from starlette.datastructures import Headers
from starlette.middleware.gzip import GZipResponder, IdentityResponder
from starlette.types import ASGIApp, Receive, Scope, Send


def _quality(accept_encoding: str, coding: str) -> float:
    qualities: dict[str, float] = {}
    for entry in accept_encoding.split(","):
        parts = [part.strip() for part in entry.split(";")]
        name = parts[0].lower()
        if not name:
            continue
        quality = 1.0
        for parameter in parts[1:]:
            key, separator, value = parameter.partition("=")
            if separator and key.strip().lower() == "q":
                try:
                    quality = float(value.strip())
                except ValueError:
                    quality = 0.0
        qualities[name] = quality
    return qualities.get(coding, qualities.get("*", 0.0))


class NegotiatedGZipMiddleware:
    """Compress substantial responses only when the client permits gzip."""

    def __init__(self, app: ASGIApp, minimum_size: int = 500, compresslevel: int = 9):
        self.app = app
        self.minimum_size = minimum_size
        self.compresslevel = compresslevel

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        if scope["type"] != "http":
            await self.app(scope, receive, send)
            return

        accepted = Headers(scope=scope).get("Accept-Encoding", "")
        if _quality(accepted, "gzip") > 0:
            responder: ASGIApp = GZipResponder(
                self.app, self.minimum_size, compresslevel=self.compresslevel
            )
        else:
            responder = IdentityResponder(self.app, self.minimum_size)
        await responder(scope, receive, send)