"""Fixer for 'raise E, V, T'

raise         -> raise

raise E       -> raise E

raise E, V    -> raise E(V)

raise E, V, T -> raise E(V).with_traceback(T)

raise (((E, E'), E''), E'''), V -> raise E(V)

raise "foo", V, T               -> warns about string exceptions

CAVEATS:

1) "raise E, V" will be incorrectly translated if V is an exception

   instance. The correct Python 3 idiom is

        raise E from V

   but since we can't detect instance-hood by syntax alone and since

   any client code would have to be changed as well, we don't automate

   this.

"""

# Author: Collin Winter

# Local imports

from .. import pytree

from ..pgen2 import token

from .. import fixer_base

from ..fixer_util import Name, Call, Attr, ArgList, is_tuple

class FixRaise(fixer_base.BaseFix):

    PATTERN = """

    raise_stmt< 'raise' exc=any [',' val=any [',' tb=any]] >

    """

    def transform(self, node, results):

        syms = self.syms

        exc = results["exc"].clone()

        if exc.type is token.STRING:

            self.cannot_convert(node, "Python 3 does not support string exceptions")

            return

        # Python 2 supports

        #  raise ((((E1, E2), E3), E4), E5), V

        # as a synonym for

        #  raise E1, V

        # Since Python 3 will not support this, we recurse down any tuple

        # literals, always taking the first element.

        if is_tuple(exc):

            while is_tuple(exc):

                # exc.children[1:-1] is the unparenthesized tuple

                # exc.children[1].children[0] is the first element of the tuple

                exc = exc.children[1].children[0].clone()

            exc.set_prefix(" ")

        if "val" not in results:

            # One-argument raise

            new = pytree.Node(syms.raise_stmt, [Name("raise"), exc])

            new.set_prefix(node.get_prefix())

            return new

        val = results["val"].clone()

        if is_tuple(val):

            args = [c.clone() for c in val.children[1:-1]]

        else:

            val.set_prefix("")

            args = [val]

        if "tb" in results:

            tb = results["tb"].clone()

            tb.set_prefix("")

            e = Call(exc, args)

            with_tb = Attr(e, Name('with_traceback')) + [ArgList([tb])]

            new = pytree.Node(syms.simple_stmt, [Name("raise")] + with_tb)

            new.set_prefix(node.get_prefix())

            return new

        else:

            return pytree.Node(syms.raise_stmt,

                               [Name("raise"), Call(exc, args)],

                               prefix=node.get_prefix())