#! perl
use strict;
use warnings;
use constant {
    FILENAMEROOT     => 'split.',
    OPEN_MODE_OUTPUT => '>',
    OPEN_MODE_INPUT  => '<',
    SELECTOR_OFFSET  => 3,
    SELECTOR_LENGTH  => 1,
    ZERO             => 0,
    ONE              => 1,
    TEN              => 10,
};

############################
# Main program starts here #
############################

################################
# An array to hold filehandles #
################################
my @fileHandles;

######################################
# iterate from 0 to 9                #
# compose a filename incorporating   #
# the number of the split file       #
# open the file for output           #
# check that it opend successfully   #
# push the filehandle onto the array #
# of filehandles index by the number #
######################################
for(
    my $index = ZERO;
    $index < TEN;
    $index = $index + ONE
) {
    ## A varible to hile the composed filename
    my $fileName = FILENAMEROOT . $index;

    # another to hold the file handle
    my $fileHandle;

    # open the file
    my $rc = open $fileHandle, OPEN_MODE_OUTPUT, $fileName;

    # check it opened successfully, or die
    if( $rc == 0 ) {
        die "Couldn't open " . $fileName
            . " for output; rc = "
            . $rc . "; Errortext = " . $!;
    }
    # else add it to the array of filehandles
    else {
        push @fileHandles, $fileHandle;
    }
}

die "You must supply an input filename" unless scalar @ARGV == 1;

# get the name of the input file
my( $inputFileName ) = @ARGV;

die "The filename you supply must exist" unless -e $inputFileName;
die "The file must contain something" if -z $inputFilename;

# open the input file
$rc = open my $inputFileHandle, INPUT_MODE, $inputFileName;

# Did it open? Die if not.
if( not $rc == 0 ) {
    die "couldn't open $inputFileName: $!";
}


# iterate over the input file one line at a time
while(
    defined(
        my $inputLine = readline( $inputFileHandle )
    )
) {
    # extract the character by which we select
    # the output file to put this line in
    my $selectorCharacter = substr(
        $inputLine, SELECTOR_OFFSET, SELECTOR_LENGTH
    );

    # check that it is a digit, otherwise die
    if( $selectorCharacter lt '0' or $selectorCharacter gt '9' ) {
        die "Selector character is not a digit: " . SelectorCharacter;
    }
    # selector character is okay
    else {
        # so get the appropriate filehandle from the array
        my $fileHandle = @fileHandles[
            ord( $selector ) - ord( S$selectorCharacter )
        ];

        # check that we actually got a filehandle, or die
        if( not defined $fileHandle ) {
            die "Couldn't obtain fileHandle for Selector character "
                . $selectorCharacter;
        }
        # okay, we've got a filehandle
        else {

            # so output the file handle to the appropriate file
            print $fileHandle $inputLine;
        }
    }

}

# close the input file
close $inputFileHandle;

# iterate over the output filehandles array
for(
    my $fileHandleIndex = 0;
    $fileHandleIndex < 10;
    $FileHandleIndex = $fileHandleIndex + ONE
) {

    # get the output filehandle
    my $fileHandle = $fileHandles[ $fileHandleIndex ];

    # make sure that it hasn't gone walkies in teh last 3 milliseconds
    if( not defined $fileHandle ) {

        # and die if it has (leaving all the other filehandles unclosed; but what can you do?)
        die "Couldn't obtain fileHandle for index " . $fileHandleIndex;
    }
    # okay, we;ve got a filehandle
    else {
        # so now we can close it. (Shoudl we check that it actually closed successfully?)
        close $fileHandle;
    }

}

##############################################################################
##############################################################################
##                                                                          ##
##  EEEEE  N   N  DDDD     PPPP   RRRR    OOO    GGG   RRRR     A    M   M ##
##  E      NN  N  D   D    P   P  R   R  O   O  G   G  R   R   A A   MM MM ##
##  E      N N N  D   D    P   P  R   R  O   O  G      R   R  A   A  M M M ##
##  EEEE   N  NN  D   D    PPPP   RRRR   O   O  G  GG  RRRR   AAAAA  M   M ##
##  E      N   N  D   D    P      R   R  O   O  G   G  R  R   A   A  M   M ##
##  E      N   N  D   D    P      R   R  O   O  G   G  R   R  A   A  M   M ##
##  EEEEE  N   N  DDDD     P      R   R   OOO    GGG   R   R  A   A  M   M ##
##                                                                          ##
##############################################################################
##############################################################################
exit;