import os
import ssl

from typing import Iterable, Optional, Union

from sanic.log import logger


# Only allow secure ciphers, notably leaving out AES-CBC mode
# OpenSSL chooses ECDSA or RSA depending on the cert in use
CIPHERS_TLS12 = [
    "ECDHE-ECDSA-CHACHA20-POLY1305",
    "ECDHE-ECDSA-AES256-GCM-SHA384",
    "ECDHE-ECDSA-AES128-GCM-SHA256",
    "ECDHE-RSA-CHACHA20-POLY1305",
    "ECDHE-RSA-AES256-GCM-SHA384",
    "ECDHE-RSA-AES128-GCM-SHA256",
]


def create_context(
    certfile: Optional[str] = None,
    keyfile: Optional[str] = None,
    password: Optional[str] = None,
) -> ssl.SSLContext:
    """Create a context with secure crypto and HTTP/1.1 in protocols."""
    context = ssl.create_default_context(purpose=ssl.Purpose.CLIENT_AUTH)
    context.minimum_version = ssl.TLSVersion.TLSv1_2
    context.set_ciphers(":".join(CIPHERS_TLS12))
    context.set_alpn_protocols(["http/1.1"])
    context.sni_callback = server_name_callback
    if certfile and keyfile:
        context.load_cert_chain(certfile, keyfile, password)
    return context


def shorthand_to_ctx(
    ctxdef: Union[None, ssl.SSLContext, dict, str]
) -> Optional[ssl.SSLContext]:
    """Convert an ssl argument shorthand to an SSLContext object."""
    if ctxdef is None or isinstance(ctxdef, ssl.SSLContext):
        return ctxdef
    if isinstance(ctxdef, str):
        return load_cert_dir(ctxdef)
    if isinstance(ctxdef, dict):
        return CertSimple(**ctxdef)
    raise ValueError(
        f"Invalid ssl argument {type(ctxdef)}."
        " Expecting a list of certdirs, a dict or an SSLContext."
    )


def process_to_context(
    ssldef: Union[None, ssl.SSLContext, dict, str, list, tuple]
) -> Optional[ssl.SSLContext]:
    """Process app.run ssl argument from easy formats to full SSLContext."""
    return (
        CertSelector(map(shorthand_to_ctx, ssldef))
        if isinstance(ssldef, (list, tuple))
        else shorthand_to_ctx(ssldef)
    )


def load_cert_dir(p: str) -> ssl.SSLContext:
    if os.path.isfile(p):
        raise ValueError(f"Certificate folder expected but {p} is a file.")
    keyfile = os.path.join(p, "privkey.pem")
    certfile = os.path.join(p, "fullchain.pem")
    if not os.access(keyfile, os.R_OK):
        raise ValueError(
            f"Certificate not found or permission denied {keyfile}"
        )
    if not os.access(certfile, os.R_OK):
        raise ValueError(
            f"Certificate not found or permission denied {certfile}"
        )
    return CertSimple(certfile, keyfile)


class CertSimple(ssl.SSLContext):
    """A wrapper for creating SSLContext with a sanic attribute."""

    def __new__(cls, cert, key, **kw):
        # try common aliases, rename to cert/key
        certfile = kw["cert"] = kw.pop("certificate", None) or cert
        keyfile = kw["key"] = kw.pop("keyfile", None) or key
        password = kw.pop("password", None)
        if not certfile or not keyfile:
            raise ValueError("SSL dict needs filenames for cert and key.")
        subject = {}
        if "names" not in kw:
            cert = ssl._ssl._test_decode_cert(certfile)  # type: ignore
            kw["names"] = [
                name
                for t, name in cert["subjectAltName"]
                if t in ["DNS", "IP Address"]
            ]
            subject = {k: v for item in cert["subject"] for k, v in item}
        self = create_context(certfile, keyfile, password)
        self.__class__ = cls
        self.sanic = {**subject, **kw}
        return self

    def __init__(self, cert, key, **kw):
        pass  # Do not call super().__init__ because it is already initialized


class CertSelector(ssl.SSLContext):
    """Automatically select SSL certificate based on the hostname that the
    client is trying to access, via SSL SNI. Paths to certificate folders
    with privkey.pem and fullchain.pem in them should be provided, and
    will be matched in the order given whenever there is a new connection.
    """

    def __new__(cls, ctxs):
        return super().__new__(cls)

    def __init__(self, ctxs: Iterable[Optional[ssl.SSLContext]]):
        super().__init__()
        self.sni_callback = selector_sni_callback  # type: ignore
        self.sanic_select = []
        self.sanic_fallback = None
        all_names = []
        for i, ctx in enumerate(ctxs):
            if not ctx:
                continue
            names = dict(getattr(ctx, "sanic", {})).get("names", [])
            all_names += names
            self.sanic_select.append(ctx)
            if i == 0:
                self.sanic_fallback = ctx
        if not all_names:
            raise ValueError(
                "No certificates with SubjectAlternativeNames found."
            )
        logger.info(f"Certificate vhosts: {', '.join(all_names)}")


def find_cert(self: CertSelector, server_name: str):
    """Find the first certificate that matches the given SNI.

    :raises ssl.CertificateError: No matching certificate found.
    :return: A matching ssl.SSLContext object if found."""
    if not server_name:
        if self.sanic_fallback:
            return self.sanic_fallback
        raise ValueError(
            "The client provided no SNI to match for certificate."
        )
    for ctx in self.sanic_select:
        if match_hostname(ctx, server_name):
            return ctx
    if self.sanic_fallback:
        return self.sanic_fallback
    raise ValueError(f"No certificate found matching hostname {server_name!r}")


def match_hostname(
    ctx: Union[ssl.SSLContext, CertSelector], hostname: str
) -> bool:
    """Match names from CertSelector against a received hostname."""
    # Local certs are considered trusted, so this can be less pedantic
    # and thus faster than the deprecated ssl.match_hostname function is.
    names = dict(getattr(ctx, "sanic", {})).get("names", [])
    hostname = hostname.lower()
    for name in names:
        if name.startswith("*."):
            if hostname.split(".", 1)[-1] == name[2:]:
                return True
        elif name == hostname:
            return True
    return False


def selector_sni_callback(
    sslobj: ssl.SSLObject, server_name: str, ctx: CertSelector
) -> Optional[int]:
    """Select a certificate mathing the SNI."""
    # Call server_name_callback to store the SNI on sslobj
    server_name_callback(sslobj, server_name, ctx)
    # Find a new context matching the hostname
    try:
        sslobj.context = find_cert(ctx, server_name)
    except ValueError as e:
        logger.warning(f"Rejecting TLS connection: {e}")
        # This would show ERR_SSL_UNRECOGNIZED_NAME_ALERT on client side if
        # asyncio/uvloop did proper SSL shutdown. They don't.
        return ssl.ALERT_DESCRIPTION_UNRECOGNIZED_NAME
    return None  # mypy complains without explicit return


def server_name_callback(
    sslobj: ssl.SSLObject, server_name: str, ctx: ssl.SSLContext
) -> None:
    """Store the received SNI as sslobj.sanic_server_name."""
    sslobj.sanic_server_name = server_name  # type: ignore