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from abc import ABCMeta
import os

from .downloader import get_resource

from typing import Optional

"""
A Resource object encapsulates a gem5 resource. Resources are items needed to
run a simulation, such as a disk image, kernel, or binary. The gem5 project
provides pre-built resources, with sources, at <resources.gem5.org>.

The purpose of this encapsulation is two fold:

1. It allows automatic retrieval of gem5 resources. E.g., specifying a resource
   which is not local will initiate a download.
2. It provides a location where code may be added to record the resources used
   within a simulation. At present this is a TODO work-item.
"""


class AbstractResource:

    __metaclass__ = ABCMeta

    def __init__(self, local_path: str):
        self._local_path = local_path

    def get_local_path(self) -> str:
        return self._local_path


class CustomResource(AbstractResource):
    """
    A custom gem5 resource. This can be used to encapsulate a resource provided
    by a gem5 user as opposed to one available within the gem5 resources
    repository.
    """

    def __init__(self, local_path: str):
        """
        :param local_path: The path of the resource on the host system.
        """
        super().__init__(local_path=local_path)


class Resource(AbstractResource):
    """
    An official gem5 resources as hosted within our gem5 resources repository
    (<resources.gem5.org>).

    A user need only specify the name of the resource during construction. The
    resource will be downloaded if needed. A list of available resources can
    be obtained via `downloader.list_resources()`.
    """

    def __init__(
        self,
        resource_name: str,
        resource_directory: Optional[str] = None,
        override: Optional[bool] = False,
    ):
        """
        :param resource_name: The name of the gem5 resource.
        :param resource_directory: The location of the directory in which the
        resource is to be stored.
        :param override: If the resource is present, but does not have the
        correct md5 value, the resoruce will be deleted and re-downloaded if
        this value is True. Otherwise an exception will be thrown. False by
        default.
        """

        if resource_directory != None:
            if not os.path.exists(resource_directory):
                os.makedirs(resource_directory)
            to_path = os.path.join(resource_directory, resource_name)
        else:
            to_path = resource_name

        super(Resource, self).__init__(local_path=to_path)
        get_resource(
            resource_name=resource_name, to_path=to_path, override=override
        )