#!/usr/local/bin/perl -w
#
# Library of routines for managing id lists
#

package IdChecker;
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw( ReadIDs
              PrintIDs
              PrintIDsStdout
              Union
              Intersection
              Difference
              GetChainLetter
   );

#open file named in argument, read ids,
#return a hash which has ids as keys
sub ReadIDs($){
    use strict;
    my($infilename) = @_;
    my %my_ids;
    open(INFILE, "$infilename") || die "Fatal Error: ReadIDs: can't open $infilename for reading\n";
    while(my $line=<INFILE>){
#skip if blank line or comment line
     next if( $line =~ /^\s*$/ || $line =~ /^\#/);
        my @cols = split(/ /, $line);
        if ($cols[0] =~ /\w+/) {
            chomp $cols[0];
            $my_ids{$cols[0]} = 1;
        } else {
            print STDERR "Error: $infilename: Bogus id $cols[0]\n";
        }
    }
    close(INFILE);
    return %my_ids;
}

#open a file and print the keys of the hash
#to the specified file
sub PrintIDs($%) {
   use strict;
    my ($outfilename, $my_ids) = @_;
    my $key; 
   open(OUTFILE, ">$outfilename") || die "Fatal Error: PrintIDs: can't open $outfilename for writing\n";
   foreach $key (keys(%$my_ids)){
       print OUTFILE "$key\n";
    }
   close(OUTFILE);
}

#print the keys of the hash to STDOUT
sub PrintIDsStdout(%) {
   use strict;
    my ($my_ids) = @_;
    my $key; 
   foreach $key (keys(%$my_ids)){
       print "$key\n";
    }
}

#return a hash representing the set union of
#the arguments
#could also do this with this one-liner
#%u = map { $_ => 1 } keys %a, keys %b;
sub Union(%%){
    use strict;
    my ($idhash1, $idhash2) = @_;
    my $key;
    my %my_ids;
    foreach $key (keys(%$idhash1)){
        $my_ids{$key} = 1 ;
    }
    foreach $key (keys(%$idhash2)){
        $my_ids{$key} = 1 ;
    }
    return %my_ids;
}
#return a hash representing the set intersection
#of the arguments
#could also do this with this one-liner
#%i = map { $_ => 1 } grep { $b{$_} } keys %a;  see p. 730
sub Intersection(%%){
    use strict;
    my ($idhash1, $idhash2) = @_;
    my %my_ids =  map { $_ => 1 } grep { $$idhash2{$_} } keys %$idhash1;
     return %my_ids;
}
#return a hash representing the set difference of the arguments
#(first - second)
#http://www.google.com/search?q=cache:G8-KU-Scf4M:www.stonehenge.com/merlyn/UnixReview/col11.html+Perl+set+difference&hl=en
sub Difference(%%){
    use strict;
    my ($idhash1, $idhash2) = @_;
    my $key;
    foreach $key (keys(%$idhash2)){
        delete $$idhash1{$key};
    }
    return %$idhash1;
}    

#given a chain ID, return the chain letter if it exists
sub getChainLetter($){
    use strict;
    my ($chainName) = @_;
    my $chainLetter = "";
    if (length($chainName)==5){
        $chainLetter = substr($chainName, 4, 1);
    }

    return $chainLetter;
}


# packages must end with a true value---a restriction that seems
# to be poorly documented.
1;