package Directory::Simplify::Instruction::Generator;
# vi: et sts=4 sw=4 ts=4
use strict;
use warnings;
use overload '""' => 'as_string';
use File::Basename qw/ dirname /;
use File::Compare qw/ compare /;

# :squash-ignore-start:
require Directory::Simplify::Instruction::CopyTimestamp;
require Directory::Simplify::Instruction::Hardlink;
# :squash-ignore-end:

sub new {
    my $class = shift;
    return bless {
        filehash => undef,
        min_size => 1,
        @_,
    }, $class;
}

sub as_string {
    my $self = shift;
    join "\n", $self->instructions;
}

sub buckets {
    my $self = shift;

    my @candidate_lists = $self->{filehash}->entries;

    my @buckets;
    foreach my $candidates (@candidate_lists) {
        my @ca = @{$candidates}; # make a clone
        my @these_buckets;

        # at least two files needed to link together
        if (@ca > 1) {
            ELIMINATOR: while (@ca) {
                my $entry = shift @ca;

                next ELIMINATOR if $self->_entry_should_be_skipped($entry);

                foreach my $bucket_idx (0 .. $#these_buckets) {
                    if (&_entries_are_hard_linkable($these_buckets[$bucket_idx]->[0], $entry)) {
                        push @{$these_buckets[$bucket_idx]}, $entry;
                        next ELIMINATOR;
                    }
                }
                # didn't find a bucket (even though the hash matched!)
                # -> new bucket
                push @these_buckets, [$entry];
            }
        }
        push @buckets, @these_buckets;
    }

    @buckets
}

sub _entry_should_be_skipped {
    my ($self, $entry_a) = @_;
    # too small to be hard-linked
    if ($entry_a->{size} < $self->{min_size}) {
        return 1;
    }
    return 0;
}

sub _entries_are_hard_linkable {
    my ($entry_a, $entry_b) = @_;

    # obviously, if the sizes aren't the same, they're not the same file
    unless (&_entries_sizes_match($entry_a, $entry_b)) {
        return 0;
    }

    # they're the same file, don't try it
    if (&_entries_are_already_hard_linked($entry_a, $entry_b)) {
        return 0;
    }

    if (&_entries_contents_match($entry_a, $entry_b)) {
        return 1;
    }
    return 0;
}

sub oldest_mtime {
    my $self = shift;
    return sort {
        $a->{mtime} <=> $b->{mtime}
    } @_;
}

sub more_linked {
    my $self = shift;
    my %warned;
    return sort {
        if (! -w &dirname($a->{name})) {
            warn "Warning: $a->{name} not able to be unlinked!" unless $warned{$a->{name}}++;
            return 1; # favor a -> front
        } elsif (! -w &dirname($b->{name})) {
            warn "Warning: $b->{name} not able to be unlinked!" unless $warned{$b->{name}}++;
            return -1; # favor b -> front
        }
        $b->{nlink} <=> $a->{nlink}
    } @_;
}

sub _entries_are_already_hard_linked {
    my ($entry_a, $entry_b) = @_;

    if ($entry_a->{ino} == $entry_b->{ino} and
        $entry_a->{dev} == $entry_b->{dev}) {
        return 1;
    }

    return 0;
}

sub _entries_sizes_match {
    my ($entry_a, $entry_b) = @_;
    if ($entry_a->{size} != $entry_b->{size}) {
        return 0;
    }
    return 1;
}
sub _entries_contents_match {
    my ($entry_a, $entry_b) = @_;

    my $contents_same = (0 == &File::Compare::compare($entry_a->{name}, $entry_b->{name}));

    # warn about hash collision
    unless ($contents_same) {
        warn "Hash collision between files:\n* $entry_a->{name}\n* $entry_b->{name}\n  (don't panic)\n";
    }
    return $contents_same;
}

# generate hardlink instructions
sub instructions {
    require Scalar::Util;
    my $self = shift;

    # start generating instructions
    my @inst;
    foreach my $bucket ($self->buckets) {

        # of the bucket, find the oldest timestamp
        my ($oldest_entry) = $self->oldest_mtime(@{$bucket});

        # of the bucket, find the file most embedded in the file system
        my @to_link = $self->more_linked(@{$bucket});
        my $most_linked_entry = shift @to_link;
        foreach my $entry (@to_link) {
            # XXX there shouldn't be a need to update entries' link counts,
            # since this generates all the instructions at once
            push @inst, Directory::Simplify::Instruction::Hardlink->new(
                source => $most_linked_entry,
                target => $entry,
            );
            push @inst, Directory::Simplify::Instruction::CopyTimestamp->new(
                source => $oldest_entry,
                target => $entry,
            );
        }
        if (&Scalar::Util::refaddr($most_linked_entry) != &Scalar::Util::refaddr($oldest_entry)) {
            # most_linked_entry should get its timestamp updated
            push @inst, Directory::Simplify::Instruction::CopyTimestamp->new(
                source => $oldest_entry,
                target => $most_linked_entry,
            );
        }
    }
    @inst
}

1;