from __future__ import annotations

import atexit
import threading
import time
from contextlib import contextmanager
from functools import cached_property
from http import HTTPStatus
from typing import TYPE_CHECKING, Any, ClassVar, Generic, Protocol, TypeVar

import requests
from requests.adapters import HTTPAdapter
from urllib3.util.retry import Retry

from beets import __version__

if TYPE_CHECKING:
    from collections.abc import Iterator


class BeetsHTTPError(requests.exceptions.HTTPError):
    STATUS: ClassVar[HTTPStatus]

    def __init__(self, *args, **kwargs) -> None:
        super().__init__(
            f"HTTP Error: {self.STATUS.value} {self.STATUS.phrase}",
            *args,
            **kwargs,
        )


class HTTPNotFoundError(BeetsHTTPError):
    STATUS = HTTPStatus.NOT_FOUND


class Closeable(Protocol):
    """Protocol for objects that have a close method."""

    def close(self) -> None: ...


C = TypeVar("C", bound=Closeable)


class SingletonMeta(type, Generic[C]):
    """Metaclass ensuring a single shared instance per class.

    Creates one instance per class type on first instantiation, reusing it
    for all subsequent calls. Automatically registers cleanup on program exit
    for proper resource management.
    """

    _instances: ClassVar[dict[type[Any], Any]] = {}
    _lock: ClassVar[threading.Lock] = threading.Lock()

    def __call__(cls, *args: Any, **kwargs: Any) -> C:
        if cls not in cls._instances:
            with cls._lock:
                if cls not in SingletonMeta._instances:
                    instance = super().__call__(*args, **kwargs)
                    SingletonMeta._instances[cls] = instance
                    atexit.register(instance.close)
        return SingletonMeta._instances[cls]


class TimeoutAndRetrySession(requests.Session, metaclass=SingletonMeta):
    """HTTP session with sensible defaults.

    * default beets User-Agent header
    * default request timeout
    * automatic retries on transient connection or server errors
    * raises exceptions for HTTP error status codes
    """

    def __init__(self, *args, **kwargs) -> None:
        super().__init__(*args, **kwargs)
        self.headers["User-Agent"] = f"beets/{__version__} https://beets.io/"

        retry = Retry(
            total=6,
            backoff_factor=0.5,
            # Retry on server errors
            status_forcelist=[
                HTTPStatus.INTERNAL_SERVER_ERROR,
                HTTPStatus.BAD_GATEWAY,
                HTTPStatus.SERVICE_UNAVAILABLE,
                HTTPStatus.GATEWAY_TIMEOUT,
            ],
        )
        adapter = HTTPAdapter(max_retries=retry)
        self.mount("https://", adapter)
        self.mount("http://", adapter)

    def request(self, *args, **kwargs):
        """Execute HTTP request with automatic timeout and status validation.

        Ensures all requests have a timeout (defaults to 10 seconds) and raises
        an exception for HTTP error status codes.
        """
        kwargs.setdefault("timeout", 10)
        r = super().request(*args, **kwargs)
        r.raise_for_status()

        return r


class RateLimitAdapter(HTTPAdapter):
    """HTTPAdapter that enforces minimum interval between requests.

    Prevents server overload and 429 errors by sleeping when requests
    come too fast. Thread-safe via lock.

    Attributes:
        rate_limit: Minimum seconds between requests. Default 0.25 (4/sec).

    Override `_wait_time()` for custom strategies (token bucket, burst, etc.).
    """

    def __init__(self, rate_limit: float = 0.25, **kwargs):
        super().__init__(**kwargs)
        self.rate_limit = rate_limit
        self._last_request_time = 0.0
        self._lock = threading.Lock()

    def _wait_time(self, elapsed: float) -> float:
        """Return seconds to wait. Override for custom rate limiting."""
        return max(0, self.rate_limit - elapsed)

    def send(self, request: requests.PreparedRequest, *args, **kwargs):
        with self._lock:
            elapsed = time.monotonic() - self._last_request_time
            wait = self._wait_time(elapsed)
            if wait > 0:
                time.sleep(wait)
            self._last_request_time = time.monotonic()
        return super().send(request, *args, **kwargs)


class RequestHandler:
    """Manages HTTP requests with custom error handling and session management.

    Provides a reusable interface for making HTTP requests with automatic
    conversion of standard HTTP errors to beets-specific exceptions. Supports
    custom session types and error mappings that can be overridden by
    subclasses.

    Usage:
        Subclass and override :class:`RequestHandler.create_session`,
        :class:`RequestHandler.explicit_http_errors` or
        :class:`RequestHandler.status_to_error()` to customize behavior.

    Use

    - :class:`RequestHandler.get_json()` to get JSON response data
    - :class:`RequestHandler.get()` to get HTTP response object
    - :class:`RequestHandler.request()` to invoke arbitrary HTTP methods

    Feel free to define common methods that are used in multiple plugins.
    """

    #: List of custom exceptions to be raised for specific status codes.
    explicit_http_errors: ClassVar[list[type[BeetsHTTPError]]] = [
        HTTPNotFoundError
    ]

    def create_session(self) -> TimeoutAndRetrySession:
        """Create a new HTTP session instance.

        Can be overridden by subclasses to provide custom session types.
        """
        return TimeoutAndRetrySession()

    @cached_property
    def session(self) -> TimeoutAndRetrySession:
        return self.create_session()

    def status_to_error(
        self, code: int
    ) -> type[requests.exceptions.HTTPError] | None:
        """Map HTTP status codes to beets-specific exception types.

        Searches the configured explicit HTTP errors for a matching status code.
        Returns None if no specific error type is registered for the given code.
        """
        return next(
            (e for e in self.explicit_http_errors if e.STATUS == code), None
        )

    @contextmanager
    def handle_http_error(self) -> Iterator[None]:
        """Convert standard HTTP errors to beets-specific exceptions.

        Wraps operations that may raise HTTPError, automatically translating
        recognized status codes into their corresponding beets exception types.
        Unrecognized errors are re-raised unchanged.
        """
        try:
            yield
        except requests.exceptions.HTTPError as e:
            if beets_error := self.status_to_error(e.response.status_code):
                raise beets_error(response=e.response) from e

            raise

    def request(self, *args, **kwargs) -> requests.Response:
        """Perform HTTP request using the session with automatic error handling.

        Delegates to the underlying session method while converting recognized
        HTTP errors to beets-specific exceptions through the error handler.
        """
        with self.handle_http_error():
            return self.session.request(*args, **kwargs)

    def get(self, *args, **kwargs) -> requests.Response:
        """Perform HTTP GET request with automatic error handling."""
        return self.request("get", *args, **kwargs)

    def put(self, *args, **kwargs) -> requests.Response:
        """Perform HTTP PUT request with automatic error handling."""
        return self.request("put", *args, **kwargs)

    def delete(self, *args, **kwargs) -> requests.Response:
        """Perform HTTP DELETE request with automatic error handling."""
        return self.request("delete", *args, **kwargs)

    def get_json(self, *args, **kwargs):
        """Fetch and parse JSON data from an HTTP endpoint."""
        return self.get(*args, **kwargs).json()
