package Tree::Transform::XSLTish::Optimizer;
use strict;
use warnings;
use Tree::XPathEngine;
use Scalar::Util qw(blessed looks_like_number reftype);

my $NCName = qr{(?: [A-Za-z_] [\w\\.\\-]* )}x;
my $QName = qr{(?: $NCName : )? $NCName}x;

sub optimize_single_step {
    my ($path) = @_;

    my $s=$path->as_string;

warn "single: $s\n";

    if ($s =~ m{\A \( child:: ($QName) \) \z}x) {
        return "self::$1",0,0,'any';
    }

    if ($s =~ m{\A \( /descendant:: ($QName) (?: /self::node\(\) )? \) \z}x) {
        return "self::$1",0,0,'any';
    }

    return;
}

sub optimize_simple_path {
    my ($path) = @_;

    my $s=$path->as_string;
    $s =~ s{/self::node\(\)/}{/}g;

warn "simple: $s\n";

    return unless $s =~ m{\A \(
      (?: (?:child|/descendant) :: $QName )
      (?: / (?:child|descendant) :: $QName )+
    \) \z}x;

    $s =~ s{/self::node\(\)/}{/}g;
    my @steps= reverse grep {$_} split '/',substr($s,1,-1);

    my @new=();

    while (my $step = shift @steps) {
        if ($step =~ m{^child::($QName)$}) {
            if (@new) {
                push @new,"parent::$1";
            }
            else {
                push @new,"self::$1";
            }
        }
        elsif ($step =~ m{^descendant::($QName)$}) {
            if (@steps) {
                push @new,"ancestor::$1";
            }
            else {
                push @new,"parent::$1";
            }
        }
    }

    return unless @new;

    return join('/',@new),0,0,'any';
}

my @rules = (
    \&optimize_single_step,
    \&optimize_simple_path,
);

my @flds=qw(opt_pattern min_depth max_depth expected_result);
sub optimize {
    my ($class,$rule) = @_;

    return unless $rule->{match};

    my $path = Tree::XPathEngine->new(NAME=>$QName)->_parse($rule->{match});

    for my $opt (@rules) {
        if (my @ret=$opt->($path)) {
            @{$rule}{@flds}=@ret;
            return;
        }
    }

    return;
}

1;