package Book::Calendar;

use Date::Calc ();

my %HTML_CAL_CACHE = ();
my %TXT_CAL_CACHE = ();
my $CURRENT_MONTH_LAST_CACHED_DAY = 0;

use constant DEBUG => 0;

# prebuild this month's, 3 months back and 1 month forward calendars
my($cyear, $cmonth) = Date::Calc::Today();
for my $i (-3..1) {
    my($year, $month) = Date::Calc::Add_Delta_YMD($cyear, $cmonth, 1, 0, $i, 0);
    my $cal = '';
    get_html_calendar(\$cal, $year, $month); # disregard the returned calendar
}

# $cal = create_text_calendar($year, $month);
# the created calendar is cached
######################
sub get_text_calendar {
    my($year,$month) = @_;
    unless ($TXT_CAL_CACHE{$year}{$month}) {
        $TXT_CAL_CACHE{$year}{$month} = Date::Calc::Calendar($year, $month);
        # remove extra new line at the end
        chomp $TXT_CAL_CACHE{$year}{$month};
    }
    return $TXT_CAL_CACHE{$year}{$month};
}

# get_html_calendar(\$calendar,1999,7);
######################
sub get_html_calendar {
    my $r_calendar = shift;
    my $year   = shift || 1;
    my $month  = shift || 1;

    my($cur_year, $cur_month, $cur_day) = Date::Calc::Today();

    # should requested calendar be updated if it exists already?
    my $must_update_current_month_cache = 0;
    for my $i (-1..1) {
        my ($t_year, $t_month) = 
            Date::Calc::Add_Delta_YMD($year, $month, 1, 0, $i, 0);
        $must_update_current_month_cache = 1
            if $t_year == $cur_year and $t_month == $cur_month 
                and $CURRENT_MONTH_LAST_CACHED_DAY < $cur_day;
        last if $must_update_current_month_cache;
    }

    unless (exists $HTML_CAL_CACHE{$year}{$month}
            and not $must_update_current_month_cache) {

        warn "creating a new calendar for $year $month\n" if DEBUG;

        my @cal = ();

        for my $i (-1..1) {
            my $id = $i+1;

            my ($t_year, $t_month) = 
                Date::Calc::Add_Delta_YMD($year, $month, 1, 0, $i, 0);

            # link the calendar from passed month
            $cal[$id] = get_text_calendar($t_year, $t_month); # get a copy
            my $yearmonth = sprintf("%0.4d%0.2d", $t_year, $t_month);
            my $cur_yearmonth = sprintf("%0.4d%0.2d", $cur_year, $cur_month);

            # tri-state: ppf (past/present/future)
            my $ppf = $yearmonth <=> $cur_yearmonth;

            $cal[$id] =~ s{(\s\d|\b\d\d)\b}
                          {link_days($1, $yearmonth, $ppf, $cur_day)}eg;
        }

        # cache the html calendar for future use
        $HTML_CAL_CACHE{$year}{$month} =
        qq{
         <table border="0" cellspacing="0" 
          cellpadding="1" bgcolor="#000000">
           <tr>
             <td>
               <table border="0" cellspacing="0" 
                cellpadding="10" bgcolor="#ccccff">
                 <tr>
                   <td valign="top"><pre>$cal[0]</pre></td>
                   <td valign="top"><pre>$cal[1]</pre></td>
                   <td valign="top"><pre>$cal[2]</pre></td>
                 </tr>
               </table>
             </td>
           </tr>
         </table>
        };

        $CURRENT_MONTH_LAST_CACHED_DAY = $cur_day
            if $must_update_current_month_cache;

    }

    $$r_calendar = $HTML_CAL_CACHE{$year}{$month};

} # end of sub calendar

#
# link_days($token,199901,1,10);
###########
sub link_days {
    my($token, $yearmonth, $ppf, $cur_day) = @_;
    # $cur_day relevant only if $ppf == 0

    # skip non-days (non (\d or \d\d) )
    return $token unless my ($c1, $c2) = $token =~ /(\s|\d)(\d)/;

    my($fill, $day) = ($c1 =~ /\d/) ? ('', $c1.$c2) : ($c1, $c2) ;

    # don't link days in the future
    return $token if $ppf == 1 or ($ppf == 0 and $day > $cur_day);

    # link the date with placeholders to be replaced later
    return qq{$fill<a href="[URL]?date=$yearmonth}.
           sprintf("%0.2d",$day).
           qq{&[PARAMS]" class="nolink">$day</a>};

} # end of sub link_days


# replace the placeholders with live data
# customize_calendar(\$calendar,$url,$params);
#######################
sub customize_calendar {
    my $r_calendar = shift;
    my $url        = shift || '';
    my $params     = shift || '';
    my %map = (
        URL    => $url,
        PARAMS => $params,
    );
    $$r_calendar =~ s/\[(\w+)\]/$map{$1}/g;

} # end of sub calendar

1;