"""Backport of Python 2.6 `ast` module.

AST classes are wrappers around classes in Python 2.5 `_ast` module.
The rest is copied from Python 2.6 `ast.py`.
"""

import inspect
import _ast
from _ast import PyCF_ONLY_AST
from _ast import AST

for name, cls in inspect.getmembers(_ast, inspect.isclass) :
    if issubclass(cls, AST) :
        if cls is AST :
            continue
        class _Ast (cls, AST) :
            def __init__ (self, *larg, **karg) :
                if len(larg) > 0 and len(larg) != len(self._fields) :
                    raise TypeError, ("%s constructor takes either 0 or "
                                      "%u positional arguments"
                                      % (self.__class__.__name__,
                                         len(self._fields)))
                for name, arg in zip(self._fields, larg) + karg.items() :
                    if name in self._fields :
                        setattr(self, name, arg)
        try :
            _Ast._fields = tuple(cls._fields)
        except :
            _Ast._fields = ()
        _Ast.__name__ = name
        globals()[name] = _Ast

del _Ast, cls, name

def literal_eval(node_or_string):
    """Safely evaluate an expression node or a string containing a
    Python expression. The string or node provided may only consist of
    the following Python literal structures: strings, numbers, tuples,
    lists, dicts, booleans, and `None`.
    """
    _safe_names = {'None': None, 'True': True, 'False': False}
    if isinstance(node_or_string, basestring):
        node_or_string = parse(node_or_string, mode='eval')
    if isinstance(node_or_string, Expression):
        node_or_string = node_or_string.body
    def _convert(node):
        if isinstance(node, Str):
            return node.s
        elif isinstance(node, Num):
            return node.n
        elif isinstance(node, Tuple):
            return tuple(map(_convert, node.elts))
        elif isinstance(node, List):
            return list(map(_convert, node.elts))
        elif isinstance(node, Dict):
            return dict((_convert(k), _convert(v)) for k, v
                        in zip(node.keys, node.values))
        elif isinstance(node, Name):
            if node.id in _safe_names:
                return _safe_names[node.id]
        raise ValueError('malformed string')
    return _convert(node_or_string)

def dump(node, annotate_fields=True, include_attributes=False):
    """Return a formatted dump of the tree in `node`. This is mainly
    useful for debugging purposes. The returned string will show the
    names and the values for fields. This makes the code impossible to
    evaluate, so if evaluation is wanted `annotate_fields` must be set
    to `False`. Attributes such as line numbers and column offsets are
    not dumped by default. If this is wanted, `include_attributes` can
    be set to `True`.
    """
    def _format(node):
        if isinstance(node, AST):
            fields = [(a, _format(b)) for a, b in iter_fields(node)]
            rv = '%s(%s' % (node.__class__.__name__, ', '.join(
                ('%s=%s' % field for field in fields)
                if annotate_fields else
                (b for a, b in fields)
            ))
            if include_attributes and node._attributes:
                rv += fields and ', ' or ' '
                rv += ', '.join('%s=%s' % (a, _format(getattr(node, a)))
                                for a in node._attributes)
            return rv + ')'
        elif isinstance(node, list):
            return '[%s]' % ', '.join(_format(x) for x in node)
        return repr(node)
    if not isinstance(node, AST):
        raise TypeError('expected AST, got %r' % node.__class__.__name__)
    return _format(node)

def copy_location(new_node, old_node):
    """Copy source location (`lineno` and `col_offset` attributes)
    from `old_node` to `new_node` if possible, and return `new_node`.
    """
    for attr in 'lineno', 'col_offset':
        if attr in old_node._attributes and attr in new_node._attributes \
           and hasattr(old_node, attr):
            setattr(new_node, attr, getattr(old_node, attr))
    return new_node

def fix_missing_locations(node):
    """When you compile a node tree with `compile()`, the compiler
    expects `lineno` and `col_offset` attributes for every node that
    supports them. This is rather tedious to fill in for generated
    nodes, so this helper adds these attributes recursively where not
    already set, by setting them to the values of the parent node. It
    works recursively starting at `node`.
    """
    def _fix(node, lineno, col_offset):
        if 'lineno' in node._attributes:
            if not hasattr(node, 'lineno'):
                node.lineno = lineno
            else:
                lineno = node.lineno
        if 'col_offset' in node._attributes:
            if not hasattr(node, 'col_offset'):
                node.col_offset = col_offset
            else:
                col_offset = node.col_offset
        for child in iter_child_nodes(node):
            _fix(child, lineno, col_offset)
    _fix(node, 1, 0)
    return node

def increment_lineno(node, n=1):
    '''Increment the line number of each node in the tree starting at
    `node` by `n`. This is useful to "move code" to a different
    location in a file.
    '''
    if 'lineno' in node._attributes:
        node.lineno = getattr(node, 'lineno', 0) + n
    for child in walk(node):
        if 'lineno' in child._attributes:
            child.lineno = getattr(child, 'lineno', 0) + n
    return node

def iter_fields(node):
    """Yield a tuple of `(fieldname, value)` for each field in
    `node._fields` that is present on `node`.
    """
    for field in node._fields:
        try:
            yield field, getattr(node, field)
        except AttributeError:
            pass

def iter_child_nodes(node):
    """Yield all direct child nodes of `node`, that is, all fields
    that are nodes and all items of fields that are lists of nodes.
    """
    for name, field in iter_fields(node):
        if isinstance(field, AST):
            yield field
        elif isinstance(field, list):
            for item in field:
                if isinstance(item, AST):
                    yield item

def get_docstring(node, clean=True):
    """Return the docstring for the given `node` or `None` if no
    docstring can be found. If the node provided does not have
    docstrings a `TypeError` will be raised.
    """
    if not isinstance(node, (FunctionDef, ClassDef, Module)):
        raise TypeError("%r can't have docstrings" % node.__class__.__name__)
    if node.body and isinstance(node.body[0], Expr) and \
       isinstance(node.body[0].value, Str):
        if clean:
            return inspect.cleandoc(node.body[0].value.s)
        return node.body[0].value.s

def walk(node):
    """Recursively yield all child nodes of `node`, in no specified
    order. This is useful if you only want to modify nodes in place
    and don't care about the context.
    """
    from collections import deque
    todo = deque([node])
    while todo:
        node = todo.popleft()
        todo.extend(iter_child_nodes(node))
        yield node

class NodeVisitor(object):
    """A node visitor base class that walks the abstract syntax tree
    and calls a visitor function for every node found. This function
    may return a value which is forwarded by the `visit` method.

    This class is meant to be subclassed, with the subclass adding
    visitor methods.

    Per default the visitor functions for the nodes are `visit_` +
    class name of the node. So a `TryFinally` node visit function
    would be `visit_TryFinally`. This behavior can be changed by
    overriding the `visit` method. If no visitor function exists for a
    node (return value `None`) the `generic_visit` visitor is used
    instead.

    Don't use the `NodeVisitor` if you want to apply changes to nodes
    during traversing. For this a special visitor exists
    (`NodeTransformer`) that allows modifications.
    """
    def visit(self, node):
        """Visit a node."""
        method = 'visit_' + node.__class__.__name__
        visitor = getattr(self, method, self.generic_visit)
        return visitor(node)
    def generic_visit(self, node):
        """Called if no explicit visitor function exists for a node."""
        for field, value in iter_fields(node):
            if isinstance(value, list):
                for item in value:
                    if isinstance(item, AST):
                        self.visit(item)
            elif isinstance(value, AST):
                self.visit(value)

class NodeTransformer(NodeVisitor):
    """A `NodeVisitor` subclass that walks the abstract syntax tree
    and allows modification of nodes.

    The `NodeTransformer` will walk the AST and use the return value
    of the visitor methods to replace or remove the old node. If the
    return value of the visitor method is `None`, the node will be
    removed from its location, otherwise it is replaced with the
    return value. The return value may be the original node in which
    case no replacement takes place.

    Here is an example transformer that rewrites all occurrences of
    name lookups (`foo`) to `data['foo']`:

        class RewriteName(NodeTransformer):
            def visit_Name(self, node):
                return copy_location(Subscript(
                    value=Name(id='data', ctx=Load()),
                    slice=Index(value=Str(s=node.id)),
                    ctx=node.ctx
                   ), node)

    Keep in mind that if the node you're operating on has child
    nodes you must either transform the child nodes yourself or call
    the `generic_visit` method for the node first.

    For nodes that were part of a collection of statements (that
    applies to all statement nodes), the visitor may also return a
    list of nodes rather than just a single node.

    Usually you use the transformer like this:

        node = YourTransformer().visit(node)

    """
    def generic_visit(self, node):
        for field, old_value in iter_fields(node):
            old_value = getattr(node, field, None)
            if isinstance(old_value, list):
                new_values = []
                for value in old_value:
                    if isinstance(value, AST):
                        value = self.visit(value)
                        if value is None:
                            continue
                        elif not isinstance(value, AST):
                            new_values.extend(value)
                            continue
                    new_values.append(value)
                old_value[:] = new_values
            elif isinstance(old_value, AST):
                new_node = self.visit(old_value)
                if new_node is None:
                    delattr(node, field)
                else:
                    setattr(node, field, new_node)
        return node

def _ast2ast (node) :
    new = globals()[node.__class__.__name__]()
    if not hasattr(node, "_fields") or node._fields is None :
        node._fields = ()
    for name, field in iter_fields(node) :
        new_field = field
        if field is None :
            new_field = None
        elif isinstance(field, AST) :
            new_field = _ast2ast(field)
        elif isinstance(field, list) :
            new_field = []
            for value in field :
                if isinstance(value, AST) :
                    new_field.append(_ast2ast(value))
                else :
                    new_field.append(value)
        setattr(new, name, new_field)
    copy_location(new, node)
    return new

def parse(expr, filename='<unknown>', mode='exec'):
    """Parse an expression into an AST node. Equivalent to
    `compile(expr, filename, mode, PyCF_ONLY_AST)`.
    """
    return _ast2ast(compile(expr, filename, mode, PyCF_ONLY_AST))