# Copyright 2016 Pants project contributors (see CONTRIBUTORS.md).
# Licensed under the Apache License, Version 2.0 (see LICENSE).

from pants.base.exceptions import TargetDefinitionException
from pants.build_graph.build_file_aliases import TargetMacro
from pants.build_graph.target import Target


class AliasTarget(Target):
    """A target that gets replaced by its dependencies."""


class AliasTargetMacro(TargetMacro):
    """Macro for creating target aliases."""

    def __init__(self, parse_context):
        self._parse_context = parse_context

    def expand(self, name=None, target=None, **kwargs):
        """
        :param string name: The name for this alias.
        :param string target: The address of the destination target.
        """
        if name is None:
            raise TargetDefinitionException(
                "{}:?".format(self._parse_context.rel_path), "The alias() must have a name!"
            )
        if target is None:
            raise TargetDefinitionException(
                "{}:{}".format(self._parse_context.rel_path, name),
                'The alias() must have a "target" parameter.',
            )
        self._parse_context.create_object(
            AliasTarget,
            type_alias="alias",
            name=name,
            dependencies=[target] if target else [],
            **kwargs
        )


class AliasTargetFactory(TargetMacro.Factory):
    """Creates an alias for a target, so that it can be referred to with another spec.

    Note that this does not current work with deferred source (from_target()); you must still use
    the target's actual address in that case.
    """

    @property
    def target_types(self):
        return {AliasTarget}

    def macro(self, parse_context):
        return AliasTargetMacro(parse_context)