#!/usr/bin/env perl -w
use strict;

if (!@ARGV) { #no command line arguments, do part A
    my ($dir, @files, $num, @lines);
    
    print "Please enter a directory name: \n";
    chomp ($dir = <STDIN>);

    if (!(-e $dir && -d $dir)){ 
        #if directory does not exist, or is not a directory
	print "Sorry, that is not a valid directory, exiting program\n";
	exit;
    }

    opendir DIR, $dir or die "Cannot open directory $dir: $!\n";

    @files = readdir DIR;
    print "There are " . @files . " in directory $dir, and they are:\n";
    for (my $i = 0; $i < @files; $i++){
	print "File #" . ($i + 1) . ": $files[$i]\n";
    }

    print "Which file do you wish to open? (Enter a number from 1 to " . @files . ")\n";
    chomp ($num = <STDIN>);
    if ($num < 1 or $num > @files) {
	print "Sorry, that is not a valid number.  Exiting.\n";
	exit;
    }
    
    if (-d $files[$num-1]){
	print "Sorry, $files[$num-1] is a directory, not a file\n";
	exit;
    }

    open FILE, "$dir/$files[$num-1]" or die "Could not open file $files[$num-1]: $!\n";
    @lines = <FILE>;
    close FILE;

    if (@lines % 2 == 0) { #if there are an even number of lines...
	print "The middle lines are:\n";
	print $lines[(@lines / 2) - 1];
	print $lines[@lines / 2];
    } else { #there are an odd number of lines
	print "The middle line is: \n";
	print $lines[@lines / 2];
    }

    open AFILE, ">>$dir/$files[$num-1]" or 
	die "Cannot open $files[$num-1] for appending: $!\n";
    
    print AFILE "\U$lines[0]$lines[-1]\E";
    close AFILE;

    print "$files[$num-1] has been updated\n";
}

else {  #Part B
    my (@words, %words);
    die "Incorrect number of command line arguments\n" if @ARGV != 2;
    if ($ARGV[1] ne "sort" && $ARGV[1] ne "count" && $ARGV[1] ne "both"){
	die "Invalid option for second argument\n";
    }

    open FILE, "$ARGV[0]" or die "Cannot open file $ARGV[0]: $!\n";
    foreach (<FILE>){ #iterate through the entire file
	chomp;
	@words = split / /; #create an array of words from this line
	foreach (@words){
	    #if this word is already in the hash, increment its value
	    #otherwise, we're incrementing 'undef', which results in 
	    #the value 1, marking the first time the word has been
	    #seen in the hash
	    $words{$_}++;
	}
    }
    
    if ($ARGV[1] eq "count" or $ARGV[1] eq "both"){
	# Now we print the counting
	foreach (keys %words){
	    print "Number of times '$_' appeared in $ARGV[0]: $words{$_}\n";
	}
    }
    print "\n";
    if ($ARGV[1] eq "sort" or $ARGV[1] eq "both"){
	print "All words in $ARGV[0] in sorted order:\n";
	$, = "\n";
	print (sort keys %words, "\n");
    }
}