# Copyright The OpenTelemetry Authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from __future__ import annotations

import logging
import typing
from contextvars import Token
from os import environ
from uuid import uuid4

# pylint: disable=wrong-import-position
from opentelemetry.context.context import Context, _RuntimeContext  # noqa
from opentelemetry.environment_variables import OTEL_PYTHON_CONTEXT
from opentelemetry.util._importlib_metadata import entry_points

logger = logging.getLogger(__name__)


def _load_runtime_context() -> _RuntimeContext:
    """Initialize the RuntimeContext

    Returns:
        An instance of RuntimeContext.
    """

    # FIXME use a better implementation of a configuration manager
    # to avoid having to get configuration values straight from
    # environment variables
    default_context = "contextvars_context"

    configured_context = environ.get(OTEL_PYTHON_CONTEXT, default_context)  # type: str

    try:
        return next(  # type: ignore
            iter(  # type: ignore
                entry_points(  # type: ignore
                    group="opentelemetry_context",
                    name=configured_context,
                )
            )
        ).load()()
    except Exception:  # pylint: disable=broad-exception-caught
        logger.exception(
            "Failed to load context: %s, fallback to %s",
            configured_context,
            default_context,
        )
        return next(  # type: ignore
            iter(  # type: ignore
                entry_points(  # type: ignore
                    group="opentelemetry_context",
                    name=default_context,
                )
            )
        ).load()()


_RUNTIME_CONTEXT = _load_runtime_context()


def create_key(keyname: str) -> str:
    """To allow cross-cutting concern to control access to their local state,
    the RuntimeContext API provides a function which takes a keyname as input,
    and returns a unique key.
    Args:
        keyname: The key name is for debugging purposes and is not required to be unique.
    Returns:
        A unique string representing the newly created key.
    """
    return keyname + "-" + str(uuid4())


def get_value(key: str, context: typing.Optional[Context] = None) -> "object":
    """To access the local state of a concern, the RuntimeContext API
    provides a function which takes a context and a key as input,
    and returns a value.

    Args:
        key: The key of the value to retrieve.
        context: The context from which to retrieve the value, if None, the current context is used.

    Returns:
        The value associated with the key.
    """
    return context.get(key) if context is not None else get_current().get(key)


def set_value(
    key: str, value: "object", context: typing.Optional[Context] = None
) -> Context:
    """To record the local state of a cross-cutting concern, the
    RuntimeContext API provides a function which takes a context, a
    key, and a value as input, and returns an updated context
    which contains the new value.

    Args:
        key: The key of the entry to set.
        value: The value of the entry to set.
        context: The context to copy, if None, the current context is used.

    Returns:
        A new `Context` containing the value set.
    """
    if context is None:
        context = get_current()
    new_values = context.copy()
    new_values[key] = value
    return Context(new_values)


def get_current() -> Context:
    """To access the context associated with program execution,
    the Context API provides a function which takes no arguments
    and returns a Context.

    Returns:
        The current `Context` object.
    """
    return _RUNTIME_CONTEXT.get_current()


def attach(context: Context) -> Token[Context]:
    """Associates a Context with the caller's current execution unit. Returns
    a token that can be used to restore the previous Context.

    Args:
        context: The Context to set as current.

    Returns:
        A token that can be used with `detach` to reset the context.
    """
    return _RUNTIME_CONTEXT.attach(context)


def detach(token: Token[Context]) -> None:
    """Resets the Context associated with the caller's current execution unit
    to the value it had before attaching a specified Context.

    Args:
        token: The Token that was returned by a previous call to attach a Context.
    """
    try:
        _RUNTIME_CONTEXT.detach(token)
    except Exception:  # pylint: disable=broad-exception-caught
        logger.exception("Failed to detach context")


# FIXME This is a temporary location for the suppress instrumentation key.
# Once the decision around how to suppress instrumentation is made in the
# spec, this key should be moved accordingly.
_SUPPRESS_INSTRUMENTATION_KEY = create_key("suppress_instrumentation")
_SUPPRESS_HTTP_INSTRUMENTATION_KEY = create_key(
    "suppress_http_instrumentation"
)

__all__ = [
    "Context",
    "attach",
    "create_key",
    "detach",
    "get_current",
    "get_value",
    "set_value",
]