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# copyright 2003-2015 LOGILAB S.A. (Paris, FRANCE), all rights reserved.

# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr

#

# This file is part of astroid.

#

# astroid is free software: you can redistribute it and/or modify it

# under the terms of the GNU Lesser General Public License as published by the

# Free Software Foundation, either version 2.1 of the License, or (at your

# option) any later version.

#

# astroid is distributed in the hope that it will be useful, but

# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License

# for more details.

#

# You should have received a copy of the GNU Lesser General Public License along

# with astroid. If not, see <http://www.gnu.org/licenses/>.

"""Small AST optimizations."""

import _ast

from astroid import nodes

__all__ = ('ASTPeepholeOptimizer', )

try:

    _TYPES = (_ast.Str, _ast.Bytes)

except AttributeError:

    _TYPES = (_ast.Str, )

class ASTPeepholeOptimizer(object):

    """Class for applying small optimizations to generate new AST."""

    def optimize_binop(self, node):

        """Optimize BinOps with string Const nodes on the lhs.

        This fixes an infinite recursion crash, where multiple

        strings are joined using the addition operator. With a

        sufficient number of such strings, astroid will fail

        with a maximum recursion limit exceeded. The

        function will return a Const node with all the strings

        already joined.

        Return ``None`` if no AST node can be obtained

        through optimization.

        """

        ast_nodes = []

        current = node

        while isinstance(current, _ast.BinOp):

            # lhs must be a BinOp with the addition operand.

            if not isinstance(current.left, _ast.BinOp):

                return

            if (not isinstance(current.left.op, _ast.Add)

                    or not isinstance(current.op, _ast.Add)):

                return

            # rhs must a str / bytes.

            if not isinstance(current.right, _TYPES):

                return

            ast_nodes.append(current.right.s)

            current = current.left

            if (isinstance(current, _ast.BinOp)

                    and isinstance(current.left, _TYPES)

                    and isinstance(current.right, _TYPES)):

                # Stop early if we are at the last BinOp in

                # the operation

                ast_nodes.append(current.right.s)

                ast_nodes.append(current.left.s)

                break

        if not ast_nodes:

            return

        # If we have inconsistent types, bail out.

        known = type(ast_nodes[0])

        if any(type(element) is not known

               for element in ast_nodes[1:]):

            return

        value = known().join(reversed(ast_nodes))

        newnode = nodes.Const(value)

        return newnode