from compiler import ast

# XXX should probably rename ASTVisitor to ASTWalker

# XXX can it be made even more generic?

class ASTVisitor:

    """Performs a depth-first walk of the AST

    The ASTVisitor will walk the AST, performing either a preorder or

    postorder traversal depending on which method is called.

    methods:

    preorder(tree, visitor)

    postorder(tree, visitor)

        tree: an instance of ast.Node

        visitor: an instance with visitXXX methods

    The ASTVisitor is responsible for walking over the tree in the

    correct order.  For each node, it checks the visitor argument for

    a method named 'visitNodeType' where NodeType is the name of the

    node's class, e.g. Class.  If the method exists, it is called

    with the node as its sole argument.

    The visitor method for a particular node type can control how

    child nodes are visited during a preorder walk.  (It can't control

    the order during a postorder walk, because it is called _after_

    the walk has occurred.)  The ASTVisitor modifies the visitor

    argument by adding a visit method to the visitor; this method can

    be used to visit a child node of arbitrary type.

    """

    VERBOSE = 0

    def __init__(self):

        self.node = None

        self._cache = {}

    def default(self, node, *args):

        for child in node.getChildNodes():

            self.dispatch(child, *args)

    def dispatch(self, node, *args):

        self.node = node

        klass = node.__class__

        meth = self._cache.get(klass, None)

        if meth is None:

            className = klass.__name__

            meth = getattr(self.visitor, 'visit' + className, self.default)

            self._cache[klass] = meth

##        if self.VERBOSE > 0:

##            className = klass.__name__

##            if self.VERBOSE == 1:

##                if meth == 0:

##                    print "dispatch", className

##            else:

##                print "dispatch", className, (meth and meth.__name__ or '')

        return meth(node, *args)

    def preorder(self, tree, visitor, *args):

        """Do preorder walk of tree using visitor"""

        self.visitor = visitor

        visitor.visit = self.dispatch

        self.dispatch(tree, *args) # XXX *args make sense?

class ExampleASTVisitor(ASTVisitor):

    """Prints examples of the nodes that aren't visited

    This visitor-driver is only useful for development, when it's

    helpful to develop a visitor incrementally, and get feedback on what

    you still have to do.

    """

    examples = {}

    def dispatch(self, node, *args):

        self.node = node

        meth = self._cache.get(node.__class__, None)

        className = node.__class__.__name__

        if meth is None:

            meth = getattr(self.visitor, 'visit' + className, 0)

            self._cache[node.__class__] = meth

        if self.VERBOSE > 1:

            print "dispatch", className, (meth and meth.__name__ or '')

        if meth:

            meth(node, *args)

        elif self.VERBOSE > 0:

            klass = node.__class__

            if not self.examples.has_key(klass):

                self.examples[klass] = klass

                print

                print self.visitor

                print klass

                for attr in dir(node):

                    if attr[0] != '_':

                        print "\t", "%-12.12s" % attr, getattr(node, attr)

                print

            return self.default(node, *args)

# XXX this is an API change

_walker = ASTVisitor

def walk(tree, visitor, walker=None, verbose=None):

    if walker is None:

        walker = _walker()

    if verbose is not None:

        walker.VERBOSE = verbose

    walker.preorder(tree, visitor)

    return walker.visitor

def dumpNode(node):

    print node.__class__

    for attr in dir(node):

        if attr[0] != '_':

            print "\t", "%-10.10s" % attr, getattr(node, attr)