#!/usr/bin/perl

# file to generate a randomisation of a set of sequential numbers,  leans heavily on:
## $Header: /cys/people/brenner/http/docs/web/perl5/RCS/simple-form.cgi,v 1.5 1996/03/29 22:58:40 brenner Exp $
## Copyright (C) 1994 Steven E. Brenner
## This is a small demonstration script to demonstrate the use of the cgi-lib.pl library
# this file was written by Chris Evans (C.Evans@sghms.ac.uk) and I claim copyright on it but
# anyone is welcome to use it and adapt it provided:
# a) you let me know
# b) you credit me like this
# c) you retain these conditions
# d) you don't make any money out of it (without sharing with me!)
#
# the correct citation for this file is:
# Evans (1997) random1.prl http://www.psyctc.org/scripts/random1.prl
# 9.ii.97

require 5.001;
use strict;
require "cgi-lib.pl";

MAIN:
{
  my (%input,   # The CGI data then the following are munged
      $upper,   # upper end of sequence
      $lower,   # lower end of sequence
      $diff,    # difference between those
      $seed,    # seed
      $current, # latest number generated
      $test,    # a flag variable
      %used,    # array flagging whether $current has been done already
      $dump,    # flag variable
      $i,       # counter
      $field);  # Each of the fields (used for testing) 

  # Read in all the variables set by the form
  &ReadParse(\%input);

  # Check that everything has been entered
  foreach $field (qw(lowest highest seed)) {
    &CgiDie("Error: Missing field '$field'\n") unless defined $input{$field};
  }

  # Print the header
  print &PrintHeader;
  print &HtmlTop ("Random numbers as permuted with seed $input{'seed'}");

  # Do some processing, and print some output

   $upper = $input{'highest'};
   $lower = $input{'lowest'};
   $seed = $input{'seed'};

   $test = 0;
   $diff = $upper - $lower;
   if ($diff < 1) {
      print "Upper number MUST be at least one bigger than lower\n";
      print "Use &quot;back&quot; in your browser to go back and try again\n";
      exit;
   }
      

   # now set up associative array to 
   # keep track of numbers you've used
   for ($i = $lower; $i <= $upper; $i++) {
      $used{$i} = 1;
   }

   srand($seed);
   $dump = $lower + int(rand($diff + 1));

   while ($test < $diff) {
      # perl random number generator rand(x)
      # returns fractional number between
      # 0 and x
      $current = $lower + int(rand($diff + 1));
      if ($used{$current} == 1) {
         # hasn't already been used
         $used{$current} = 0;
         $test++;
         print "$current\n";
      }
   }

   # now find the one unused number      
   for ($i = $lower; $i <= $upper; $i++) {
      if ($used{$i} == 1) {
         print "$i\n";
         last; # exit the loop
      }
   }



  # Close the document cleanly.
  print &HtmlBot;


}