from_config.py

from copy import deepcopy
from functools import partial
import importlib
import json
import os
import re
import yaml

from ray.rllib.utils import force_list, merge_dicts


def from_config(cls, config=None, **kwargs):
    """
    Uses the given config to create an object.
    If `config` is a dict, an optional "type" key can be used as a
    "constructor hint" to specify a certain class of the object.
    If `config` is not a dict, `config`'s value is used directly as this
    "constructor hint".

    The rest of `config` (if it's a dict) will be used as kwargs for the
    constructor. Additional keys in **kwargs will always have precedence
    (overwrite keys in `config` (if a dict)).
    Also, if the config-dict or **kwargs contains the special key "_args",
    it will be popped from the dict and used as *args list to be passed
    separately to the constructor.

    The following constructor hints are valid:
    - None: Use `cls` as constructor.
    - An already instantiated object: Will be returned as is; no
        constructor call.
    - A string or an object that is a key in `cls`'s `__type_registry__`
        dict: The value in `__type_registry__` for that key will be used
        as the constructor.
    - A python callable: Use that very callable as constructor.
    - A string: Either a json/yaml filename or the name of a python
        module+class (e.g. "ray.rllib. [...] .[some class name]")

    Args:
        cls (class): The class to build an instance for (from `config`).
        config (Optional[dict,str]): The config dict or type-string or
            filename.

    Keyword Args:
        kwargs (any): Optional possibility to pass the constructor arguments in
            here and use `config` as the type-only info. Then we can call
            this like: from_config([type]?, [**kwargs for constructor])
            If `config` is already a dict, then `kwargs` will be merged
            with `config` (overwriting keys in `config`) after "type" has
            been popped out of `config`.
            If a constructor of a Configurable needs *args, the special
            key `_args` can be passed inside `kwargs` with a list value
            (e.g. kwargs={"_args": [arg1, arg2, arg3]}).

    Returns:
        any: The object generated from the config.
    """
    # `cls` is the config (config is None).
    if config is None and isinstance(cls, (dict, str)):
        config = cls
        cls = None
    # `config` is already a created object of this class ->
    # Take it as is.
    elif isinstance(cls, type) and isinstance(config, cls):
        return config

    # `type_`: Indicator for the Configurable's constructor.
    # `ctor_args`: *args arguments for the constructor.
    # `ctor_kwargs`: **kwargs arguments for the constructor.
    # Try to copy, so caller can reuse safely.
    try:
        config = deepcopy(config)
    except Exception:
        pass
    if isinstance(config, dict):
        type_ = config.pop("type", None)
        if type_ is None and isinstance(cls, str):
            type_ = cls
        ctor_kwargs = config
        # Give kwargs priority over things defined in config dict.
        # This way, one can pass a generic `spec` and then override single
        # constructor parameters via the kwargs in the call to `from_config`.
        ctor_kwargs.update(kwargs)
    else:
        type_ = config
        if type_ is None and "type" in kwargs:
            type_ = kwargs.pop("type")
        ctor_kwargs = kwargs
    # Special `_args` field in kwargs for *args-utilizing constructors.
    ctor_args = force_list(ctor_kwargs.pop("_args", []))

    # Figure out the actual constructor (class) from `type_`.
    # None: Try __default__object (if no args/kwargs), only then
    # constructor of cls (using args/kwargs).
    if type_ is None:
        # We have a default constructor that was defined directly by cls
        # (not by its children).
        if cls is not None and hasattr(cls, "__default_constructor__") and \
                cls.__default_constructor__ is not None and \
                ctor_args == [] and \
                (
                        not hasattr(cls.__bases__[0],
                                    "__default_constructor__")
                        or
                        cls.__bases__[0].__default_constructor__ is None or
                        cls.__bases__[0].__default_constructor__ is not
                        cls.__default_constructor__
                ):
            constructor = cls.__default_constructor__
            # Default constructor's keywords into ctor_kwargs.
            if isinstance(constructor, partial):
                kwargs = merge_dicts(ctor_kwargs, constructor.keywords)
                constructor = partial(constructor.func, **kwargs)
                ctor_kwargs = {}  # erase to avoid duplicate kwarg error
        # No default constructor -> Try cls itself as constructor.
        else:
            constructor = cls
    # Try the __type_registry__ of this class.
    else:
        constructor = lookup_type(cls, type_)

        # Found in cls.__type_registry__.
        if constructor is not None:
            pass
        # type_ is False or None (and this value is not registered) ->
        # return value of type_.
        elif type_ is False or type_ is None:
            return type_
        # Python callable.
        elif callable(type_):
            constructor = type_
        # A string: Filename or a python module+class or a json/yaml str.
        elif isinstance(type_, str):
            if re.search("\\.(yaml|yml|json)$", type_):
                return from_file(cls, type_, *ctor_args, **ctor_kwargs)
            # Try un-json/un-yaml'ing the string into a dict.
            obj = yaml.safe_load(type_)
            if isinstance(obj, dict):
                return from_config(cls, obj)
            try:
                obj = from_config(cls, json.loads(type_))
            except json.JSONDecodeError:
                pass
            else:
                return obj

            # Test for absolute module.class specifier.
            if type_.find(".") != -1:
                module_name, function_name = type_.rsplit(".", 1)
                try:
                    module = importlib.import_module(module_name)
                    constructor = getattr(module, function_name)
                except (ModuleNotFoundError, ImportError):
                    pass
            # If constructor still not found, try attaching cls' module,
            # then look for type_ in there.
            if constructor is None:
                try:
                    module = importlib.import_module(cls.__module__)
                    constructor = getattr(module, type_)
                except (ModuleNotFoundError, ImportError, AttributeError):
                    # Try the package as well.
                    try:
                        package_name = importlib.import_module(
                            cls.__module__).__package__
                        module = __import__(package_name, fromlist=[type_])
                        constructor = getattr(module, type_)
                    except (ModuleNotFoundError, ImportError, AttributeError):
                        pass
            if constructor is None:
                raise ValueError(
                    "String specifier ({}) in `from_config` must be a "
                    "filename, a module+class, a class within '{}', or a key "
                    "into {}.__type_registry__!".format(
                        type_, cls.__module__, cls.__name__))

    if not constructor:
        raise TypeError(
            "Invalid type '{}'. Cannot create `from_config`.".format(type_))

    # Create object with inferred constructor.
    try:
        object_ = constructor(*ctor_args, **ctor_kwargs)
    # Catch attempts to construct from an abstract class and return None.
    except TypeError as e:
        if re.match("Can't instantiate abstract class", e.args[0]):
            return None
        raise e  # Re-raise
    # No sanity check for fake (lambda)-"constructors".
    if type(constructor).__name__ != "function":
        assert isinstance(
            object_, constructor.func
            if isinstance(constructor, partial) else constructor)

    return object_


def from_file(cls, filename, *args, **kwargs):
    """
    Create object from config saved in filename. Expects json or yaml file.

    Args:
        filename (str): File containing the config (json or yaml).

    Returns:
        any: The object generated from the file.
    """
    path = os.path.join(os.getcwd(), filename)
    if not os.path.isfile(path):
        raise FileNotFoundError("File '{}' not found!".format(filename))

    with open(path, "rt") as fp:
        if path.endswith(".yaml") or path.endswith(".yml"):
            config = yaml.safe_load(fp)
        else:
            config = json.load(fp)

    # Add possible *args.
    config["_args"] = args
    return from_config(cls, config=config, **kwargs)


def lookup_type(cls, type_):
    if cls is not None and hasattr(cls, "__type_registry__") and \
            isinstance(cls.__type_registry__, dict) and (
            type_ in cls.__type_registry__ or (
            isinstance(type_, str) and
            re.sub("[\\W_]", "", type_.lower()) in cls.__type_registry__)):
        available_class_for_type = cls.__type_registry__.get(type_)
        if available_class_for_type is None:
            available_class_for_type = \
                cls.__type_registry__[re.sub("[\\W_]", "", type_.lower())]
        return available_class_for_type
    return None