import gzip
import io

from starlette.datastructures import Headers, MutableHeaders
from starlette.types import ASGIApp, Message, Receive, Scope, Send


class GZipMiddleware:
    def __init__(self, app: ASGIApp, minimum_size: int = 500) -> None:
        self.app = app
        self.minimum_size = minimum_size

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        if scope["type"] == "http":
            headers = Headers(scope=scope)
            if "gzip" in headers.get("Accept-Encoding", ""):
                responder = GZipResponder(self.app, self.minimum_size)
                await responder(scope, receive, send)
                return
        await self.app(scope, receive, send)


class GZipResponder:
    def __init__(self, app: ASGIApp, minimum_size: int) -> None:
        self.app = app
        self.minimum_size = minimum_size
        self.send = unattached_send  # type: Send
        self.initial_message = {}  # type: Message
        self.started = False
        self.gzip_buffer = io.BytesIO()
        self.gzip_file = gzip.GzipFile(mode="wb", fileobj=self.gzip_buffer)

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        self.send = send
        await self.app(scope, receive, self.send_with_gzip)

    async def send_with_gzip(self, message: Message) -> None:
        message_type = message["type"]
        if message_type == "http.response.start":
            # Don't send the initial message until we've determined how to
            # modify the ougoging headers correctly.
            self.initial_message = message
        elif message_type == "http.response.body" and not self.started:
            self.started = True
            body = message.get("body", b"")
            more_body = message.get("more_body", False)
            if len(body) < self.minimum_size and not more_body:
                # Don't apply GZip to small outgoing responses.
                await self.send(self.initial_message)
                await self.send(message)
            elif not more_body:
                # Standard GZip response.
                self.gzip_file.write(body)
                self.gzip_file.close()
                body = self.gzip_buffer.getvalue()

                headers = MutableHeaders(raw=self.initial_message["headers"])
                headers["Content-Encoding"] = "gzip"
                headers["Content-Length"] = str(len(body))
                headers.add_vary_header("Accept-Encoding")
                message["body"] = body

                await self.send(self.initial_message)
                await self.send(message)
            else:
                # Initial body in streaming GZip response.
                headers = MutableHeaders(raw=self.initial_message["headers"])
                headers["Content-Encoding"] = "gzip"
                headers.add_vary_header("Accept-Encoding")
                del headers["Content-Length"]

                self.gzip_file.write(body)
                message["body"] = self.gzip_buffer.getvalue()
                self.gzip_buffer.seek(0)
                self.gzip_buffer.truncate()

                await self.send(self.initial_message)
                await self.send(message)

        elif message_type == "http.response.body":
            # Remaining body in streaming GZip response.
            body = message.get("body", b"")
            more_body = message.get("more_body", False)

            self.gzip_file.write(body)
            if not more_body:
                self.gzip_file.close()

            message["body"] = self.gzip_buffer.getvalue()
            self.gzip_buffer.seek(0)
            self.gzip_buffer.truncate()

            await self.send(message)


async def unattached_send(message: Message) -> None:
    raise RuntimeError("send awaitable not set")  # pragma: no cover