package Tree::Simple;

use strict;
use warnings;

our $VERSION = '1.22';

use Scalar::Util qw(blessed);

## -----------------------------------------------
## Tree::Simple
## -----------------------------------------------

my $USE_WEAK_REFS;

sub import {
    shift;
    return unless @_;
    if (lc($_[0]) eq 'use_weak_refs') {
        $USE_WEAK_REFS++;
        *Tree::Simple::weaken = \&Scalar::Util::weaken;
    }
}

## class constants
use constant ROOT => "root";

### constructor

sub new {
    my ($_class, $node, $parent) = @_;
    my $class = ref($_class) || $_class;
    my $tree = bless({}, $class);
    $tree->_init($node, $parent, []);
    return $tree;
}

### -----------------------------------------------
### methods
### -----------------------------------------------

## -----------------------------------------------
## private methods

sub _init {
    my ($self, $node, $parent, $children) = @_;
    # set the value of the unique id
    ($self->{_uid}) = ("$self" =~ /\((.*?)\)$/);
    # set the value of the node
    $self->{_node} = $node;
    # and set the value of _children
    $self->{_children} = $children;
    $self->{_height} = 1;
    $self->{_width} = 1;
    # Now check our $parent value
    if (defined($parent)) {
        if (blessed($parent) && $parent->isa("Tree::Simple")) {
            # and set it as our parent
            $parent->addChild($self);
        }
        elsif ($parent eq $self->ROOT) {
            $self->_setParent( $self->ROOT );
        }
        else {
            die "Insufficient Arguments : parent argument must be a Tree::Simple object";
        }
    }
    else {
        $self->_setParent( $self->ROOT );
    }
}

sub _setParent {
    my ($self, $parent) = @_;
    (defined($parent) &&
        (($parent eq $self->ROOT) || (blessed($parent) && $parent->isa("Tree::Simple"))))
        || die "Insufficient Arguments : parent also must be a Tree::Simple object";
    $self->{_parent} = $parent;
    if ($parent eq $self->ROOT) {
        $self->{_depth} = -1;
    }
    else {
        weaken($self->{_parent}) if $USE_WEAK_REFS;
        $self->{_depth} = $parent->getDepth() + 1;
    }
}

sub _detachParent {
    return if $USE_WEAK_REFS;
    my ($self) = @_;
    $self->{_parent} = undef;
}

sub _setHeight {
    my ($self, $child) = @_;
    my $child_height = $child->getHeight();
    return if ($self->{_height} >= $child_height + 1);
    $self->{_height} = $child_height + 1;

    # and now bubble up to the parent (unless we are the root)
    $self->getParent()->_setHeight($self) unless $self->isRoot();
}

sub _setWidth {
    my ($self, $child_width) = @_;
    $self->{_width} += $child_width;
    # and now bubble up to the parent (unless we are the root)
    $self->getParent()->_setWidth($child_width) unless $self->isRoot();
}

## -----------------------------------------------
## mutators

sub setNodeValue {
    my ($self, $node_value) = @_;
    (defined($node_value)) || die "Insufficient Arguments : must supply a value for node";
    $self->{_node} = $node_value;
}

sub setUID {
    my ($self, $uid) = @_;
    ($uid) || die "Insufficient Arguments : Custom Unique ID's must be a true value";
    $self->{_uid} = $uid;
}

## -----------------------------------------------
## child methods

sub addChild {
    splice @_, 1, 0, $_[0]->getChildCount;
    goto &insertChild;
}

sub addChildren {
    splice @_, 1, 0, $_[0]->getChildCount;
    goto &insertChildren;
}

sub _insertChildAt {
    my ($self, $index, @trees) = @_;

    (defined($index))
        || die "Insufficient Arguments : Cannot insert child without index";

    # check the bounds of our children
    # against the index given
    my $max = $self->getChildCount();
    ($index <= $max)
        || die "Index Out of Bounds : got ($index) expected no more than (" . $self->getChildCount() . ")";

    (@trees)
        || die "Insufficient Arguments : no tree(s) to insert";

	my($new_width) = 0;

    foreach my $tree (@trees) {
        (blessed($tree) && $tree->isa("Tree::Simple"))
            || die "Insufficient Arguments : Child must be a Tree::Simple object";
        $tree->_setParent($self);
        $self->_setHeight($tree);

		$new_width += getWidth($tree);

        $tree->fixDepth() unless $tree->isLeaf();
    }

	$self -> _setWidth($new_width - ($self -> isLeaf ? 1 : 0) );

    # if index is zero, use this optimization
    if ($index == 0) {
        unshift @{$self->{_children}} => @trees;
    }
    # if index is equal to the number of children
    # then use this optimization
    elsif ($index == $max) {
        push @{$self->{_children}} => @trees;
    }
    # otherwise do some heavy lifting here
    else {
        splice @{$self->{_children}}, $index, 0, @trees;
    }

    $self;
}

*insertChildren = \&_insertChildAt;

# insertChild is really the same as insertChildren, you are just
# inserting an array of one tree
*insertChild = \&insertChildren;

sub removeChildAt {
    my ($self, $index) = @_;
    (defined($index))
        || die "Insufficient Arguments : Cannot remove child without index.";
    ($self->getChildCount() != 0)
        || die "Illegal Operation : There are no children to remove";
    # check the bounds of our children
    # against the index given
    ($index < $self->getChildCount())
        || die "Index Out of Bounds : got ($index) expected no more than (" . $self->getChildCount() . ")";
    my $removed_child;
    # if index is zero, use this optimization
    if ($index == 0) {
        $removed_child = shift @{$self->{_children}};
    }
    # if index is equal to the number of children
    # then use this optimization
    elsif ($index == $#{$self->{_children}}) {
        $removed_child = pop @{$self->{_children}};
    }
    # otherwise do some heavy lifting here
    else {
        $removed_child = $self->{_children}->[$index];
        splice @{$self->{_children}}, $index, 1;
    }
    # make sure we fix the height
    $self->fixHeight();
    $self->fixWidth();
    # make sure that the removed child
    # is no longer connected to the parent
    # so we change its parent to ROOT
    $removed_child->_setParent($self->ROOT);
    # and now we make sure that the depth
    # of the removed child is aligned correctly
    $removed_child->fixDepth() unless $removed_child->isLeaf();
    # return this removed child
    # it is the responsibility
    # of the user of this module
    # to properly dispose of this
    # child (and all its sub-children)
    return $removed_child;
}

sub removeChild {
    my ($self, $child_to_remove) = @_;
    (defined($child_to_remove))
        || die "Insufficient Arguments : you must specify a child to remove";
    # maintain backwards compatibility
    # so any non-ref arguments will get
    # sent to removeChildAt
    return $self->removeChildAt($child_to_remove) unless ref($child_to_remove);
    # now that we are confident it's a reference
    # make sure it is the right kind
    (blessed($child_to_remove) && $child_to_remove->isa("Tree::Simple"))
        || die "Insufficient Arguments : Only valid child type is a Tree::Simple object";
    my $index = 0;
    foreach my $child ($self->getAllChildren()) {
        ("$child" eq "$child_to_remove") && return $self->removeChildAt($index);
        $index++;
    }
    die "Child Not Found : cannot find object ($child_to_remove) in self";
}

sub getIndex {
    my ($self) = @_;
    return -1 if $self->{_parent} eq $self->ROOT;
    my $index = 0;
    foreach my $sibling ($self->{_parent}->getAllChildren()) {
        ("$sibling" eq "$self") && return $index;
        $index++;
    }
}

## -----------------------------------------------
## Sibling methods

# these addSibling and addSiblings functions
# just pass along their arguments to the addChild
# and addChildren method respectively, this
# eliminates the need to overload these method
# in things like the Keyable Tree object

sub addSibling {
    my ($self, @args) = @_;
    (!$self->isRoot())
        || die "Insufficient Arguments : cannot add a sibling to a ROOT tree";
    $self->{_parent}->addChild(@args);
}

sub addSiblings {
    my ($self, @args) = @_;
    (!$self->isRoot())
        || die "Insufficient Arguments : cannot add siblings to a ROOT tree";
    $self->{_parent}->addChildren(@args);
}

sub insertSiblings {
    my ($self, @args) = @_;
    (!$self->isRoot())
        || die "Insufficient Arguments : cannot insert sibling(s) to a ROOT tree";
    $self->{_parent}->insertChildren(@args);
}

# insertSibling is really the same as
# insertSiblings, you are just inserting
# and array of one tree
*insertSibling = \&insertSiblings;

# I am not permitting the removal of siblings
# as I think in general it is a bad idea

## -----------------------------------------------
## accessors

sub getUID       { $_[0]{_uid}    }
sub getParent    { $_[0]{_parent} }
sub getDepth     { $_[0]{_depth}  }
sub getNodeValue { $_[0]{_node}   }
sub getWidth     { $_[0]{_width}  }
sub getHeight    { $_[0]{_height} }

# for backwards compatibility
*height = \&getHeight;

sub getChildCount { $#{$_[0]{_children}} + 1 }

sub getChild {
    my ($self, $index) = @_;
    (defined($index))
        || die "Insufficient Arguments : Cannot get child without index";
    return $self->{_children}->[$index];
}

sub getAllChildren {
    my ($self) = @_;
    return wantarray ?
        @{$self->{_children}}
        :
        $self->{_children};
}

sub getSibling {
    my ($self, $index) = @_;
    (!$self->isRoot())
        || die "Insufficient Arguments : cannot get siblings from a ROOT tree";
    $self->getParent()->getChild($index);
}

sub getAllSiblings {
    my ($self) = @_;
    (!$self->isRoot())
        || die "Insufficient Arguments : cannot get siblings from a ROOT tree";
    $self->getParent()->getAllChildren();
}

## -----------------------------------------------
## informational

sub isLeaf { $_[0]->getChildCount == 0 }

sub isRoot {
    my ($self) = @_;
    return (!defined($self->{_parent}) || $self->{_parent} eq $self->ROOT);
}

sub size {
    my ($self) = @_;
    my $size = 1;
    foreach my $child ($self->getAllChildren()) {
        $size += $child->size();
    }
    return $size;
}

## -----------------------------------------------
## misc

# NOTE:
# Occasionally one wants to have the
# depth available for various reasons
# of convenience. Sometimes that depth
# field is not always correct.
# If you create your tree in a top-down
# manner, this is usually not an issue
# since each time you either add a child
# or create a tree you are doing it with
# a single tree and not a hierarchy.
# If however you are creating your tree
# bottom-up, then you might find that
# when adding hierarchies of trees, your
# depth fields are all out of whack.
# This is where this method comes into play
# it will recurse down the tree and fix the
# depth fields appropriately.
# This method is called automatically when
# a subtree is added to a child array
sub fixDepth {
    my ($self) = @_;
    # make sure the tree's depth
    # is up to date all the way down
    $self->traverse(sub {
            my ($tree) = @_;
            return if $tree->isRoot();
            $tree->{_depth} = $tree->getParent()->getDepth() + 1;
        }
    );
}

# NOTE:
# This method is used to fix any height
# discrepancies which might arise when
# you remove a sub-tree
sub fixHeight {
    my ($self) = @_;
    # we must find the tallest sub-tree
    # and use that to define the height
    my $max_height = 0;
    unless ($self->isLeaf()) {
        foreach my $child ($self->getAllChildren()) {
            my $child_height = $child->getHeight();
            $max_height = $child_height if ($max_height < $child_height);
        }
    }
    # if there is no change, then we
    # need not bubble up through the
    # parents
    return if ($self->{_height} == ($max_height + 1));
    # otherwise ...
    $self->{_height} = $max_height + 1;
    # now we need to bubble up through the parents
    # in order to rectify any issues with height
    $self->getParent()->fixHeight() unless $self->isRoot();
}

sub fixWidth {
    my ($self) = @_;
    my $fixed_width = 0;
    $fixed_width += $_->getWidth() foreach $self->getAllChildren();
    $self->{_width} = $fixed_width;
    $self->getParent()->fixWidth() unless $self->isRoot();
}

sub traverse {
    my ($self, $func, $post) = @_;
    (defined($func)) || die "Insufficient Arguments : Cannot traverse without traversal function";
    (ref($func) eq "CODE") || die "Incorrect Object Type : traversal function is not a function";
    (ref($post) eq "CODE") || die "Incorrect Object Type : post traversal function is not a function"
        if defined($post);
    foreach my $child ($self->getAllChildren()) {
        $func->($child);
        $child->traverse($func, $post);
        defined($post) && $post->($child);
    }
}

# this is an improved version of the
# old accept method, it now it more
# accepting of its arguments
sub accept {
    my ($self, $visitor) = @_;
    # it must be a blessed reference and ...
    (blessed($visitor) &&
        # either a Tree::Simple::Visitor object, or ...
        ($visitor->isa("Tree::Simple::Visitor") ||
            # it must be an object which has a 'visit' method available
            $visitor->can('visit')))
        || die "Insufficient Arguments : You must supply a valid Visitor object";
    $visitor->visit($self);
}

## -----------------------------------------------
## cloning

sub clone {
    my ($self) = @_;
    # first clone the value in the node
    my $cloned_node = _cloneNode($self->getNodeValue());
    # create a new Tree::Simple object
    # here with the cloned node, however
    # we do not assign the parent node
    # since it really does not make a lot
    # of sense. To properly clone it would
    # be to clone back up the tree as well,
    # which IMO is not intuitive. So in essence
    # when you clone a tree, you detach it from
    # any parentage it might have
    my $clone = $self->new($cloned_node);
    # however, because it is a recursive thing
    # when you clone all the children, and then
    # add them to the clone, you end up setting
    # the parent of the children to be that of
    # the clone (which is correct)
    $clone->addChildren(
                map { $_->clone() } $self->getAllChildren()
                ) unless $self->isLeaf();
    # return the clone
    return $clone;
}

# this allows cloning of single nodes while
# retaining connections to a tree, this is sloppy
sub cloneShallow {
    my ($self) = @_;
    my $cloned_tree = { %{$self} };
    bless($cloned_tree, ref($self));
    # just clone the node (if you can)
    $cloned_tree->setNodeValue(_cloneNode($self->getNodeValue()));
    return $cloned_tree;
}

# this is a helper function which
# recursively clones the node
sub _cloneNode {
    my ($node, $seen) = @_;
    # create a cache if we don't already
    # have one to prevent circular refs
    # from being copied more than once
    $seen = {} unless defined $seen;
    # now here we go...
    my $clone;
    # if it is not a reference, then lets just return it
    return $node unless ref($node);
    # if it is in the cache, then return that
    return $seen->{$node} if exists ${$seen}{$node};
    # if it is an object, then ...
    if (blessed($node)) {
        # see if we can clone it
        if ($node->can('clone')) {
            $clone = $node->clone();
        }
        # otherwise respect that it does
        # not want to be cloned
        else {
            $clone = $node;
        }
    }
    else {
        # if the current slot is a scalar reference, then
        # dereference it and copy it into the new object
        if (ref($node) eq "SCALAR" || ref($node) eq "REF") {
            my $var = "";
            $clone = \$var;
            ${$clone} = _cloneNode(${$node}, $seen);
        }
        # if the current slot is an array reference
        # then dereference it and copy it
        elsif (ref($node) eq "ARRAY") {
            $clone = [ map { _cloneNode($_, $seen) } @{$node} ];
        }
        # if the current reference is a hash reference
        # then dereference it and copy it
        elsif (ref($node) eq "HASH") {
            $clone = {};
            foreach my $key (keys %{$node}) {
                $clone->{$key} = _cloneNode($node->{$key}, $seen);
            }
        }
        else {
            # all other ref types are not copied
            $clone = $node;
        }
    }
    # store the clone in the cache and
    $seen->{$node} = $clone;
    # then return the clone
    return $clone;
}


## -----------------------------------------------
## Desctructor

sub DESTROY {
    # if we are using weak refs
    # we don't need to worry about
    # destruction, it will just happen
    return if $USE_WEAK_REFS;
    my ($self) = @_;
    # we want to detach all our children from
    # ourselves, this will break most of the
    # connections and allow for things to get
    # reaped properly
    unless (!$self->{_children} && scalar(@{$self->{_children}}) == 0) {
        foreach my $child (@{$self->{_children}}) {
            defined $child && $child->_detachParent();
        }
    }
    # we do not need to remove or undef the _children
    # of the _parent fields, this will cause some
    # unwanted releasing of connections.
}

## -----------------------------------------------
## end Tree::Simple
## -----------------------------------------------

1;

__END__

=head1 NAME

Tree::Simple - A simple tree object

=head1 SYNOPSIS

  use Tree::Simple;

  # make a tree root
  my $tree = Tree::Simple->new("0", Tree::Simple->ROOT);

  # explicity add a child to it
  $tree->addChild(Tree::Simple->new("1"));

  # specify the parent when creating
  # an instance and it adds the child implicity
  my $sub_tree = Tree::Simple->new("2", $tree);

  # chain method calls
  $tree->getChild(0)->addChild(Tree::Simple->new("1.1"));

  # add more than one child at a time
  $sub_tree->addChildren(
            Tree::Simple->new("2.1"),
            Tree::Simple->new("2.2")
            );

  # add siblings
  $sub_tree->addSibling(Tree::Simple->new("3"));

  # insert children a specified index
  $sub_tree->insertChild(1, Tree::Simple->new("2.1a"));

  # clean up circular references
  $tree->DESTROY();

=head1 DESCRIPTION

This module in an fully object-oriented implementation of a simple n-ary
tree. It is built upon the concept of parent-child relationships, so
therefore every B<Tree::Simple> object has both a parent and a set of
children (who themselves may have children, and so on). Every B<Tree::Simple>
object also has siblings, as they are just the children of their immediate
parent.

It is can be used to model hierarchal information such as a file-system,
the organizational structure of a company, an object inheritance hierarchy,
versioned files from a version control system or even an abstract syntax
tree for use in a parser. It makes no assumptions as to your intended usage,
but instead simply provides the structure and means of accessing and
traversing said structure.

This module uses exceptions and a minimal Design By Contract style. All method
arguments are required unless specified in the documentation, if a required
argument is not defined an exception will usually be thrown. Many arguments
are also required to be of a specific type, for instance the C<$parent>
argument to the constructor B<must> be a B<Tree::Simple> object or an object
derived from B<Tree::Simple>, otherwise an exception is thrown. This may seems
harsh to some, but this allows me to have the confidence that my code works as
I intend, and for you to enjoy the same level of confidence when using this
module. Note however that this module does not use any Exception or Error module,
the exceptions are just strings thrown with C<die>.

I consider this module to be production stable, it is based on a module which has
been in use on a few production systems for approx. 2 years now with no issue.
The only difference is that the code has been cleaned up a bit, comments added and
the thorough tests written for its public release. I am confident it behaves as
I would expect it to, and is (as far as I know) bug-free. I have not stress-tested
it under extreme duress, but I don't so much intend for it to be used in that
type of situation. If this module cannot keep up with your Tree needs, i suggest
switching to one of the modules listed in the L<OTHER TREE MODULES> section below.

=head1 CONSTANTS

=over 4

=item B<ROOT>

This class constant serves as a placeholder for the root of our tree. If a tree
does not have a parent, then it is considered a root.

=back

=head1 METHODS

=head2 Constructor

=over 4

=item B<new ($node, $parent)>

The constructor accepts two arguments a C<$node> value and an optional C<$parent>.
The C<$node> value can be any scalar value (which includes references and objects).
The optional C<$parent> value must be a B<Tree::Simple> object, or an object
derived from B<Tree::Simple>. Setting this value implies that your new tree is a
child of the parent tree, and therefore adds it to the parent's children. If the
C<$parent> is not specified then its value defaults to ROOT.

=back

=head2 Mutator Methods

=over 4

=item B<setNodeValue ($node_value)>

This sets the node value to the scalar C<$node_value>, an exception is thrown if
C<$node_value> is not defined.

=item B<setUID ($uid)>

This allows you to set your own unique ID for this specific Tree::Simple object.
A default value derived from the object's hex address is provided for you, so use
of this method is entirely optional. It is the responsibility of the user to
ensure the value's uniqueness, all that is tested by this method is that C<$uid>
is a true value (evaluates to true in a boolean context). For even more information
about the Tree::Simple UID see the C<getUID> method.

=item B<addChild ($tree)>

This method accepts only B<Tree::Simple> objects or objects derived from
B<Tree::Simple>, an exception is thrown otherwise. This method will append
the given C<$tree> to the end of it's children list, and set up the correct
parent-child relationships. This method is set up to return its invocant so
that method call chaining can be possible. Such as:

  my $tree = Tree::Simple->new("root")->addChild(Tree::Simple->new("child one"));

Or the more complex:

  my $tree = Tree::Simple->new("root")->addChild(
                         Tree::Simple->new("1.0")->addChild(
                                     Tree::Simple->new("1.0.1")
                                     )
                         );

=item B<addChildren (@trees)>

This method accepts an array of B<Tree::Simple> objects, and adds them to
it's children list. Like C<addChild> this method will return its invocant
to allow for method call chaining.

=item B<insertChild ($index, $tree)>

This method accepts a numeric C<$index> and a B<Tree::Simple> object (C<$tree>),
and inserts the C<$tree> into the children list at the specified C<$index>.
This results in the shifting down of all children after the C<$index>. The
C<$index> is checked to be sure it is the bounds of the child list, if it
out of bounds an exception is thrown. The C<$tree> argument's type is
verified to be a B<Tree::Simple> or B<Tree::Simple> derived object, if
this condition fails, an exception is thrown.

=item B<insertChildren ($index, @trees)>

This method functions much as insertChild does, but instead of inserting a
single B<Tree::Simple>, it inserts an array of B<Tree::Simple> objects. It
too bounds checks the value of C<$index> and type checks the objects in
C<@trees> just as C<insertChild> does.

=item B<removeChild> ($child | $index)>

Accepts two different arguments. If given a B<Tree::Simple> object (C<$child>),
this method finds that specific C<$child> by comparing it with all the other
children until it finds a match. At which point the C<$child> is removed. If
no match is found, and exception is thrown. If a non-B<Tree::Simple> object
is given as the C<$child> argument, an exception is thrown.

This method also accepts a numeric C<$index> and removes the child found at
that index from it's list of children. The C<$index> is bounds checked, if
this condition fail, an exception is thrown.

When a child is removed, it results in the shifting up of all children after
it, and the removed child is returned. The removed child is properly
disconnected from the tree and all its references to its old parent are
removed. However, in order to properly clean up and circular references
the removed child might have, it is advised to call it's C<DESTROY> method.
See the L<CIRCULAR REFERENCES> section for more information.

=item B<addSibling ($tree)>

=item B<addSiblings (@trees)>

=item B<insertSibling ($index, $tree)>

=item B<insertSiblings ($index, @trees)>

The C<addSibling>, C<addSiblings>, C<insertSibling> and C<insertSiblings>
methods pass along their arguments to the C<addChild>, C<addChildren>,
C<insertChild> and C<insertChildren> methods of their parent object
respectively. This eliminates the need to overload these methods in subclasses
which may have specialized versions of the *Child(ren) methods. The one
exceptions is that if an attempt it made to add or insert siblings to the
B<ROOT> of the tree then an exception is thrown.

=back

B<NOTE:>
There is no C<removeSibling> method as I felt it was probably a bad idea.
The same effect can be achieved by manual upwards traversal.

=head2 Accessor Methods

=over 4

=item B<getNodeValue>

This returns the value stored in the object's node field.

=item B<getUID>

This returns the unique ID associated with this particular tree. This can
be custom set using the C<setUID> method, or you can just use the default.
The default is the hex-address extracted from the stringified Tree::Simple
object. This may not be a I<universally> unique identifier, but it should
be adequate for at least the current instance of your perl interpreter. If
you need a UUID, one can be generated with an outside module (there are
    many to choose from on CPAN) and the C<setUID> method (see above).

=item B<getChild ($index)>

This returns the child (a B<Tree::Simple> object) found at the specified
C<$index>. Note that we do use standard zero-based array indexing.

=item B<getAllChildren>

This returns an array of all the children (all B<Tree::Simple> objects).
It will return an array reference in scalar context.

=item B<getSibling ($index)>

=item B<getAllSiblings>

Much like C<addSibling> and C<addSiblings>, these two methods simply call
C<getChild> and C<getAllChildren> on the invocant's parent.

=item B<getDepth>

Returns a number representing the invocant's depth within the hierarchy of
B<Tree::Simple> objects.

B<NOTE:> A C<ROOT> tree has the depth of -1. This be because Tree::Simple
assumes that a tree's root will usually not contain data, but just be an
anchor for the data-containing branches. This may not be intuitive in all
cases, so I mention it here.

=item B<getParent>

Returns the invocant's parent, which could be either B<ROOT> or a
B<Tree::Simple> object.

=item B<getHeight>

Returns a number representing the length of the longest path from the current
tree to the furthest leaf node.

=item B<getWidth>

Returns the a number representing the breadth of the current tree, basically
it is a count of all the leaf nodes.

=item B<getChildCount>

Returns the number of children the invocant contains.

=item B<getIndex>

Returns the index of this tree within its parent's child list. Returns -1 if
the tree is the root.

=back

=head2 Predicate Methods

=over 4

=item B<isLeaf>

Returns true (1) if the invocant does not have any children, false (0) otherwise.

=item B<isRoot>

Returns true (1) if the invocant's "parent" field is B<ROOT>, returns false
(0) otherwise.

=back

=head2 Recursive Methods

=over 4

=item B<traverse ($func, ?$postfunc)>

This method accepts two arguments a mandatory C<$func> and an optional
C<$postfunc>. If the argument C<$func> is not defined then an exception
is thrown. If C<$func> or C<$postfunc> are not in fact CODE references
then an exception is thrown. The function C<$func> is then applied
recursively to all the children of the invocant. If given, the function
C<$postfunc> will be applied to each child after the child's children
have been traversed.

Here is an example of a traversal function that will print out the
hierarchy as a tabbed in list.

  $tree->traverse(sub {
      my ($_tree) = @_;
      print (("\t" x $_tree->getDepth()), $_tree->getNodeValue(), "\n");
  });

Here is an example of a traversal function that will print out the
hierarchy in an XML-style format.

  $tree->traverse(sub {
      my ($_tree) = @_;
      print ((' ' x $_tree->getDepth()),
              '<', $_tree->getNodeValue(),'>',"\n");
  },
  sub {
      my ($_tree) = @_;
      print ((' ' x $_tree->getDepth()),
              '</', $_tree->getNodeValue(),'>',"\n");
  });

=item B<size>

Returns the total number of nodes in the current tree and all its sub-trees.

=item B<height>

This method has also been B<deprecated> in favor of the C<getHeight> method above,
it remains as an alias to C<getHeight> for backwards compatibility.

B<NOTE:> This is also no longer a recursive method which get's it's value on demand,
but a value stored in the Tree::Simple object itself, hopefully making it much
more efficient and usable.

=back

=head2 Visitor Methods

=over 4

=item B<accept ($visitor)>

It accepts either a B<Tree::Simple::Visitor> object (which includes classes derived
    from B<Tree::Simple::Visitor>), or an object who has the C<visit> method available
    (tested with C<$visitor-E<gt>can('visit')>). If these qualifications are not met,
    and exception will be thrown. We then run the Visitor's C<visit> method giving the
    current tree as its argument.

I have also created a number of Visitor objects and packaged them into the
B<Tree::Simple::VisitorFactory>.

=back

=head2 Cloning Methods

Cloning a tree can be an extremely expensive operation for large trees, so we provide
two options for cloning, a deep clone and a shallow clone.

When a Tree::Simple object is cloned, the node is deep-copied in the following manner.
If we find a normal scalar value (non-reference), we simply copy it. If we find an
object, we attempt to call C<clone> on it, otherwise we just copy the reference (since
we assume the object does not want to be cloned). If we find a SCALAR, REF reference we
copy the value contained within it. If we find a HASH or ARRAY reference we copy the
reference and recursively copy all the elements within it (following these exact
guidelines). We also do our best to assure that circular references are cloned
only once and connections restored correctly. This cloning will not be able to copy
CODE, RegExp and GLOB references, as they are pretty much impossible to clone. We
also do not handle C<tied> objects, and they will simply be copied as plain
references, and not re-C<tied>.

=over 4

=item B<clone>

The clone method does a full deep-copy clone of the object, calling C<clone> recursively
on all its children. This does not call C<clone> on the parent tree however. Doing
this would result in a slowly degenerating spiral of recursive death, so it is not
recommended and therefore not implemented. What happens is that the tree instance
that C<clone> is actually called upon is detached from the tree, and becomes a root
node, all if the cloned children are then attached as children of that tree. I personally
think this is more intuitive then to have the cloning crawl back I<up> the tree is not
what I think most people would expect.

=item B<cloneShallow>

This method is an alternate option to the plain C<clone> method. This method allows the
cloning of single B<Tree::Simple> object while retaining connections to the rest of the
tree/hierarchy.

=back

=head2 Misc. Methods

=over 4

=item B<DESTROY>

To avoid memory leaks through uncleaned-up circular references, we implement the
C<DESTROY> method. This method will attempt to call C<DESTROY> on each of its
children (if it has any). This will result in a cascade of calls to C<DESTROY> on
down the tree. It also cleans up it's parental relations as well.

Because of perl's reference counting scheme and how that interacts with circular
references, if you want an object to be properly reaped you should manually call
C<DESTROY>. This is especially necessary if your object has any children. See the
section on L<CIRCULAR REFERENCES> for more information.

=item B<fixDepth>

Tree::Simple will manage your tree's depth field for you using this method. You
should never need to call it on your own, however if you ever did need to, here
is it. Running this method will traverse your all the invocant's sub-trees
correcting the depth as it goes.

=item B<fixHeight>

Tree::Simple will manage your tree's height field for you using this method.
You should never need to call it on your own, however if you ever did need to,
here is it. Running this method will correct the heights of the current tree
and all it's ancestors.

=item B<fixWidth>

Tree::Simple will manage your tree's width field for you using this method. You
should never need to call it on your own, however if you ever did need to,
here is it. Running this method will correct the widths of the current tree
and all it's ancestors.

=back

=head2 Private Methods

I would not normally document private methods, but in case you need to subclass
Tree::Simple, here they are.

=over 4

=item B<_init ($node, $parent, $children)>

This method is here largely to facilitate subclassing. This method is called by
new to initialize the object, where new's primary responsibility is creating
the instance.

=item B<_setParent ($parent)>

This method sets up the parental relationship. It is for internal use only.

=item B<_setHeight ($child)>

This method will set the height field based upon the height of the given C<$child>.

=back

=head1 CIRCULAR REFERENCES

I have revised the model by which Tree::Simple deals with circular references.
In the past all circular references had to be manually destroyed by calling
DESTROY. The call to DESTROY would then call DESTROY on all the children, and
therefore cascade down the tree. This however was not always what was needed,
nor what made sense, so I have now revised the model to handle things in what
I feel is a more consistent and sane way.

Circular references are now managed with the simple idea that the parent makes
the decisions for the child. This means that child-to-parent references are
weak, while parent-to-child references are strong. So if a parent is destroyed
it will force all it's children to detach from it, however, if a child is
destroyed it will not be detached from it's parent.

=head2 Optional Weak References

By default, you are still required to call DESTROY in order for things to
happen. However I have now added the option to use weak references, which
alleviates the need for the manual call to DESTROY and allows Tree::Simple
to manage this automatically. This is accomplished with a compile time
setting like this:

  use Tree::Simple 'use_weak_refs';

And from that point on Tree::Simple will use weak references to allow for
perl's reference counting to clean things up properly.

For those who are unfamiliar with weak references, and how they affect the
reference counts, here is a simple illustration. First is the normal model
that Tree::Simple uses:

 +---------------+
 | Tree::Simple1 |<---------------------+
 +---------------+                      |
 | parent        |                      |
 | children      |-+                    |
 +---------------+ |                    |
                   |                    |
                   |  +---------------+ |
                   +->| Tree::Simple2 | |
                      +---------------+ |
                      | parent        |-+
                      | children      |
                      +---------------+

Here, Tree::Simple1 has a reference count of 2 (one for the original
variable it is assigned to, and one for the parent reference in
Tree::Simple2), and Tree::Simple2 has a reference count of 1 (for the
child reference in Tree::Simple1).

Now, with weak references:

 +---------------+
 | Tree::Simple1 |.......................
 +---------------+                      :
 | parent        |                      :
 | children      |-+                    : <--[ weak reference ]
 +---------------+ |                    :
                   |                    :
                   |  +---------------+ :
                   +->| Tree::Simple2 | :
                      +---------------+ :
                      | parent        |..
                      | children      |
                      +---------------+

Now Tree::Simple1 has a reference count of 1 (for the variable it is
assigned to) and 1 weakened reference (for the parent reference in
Tree::Simple2). And Tree::Simple2 has a reference count of 1, just
as before.

=head1 BUGS

None that I am aware of. The code is pretty thoroughly tested (see
L<CODE COVERAGE> below) and is based on an (non-publicly released)
module which I had used in production systems for about 3 years without
incident. Of course, if you find a bug, let me know, and I will be sure
to fix it.

=head1 CODE COVERAGE

I use L<Devel::Cover> to test the code coverage of my tests, below
is the L<Devel::Cover> report on this module's test suite.

 ---------------------------- ------ ------ ------ ------ ------ ------ ------
 File                           stmt branch   cond    sub    pod   time  total
 ---------------------------- ------ ------ ------ ------ ------ ------ ------
 Tree/Simple.pm                 99.6   96.0   92.3  100.0   97.0   95.5   98.0
 Tree/Simple/Visitor.pm        100.0   96.2   88.2  100.0  100.0    4.5   97.7
 ---------------------------- ------ ------ ------ ------ ------ ------ ------
 Total                          99.7   96.1   91.1  100.0   97.6  100.0   97.9
 ---------------------------- ------ ------ ------ ------ ------ ------ ------

=head1 SEE ALSO

I have written a number of other modules which use or augment this
module, they are describes below and available on CPAN.

=over 4

=item L<Tree::Parser> - A module for parsing formatted files into Tree::Simple hierarchies.

=item L<Tree::Simple::View> - A set of classes for viewing Tree::Simple hierarchies in various output formats.

=item L<Tree::Simple::VisitorFactory> - A set of several useful Visitor objects for Tree::Simple objects.

=item L<Tree::Binary> - If you are looking for a binary tree, this you might want to check this one out.

=back

Also, the author of L<Data::TreeDumper> and I have worked together
to make sure that B<Tree::Simple> and his module work well together.
If you need a quick and handy way to dump out a Tree::Simple hierarchy,
this module does an excellent job (and plenty more as well).

I have also recently stumbled upon some packaged distributions of
Tree::Simple for the various Unix flavors. Here  are some links:

=over 4

=item FreeBSD Port - L<http://www.freshports.org/devel/p5-Tree-Simple/>

=item Debian Package - L<http://packages.debian.org/unstable/perl/libtree-simple-perl>

=item Linux RPM - L<http://rpmpan.sourceforge.net/Tree.html>

=back

=head1 OTHER TREE MODULES

There are a few other Tree modules out there, here is a quick comparison
between B<Tree::Simple> and them. Obviously I am biased, so take what I say
with a grain of salt, and keep in mind, I wrote B<Tree::Simple> because I
could not find a Tree module that suited my needs. If B<Tree::Simple> does
not fit your needs, I recommend looking at these modules. Please note that
I am only listing Tree::* modules I am familiar with here, if you think I
have missed a module, please let me know. I have also seen a few tree-ish
modules outside of the Tree::* namespace, but most of them are part of
another distribution (B<HTML::Tree>, B<Pod::Tree>, etc) and are likely
specialized in purpose.

=over 4

=item L<Tree::DAG_Node>

This module seems pretty stable and very robust with a lot of functionality.
However, B<Tree::DAG_Node> does not come with any automated tests. It's
I<test.pl> file simply checks the module loads and nothing else. While I
am sure the author tested his code, I would feel better if I was able to
see that. The module is approx. 3000 lines with POD, and 1,500 without the
POD. The shear depth and detail of the documentation and the ratio of code
to documentation is impressive, and not to be taken lightly. But given that
it is a well known fact that the likeliness of bugs increases along side the
size of the code, I do not feel comfortable with large modules like this
which have no tests.

All this said, I am not a huge fan of the API either, I prefer the gender
neutral approach in B<Tree::Simple> to the mother/daughter style of B<Tree::DAG_Node>.
I also feel very strongly that B<Tree::DAG_Node> is trying to do much more
than makes sense in a single module, and is offering too many ways to do
the same or similar things.

However, of all the Tree::* modules out there, B<Tree::DAG_Node> seems to
be one of the favorites, so it may be worth investigating.

=item L<Tree::MultiNode>

I am not very familiar with this module, however, I have heard some good
reviews of it, so I thought it deserved mention here. I believe it is
based upon C++ code found in the book I<Algorithms in C++> by Robert Sedgwick.
It uses a number of interesting ideas, such as a ::Handle object to traverse
the tree with (similar to Visitors, but also seem to be to be kind of like
a cursor). However, like B<Tree::DAG_Node>, it is somewhat lacking in tests
and has only 6 tests in its suite. It also has one glaring bug, which is
that there is currently no way to remove a child node.

=item L<Tree::Nary>

It is a (somewhat) direct translation of the N-ary tree from the GLIB
library, and the API is based on that. GLIB is a C library, which means
this is a very C-ish API. That doesn't appeal to me, it might to you, to
each their own.

This module is similar in intent to B<Tree::Simple>. It implements a tree
with I<n> branches and has polymorphic node containers. It implements much
of the same methods as B<Tree::Simple> and a few others on top of that, but
being based on a C library, is not very OO. In most of the method calls
the C<$self> argument is not used and the second argument C<$node> is.
B<Tree::Simple> is a much more OO module than B<Tree::Nary>, so while they
are similar in functionality they greatly differ in implementation style.

=item L<Tree>

This module is pretty old, it has not been updated since Oct. 31, 1999 and
is still on version 0.01. It also seems to be (from the limited documentation)
a binary and a balanced binary tree, B<Tree::Simple> is an I<n>-ary tree, and
makes no attempt to balance anything.

=item L<Tree::Ternary>

This module is older than B<Tree>, last update was Sept. 24th, 1999. It
seems to be a special purpose tree, for storing and accessing strings,
not general purpose like B<Tree::Simple>.

=item L<Tree::Ternary_XS>

This module is an XS implementation of the above tree type.

=item L<Tree::Trie>

This too is a specialized tree type, it sounds similar to the B<Tree::Ternary>,
but it much newer (latest release in 2003). It seems specialized for the lookup
and retrieval of information like a hash.

=item L<Tree::M>

Is a wrapper for a C++ library, whereas B<Tree::Simple> is pure-perl. It also
seems to be a more specialized implementation of a tree, therefore not really
the same as B<Tree::Simple>.

=item L<Tree::Fat>

Is a wrapper around a C library, again B<Tree::Simple> is pure-perl. The author
describes FAT-trees as a combination of a Tree and an array. It looks like a
pretty mean and lean module, and good if you need speed and are implementing a
custom data-store of some kind. The author points out too that the module is
designed for embedding and there is not default embedding, so you can't really
use it "out of the box".

=back

=head1 ACKNOWLEDGEMENTS

=over 4

=item Thanks to Nadim Ibn Hamouda El Khemir for making L<Data::TreeDumper> work
with B<Tree::Simple>.

=item Thanks to Brett Nuske for his idea for the C<getUID> and C<setUID> methods.

=item Thanks to whomever submitted the memory leak bug to RT (#7512).

=item Thanks to Mark Thomas for his insight into how to best handle the I<height>
and I<width> properties without unnecessary recursion.

=item Thanks for Mark Lawrence for the &traverse post-func patch, tests and docs.

=back

=head1 AUTHOR

Stevan Little, E<lt>stevan@iinteractive.comE<gt>

Rob Kinyon, E<lt>rob@iinteractive.comE<gt>

Ron Savage E<lt>ron@savage.net.auE<gt> has taken over maintenance as of V 1.19.

=head1 REPOSITORY

L<https://github.com/stevan/tree-simple>.

=head1 COPYRIGHT AND LICENSE

Copyright 2004-2006 by Infinity Interactive, Inc.

L<http://www.iinteractive.com>

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

=cut
