $student_answer = $Answer{$key}->[1];
        }
        $returnvalue = $student_answer;
    } else {
        if (exists($Answer{$prefix.'.shown'})) {
            # The response has foils
            my %values;
            while (my ($k,$v) = each(%Answer)) {
                next if ($k !~ /^$prefix\.foil\.(value|area)\.(.*)$/);
                my $foilname = $2;
                $values{$foilname}=$v;
            }
            foreach my $foil (@{$Answer{$prefix.'.shown'}}) {
                if (ref($values{$foil}) eq 'ARRAY') {
                    $returnvalue.=&HTML::Entities::encode($foil,'<>&"').'='.
                        join(',',map {&HTML::Entities::encode($_,'<>&"')} @{$values{$foil}}).'&';
                } else {
                    $returnvalue.=&HTML::Entities::encode($foil,'<>&"').'='.
                        &HTML::Entities::encode($values{$foil},'<>&"').'&';
                }
            }
            $returnvalue =~ s/ /\%20/g;
            chop ($returnvalue);
        }
    }
    return $returnvalue;
}


#####################################################
#####################################################

=pod

=item Caching routines

=over 4

=item &load_answer_cache($symb)

Loads the cache for the given symb into memory from disk.  
Requires the cache filename be set.  
Only should be called by &ensure_proper_cache.

=cut

#####################################################
#####################################################
{
    my $cache_filename = undef;
    my $current_symb = undef;
    my %cache;

sub load_answer_cache {
    my ($symb) = @_;
    return if (! defined($cache_filename));
    if (! defined($current_symb) || $current_symb ne $symb) {
        undef(%cache);
        my $storedstring;
        my %cache_db;
        if (tie(%cache_db,'GDBM_File',$cache_filename,&GDBM_READER(),0640)) {
            $storedstring = $cache_db{&Apache::lonnet::escape($symb)};
            untie(%cache_db);
        }
        if (defined($storedstring)) {
            %cache = %{thaw($storedstring)};
        }
    }
    return;
}

#####################################################
#####################################################

=pod

=item &get_from_answer_cache($sname,$sdom,$symb,$partid,$respid)

Returns the appropriate data from the cache, or undef if no data exists.
If $respid is undefined, a hash ref containing the answers for the given 
$partid is returned.  If $partid is undefined, a hash ref containing answers
for all of the parts is returned.

=cut

#####################################################
#####################################################
sub get_from_answer_cache {
    my ($sname,$sdom,$symb,$partid,$respid) = @_;
    &ensure_proper_cache($symb);
    my $returnvalue;
    if (exists($cache{$sname.':'.$sdom}) &&
        ref($cache{$sname.':'.$sdom}) eq 'HASH') {
        if (defined($partid) &&
            exists($cache{$sname.':'.$sdom}->{$partid})) {
            if (defined($respid) &&
                exists($cache{$sname.':'.$sdom}->{$partid}->{$respid})) {
                $returnvalue = $cache{$sname.':'.$sdom}->{$partid}->{$respid};
            } else {
                $returnvalue = $cache{$sname.':'.$sdom}->{$partid};
            }
        } else {
            $returnvalue = $cache{$sname.':'.$sdom};
        }
    } else {
        $returnvalue = undef;
    }
    return $returnvalue;
}

#####################################################
#####################################################

=pod

=item &write_answer_cache($symb)

Writes the in memory cache to disk so that it can be read in with
&load_answer_cache($symb).

=cut

#####################################################
#####################################################
sub write_answer_cache {
    return if (! defined($current_symb) || ! defined($cache_filename));
    my %cache_db;
    my $key = &Apache::lonnet::escape($current_symb);
    if (tie(%cache_db,'GDBM_File',$cache_filename,&GDBM_WRCREAT(),0640)) {
        my $storestring = freeze(\%cache);
        $cache_db{$key}=$storestring;
        $cache_db{$key.'.time'}=time;
        untie(%cache_db);
    }
    undef(%cache);
    undef($current_symb);
    undef($cache_filename);
    return;
}

#####################################################
#####################################################

=pod

=item &ensure_proper_cache($symb)

Called to make sure we have the proper cache set up.  This is called
prior to every answer lookup.

=cut

#####################################################
#####################################################
sub ensure_proper_cache {
    my ($symb) = @_;
    my $cid = $ENV{'request.course.id'};
    my $new_filename =  '/home/httpd/perl/tmp/'.
        'problemanalysis_'.$cid.'_answer_cache.db';
    if (! defined($cache_filename) ||
        $cache_filename ne $new_filename ||
        ! defined($current_symb)   ||
        $current_symb ne $symb) {
        $cache_filename = $new_filename;
        # Notice: $current_symb is not set to $symb until after the cache is
        # loaded.  This is what tells &load_answer_cache to load in a new
        # symb cache.
        &load_answer_cache($symb);
        $current_symb = $symb;
    }
}

#####################################################
#####################################################

=pod

=item &store_answer($sname,$sdom,$symb,$partid,$respid,$dataset)

Stores the answer data in the in memory cache.

=cut

#####################################################
#####################################################
sub store_answer {
    my ($sname,$sdom,$symb,$partid,$respid,$dataset) = @_;
    return if ($symb ne $current_symb);
    if (defined($partid)) {
        if (defined($respid)) {
            $cache{$sname.':'.$sdom}->{$partid}->{$respid} = $dataset;
        } else {
            $cache{$sname.':'.$sdom}->{$partid} = $dataset;
        }
    } else {
        $cache{$sname.':'.$sdom}=$dataset;
    }
    return;
}

}
#####################################################
#####################################################

=pod

=back

=cut

#####################################################
#####################################################

##
## The following is copied from datecalc1.pl, part of the 
## Spreadsheet::WriteExcel CPAN module.
##
##
######################################################################
#
# Demonstration of writing date/time cells to Excel spreadsheets,
# using UNIX/Perl time as source of date/time.
#
# Copyright 2000, Andrew Benham, adsb@bigfoot.com
#
######################################################################
#
# UNIX/Perl time is the time since the Epoch (00:00:00 GMT, 1 Jan 1970)
# measured in seconds.
#
# An Excel file can use exactly one of two different date/time systems.
# In these systems, a floating point number represents the number of days
# (and fractional parts of the day) since a start point. The floating point
# number is referred to as a 'serial'.
# The two systems ('1900' and '1904') use different starting points:
#  '1900'; '1.00' is 1 Jan 1900 BUT 1900 is erroneously regarded as
#          a leap year - see:
#            http://support.microsoft.com/support/kb/articles/Q181/3/70.asp
#          for the excuse^H^H^H^H^H^Hreason.
#  '1904'; '1.00' is 2 Jan 1904.
#
# The '1904' system is the default for Apple Macs. Windows versions of
# Excel have the option to use the '1904' system.
#
# Note that Visual Basic's "DateSerial" function does NOT erroneously
# regard 1900 as a leap year, and thus its serials do not agree with
# the 1900 serials of Excel for dates before 1 Mar 1900.
#
# Note that StarOffice (at least at version 5.2) does NOT erroneously
# regard 1900 as a leap year, and thus its serials do not agree with
# the 1900 serials of Excel for dates before 1 Mar 1900.
#
######################################################################
#
# Calculation description
# =======================
#
# 1900 system
# -----------
# Unix time is '0' at 00:00:00 GMT 1 Jan 1970, i.e. 70 years after 1 Jan 1900.
# Of those 70 years, 17 (1904,08,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68)
# were leap years with an extra day.
# Thus there were 17 + 70*365 days = 25567 days between 1 Jan 1900 and
# 1 Jan 1970.
# In the 1900 system, '1' is 1 Jan 1900, but as 1900 was not a leap year
# 1 Jan 1900 should really be '2', so 1 Jan 1970 is '25569'.
#
# 1904 system
# -----------
# Unix time is '0' at 00:00:00 GMT 1 Jan 1970, i.e. 66 years after 1 Jan 1904.
# Of those 66 years, 17 (1904,08,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68)
# were leap years with an extra day.
# Thus there were 17 + 66*365 days = 24107 days between 1 Jan 1904 and
# 1 Jan 1970.
# In the 1904 system, 2 Jan 1904 being '1', 1 Jan 1970 is '24107'.
#
######################################################################
#
# Copyright (c) 2000, Andrew Benham.
# This program is free software. It may be used, redistributed and/or
# modified under the same terms as Perl itself.
#
# Andrew Benham, adsb@bigfoot.com
# London, United Kingdom
# 11 Nov 2000
#
######################################################################
#-----------------------------------------------------------
# calc_serial()
#
# Called with (up to) 2 parameters.
#   1.  Unix timestamp.  If omitted, uses current time.
#   2.  GMT flag. Set to '1' to return serial in GMT.
#       If omitted, returns serial in appropriate timezone.
#
# Returns date/time serial according to $DATE_SYSTEM selected
#-----------------------------------------------------------
sub calc_serial {
    # Use 1900 date system on all platforms other than Apple Mac (for which
    # use 1904 date system).
    my $DATE_SYSTEM = ($^O eq 'MacOS') ? 1 : 0;
    my $time = (defined $_[0]) ? $_[0] : time();
    my $gmtflag = (defined $_[1]) ? $_[1] : 0;
    #
    # Divide timestamp by number of seconds in a day.
    # This gives a date serial with '0' on 1 Jan 1970.
    my $serial = $time / 86400;
    #
    # Adjust the date serial by the offset appropriate to the
    # currently selected system (1900/1904).
    if ($DATE_SYSTEM == 0) {        # use 1900 system
        $serial += 25569;
    } else {                        # use 1904 system
        $serial += 24107;
    }
    #
    unless ($gmtflag) {
        # Now have a 'raw' serial with the right offset. But this
        # gives a serial in GMT, which is false unless the timezone
        # is GMT. We need to adjust the serial by the appropriate
        # timezone offset.
        # Calculate the appropriate timezone offset by seeing what
        # the differences between localtime and gmtime for the given
        # time are.
        #    
        my @gmtime = gmtime($time);
        my @ltime  = localtime($time);
        #
        # For the first 7 elements of the two arrays, adjust the
        # date serial where the elements differ.
        for (0 .. 6) {
            my $diff = $ltime[$_] - $gmtime[$_];
            if ($diff) {
                $serial += _adjustment($diff,$_);
            }
        }
    }
    #
    # Perpetuate the error that 1900 was a leap year by decrementing
    # the serial if we're using the 1900 system and the date is prior to
    # 1 Mar 1900. This has the effect of making serial value '60'
    # 29 Feb 1900.
    #
    # This fix only has any effect if UNIX/Perl time on the platform
    # can represent 1900. Many can't.
    #
    unless ($DATE_SYSTEM) {
        $serial-- if ($serial < 61);    # '61' is 1 Mar 1900
    }
    return $serial;
}

sub _adjustment {
    # Based on the difference in the localtime/gmtime array elements
    # number, return the adjustment required to the serial.
    #
    # We only look at some elements of the localtime/gmtime arrays:
    #    seconds    unlikely to be different as all known timezones
    #               have an offset of integral multiples of 15 minutes,
    #               but it's easy to do.
    #    minutes    will be different for timezone offsets which are
    #               not an exact number of hours.
    #    hours      very likely to be different.
    #    weekday    will differ when localtime/gmtime difference
    #               straddles midnight.
    #
    # Assume that difference between localtime and gmtime is less than
    # 5 days, then don't have to do maths for day of month, month number,
    # year number, etc...
    #
    my ($delta,$element) = @_;
    my $adjust = 0;
    #
    if ($element == 0) {            # Seconds
        $adjust = $delta/86400;         # 60 * 60 * 24
    } elsif ($element == 1) {       # Minutes
        $adjust = $delta/1440;          # 60 * 24
    } elsif ($element == 2) {       # Hours
        $adjust = $delta/24;            # 24
    } elsif ($element == 6) {       # Day of week number
        # Catch difference straddling Sat/Sun in either direction
        $delta += 7 if ($delta < -4);
        $delta -= 7 if ($delta > 4);
        #    
        $adjust = $delta;
    }
    return $adjust;
}

###########################################################
###########################################################

=pod

=item get_problem_data

Returns a data structure describing the problem.

Inputs: $url

Returns: %Partdata

=cut

## note: we must force each foil and option to not begin or end with
##       spaces as they are stored without such data.
##
###########################################################
###########################################################
sub get_problem_data {
    my ($url) = @_;
    my $Answ=&Apache::lonnet::ssi($url,('grade_target' => 'analyze'));
    (my $garbage,$Answ)=split(/_HASH_REF__/,$Answ,2);
    my %Answer;
    %Answer=&Apache::lonnet::str2hash($Answ);
    my %Partdata;
    foreach my $part (@{$Answer{'parts'}}) {
        while (my($key,$value) = each(%Answer)) {
            #
            # Logging code:
            if (0) {
                &Apache::lonnet::logthis($part.' got key "'.$key.'"');
                if (ref($value) eq 'ARRAY') {
                    &Apache::lonnet::logthis('    @'.join(',',@$value));
                } else {
                    &Apache::lonnet::logthis('    '.$value);
                }
            }
            # End of logging code
            next if ($key !~ /^$part/);
            $key =~ s/^$part\.//;
            if (ref($value) eq 'ARRAY') {
                if ($key eq 'options') {
                    $Partdata{$part}->{'_Options'}=$value;
                } elsif ($key eq 'concepts') {
                    $Partdata{$part}->{'_Concepts'}=$value;
                } elsif ($key =~ /^concept\.(.*)$/) {
                    my $concept = $1;
                    foreach my $foil (@$value) {
                        $Partdata{$part}->{'_Foils'}->{$foil}->{'_Concept'}=
                                                                      $concept;
                    }
                } elsif ($key =~ /^(incorrect|answer|ans_low|ans_high)$/) {
                    $Partdata{$part}->{$key}=$value;
                }
            } else {
                if ($key=~ /^foil\.text\.(.*)$/) {
                    my $foil = $1;
                    $Partdata{$part}->{'_Foils'}->{$foil}->{'name'}=$foil;
                    $value =~ s/(\s*$|^\s*)//g;
                    $Partdata{$part}->{'_Foils'}->{$foil}->{'text'}=$value;
                } elsif ($key =~ /^foil\.value\.(.*)$/) {
                    my $foil = $1;
                    $Partdata{$part}->{'_Foils'}->{$foil}->{'value'}=$value;
                }
            }
        }
    }
    return %Partdata;
}

####################################################
####################################################

=pod

=item &limit_by_time()

=cut

####################################################
####################################################
sub limit_by_time_form {
    my $Starttime_form = '';
    my $starttime = &Apache::lonhtmlcommon::get_date_from_form
        ('limitby_startdate');
    my $endtime = &Apache::lonhtmlcommon::get_date_from_form
        ('limitby_enddate');
    if (! defined($endtime)) {
        $endtime = time;
    }
    if (! defined($starttime)) {
        $starttime = $endtime - 60*60*24*7;
    }
    my $state;
    if (&limit_by_time()) {
        $state = '';
    } else {
        $state = 'disabled';
    }
    my $startdateform = &Apache::lonhtmlcommon::date_setter
        ('Statistics','limitby_startdate',$starttime,undef,undef,$state);
    my $enddateform = &Apache::lonhtmlcommon::date_setter
        ('Statistics','limitby_enddate',$endtime,undef,undef,$state);
    my $Str;
    $Str .= '<script language="Javascript" >';
    $Str .= 'function toggle_limitby_activity(state) {';
    $Str .= '    if (state) {';
    $Str .= '        limitby_startdate_enable();';
    $Str .= '        limitby_enddate_enable();';
    $Str .= '    } else {';
    $Str .= '        limitby_startdate_disable();';
    $Str .= '        limitby_enddate_disable();';
    $Str .= '    }';    
    $Str .= '}';
    $Str .= '</script>';
    $Str .= '<fieldset>';
    my $timecheckbox = '<input type="checkbox" name="limit_by_time" ';
    if (&limit_by_time()) {
        $timecheckbox .= ' checked ';
    } 
    $timecheckbox .= 'OnChange="javascript:toggle_limitby_activity(this.checked);" ';
    $timecheckbox .= ' />';
    $Str .= '<legend>'.&mt('[_1] Limit by time',$timecheckbox).'</legend>';
    $Str .= &mt('Start Time: [_1]',$startdateform).'<br />';
    $Str .= &mt('&nbsp;End Time: [_1]',$enddateform).'<br />';
    $Str .= '</fieldset>';
    return $Str;
}

sub limit_by_time {
    if (exists($ENV{'form.limit_by_time'}) &&
        $ENV{'form.limit_by_time'} ne '' ) {
        return 1;
    } else {
        return 0;
    }
}

sub get_time_limits {
    my $starttime = &Apache::lonhtmlcommon::get_date_from_form
        ('limitby_startdate');
    my $endtime = &Apache::lonhtmlcommon::get_date_from_form
        ('limitby_enddate');
    return ($starttime,$endtime);
}



####################################################
####################################################

=pod

=item sections_description 

Inputs: @Sections, an array of sections

Returns: A text description of the sections selected.

=cut

####################################################
####################################################
sub sections_description {
    my @Sections = @_;
    my $sectionstring = '';
    if (scalar(@Sections) > 1) {
        if (scalar(@Sections) > 2) {
            my $last = pop(@Sections);
            $sectionstring = "Sections ".join(', ',@Sections).', and '.$last;
        } else {
            $sectionstring = "Sections ".join(' and ',@Sections);
        }
    } else {
        if ($Sections[0] eq 'all') {
            $sectionstring = "All sections";
        } else {
            $sectionstring = "Section ".$Sections[0];
        }
    }
    return $sectionstring;
}

####################################################
####################################################

=pod

=item &manage_caches

Inputs: $r, apache request object

Returns: An array of scalars containing html for buttons.

=cut

####################################################
####################################################
sub manage_caches {
    my ($r,$formname,$inputname,$update_message) = @_;
    &Apache::loncoursedata::clear_internal_caches();
    my $sectionkey = 
        join(',',
             map {
                     &Apache::lonnet::escape($_);
                 } sort(@Apache::lonstatistics::SelectedSections)
             );
    my $statuskey = $Apache::lonstatistics::enrollment_status;
    if (exists($ENV{'form.ClearCache'}) || 
        exists($ENV{'form.updatecaches'}) || 
        (exists($ENV{'form.firstrun'}) && $ENV{'form.firstrun'} ne 'no') ||
        (exists($ENV{'form.prevsection'}) &&
            $ENV{'form.prevsection'} ne $sectionkey) ||
        (exists($ENV{'form.prevenrollstatus'}) &&
            $ENV{'form.prevenrollstatus'} ne $statuskey)
        ) {
        if (defined($update_message)) {
            $r->print($update_message);
        }
        &Apache::lonstatistics::Gather_Full_Student_Data($r,$formname,
                                                         $inputname);
            
    }
    #
    my @Buttons = 
        ('<input type="submit" name="ClearCache" '.
             'value="'.&mt('Clear Caches').'" />',
         '<input type="submit" name="updatecaches" '.
             'value="'.&mt('Update Caches').'" />'.
         &Apache::loncommon::help_open_topic('Statistics_Cache'),
         '<input type="hidden" name="prevsection" value="'.$sectionkey.'" />',
         '<input type="hidden" name="prevenrollstatus" value="'.$statuskey.'" />'
         );
    #
    if (! exists($ENV{'form.firstrun'})) {
        $r->print('<input type="hidden" name="firstrun" value="yes" />');
    } else {
        $r->print('<input type="hidden" name="firstrun" value="no" />');
    }
    #
    return @Buttons;
}




####################################################
####################################################

=pod

=back

=cut

####################################################
####################################################

1;

__END__