#!/usr/bin/perl

use strict;
use warnings;

# This should print: "AABBC"
print "\n", DoubleChars("ABC", "AB");

# This should print: "LALA LLAALLAAN N"
print "\n", SingleChars("LALA LLLAAALLLLAAAAN NN", "LANG"), "\n\n";

# Okay. Now, make it more complicated...

foreach (2..7)
{
  print "\n x $_ : |",
    DoubleCharsX("ABCD", "ABXY", $_), "|";
}
print "\n\n";

foreach (2..7)
{
  print "\n x $_ : |",
    SingleCharsX("LLLLLLLL-AAAAAAAA", "ABX", $_), "|";
}

exit;

############################################
##                FUNCTIONS               ##
############################################

# This function doubles every instance of a list of characters in
# a string and returns a new string. For example, it can be used
# to double every instance of space or new line characters.
#
#    DoubleChars("Helo World!", "!lo ")  =>  "Helloo  Woorlld!!"
#    DoubleChars("Helo World!", "HHH")   =>  "HHelo World!"
#
# Usage: STRING = DoubleChars(STRING, CHARS)
#
sub DoubleChars
{
  defined $_[0] && length($_[0]) or return '';
  defined $_[1] && length($_[1]) or return $_[0];
  my $S = $_[0];
  $S =~ s/([\Q$_[1]\E]{1})/$1$1/g;
  return $S;
}

############################################
#
# This function removes certain characters that appear twice next
# to each and leaves only one instance. This can be used to undo
# the effects of the DoubleChars() function.
#
#    SingleChars(" HEELLLLLLO OO!", "OL")  =>  " HEELLLO O!"
#    SingleChars("AABBCAABBC", "AB")       =>  "ABC"
#
# Usage: STRING = DoubleChars(STRING, CHARS)
#
sub SingleChars
{
  defined $_[0] && length($_[0]) or return '';
  defined $_[1] && length($_[1]) or return $_[0];
  my $S = $_[0];
  $S =~ s/([\Q$_[1]\E]{1})\1/$1/g;
  return $S;
}

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

# This function doubles or triples every instance of
# a list of characters in a string and returns a new string.
# For example, it can be used to repeat every instance of
# the exclamation point. The second argument tells what
# to repeat, and the third argument tells how many times
# to repeat those characters.
#
#    DoubleCharsX("Hello World!", "!", 3)  =>  "Hello World!!!"
#
# Usage: STRING = DoubleCharsX(STRING, CHARS, [REP])
#
sub DoubleCharsX
{
  defined $_[0] && length($_[0]) or return '';
  defined $_[1] && length($_[1]) or return $_[0];
  my $REP = defined $_[2] ? int($_[2]) : 2;
  $REP >= 2 or $REP = 2;
  my $S = $_[0];
  $S =~ s/([\Q$_[1]\E]{1})/$1 x $REP/ge;
  return $S;
}

# This function doubles or triples every instance of
# a list of characters in a string and returns a new string.
# For example, it can be used to repeat every instance of
# the exclamation point. The second argument tells what
# to repeat, and the third argument tells how many times
# to repeat those characters.
#
#   SingleCharsX("Pressss a keeeeyyy!", "ey", 3) => "Pressss a keey!"
#
# Usage: STRING = SingleCharsX(STRING, CHARS, [REP])
#
sub SingleCharsX
{
  defined $_[0] && length($_[0]) or return '';
  defined $_[1] && length($_[1]) or return $_[0];
  my $REP = defined $_[2] ? int($_[2]) : 2;
  $REP >= 2 or $REP = 2;
  my $S = $_[0];
  foreach my $CHAR (split(//, $_[1]))
  {
    $S =~ s/\Q$CHAR\E{$REP}/\Q$CHAR\E/g;
  }
  return $S;
}