# Copyright (C) 2004, 2005, 2006, 2010  Alex Schroeder <alex@gnu.org>
#
# This program is free software: you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation, either version 3 of the License, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# this program. If not, see <http://www.gnu.org/licenses/>.
use strict;
use v5.10;

AddModuleDescription('referrer-tracking.pl', 'Automatic Link Back');

use LWP::UserAgent;

our ($q, $Now, $OpenPageName, %Action, @KnownLocks, %AdminPages,
$ScriptName, $DataDir, $EmbedWiki, $FS, @MyInitVariables,
@MyAdminCode, $FullUrlPattern, @MyFooters);

push(@KnownLocks, "refer_*");
$Action{refer} = \&DoPrintAllReferers;

our ($RefererDir, $RefererTimeLimit, $RefererLimit, $RefererFilter,
$RefererTitleLimit, %Referers);

$RefererTimeLimit = 86400; # How long referrals shall be remembered in seconds
$RefererLimit	  = 15;	   # How many different referer shall be remembered
$RefererFilter    = 'ReferrerFilter'; # Name of the filter page
$RefererTitleLimit = 70;   # This is used to shorten long titles

push(@MyInitVariables, \&RefererInit);

sub RefererInit {
  $RefererFilter = FreeToNormal($RefererFilter); # spaces to underscores
  $AdminPages{$RefererFilter} = 1;
  $RefererDir  = "$DataDir/referer"; # Stores referer data
}

push(@MyAdminCode, \&RefererMenu);

sub RefererMenu {
  my ($id, $menuref, $restref) = @_;
  push(@$menuref, ScriptLink('action=refer', T('All Referrers'), 'refer'));
}

*RefererOldExpireKeepFiles = \&ExpireKeepFiles;
*ExpireKeepFiles = \&RefererNewExpireKeepFiles;

sub RefererNewExpireKeepFiles {
  RefererOldExpireKeepFiles(@_); # call with opened page
  ReadReferers($OpenPageName);   # clean up reading (expiring) and writing
  WriteReferers($OpenPageName);
}

*RefererOldDeletePage = \&DeletePage;
*DeletePage = \&RefererNewDeletePage;

sub RefererNewDeletePage {
  my $status = RefererOldDeletePage(@_);
  return $status if $status; # this would be the error message
  my $id = shift;
  my $fname = GetRefererFile($id);
  Unlink($fname) if (IsFile($fname));
  return ''; # no error
}

## == Actual Code ==

sub GetRefererFile {
  my $id = shift;
  return "$RefererDir/$id.rf";
}

sub ReadReferers {
  my $file = GetRefererFile(shift);
  %Referers = ();
  if (IsFile($file)) {
    my ($status, $data) = ReadFile($file);
    %Referers = split(/$FS/, $data, -1) if $status;
  }
  ExpireReferers();
}

sub ExpireReferers { # no need to save the pruned list if nothing else changes
  if ($RefererTimeLimit) {
    foreach (keys %Referers) {
      if ($Now - $Referers{$_} > $RefererTimeLimit) {
	delete $Referers{$_};
      }
    }
  }
  if ($RefererLimit) {
    my @list = sort {$Referers{$a} cmp $Referers{$b}} keys %Referers;
    @list = @list[$RefererLimit .. @list-1];
    foreach (@list) {
      delete $Referers{$_};
    }
  }
}

# maybe test for valid utf-8 later?

# http://www.w3.org/International/questions/qa-forms-utf-8

# $field =~
#   m/^(
#      [\x09\x0A\x0D\x20-\x7E]            # ASCII
#    | [\xC2-\xDF][\x80-\xBF]             # non-overlong 2-byte
#    |  \xE0[\xA0-\xBF][\x80-\xBF]        # excluding overlongs
#    | [\xE1-\xEC\xEE\xEF][\x80-\xBF]{2}  # straight 3-byte
#    |  \xED[\x80-\x9F][\x80-\xBF]        # excluding surrogates
#    |  \xF0[\x90-\xBF][\x80-\xBF]{2}     # planes 1-3
#    | [\xF1-\xF3][\x80-\xBF]{3}          # planes 4-15
#    |  \xF4[\x80-\x8F][\x80-\xBF]{2}     # plane 16
#   )*$/x;

sub UrlToTitle {
  my $title = QuoteHtml(shift);
  $title = $1 if $title =~ /$FullUrlPattern/; # extract valid URL
  $title =~ s/\%([0-9a-f][0-9a-f])/chr(hex($1))/egi; # decode if possible
  $title =~ s!^https?://!!;
  $title =~ s!\.html?$!!;
  $title =~ s!/$!!;
  # shorten it if necessary
  if (length($title) > $RefererTitleLimit) {
    $title = substr($title, 0, $RefererTitleLimit - 10)
      . "..." . substr($title, -7);
  }
  return $title;
}

sub GetReferers {
  my $result = join(' ', map {
    my ($ts, $title) = split(/ /, $Referers{$_}, 2);
    $title = UrlToTitle($_) unless $title;
    $q->a({-href=>$_}, $title);
  } keys %Referers);
  return $q->div({-class=>'refer'}, $q->p(T('Referrers') . ': ' . $result))
    if $result;
}

sub PageContentToTitle {
  my ($content) = @_;
  my $title = $content =~ m!<h1.*?>(.*?)</h1>! ? $1 : '';
  $title = $1 if not $title and $content =~ m!<title>(.*?)</title>!;
  # get rid of extra tags
  $title =~ s!<.*?>!!g;
  # trimming
  $title =~ s!\s+! !g;
  $title =~ s!^ !!;
  $title =~ s! $!!;
  $title = substr($title, 0, $RefererTitleLimit) . "..."
    if length($title) > $RefererTitleLimit;
  return $title;
}

sub UpdateReferers {
  my $self = $ScriptName;
  my $referer = $q->referer();
  return  unless $referer and $referer !~ /$self/;
  foreach (split(/\n/,GetPageContent($RefererFilter))) {
    if (/^ ([^ ]+)[ \t]*$/) {  # only read lines with one word after one space
      my $regexp = $1;
      return  if $referer =~ /$regexp/i;
    }
  }
  my $ua = LWP::UserAgent->new;
  my $response = $ua->get($referer);
  return unless $response->is_success and $response->decoded_content =~ /$self/;
  my $title = PageContentToTitle($response->decoded_content);
  # starting with a timestamp makes sure that numerical comparisons still work!
  $Referers{$referer} = "$Now $title";
  return 1;
}

sub WriteReferers {
  my $id = shift;
  return unless RequestLockDir('refer_' . $id); # not fatal
  my $data = join($FS, %Referers);
  my $file = GetRefererFile($id);
  if ($data) {
    CreateDir($RefererDir);
    WriteStringToFile($file, $data);
  } else {
    Unlink($file); # just try it, doesn't matter if it fails
  }
  ReleaseLockDir('refer_' . $id);
}

if ($MyFooters[-1] == \&DefaultFooter) {
  splice(@MyFooters, -1, 0, \&RefererTrack);
} else {
  push(@MyFooters, \&RefererTrack);
}

sub RefererTrack {
  my $id = shift;
  return unless $id;
  ReadReferers($id);
  WriteReferers($id) if UpdateReferers($id);
  return GetReferers();
}

sub DoPrintAllReferers {
  print GetHeader('', T('All Referrers'), ''), $q->start_div({-class=>'content refer'});
  PrintAllReferers(AllPagesList());
  print $q->end_div();
  PrintFooter();
}

sub PrintAllReferers {
  for my $id (@_) {
    ReadReferers($id);
    print $q->div({-class=>'page'},
		  $q->p(GetPageLink($id)),
		  GetReferers()) if %Referers;
  }
}