experimental-projects/cgi-projects/dark-search-engine/search_berkeley_deep.fcgi

#!/usr/bin/perl

# Author: Trizen
# Date: 08 January 2022
# Edit: 05 February 2022
# https://github.com/trizen

# A private search engine, with its own crawler running over Tor (respecting robots.txt).

# Using some HTML and CSS code from the searX project (++):
#   https://github.com/searx/searx

# To crawl an website, pass it as an argument to this script.
# By default, depth = 0. Use --depth=i to increase the crawling depth.

# Example:
#   perl search.fcgi --depth=i [URL]

# Other script options:
#   --recrawl           : activate recrawl mode
#   --fix-index         : fix the index in case it gets messed up (slow operation)
#   --sanitize-index    : sanitize the index and show some stats

# Limitations:
#   - the search engine cannot be used while the crawler is being used
#   - the crawler cannot be used while the search engine is being used

# Useful videos on this topic:
#
#   The Inverted Index Stanford NLP Professor Dan Jurafsky & Chris Manning
#       https://yewtu.be/watch?v=bnP6TsqyF30

#   Query Processing with the Inverted Index Stanford NLP Dan Jurafsky & Chris Manning
#       https://yewtu.be/watch?v=B-e297yK50U

#   Phrase Queries and Positional Indexes Stanford NLP Professor Dan Jurafsky & Chris Manning
#       https://yewtu.be/watch?v=PkjuJZSrudE

use utf8;
use 5.036;

no warnings qw(once);

#use autodie;
#use experimental qw(signatures);

use CGI::Fast;
use CGI qw/:standard *table -utf8/;

#use CGI::Carp qw(fatalsToBrowser);

#use IO::Compress::Zstd qw(zstd);
#use IO::Uncompress::UnZstd qw(unzstd);
#use URI::Escape qw(uri_escape_utf8);

use Text::Unidecode  qw(unidecode);
use Text::ParseWords qw(quotewords);
use HTML::Entities   qw(encode_entities);
use Time::HiRes      qw(gettimeofday tv_interval);

use ntheory    qw(forcomb binomial);
use List::Util qw(uniq max);

use JSON::XS qw(decode_json encode_json);
use Encode   qw(decode_utf8 encode_utf8);

use constant {

    # Cache HTML content (using CHI and WWW::Mechanize::Cached)
    CACHE => 0,

    # Use Tor proxy for crawling (127.0.0.1:9050)
    USE_TOR => 0,

    # Compress the values of the content database with Zstandard.
    # When enabled, the content database will be ~3x smaller.
    USE_ZSTD => 1,

    # xxHash seed (don't change it)
    XXHASH_SEED => 42,

    # Minimum and maximum number of characters for words stored in the index.
    WORD_MIN_LEN => 3,
    WORD_MAX_LEN => 45,

    # Maximum number of top best search results to return.
    MAX_SEARCH_RESULTS => 200,

    # Show the description of each website in search results (if available).
    # When disabled, a snippet of the content will be shown instead.
    SHOW_DESCRIPTION => 1,

    # Respect the rules from robots.txt
    RESPECT_ROBOT_RULES => 1,

    # Include only the results that fully match the given query
    EXACT_MATCH => 0,

    # Include all the results that include all the words from the given query, but not necessarily consecutive
    FAST_MATCH => 1,

    # Highlight all words from the query in search results (will produce longer descriptions)
    HIGHLIGHT_ALL_KEYWORDS => 1,

    # Rank the results based on content of the pages (better ranking, but it's much slower)
    RANK_ON_CONTENT => 1,

    # Rank the results based on boundary matches (with \b)
    RANK_ON_BOUNDARY_MATCH => 0,

    # Rank the results based on non-boundary matches (without \b)
    RANK_ON_NON_BOUNDARY_MATCH => 1,

    # Maximum number of iterations to spend during the ranking process.
    MAX_RANK_ITERATIONS => 10_000,

    # Make sure the SSL certificate is valid.
    SSL_VERIFY_HOSTNAME => 0,

    # Extract the date of the article and display it in search results (slow)
    EXTRACT_DATE => 0,

    # On "403 Forbidden" or "429 Too Many Requests" status, try to crawl the Web Archive version.
    CRAWL_ARCHIVE_FORBIDDEN => 1,

    # Word popularity limit (ignore words with popularity larger than this)
    MAX_WORD_POPULARITY => 10_000,
};

# List of tracking query parameters to remove from URLs
my @tracking_parameters = qw(

  ac itc

  yclid fbclid gclsrc

  utm_source utm_medium utm_term
  utm_content utm_campaign utm_referrer

  mtm_kwd mtm_campaign mtm_medium

  __hssc __hstc __s _hsenc _openstat dclid fb_ref gclid
  hsCtaTracking igshid mc_eid mkt_tok ml_subscriber ml_subscriber_hash
  msclkid oly_anon_id oly_enc_id rb_clickid s_cid vero_conv vero_id wickedid

);

binmode(STDOUT, ':utf8');
binmode(STDIN,  ':utf8');
binmode(STDERR, ':utf8');

if (USE_ZSTD) {
    require IO::Compress::Zstd;
    require IO::Uncompress::UnZstd;
}

my %hostname_alternatives = (
                             youtube => 'yewtu.be',
                             reddit  => 'teddit.net',
                             medium  => 'scribe.rip',
                             twitter => 'nitter.net',
                             odysee  => 'lbry.projectsegfau.lt',
                            );

my $cookie_file     = 'cookies.txt';
my $crawled_db_file = "content_berkeley_deep.db";
my $index_db_file   = "index_berkeley_deep.db";

use DB_File;

my $DB_OPTIONS = O_RDONLY;

if (@ARGV) {
    $DB_OPTIONS = O_CREAT | O_RDWR;
}

my $content_db = tie(my %CONTENT_DB, 'DB_File', $crawled_db_file, $DB_OPTIONS, 0666, $DB_HASH)
  or die "Can't create/access database <<$crawled_db_file>>: $!";

my $index_db = tie(my %WORDS_INDEX, 'DB_File', $index_db_file, $DB_OPTIONS, 0666, $DB_HASH)
  or die "Can't create/access database <<$index_db_file>>: $!";

local $SIG{INT} = sub {
    $index_db->sync;
    $content_db->sync;

    #untie %CONTENT_DB;
    #untie %WORDS_INDEX;
    exit;
};

my ($mech, $lwp, $robot_rules);

if (@ARGV) {

    my %mech_options = (
                        timeout       => 20,
                        autocheck     => 0,
                        show_progress => 1,
                        stack_depth   => 10,
                        cookie_jar    => {},
                        ssl_opts      => {verify_hostname => SSL_VERIFY_HOSTNAME, Timeout => 20},
                        agent         => "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Firefox/91.0",
                       );

    if (CACHE) {

        require File::Basename;
        require File::Spec::Functions;

        require CHI;
        require WWW::Mechanize::Cached;

        my $cache = CHI->new(
                driver   => 'BerkeleyDB',
                root_dir => File::Spec::Functions::catdir(File::Basename::dirname(File::Spec::Functions::rel2abs($0)), 'cache')
        );

        $mech = WWW::Mechanize::Cached->new(%mech_options, cache => $cache);
    }
    else {
        require WWW::Mechanize;
        $mech = WWW::Mechanize->new(%mech_options);
    }

    $lwp = LWP::UserAgent->new(%mech_options);

    if (USE_TOR) {    # set Tor proxy
        $mech->proxy(['http', 'https'], "socks://127.0.0.1:9050");
        $lwp->proxy(['http', 'https'], "socks://127.0.0.1:9050");
    }

    require WWW::RobotRules;
    $robot_rules = WWW::RobotRules->new($mech->agent);

    state $accepted_encodings = HTTP::Message::decodable();

    my %default_headers = (
                           'Accept-Encoding' => $accepted_encodings,
                           'Accept'          => 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8',
                           'Accept-Language' => 'en-US,en;q=0.5',
                           'Connection'      => 'keep-alive',
                           'Upgrade-Insecure-Requests' => '1',
                          );

    foreach my $key (sort keys %default_headers) {
        $mech->default_header($key, $default_headers{$key});
        $lwp->default_header($key, $default_headers{$key});
    }

    require LWP::ConnCache;
    my $cache = LWP::ConnCache->new;
    $cache->total_capacity(undef);    # no limit
    $mech->conn_cache($cache);
    $lwp->conn_cache($cache);

    # Support for cookies from file
    if (defined($cookie_file) and -f $cookie_file) {

        ## Netscape HTTP Cookies

        # Firefox extension:
        #   https://addons.mozilla.org/en-US/firefox/addon/cookies-txt/

        # See also:
        #   https://github.com/ytdl-org/youtube-dl#how-do-i-pass-cookies-to-youtube-dl

        require HTTP::Cookies::Netscape;

        my $cookies = HTTP::Cookies::Netscape->new(
                                                   hide_cookie2 => 1,
                                                   autosave     => 1,
                                                   file         => $cookie_file,
                                                  );

        $cookies->load;
        $mech->cookie_jar($cookies);
    }
}

sub lwp_get ($url) {
    my $resp = $lwp->get($url);
    if ($resp->is_success) {
        return $resp->decoded_content;
    }
    return undef;
}

sub extract_words ($text) {
    grep { length($_) >= WORD_MIN_LEN and length($_) <= WORD_MAX_LEN and /[[:alnum:]]/ }
      uniq(split(/[_\W]+/, CORE::fc($text)));
}

sub zstd_encode ($data) {

    IO::Compress::Zstd::zstd(\$data, \my $zstd_data)
      or die "zstd failed: $IO::Compress::Zstd::ZstdError\n";

    return $zstd_data;
}

sub zstd_decode ($zstd_data) {

    IO::Uncompress::UnZstd::unzstd(\$zstd_data, \my $decoded_data)
      or die "unzstd failed: $IO::Uncompress::UnZstd::UnZstdError\n";

    return $decoded_data;
}

sub encode_content_entry ($entry) {

    my $data = encode_json($entry);

    if (USE_ZSTD) {
        $data = zstd_encode($data);
    }

    return $data;
}

sub decode_content_entry ($entry) {

    my $data = $entry;

    if (USE_ZSTD) {
        $data = zstd_decode($data);
    }

    return decode_json($data);
}

sub encode_index_entry ($entry) {

    my $data = $entry;

    if (USE_ZSTD) {
        $data = zstd_encode($data);
    }

    return $data;
}

sub decode_index_entry ($entry) {

    my $data = $entry;

    if (USE_ZSTD) {
        $data = zstd_decode($data);
    }

    return $data;
}

sub surprise_me {

    while (my ($word, $value) = each %WORDS_INDEX) {
        if (length($word) >= 5 and rand() < 0.1) {
            my $entry     = decode_index_entry($value);
            my $ref_count = ($entry =~ tr/ //);
            if ($ref_count >= 10 and $ref_count <= 1000) {
                return $word;
            }
        }
    }

    return undef;
}

sub sanitize_url ($url) {

    # Replace some bad hostnames with better alternatives

    my $protocol = '';

    if ($url =~ m{^(https?://)(.+)}s) {
        $protocol = $1;
        $url      = $2;
    }

    # Normalize the URL
    ## $url = normalize_url($protocol . $url);

    # YouTube
    $url =~ s{^(?:www\.)?youtube\.com(?=[/?])}{$hostname_alternatives{youtube}};
    $url =~ s{^(?:www\.)?youtu\.be(?=[/?])}{$hostname_alternatives{youtube}};

    # Reddit (doesn't work for comments)
    ## $url =~ s{^(?:www\.)?reddit\.com(?=[/?])}{$hostname_alternatives{reddit}};

    # Twitter
    $url =~ s{^(?:www\.)?twitter\.com(?=/\w+\z)}{$hostname_alternatives{twitter}};
    $url =~ s{^(?:www\.)?twitter\.com(?=/\w+/status/)}{$hostname_alternatives{twitter}};

    # Medium
    $url =~ s{^(?:www\.)?medium\.com(?=[/?])}{$hostname_alternatives{medium}};

    # Odysee / LBRY
    $url =~ s{^(?:www\.)?odysee\.com(?=[/?])}{$hostname_alternatives{odysee}};
    $url =~ s{^(?:www\.)?open\.lbry\.com(?=[/?])}{$hostname_alternatives{odysee}};
    $url =~ s{^(?:www\.)?lbry\.com(?=[/?])}{$hostname_alternatives{odysee}};
    $url =~ s{^(?:www\.)?lbry\.tv(?=[/?])}{$hostname_alternatives{odysee}};

    return ($protocol . $url);
}

sub normalize_url ($url) {

    #$url =~ s/#.*//sr =~ s{^https?://(?:www\.)?}{}r =~ s{/+\z}{}r;

    require URL::Normalize;

    my $normalizer = URL::Normalize->new(url => $url);

    # Remove tracking query parameters
    $normalizer->remove_query_parameters(\@tracking_parameters);

    my $normalize = sub ($url, $method) {
        my $obj = URL::Normalize->new(url => $url);
        $obj->$method;
        $obj->url;
    };

    my $normalized_url = $normalizer->url;

    foreach my $method (
                        qw(
                        remove_directory_index
                        remove_fragment
                        remove_fragments
                        remove_duplicate_slashes
                        remove_empty_query_parameters
                        sort_query_parameters
                        make_canonical
                        remove_empty_query
                        )
      ) {
        $normalized_url = $normalize->($normalized_url, $method);
    }

    # Remove the protocol
    $normalized_url =~ s{^https?://}{};

    return $normalized_url;
}

sub add_to_database_index ($text, $key) {

    foreach my $word (extract_words($text)) {

        if (exists $WORDS_INDEX{$word}) {

            my $entry = decode_index_entry($WORDS_INDEX{$word});

#<<<
            #~ if (($entry =~ tr/ //) >= MAX_WORD_POPULARITY) {
                #~ next;
            #~ }
#>>>

            delete $WORDS_INDEX{$word};
            $WORDS_INDEX{$word} = encode_index_entry($entry . ' ' . $key);
        }
        else {
            $WORDS_INDEX{$word} = encode_index_entry($key);
        }
    }

    return 1;
}

sub readd_to_database_index ($text, $key) {

    foreach my $word (extract_words($text)) {
        if (exists $WORDS_INDEX{$word}) {
            my $entry = decode_index_entry($WORDS_INDEX{$word});
            delete $WORDS_INDEX{$word};
            $WORDS_INDEX{$word} = encode_index_entry(join(' ', uniq(split(' ', $entry), $key)));
        }
        else {
            $WORDS_INDEX{$word} = encode_index_entry($key);
        }
    }

    return 1;
}

sub valid_content_type {
    $mech->is_html() or (lc($mech->content_type) =~ m{^(?:text/|message/)});
}

sub extract_hostname ($url) {
    normalize_url(sanitize_url("$url")) =~ s{/.*}{}sr;
}

sub extract_protocol ($url) {
    ("$url" =~ m{^https://}) ? 'https://' : 'http://';
}

sub crawl ($url, $seen_hostname = {}) {

    # Must be http:// or https://
    $url =~ m{^https?://} or return;

    # Sanitize url
    $url = sanitize_url($url);

    # Check if we're allowed to crawl this URL
    if (RESPECT_ROBOT_RULES and not $robot_rules->allowed($url)) {
        warn "Not allowed to crawl: $url\n";
        return;
    }

    require Digest::xxHash;
    my $id = Digest::xxHash::xxhash32_hex(encode_utf8(normalize_url($url)), XXHASH_SEED);

    if (keys(%$seen_hostname) and exists($CONTENT_DB{$id})) {
        return 1;
    }

    my $resp = $mech->head($url);

    if ($resp->is_success) {
        valid_content_type() || return;
    }

    $url = $mech->uri;
    $url = sanitize_url("$url");

    $resp = $mech->get($url);

    # On HTTP 400+ errors, try again with WebArchive
    if (CRAWL_ARCHIVE_FORBIDDEN and $resp->code >= 400) {
        if ($url !~ m{^https://web\.archive\.org/}) {
            return crawl(join('', "https://web.archive.org/web/1990/", extract_protocol($url), normalize_url($url)),
                         $seen_hostname);
        }
    }

    $resp->is_success or return;

    if (not valid_content_type()) {
        $mech->invalidate_last_request() if CACHE;
        return;
    }

    $url = $mech->uri;
    $url = sanitize_url("$url");

    my $normalized_url = normalize_url($url);
    my $protocol       = extract_protocol($url);

    if (not exists $CONTENT_DB{$id}) {

        my %info;
        my $decoded_content = $resp->decoded_content() // $resp->content() // return;

        if ($mech->is_html) {
            if (not exists $INC{'HTML::TreeBuilder'}) {
                require HTML::TreeBuilder;
                HTML::TreeBuilder->VERSION(5);
                HTML::TreeBuilder->import('-weak');
            }

            my $tree = HTML::TreeBuilder->new();
            $tree->parse($decoded_content);
            $tree->eof();
            $tree->elementify();    # just for safety

            require HTML::FormatText;
            my $formatter = HTML::FormatText->new(leftmargin  => 0,
                                                  rightmargin => 1000);

            $info{content} = $formatter->format($tree);
        }
        else {
            $info{content} = $decoded_content;
        }

        $info{title} = $mech->title;

        # Convert Unicode to ASCII
        $info{content} = unidecode($info{content});

        if ($mech->is_html) {

            # Parse HTML header for extracting metadata
            my $html_head_parser = HTML::HeadParser->new;
            $html_head_parser->parse($decoded_content);

            $info{title} ||= $html_head_parser->header('Title');
            $info{keywords}    = $html_head_parser->header('X-Meta-Keywords');
            $info{description} = $html_head_parser->header('X-Meta-Description');
        }

        $info{title} ||= $normalized_url;
        $info{id}  = $id;
        $info{url} = $protocol . $normalized_url;

        warn "Adding: $info{title}\nURI: $info{url}\n";

        my $relevant_content = join(' ', unidecode($normalized_url), unidecode($info{title}), $info{content});

        add_to_database_index($relevant_content, $id);
        $CONTENT_DB{$id} = encode_content_entry(\%info);
    }

    if (RESPECT_ROBOT_RULES) {
        my $host = $normalized_url =~ s{/.*}{}sr;
        ## my $host = URI->new($url)->host;

        $seen_hostname->{$host} = 1;

        my $robots_url = $protocol . join('/', $host, 'robots.txt');
        my $robots_txt = lwp_get($robots_url);

        $robot_rules->parse($robots_url, $robots_txt) if defined($robots_txt);
    }

    my @links = $mech->find_all_links(text_regex => qr/./);

    foreach my $link (@links) {

        my $abs_url = join('', $link->url_abs);
        my $host    = extract_hostname($abs_url);

        next if $seen_hostname->{$host};
        crawl($abs_url, $seen_hostname);
        $seen_hostname->{$host} = 1;
    }

    return 1;
}

sub add_match_text_to_value ($text, $value, $i, $j) {

    if (!HIGHLIGHT_ALL_KEYWORDS) {
        exists($value->{match}) and return 1;
    }

    my $prefix_len = 50;
    my $suffix_len = 200;

    my $match_content = substr($text, $i, $j - $i);

    if ($j + $suffix_len > length($text)) {
        $prefix_len += $j + $suffix_len - length($text);
    }

    if ($i - $prefix_len < 0) {
        $prefix_len = $i;
    }

    my $prefix_content = substr($text, $i - $prefix_len, $prefix_len);
    my $suffix_content = substr($text, $j,               $suffix_len);

    foreach ($match_content, $prefix_content, $suffix_content) {
        s/\s+/ /g;
        s/(\W)\1{2,}/$1/g;
    }

    $value->{match} .=
        encode_entities($prefix_content) . '<b>'
      . encode_entities($match_content) . '</b>'
      . encode_entities($suffix_content)
      . (HIGHLIGHT_ALL_KEYWORDS ? ' [...] ' : '');

    return 1;
}

sub set_intersection ($sets) {

    my @sets = @$sets;
    @sets || return;

    # Optimization: sort the sets by their number of elements
    @sets = sort { scalar(@$a) <=> scalar(@$b) } @sets;

    my $intersection = {};
    @{$intersection}{@{shift(@sets)}} = ();

    while (@sets) {

        my %curr;
        @curr{@{shift(@sets)}} = ();

        my %tmp;

        foreach my $key (keys %$intersection) {
            if (exists $curr{$key}) {
                undef $tmp{$key};
            }
        }

        $intersection = \%tmp;
    }

    return keys %$intersection;
}

sub search ($text) {

    $text = unidecode($text);

    my %seen;
    my %matches;

    my @words       = extract_words($text);
    my @known_words = grep { exists($WORDS_INDEX{$_}) } @words;

    my @ref_sets;
    my %counts;

    foreach my $word (@known_words) {
        my @refs = split(' ', decode_index_entry($WORDS_INDEX{$word}));
        $counts{$word} = scalar(@refs);
        push @ref_sets, \@refs;
    }

    foreach my $key (set_intersection(\@ref_sets)) {
        $matches{$key} = eval { decode_content_entry($CONTENT_DB{$key}) } // next;
    }

    my @original_words = map {
        join('\W+', map { quotemeta($_) } split(' '))
    } grep { length($_) >= 2 } quotewords(qr/\s+/, 0, $text);

    if (not @original_words) {
        @original_words = map { quotemeta($_) } grep { length($_) >= 2 } split(/\W+/, $text);
    }

    my $ranking_cost  = 0;
    my $matches_count = scalar(keys %matches);

    my @regexes;
    for (my $k = scalar(@original_words) ; $k >= 1 ; --$k) {

        if (FAST_MATCH) {
            $k == 1 or next;
        }

        my $current_cost =
          ((RANK_ON_NON_BOUNDARY_MATCH ? 1 : 0) + (RANK_ON_BOUNDARY_MATCH ? 1 : 0)) * binomial(scalar(@original_words), $k);

        if ($matches_count * ($ranking_cost + $current_cost) > max($matches_count, MAX_RANK_ITERATIONS)) {
            next;
        }

        $ranking_cost += $current_cost;

#<<<
        forcomb {
            my @subset = @original_words[@_];

            my $regex   = join('.{0,10}',     @subset);
            my $b_regex = join('\b.{0,10}\b', @subset);

            #my $regex   = join('\W*+',     @subset);
            #my $b_regex = join('\b\W*+\b', @subset);

            push @regexes,
              scalar {
                      (RANK_ON_NON_BOUNDARY_MATCH ? (re   => qr/$regex/si)       : ()),
                      (RANK_ON_BOUNDARY_MATCH     ? (b_re => qr/\b$b_regex\b/si) : ()),
                      factor => $k,
                     };
        } scalar(@original_words), $k;
#>>>

        EXACT_MATCH && last;
    }

    foreach my $key (keys %matches) {

        my $value = $matches{$key};

        $value->{score} = 0;

        if ($value->{url} !~ m{^https?://}) {
            $value->{url} = 'https://' . $value->{url};
        }

        my $content     = $value->{content} // '';
        my $title       = unidecode($value->{title}       // '');
        my $description = unidecode($value->{description} // '');
        my $keywords    = unidecode($value->{keywords}    // '');
        my $url         = unidecode($value->{url}         // '');

        foreach my $regex (@regexes) {

            foreach my $re_type (qw(b_re re)) {

                my $re     = $regex->{$re_type} // next;
                my $factor = $regex->{factor} * ($re_type eq 'b_re' ? 1 : 0.5);

                if ($title =~ $re) {
                    $value->{score} += 2 * $factor;
                }

                if ($description =~ $re) {

                    ## $value->{score} += 1 * $factor;

                    if (SHOW_DESCRIPTION
                        and $re_type eq (RANK_ON_BOUNDARY_MATCH ? 'b_re' : 're')) {
                        add_match_text_to_value($description, $value, $-[0], $+[0]);
                    }
                }

                if (RANK_ON_CONTENT and $content =~ $re) {

                    $value->{score} += $factor;

                    if ($re_type eq (RANK_ON_BOUNDARY_MATCH ? 'b_re' : 're')) {
                        add_match_text_to_value($content, $value, $-[0], $+[0]);
                    }
                }

                if ($keywords =~ $re) {
                    $value->{score} += 2 * $factor;
                }

                if ($url =~ $re) {
                    $value->{score} += 4 * $factor;
                }
            }
        }

        ## delete $value->{content};
    }

    my %seen_url;
    my @sorted = sort { $b->{score} <=> $a->{score} } values %matches;

    my $results_count = scalar(@sorted);

    # Keep only the top best entries
    $#sorted = (MAX_SEARCH_RESULTS - 1) if (scalar(@sorted) > MAX_SEARCH_RESULTS);

    # Keep entries with score > 0
    @sorted = grep { $_->{score} > 0 } @sorted;

    # Prefer longer content for results with the same score
    @sorted = map { $_->[0] }
      sort { ($b->[1] <=> $a->[1]) || ($b->[2] <=> $a->[2]) }
      map { [$_, $_->{score}, length($_->{content})] } @sorted;

    # Fix some ArchWiki links
    foreach my $entry (@sorted) {
        $entry->{url} =~ s{^https://wiki\.archlinux\.org//}{https://wiki.archlinux.org/title/};
    }

    # Remove duplicated entries
    @sorted = grep { !$seen_url{(($_->{url} =~ s{^https?://(?:www\.)?}{}r) =~ s{#.*}{}sr) =~ s{[/?]+\z}{}r}++ } @sorted;

    return {
            results => \@sorted,
            counts  => \%counts,
            words   => \@known_words,
            count   => $results_count,
           };
}

sub repair_index {    # very slow operation
    while (my ($key, $value) = each %CONTENT_DB) {
        my $info = eval { decode_content_entry($value) } // next;
        readd_to_database_index(unidecode($info->{title}) . ' ' . $info->{content}, $info->{id});
    }
    return 1;
}

sub sanitize_index {

    my @for_delete_keys;

    my $index_len = 0;
    my $uniq_refs = 0;

    while (my ($key, $value) = each %WORDS_INDEX) {

        my $entry = decode_index_entry($value);

        ++$index_len;

        my $ref_count = 1 + ($entry =~ tr/ //);

        if ($ref_count > MAX_WORD_POPULARITY) {
            say "$ref_count: $key";
        }

        if ($ref_count == 1) {
            ++$uniq_refs;
        }

        if (length($key) < WORD_MIN_LEN or length($key) > WORD_MAX_LEN) {
            push @for_delete_keys, $key;
        }
    }

    say ":: The words index contains $index_len entries.";
    say ":: The words index contains $uniq_refs entries with only one reference.";

    foreach my $key (@for_delete_keys) {
        delete $WORDS_INDEX{$key};
    }

    return 1;
}

if (@ARGV) {

    require Getopt::Long;
    Getopt::Long::GetOptions(

        "sanitize-index" => sub {
            warn "Sanitzing index...\n";
            sanitize_index();
            exit;
        },

        "fix-index|recover-index|repair-index" => sub {
            warn "Recovering index...\n";
            repair_index();
            exit;
        },
    );

    foreach my $url (@ARGV) {
        warn "Crawling: $url\n";
        crawl($url);
        $index_db->sync;
        $content_db->sync;
    }

    #untie(%CONTENT_DB);
    #untie(%WORDS_INDEX);
    exit;
}

while (my $c = CGI::Fast->new) {

    my $query    = $c->param('q');
    my $id       = $c->param('text');
    my $surprise = $c->param('surprise');

    my $info  = defined($id)   ? decode_content_entry($CONTENT_DB{$id})       : undef;
    my $title = defined($info) ? encode_utf8(encode_entities($info->{title})) : undef;

    print header(
                 -charset                  => 'UTF-8',
                 'Referrer-Policy'         => 'no-referrer',
                 'X-Frame-Options'         => 'DENY',
                 'X-Xss-Protection'        => '1; mode=block',
                 'X-Content-Type-Options'  => 'nosniff',
                 'Content-Security-Policy' =>
                   q{default-src 'self'; frame-ancestors 'none'; form-action 'self'; base-uri 'self'; img-src 'self' data:;},
                ),
      start_html(
        -class => 'results_endpoint',
        -title => encode_utf8($query // $title // 'Surprise'),
        -meta  => {
            'keywords' => 'dark search, search engine, private, secure',

            #'viewport' => 'width=device-width, initial-scale=1.0',
            'viewport' => 'width=device-width, initial-scale=1, maximum-scale=2.0, user-scalable=1',
            'referrer' => 'no-referrer',
                 },
        -style => [
            {
             src => 'css/logicodev-dark.min.css',
            },
            {
             src => 'css/bootstrap.min.css',
            },
            {
             src => 'css/pre.css',
            },

            #~ {
            #~ src => 'css/popup.css',
            #~ },
        ],
        -head => [
            Link(
                 {
                  -rel  => 'shortcut icon',
                  -type => 'image/png',
                  -href => 'img/favicon.png',
                 }
                ),

            (-e "opensearch.xml")
            ? Link(
                   {
                    -rel   => 'search',
                    -type  => 'application/opensearchdescription+xml',
                    -title => 'Dark search',
                    -href  => 'opensearch.xml',
                   }
                  )
            : ()
        ],
      );

    if (defined($id)) {

        say h4(
               {-class => "result_header"},
               a(
                  {
                   -href   => encode_utf8($info->{url}),
                   -target => "_blank",
                   -rel    => "noopener noreferrer",
                  },
                  b($title),
                )
              );

        print pre(encode_entities($info->{content}));
        print end_html();
        next;
    }

    print <<"EOT";
<div class="searx-navbar"><span class="instance pull-left"><a href="/search">Home</a></span><span class="pull-right"><a href="$ENV{SCRIPT_NAME}?surprise=1">Surprise me</a></span></div>
    <div class="container">

<form method="post" action="$ENV{SCRIPT_NAME}" id="search_form" role="search">
  <div class="row">
    <div class="col-xs-12 col-md-8">
      <div class="input-group search-margin">
        <input type="search" autofocus="" name="q" class="form-control autofocus" id="q" placeholder="${\encode_entities($query // '')}" aria-label="Search for..." autocomplete="off" value="" accesskey="s">
        <span class="input-group-btn">
            <button type="submit" class="btn btn-default" aria-label="Search"><span>Search</span></button>
        </span>
      </div>
    </div>
    <div class="col-xs-6 col-md-2 search-margin"><label class="visually-hidden" for="time-range">Time range</label></div>
    <div class="col-xs-6 col-md-2 search-margin"><label class="visually-hidden" for="language">Language</label></div>
  </div>
</form><!-- / #search_form_full -->
    <div class="row">

        <div class="col-sm-4 col-sm-push-8" id="sidebar_results">

        </div><!-- /#sidebar_results -->

        <div class="col-sm-8 col-sm-pull-4" id="main_results">
            <h1 class="sr-only">Search results</h1>
EOT

    if ($surprise) {
        $query = surprise_me();
    }

    say q{<div class="result result-default">};

    my $t0 = [gettimeofday];

    my @results;
    my $search_results = ((($query // '') =~ /\S/) ? search($query) : ());

    my $elapsed = tv_interval($t0, [gettimeofday]);

    if ($search_results) {

        @results = @{$search_results->{results}};
        my @words = @{$search_results->{words}};

        if (@words) {
            ## say p("Results found: ", b($search_results->{count}));
            say p("Term frequencies: " . join(", ", map { b($_) . ': ' . $search_results->{counts}{$_} } @words));
            say p(small(sprintf("Search took %.5f seconds", $elapsed)));
        }
    }

    foreach my $result (@results) {

        my $url = $result->{url};

        if ($url !~ m{^https?://}) {
            $url = 'https://' . $url;
        }

        $url = sanitize_url($url);

        my $title = $result->{title} // $url;

        if ($title !~ /\S/) {
            $title = $url;
        }

        say h4(
            {-class => "result_header"},
            a(
               {
                   #-href   => encode_utf8($url),
                   -href   => "$ENV{SCRIPT_NAME}?text=" . $result->{id},
                   -target => "_blank",
                   -rel    => "noopener noreferrer",

                   #(defined($result->{description}) ? (-class => 'popup') : ()),
               },

               #(defined($result->{description}) ? small(span(encode_utf8(encode_entities($result->{description})))) : ()),
               #small(span($result->{content} =~ s/(\R)\1{2,}/$1/gr =~ s{\R}{<br/>}gr)),
               b(encode_utf8(encode_entities($title))),
             )
        );

        say q{<p class="result-content">};
        say $result->{match};
        say q{</p>};
        say q{<div class="clearfix"></div>};
        say q{<div class="pull-right">};

        # Extract the date of the article (if any)
        if (EXTRACT_DATE) {

            require Date::Extract;
            my $date_extract = Date::Extract->new();

            if (my $dt = $date_extract->extract($result->{content})) {
                say small(scalar $dt->ymd);
                say q{<b> | </b>};
            }
        }

        # Web archive
        say small(
            a(
               {
                -href   => encode_utf8('https://web.archive.org/web/' . $url),
                -class  => 'text-info',
                -target => '_blank',
                -rel    => 'noopener noreferrer',

               },
               "cached",
             ),
        );

        say q{<b> | </b>};

        # Text only (cached version)
        say small(
            a(
               {
                   #-href   => "$ENV{SCRIPT_NAME}?text=" . $result->{id},
                   -href   => encode_utf8($url),
                   -class  => 'text-info',
                   -target => '_blank',
                   -rel    => 'noopener noreferrer',
               },
               "text",
             )
        );

        say q{<b> | </b>};
        say small("rank: $result->{score}");

        say "</div>";    # end of 'pull-right' div

        say div({-class => "external-link"}, encode_utf8($url));
    }

    say "</div>";

    print <<'EOT';

            <div class="clearfix"></div>
            <div class="clearfix"></div>

        </div><!-- /#main_results -->
    </div>
   </div>
EOT

    print end_html;
}