#!/usr/local/bin/perl -w

use strict;

my %table = (
    "lines_of_text" => "foo.html",
    "this" => "bar.html",
    "its_full" => "foobar.html",
    "this_thing" => "baz.html",
);


# create a lookup table, based on the first words of each key

my %lookup;

while (my($key, $val) = each %table) {

    # clean lookup keys, just in case
    $key =~ tr/A-Za-z_//cd;
    $key =~ tr/_//s;

    my($first) = split /_/, $key;

    push @{$lookup{$first}}, [$key, $val];

}


# sort each lookup array by length of matching text

while (my($first, $aref) = each %lookup) {

    $lookup{$first} = [ sort {length $b->[0] <=> length $a->[0]}
                        @{$lookup{$first}} ];

}


my $string;
{
    local $/;
    $string = <DATA>;
}

$string =~ /^\s*/g;



# Here's where the fun starts!

my $begin = pos($string);


# for each word, see if it's the start of any of the matching texts

FIRST:
while ($string =~ /(\S+)(\s*)/g) {

    my $end = pos($string) - length $2;

    my $first = lc $1;
    $first =~ tr/A-Za-z//cd;

    my $matches = $lookup{$first};
    next unless $matches;


    # for each possible matching text, see if a match occurs

   MATCHES:
    for my $m (0 .. $#$matches) {

        my $match = $matches->[$m];

        my $words = $first;

        my $space = 0;


        # get the appropriate number of next words

        for (1 .. $match->[0] =~ tr/_//) {
            last unless $string =~ /(\S+)(\s*)/g;
            $words .= "_$1";
            $space = length $2;
        }

        if ($words eq $match->[0]) {

            # match found: put a link around the text

            my $text = substr($string, $begin, pos($string) - $begin -
+ $space);
            my $link = qq{<A HREF="$match->[1]">$text</A>};

            substr($string, $begin, pos($string) - $begin - $space) = 
+$link;

            pos($string) = $begin + length $link;
  

            # remove this match, so only the first occurence will be l
+inked

            splice(@$matches, $m, 1);

            next FIRST;

        }

        pos($string) = $end;

    }

} continue {

    $begin = pos($string);

}

print $string;

__DATA__
This is just lines of text here, and also there.  Consider
this human readable text; it's full of letters and
punctuation.
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