import importlib.util
import os
import stat
import typing
from email.utils import parsedate

import anyio

from starlette.datastructures import URL, Headers
from starlette.exceptions import HTTPException
from starlette.responses import FileResponse, RedirectResponse, Response
from starlette.types import Receive, Scope, Send

PathLike = typing.Union[str, "os.PathLike[str]"]


class NotModifiedResponse(Response):
    NOT_MODIFIED_HEADERS = (
        "cache-control",
        "content-location",
        "date",
        "etag",
        "expires",
        "vary",
    )

    def __init__(self, headers: Headers):
        super().__init__(
            status_code=304,
            headers={
                name: value
                for name, value in headers.items()
                if name in self.NOT_MODIFIED_HEADERS
            },
        )


class StaticFiles:
    def __init__(
        self,
        *,
        directory: typing.Optional[PathLike] = None,
        packages: typing.Optional[
            typing.List[typing.Union[str, typing.Tuple[str, str]]]
        ] = None,
        html: bool = False,
        check_dir: bool = True,
        follow_symlink: bool = False,
    ) -> None:
        self.directory = directory
        self.packages = packages
        self.all_directories = self.get_directories(directory, packages)
        self.html = html
        self.config_checked = False
        self.follow_symlink = follow_symlink
        if check_dir and directory is not None and not os.path.isdir(directory):
            raise RuntimeError(f"Directory '{directory}' does not exist")

    def get_directories(
        self,
        directory: typing.Optional[PathLike] = None,
        packages: typing.Optional[
            typing.List[typing.Union[str, typing.Tuple[str, str]]]
        ] = None,
    ) -> typing.List[PathLike]:
        """
        Given `directory` and `packages` arguments, return a list of all the
        directories that should be used for serving static files from.
        """
        directories = []
        if directory is not None:
            directories.append(directory)

        for package in packages or []:
            if isinstance(package, tuple):
                package, statics_dir = package
            else:
                statics_dir = "statics"
            spec = importlib.util.find_spec(package)
            assert spec is not None, f"Package {package!r} could not be found."
            assert spec.origin is not None, f"Package {package!r} could not be found."
            package_directory = os.path.normpath(
                os.path.join(spec.origin, "..", statics_dir)
            )
            assert os.path.isdir(
                package_directory
            ), f"Directory '{statics_dir!r}' in package {package!r} could not be found."
            directories.append(package_directory)

        return directories

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        """
        The ASGI entry point.
        """
        assert scope["type"] == "http"

        if not self.config_checked:
            await self.check_config()
            self.config_checked = True

        path = self.get_path(scope)
        response = await self.get_response(path, scope)
        await response(scope, receive, send)

    def get_path(self, scope: Scope) -> str:
        """
        Given the ASGI scope, return the `path` string to serve up,
        with OS specific path separators, and any '..', '.' components removed.
        """
        return os.path.normpath(os.path.join(*scope["path"].split("/")))

    async def get_response(self, path: str, scope: Scope) -> Response:
        """
        Returns an HTTP response, given the incoming path, method and request headers.
        """
        if scope["method"] not in ("GET", "HEAD"):
            raise HTTPException(status_code=405)

        try:
            full_path, stat_result = await anyio.to_thread.run_sync(
                self.lookup_path, path
            )
        except PermissionError:
            raise HTTPException(status_code=401)
        except OSError:
            raise

        if stat_result and stat.S_ISREG(stat_result.st_mode):
            # We have a static file to serve.
            return self.file_response(full_path, stat_result, scope)

        elif stat_result and stat.S_ISDIR(stat_result.st_mode) and self.html:
            # We're in HTML mode, and have got a directory URL.
            # Check if we have 'index.html' file to serve.
            index_path = os.path.join(path, "index.html")
            full_path, stat_result = await anyio.to_thread.run_sync(
                self.lookup_path, index_path
            )
            if stat_result is not None and stat.S_ISREG(stat_result.st_mode):
                if not scope["path"].endswith("/"):
                    # Directory URLs should redirect to always end in "/".
                    url = URL(scope=scope)
                    url = url.replace(path=url.path + "/")
                    return RedirectResponse(url=url)
                return self.file_response(full_path, stat_result, scope)

        if self.html:
            # Check for '404.html' if we're in HTML mode.
            full_path, stat_result = await anyio.to_thread.run_sync(
                self.lookup_path, "404.html"
            )
            if stat_result and stat.S_ISREG(stat_result.st_mode):
                return FileResponse(
                    full_path,
                    stat_result=stat_result,
                    method=scope["method"],
                    status_code=404,
                )
        raise HTTPException(status_code=404)

    def lookup_path(
        self, path: str
    ) -> typing.Tuple[str, typing.Optional[os.stat_result]]:
        for directory in self.all_directories:
            joined_path = os.path.join(directory, path)
            if self.follow_symlink:
                full_path = os.path.abspath(joined_path)
            else:
                full_path = os.path.realpath(joined_path)
            directory = os.path.realpath(directory)
            if os.path.commonprefix([full_path, directory]) != directory:
                # Don't allow misbehaving clients to break out of the static files
                # directory.
                continue
            try:
                return full_path, os.stat(full_path)
            except (FileNotFoundError, NotADirectoryError):
                continue
        return "", None

    def file_response(
        self,
        full_path: PathLike,
        stat_result: os.stat_result,
        scope: Scope,
        status_code: int = 200,
    ) -> Response:
        method = scope["method"]
        request_headers = Headers(scope=scope)

        response = FileResponse(
            full_path, status_code=status_code, stat_result=stat_result, method=method
        )
        if self.is_not_modified(response.headers, request_headers):
            return NotModifiedResponse(response.headers)
        return response

    async def check_config(self) -> None:
        """
        Perform a one-off configuration check that StaticFiles is actually
        pointed at a directory, so that we can raise loud errors rather than
        just returning 404 responses.
        """
        if self.directory is None:
            return

        try:
            stat_result = await anyio.to_thread.run_sync(os.stat, self.directory)
        except FileNotFoundError:
            raise RuntimeError(
                f"StaticFiles directory '{self.directory}' does not exist."
            )
        if not (stat.S_ISDIR(stat_result.st_mode) or stat.S_ISLNK(stat_result.st_mode)):
            raise RuntimeError(
                f"StaticFiles path '{self.directory}' is not a directory."
            )

    def is_not_modified(
        self, response_headers: Headers, request_headers: Headers
    ) -> bool:
        """
        Given the request and response headers, return `True` if an HTTP
        "Not Modified" response could be returned instead.
        """
        try:
            if_none_match = request_headers["if-none-match"]
            etag = response_headers["etag"]
            if if_none_match == etag:
                return True
        except KeyError:
            pass

        try:
            if_modified_since = parsedate(request_headers["if-modified-since"])
            last_modified = parsedate(response_headers["last-modified"])
            if (
                if_modified_since is not None
                and last_modified is not None
                and if_modified_since >= last_modified
            ):
                return True
        except KeyError:
            pass

        return False
