#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright 2020 The Matrix.org Foundation C.I.C.
# Copyright 2014-2016 OpenMarket Ltd
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#

import collections.abc
import hashlib
import logging
from typing import Any, Callable

from canonicaljson import encode_canonical_json
from signedjson.sign import sign_json
from signedjson.types import SigningKey, VerifyKey
from unpaddedbase64 import decode_base64, encode_base64

from synapse.api.errors import Codes, SynapseError
from synapse.api.room_versions import RoomVersion
from synapse.events import EventBase
from synapse.events.utils import prune_event, prune_event_dict
from synapse.logging.opentracing import trace
from synapse.types import JsonDict, UserID

logger = logging.getLogger(__name__)

Hasher = Callable[[bytes], "hashlib._Hash"]


@trace
def check_event_content_hash(
    event: EventBase, hash_algorithm: Hasher = hashlib.sha256
) -> bool:
    """Check whether the hash for this PDU matches the contents"""
    name, expected_hash = compute_content_hash(event.get_pdu_json(), hash_algorithm)
    logger.debug(
        "Verifying content hash on %s (expecting: %s)",
        event.event_id,
        encode_base64(expected_hash),
    )

    # some malformed events lack a 'hashes'. Protect against it being missing
    # or a weird type by basically treating it the same as an unhashed event.
    hashes = event.get("hashes")
    # nb it might be a immutabledict or a dict
    if not isinstance(hashes, collections.abc.Mapping):
        raise SynapseError(
            400, "Malformed 'hashes': %s" % (type(hashes),), Codes.UNAUTHORIZED
        )

    if name not in hashes:
        raise SynapseError(
            400,
            "Algorithm %s not in hashes %s" % (name, list(hashes)),
            Codes.UNAUTHORIZED,
        )
    message_hash_base64 = hashes[name]
    try:
        message_hash_bytes = decode_base64(message_hash_base64)
    except Exception:
        raise SynapseError(
            400, "Invalid base64: %s" % (message_hash_base64,), Codes.UNAUTHORIZED
        )
    return message_hash_bytes == expected_hash


def compute_content_hash(
    event_dict: dict[str, Any], hash_algorithm: Hasher
) -> tuple[str, bytes]:
    """Compute the content hash of an event, which is the hash of the
    unredacted event.

    Args:
        event_dict: The unredacted event as a dict
        hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
            to hash the event

    Returns:
        A tuple of the name of hash and the hash as raw bytes.
    """
    event_dict = dict(event_dict)
    event_dict.pop("age_ts", None)
    event_dict.pop("unsigned", None)
    event_dict.pop("signatures", None)
    event_dict.pop("hashes", None)
    event_dict.pop("outlier", None)
    event_dict.pop("destinations", None)

    # N.B. no need to pop the room_id from create events in MSC4291 rooms
    # as they shouldn't have one.

    event_json_bytes = encode_canonical_json(event_dict)

    hashed = hash_algorithm(event_json_bytes)
    return hashed.name, hashed.digest()


def compute_event_reference_hash(
    event: EventBase, hash_algorithm: Hasher = hashlib.sha256
) -> tuple[str, bytes]:
    """Computes the event reference hash. This is the hash of the redacted
    event.

    Args:
        event
        hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
            to hash the event

    Returns:
        A tuple of the name of hash and the hash as raw bytes.
    """
    tmp_event = prune_event(event)
    event_dict = tmp_event.get_pdu_json()
    event_dict.pop("signatures", None)
    event_dict.pop("age_ts", None)
    event_dict.pop("unsigned", None)
    event_json_bytes = encode_canonical_json(event_dict)
    hashed = hash_algorithm(event_json_bytes)
    return hashed.name, hashed.digest()


def compute_event_signature(
    room_version: RoomVersion,
    event_dict: JsonDict,
    signature_name: str,
    signing_key: SigningKey,
) -> dict[str, dict[str, str]]:
    """Compute the signature of the event for the given name and key.

    Args:
        room_version: the version of the room that this event is in.
            (the room version determines the redaction algorithm and hence the
            json to be signed)

        event_dict: The event as a dict

        signature_name: The name of the entity signing the event
            (typically the server's hostname).

        signing_key: The key to sign with

    Returns:
        a dictionary in the same format of an event's signatures field.
    """
    redact_json = prune_event_dict(room_version, event_dict)
    redact_json.pop("age_ts", None)
    redact_json.pop("unsigned", None)
    if logger.isEnabledFor(logging.DEBUG):
        logger.debug("Signing event: %s", encode_canonical_json(redact_json))
    redact_json = sign_json(redact_json, signature_name, signing_key)
    if logger.isEnabledFor(logging.DEBUG):
        logger.debug("Signed event: %s", encode_canonical_json(redact_json))
    return redact_json["signatures"]


def add_hashes_and_signatures(
    room_version: RoomVersion,
    event_dict: JsonDict,
    signature_name: str,
    signing_key: SigningKey,
) -> None:
    """Add content hash and sign the event

    Args:
        room_version: the version of the room this event is in

        event_dict: The event to add hashes to and sign
        signature_name: The name of the entity signing the event
            (typically the server's hostname).
        signing_key: The key to sign with
    """

    name, digest = compute_content_hash(event_dict, hash_algorithm=hashlib.sha256)

    event_dict.setdefault("hashes", {})[name] = encode_base64(digest)

    event_dict["signatures"] = compute_event_signature(
        room_version, event_dict, signature_name=signature_name, signing_key=signing_key
    )


def resign_event(
    ev: EventBase,
    server_name: str,
    signing_key: SigningKey,
    time_now: int | None = None,
) -> JsonDict:
    """Re-sign the provided event with the given signing key. Any existing signatures on the event
    for this server_name are removed.

    If there has been no signature for this event by this server_name, the event is still re-signed.
    If there have been signatures on this event by this server_name, the event is not re-checked for
    validity. As such, only events that have valid signatures should be passed into this function
    e.g. from the event_json table in the database.
    """
    event_dict = ev.get_pdu_json(time_now=time_now)
    event_dict["signatures"].pop(
        server_name, None
    )  # remove existing signatures for this server_name
    event_dict["signatures"].update(
        compute_event_signature(
            ev.room_version,
            event_dict,
            server_name,
            signing_key,
        )
    )
    return event_dict


def event_needs_resigning(
    ev: EventBase, server_name: str, verify_key: VerifyKey
) -> bool:
    """Check if this event needs re-signing.

    This returns True if all of the following are True:
     - the event `sender` domain matches the `server_name` provided.
     - the event has not been already signed with this `verify_key`.
    """
    sender = UserID.from_string(ev.sender)
    if sender.domain != server_name:
        return False
    want_key_id = verify_key.alg + ":" + verify_key.version
    signed_with_current_key_id = ev.signatures.get(server_name, {}).get(
        want_key_id, None
    )
    if signed_with_current_key_id:
        return False

    return True
