#!/bin/bash

fn="shuffle"
seed=0
numShuffles=0

# int
_shuffle()
{
   gawk -v seed="$seed" \
	-v numShuffles="$numShuffles" \
	-v inFile="$inFile" \
   '
   BEGIN {
      # optional -- seed the random number generator
      if ( seed != "" ) {
	 srand(seed)
      }

      # build the deck
      sizeofFile=0
      while ( getline list[sizeofFile] < inFile > 0 ) {
	 sizeofFile++
      }

      # shuffle the deck
      if ( numShuffles == "" || numShuffles <= 0 ) {
	 numShuffles=2*sizeofFile
      }
      for (i=0; i<numShuffles; i++) {
	 p1 = int( rand()*sizeofFile )
	 p2 = int( rand()*sizeofFile )
	 temp = list[p1]
	 list[p1] = list[p2]
	 list[p2] = temp
      }

      # print the deck
      for (i=0; i<sizeofFile; i++) {
	 print list[i]
      }
   }'

   return $?
}

# int
_main()
{
   while [ $# -gt 0 ] ; do
      case "$1" in
	 -s) seed="$2"
	     echo >&2 "$fn: seed is $seed"
	     shift ;;
	 -n) numShuffles="$2"
	     echo >&2 "$fn: shuffle the deck $numShuffles times"
	     shift ;;
	 -h|-?)
	     echo >&2 "usage: $fn [-s seed] [-n num-shuffles] file"
	     echo >&2 " $fn takes a text file and 'shuffles' the lines inside it randomly"
	     return 0 ;;
         *)  break ;;
      esac
      shift
   done

   inFile="$1"
   if [ ! -f "$inFile" ] ; then
      echo >&2 "$fn: no input file"
      return 1
   fi

   _shuffle "$inFile"

   return $?
}

_main $*
exit $?