#!/usr/bin/env perl

use strict;
use warnings;
use v5.22;

sub get_filehandle {
    if (@ARGV !=1) {
        die "Usage: $0 [input-filename]";
    }
    my $input_filename = $ARGV[0];
    open my $filehandle, '<', $input_filename or
        die "Could not open input file $input_filename: $!";
    return $filehandle;
}

sub get_numbers {
    my $fh = shift;
    chomp( my $numbers = ( <$fh> ) );
    return (split( ",", $numbers));
}

sub initialize_boards {
    my $fh = shift;
    chomp( my @input = ( <$fh> ) );
    my (@boards, @new_board);
    foreach (@input) {
        if (/\A\s*\Z/) {
            push(@boards, [@new_board]) if (@new_board);
            @new_board = ();
        } else {
            push(@new_board, [split]);
        }
    }
    push(@boards, \@new_board);
    return (@boards);
}

sub initialize_state {
    my %state;
    my $boards = shift;
    foreach my $board (@$boards) {
        foreach my $row (@$board) {
            foreach my $column (@$row) {
                $state{$board}{$row}{$column} = 0;
            }
        }
    }
    return %state;
}

sub play_turn {
    my ($number, $boards, $state) = @_;
    foreach my $board (@$boards) {       # $board is ref to board array
        foreach my $row (@$board) {      # $row is ref to board row array
            foreach my $column (@$row) { # $column is element of row array
                if ($column == $number) {
                    $state->{$board}{$row}{$column} = 1;
                }
            }
        }
    }
}

# for debugging purposes only
sub print_board_state {
    my ($boards, $state) = @_;
    foreach my $board (@$boards) {       # $board is ref to board array
        foreach my $row (@$board) {      # $row is ref to board row array
            foreach my $column (@$row) { # $column is element of row array
                print "$board\t$row\t";
                if ($state->{$board}{$row}{$column} == 1) {
                    printf "-> %2d <-\n", $column;
                } else {
                    printf "   %2d\n", $column;
                }
            }
        }
    }
}

sub check_for_winner {
    my ($boards, $state) = @_;
    my @winning_board_ref;
# check for row wins
    foreach my $board (@$boards) {       # $board is ref to board array
        foreach my $row (@$board) {      # $row is ref to board row array
            my $total = 0;
            foreach my $column (@$row) { # $column is the actual value of
                                         # the number in @$row
                $total += $state->{$board}{$row}{$column};
            }
            if ($total == 5) {
                push (@winning_board_ref, $board);
                last;
            }
        }
# for each board, iterate through each column (0 .. 4)
        foreach (0 .. 4) {
            my $total = 0;
            foreach my $row (@$board) {
# here, $_ represents the index within the array @$row.  Because the hash key
# stores the actual value, we need to deference $row (which is an array
# reference) and then look up the value stored in the index $_
                $total += $state->{$board}{$row}{$row->[$_]};
            }
            if ($total == 5) {
                push (@winning_board_ref, $board);
                last;
            }
        }
    }
    return @winning_board_ref;
}

sub calculate_score {
    my ($number, $board, $state) = @_;
    my $score = 0;
    foreach my $row (@$board) {     # $row is ref to board row array
        foreach my $column (@$row) { # $column is element of row array
            if ($state->{$board}{$row}{$column} == 0) {
                $score += $column;
            }
        }
    }
    return $score *= $number;
}

# Advent of Code 2021 Day 04 Part 1
# initialize game variables
my $filehandle  = get_filehandle();
my @numbers     = get_numbers($filehandle);
my $number;
my @boards      = initialize_boards($filehandle);
my %state       = initialize_state(\@boards);
my $turn = 0;
my @winner_found;
my $final_board;

while ( scalar ( @boards ) ) {
    @winner_found = ();
    $turn++;
    $number = shift( @numbers );
    printf "turn: %2d, playing number %2d\n", $turn, $number;
    play_turn($number, \@boards, \%state);
    @winner_found = check_for_winner(\@boards, \%state);
    if ( @winner_found ) {
        say "found a winning board";
        say "we had ", scalar(@boards), " boards";
        foreach my $winning_board (@winner_found) {
            @boards = grep { $_ ne $winning_board } @boards;
        }
        say "we now have ", scalar(@boards), " boards";
    }
    unless (@numbers) { # if we run out of numbers
        say "Out of numbers.  No winner found.";
        exit;
    }
    $final_board = $boards[0] if ( scalar( @boards ) == 1 );
}
my $score = calculate_score($number, $final_board, \%state);
say "winning score is $score";