#!/usr/bin/perl
use strict;
use warnings;
use Algorithm::Diff;
#use Data::Dumper; $Data::Dumper::Useqq = 1; $| = 1;

{
    my @sets = (
        [ qw( a c f g e h i     ) ], # X
        [ qw( a b c d e f g h i ) ], # Y
        [ qw( a c d e f g h i   ) ], # Z
    );
    # my @sets = (
    #     [ qw( a b c f g ) ], # X
    #     [ qw( a b d f g ) ], # Y
    #     [ qw( a b e f g ) ], # Z
    # );

    my @all_merged = merge_multiple_lists( @sets );
    print dump_rotated_indexes_of_lists( @all_merged );

    # foreach (@all_merged) {
    #     my ( $item, @offsets ) = @{ $_ };
    #     @offsets = map { defined $_ ? $_  : ' ' } @offsets;
    #     print "$item @offsets\n";
    # }

    exit;
}

# Rotate @all_merged 90 degrees to match the expected output.
sub dump_rotated_indexes_of_lists {
    my @lists = @_;
    my @idx;
    foreach (@lists) {
        my ( $item, @offsets ) = @{ $_ };
        foreach my $i ( 0 .. $#offsets ) {
            push @{ $idx[$i] }, $offsets[$i];
        }
    }
    foreach (@idx) {
        my $dump = join ', ',
#                   map { sprintf '%5s', $_ }
                   map { defined $_ ? $_ : 'undef' }
                   @{ $_ };
        print "  [ $dump ],\n";
    }
}

sub merge_multiple_lists {
    my @list_arefs = @_;

    foreach my $list_aref ( @list_arefs) {
        my $count = 0;
        $list_aref = [ map { [ $_, $count++ ] } @{ $list_aref } ];
    }

    my $accumulator_aref = shift @list_arefs;
    my $offset_width = 1;
    foreach my $next_to_merge_aref ( @list_arefs ) {
        $accumulator_aref = merge_two_lists(
            $accumulator_aref, $next_to_merge_aref, $offset_width
        );
        ++$offset_width;
    }
    return @{ $accumulator_aref };
}

# Each list element will be an aref.
# The item to be compared is in position 0.
sub key_on_first_element {
    my ($self) = @_;
    return $self->[0];
}
sub merge_two_lists {
    my ( $list1_aref, $list2_aref, $offset_width ) = @_;
    $offset_width = 1 if not defined $offset_width;

    my $diff = Algorithm::Diff->new(
        $list1_aref,
        $list2_aref,
        { keyGen => \&key_on_first_element },
    );

    my @merged;
    while( $diff->Next() ) {
        my @indices1 = $diff->Range(1);
        my @indices2 = $diff->Range(2);
        my $which_list = $diff->Diff();

        # 0 means lists are identical in this chunk.
        if ( $which_list == 0 ) {
            die "Can't happen" if @indices1 != @indices2;
            foreach my $i ( 0 .. $#indices1 ) {
                my ( $item1, @offsets ) = @{ $list1_aref->[ $indices1[$i] ] };
                my ( $item2, $offset  ) = @{ $list2_aref->[ $indices2[$i] ] };
                die unless $item1 eq $item2;
                push @offsets, $offset;
                push @merged, [ $item1, @offsets ];
            }
        }
        # 1 means that only list 1 has entries in this chunk
        elsif ( $which_list == 1 ) {
            foreach ( @{ $list1_aref }[ @indices1 ] ) {
                my ( $item1, @offsets ) = @{ $_ };
                push @offsets, undef;
                push @merged, [ $item1, @offsets ];
            }
        }
        # 2 means that only list 2 has entries in this chunk
        elsif ( $which_list == 2 ) {
            foreach ( @{ $list2_aref }[ @indices2 ] ) {
                my ( $item2, $offset ) = @{ $_ };
                my @offsets = map { undef() } 1 .. $offset_width;
                push @offsets, $offset;
                push @merged, [ $item2, @offsets ];
            }
        }
        # 3 means both lists have entries in this chunk.
        # XXX
        # This is the "each set having a unique element" situation.
        # Extra code may be needed to put these into a desired order.
        elsif ( $which_list == 3 ) {
            # XXX Dup code from which_list==(1|2)
            foreach ( @{ $list1_aref }[ @indices1 ] ) {
                my ( $item1, @offsets ) = @{ $_ };
                push @offsets, undef;
                push @merged, [ $item1, @offsets ];
            }
            foreach ( @{ $list2_aref }[ @indices2 ] ) {
                my ( $item2, $offset ) = @{ $_ };
                my @offsets = map { undef() } 1 .. $offset_width;
                push @offsets, $offset;
                push @merged, [ $item2, @offsets ];
            }
        }
        else {
            die "Can't happen";
        }

    }

    return \@merged;
}