#!/local/bin/perl

@day_of_week = ("Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun");

print "Enter \"a\" if you would like to see a specific week\n";
print "Enter \"b\" if you would like to add appointments\n";
$choice = <STDIN>;
chomp $choice;

while ($choice ne "c") {
    if ($choice eq "a") {
	print "Enter a date in the following format: dd/mm/yy ";
	$date = <STDIN>;
	chomp $date;
	($day, $month, $year) = split (/\//, $date);
	
	($this_year, $this_month, $this_day)=
	    find_monday ($year, $month, $day);

	for ($i = 0 ; $i < 7; $i++) {
	    print "$day_of_week[$i] $this_day/$this_month/$this_year";
	    foreach $elem (@appts) {
		if ($elem =~ /^$this_day\/$this_month\/$this_year (.*)/) {
		    print " $1";
		    last;
		}
	    }
	    print "\n";
	    $this_day++;
	    ($this_day, $this_month, $this_year) 
		= end_of_month ($this_day, $this_month, $this_year);
	}

    } elsif ($choice eq "b") {
	print "Enter a date in the following format: dd/mm/yy ";
	$date = <STDIN>;
	chomp $date;

	$is_this_new = check_for_existing_appt ($date);
	if ($is_this_new ne "no") {
	    print "Enter new appointment:\n";
	    $new_appt = <STDIN>;
	    chomp $new_appt;
	    $elem = "$date $new_appt";
	    push (@appts, $elem);
	}
    }
    print "Enter \"a\" if you would like to see a specific week\n";
    print "Enter \"b\" if you would like to add appointments\n";
    print "Enter \"c\" to exit this program\n";
    $choice = <STDIN>;
    chomp $choice;
}

##### end of main program #################################

#### subroutines ##########################################

sub end_of_month {

    ### this subroutine deals with the end of the month/year

    my $this_month = $this_month;
    my $this_day = $this_day;
    my $this_year = $this_year;

    if (($this_month eq "12") and ($this_day eq "32")) {
	$this_day = "01";
	$this_month = "01";
	$this_year = "02";
    } elsif (($this_month eq "01") and ($this_day eq "32")) {
	$this_day = "01";
	$this_month = "02";
    } elsif (($this_month eq "02") and ($this_day eq "29")) {
	$this_day = "01";
	$this_month = "03";
    } elsif (($this_month eq "03") and ($this_day eq "32")) {
	$this_day = "01";
	$this_month = "04";
    } elsif (($this_month eq "04") and ($this_day eq "31")) {
	$this_day = "01";
	$this_month = "05";
    }
    return ($this_day, $this_month, $this_year);
}

#####################################################################

sub find_monday {

    #### To determine in which week a date belongs, the date is
    #### compared to the array @mondays. All dates are reversed.
    #### That facilitates comparing them based on their
    #### alphabetical ordering.

    @mondays=("01/12/03", "01/12/10", "01/12/17", "01/12/24", "01/12/31",
	      "02/01/07", "02/01/14", "02/01/21", "02/01/28", 
	      "02/02/04", "02/02/11", "02/02/18", "02/02/25", 
	      "02/03/04", "02/03/11", "02/03/18", "02/03/25", 
	      "02/04/01", "02/04/08", "02/04/15", "02/04/29");
    
    my $day = $day;
    my $month = $month;
    my $year = $year;

    $reverse_date = "$year/$month/$day";
    $this_monday = "";
    foreach $elem (@mondays) {
	if ($reverse_date ge $elem) {
	    $this_monday = $elem;
	}		
	if (($reverse_date lt $elem) and $this_monday) {
	    last;
	}
    }
    ($this_year, $this_month, $this_day) = split (/\//, $this_monday);
    return ($this_year, $this_month, $this_day);
}

##############################################################

sub check_for_existing_appt {
    my $date = $date;
    $is_this_new = "";
    foreach $elem (@appts) {
	if ($elem =~ /^$date/) {
	    $is_this_new = "no";
	    print "This date already has an appointment\n";
	    print "Enter \"d\" to delete the old appointment\n";  
	    print "Enter \"r\" to replace the old appointment\n";
	    print "Enter \"a\" to  add a second appointment\n";
	    $which = <STDIN>;
	    chomp $which;
	    if ($which eq "d") {
		$elem = "";
	    } elsif ($which eq "r") {
		print "Enter new appointment:\n";
		$new_appt = <STDIN>;
		chomp $new_appt;
		$elem = "$date $new_appt";
	    } elsif ($which eq "a") {
		print "Enter new appointment:\n";
		$new_appt = <STDIN>;
		chomp $new_appt;
		$elem = "$elem $new_appt";
	    }
	}
    }
    return $is_this_new;
}