"""
What the session does with each message it can be sent, recorded once and held.

A characterisation test: it states no rule of its own, it pins the behaviour
the node has, so that code can be moved and restructured underneath it —
`_dispatch_message` and `_do_admin_response` especially, whose order of checks
is itself the rule (a bundle fetch is served before the proof, a join request
with a nonce, everything else only after it).

Every message type the protocol names, plus two that it does not, is sent to a
fresh session in each state a peer can be in, in four shapes: bare, and with every
field any handler reads set to a string, to a number and to a list. What is recorded
is the reply the peer would receive (with its `req_id`), what was audited, which
coroutine was started in the background — started, not run: what those do is
the business of the tests written for them — and the lines logged, as
templates, since their arguments carry object addresses.

Then every signed operation's answer is sent against a challenge that is
pending for it, which is the table `_do_admin_response` dispatches on.

The recording is `golden/dispatch.json`. When a change to this behaviour is
intended, regenerate it with MESHBAY_GOLDEN_WRITE=1 and read the diff: that
diff is the behaviour change, stated message by message.
"""

import base64
import json
import logging
import os
import struct
import time
from pathlib import Path

import msgpack
from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
from meshbay_common import adminop
from meshbay_common.protocol import MNP
from meshbay_node.transport.webrtc_server import WebRTCPeerSession

GOLDEN = Path(__file__).parent / "golden" / "dispatch.json"
GROUP = "g" * 32
REQ_ID = 4242
# Values that differ between runs and mean nothing for the comparison.
VOLATILE = {"nonce", "op_id", "ts"}


class _Channel:
    readyState = "open"

    def __init__(self):
        self.sent = []

    def send(self, data: bytes) -> None:
        (n,) = struct.unpack(">I", data[:4])
        self.sent.append(msgpack.unpackb(data[4:4 + n], raw=False))


class _PC:
    connectionState = "connected"
    iceConnectionState = "connected"
    remoteDescription = None
    localDescription = None
    sctp = None


class _Log(logging.Handler):
    def __init__(self):
        super().__init__(level=logging.DEBUG)
        self.lines = []

    def emit(self, record):
        if record.levelno >= logging.INFO:
            self.lines.append(f"{record.levelname} {record.msg}")


def _clean(value):
    if isinstance(value, dict):
        return {k: ("<volatile>" if k in VOLATILE else _clean(v))
                for k, v in sorted(value.items())}
    if isinstance(value, (list, tuple)):
        return [_clean(v) for v in value]
    if isinstance(value, bytes):
        return f"<{len(value)} bytes>"
    return value


def _ctx():
    return {
        "sk_node": Ed25519PrivateKey.from_private_bytes(b"\x01" * 32),
        "groups": {GROUP: {}},
    }


def _session(state: str):
    s = WebRTCPeerSession(_PC(), _ctx(), peer_id="peer")
    s._channel = _Channel()
    s.spawned, s.audited = [], []

    def spawn(coro):
        # The function's name, not its qualified name: which class it sits in is
        # exactly what may change underneath this recording.
        s.spawned.append(coro.cr_code.co_name)
        coro.close()

    s._spawn = spawn
    s._audit = lambda event, detail="": s.audited.append([event, detail])
    if state in ("challenged", "member", "operator"):
        s._gek_challenge = b"\x02" * 32
        s._nonce_node = b"\x02" * 32
        s._nonce_client = b"\x03" * 32
    if state in ("member", "operator"):
        s._gek_challenge = None
        s._user_id = "alice"
        s._username = "Alice"
        s._group_id = GROUP
        s._device_confirmed = True
        s._pinned_pk = base64.b64encode(b"\x04" * 32).decode()
    if state == "operator":
        s._ctx["has_admin_authority"] = True
    return s


def _run(s, msg: dict) -> dict:
    handler = _Log()
    logger = logging.getLogger("meshbay_node.transport.webrtc_server")
    # Pinned rather than assumed: an earlier test may have raised the level or
    # disabled the logger, and a recording that depends on that is not one.
    saved = logger.level, logger.disabled, logger.propagate
    logger.setLevel(logging.DEBUG)
    logger.disabled = False
    logger.propagate = False
    logger.addHandler(handler)
    try:
        s._handle_message(msg)
    finally:
        logger.removeHandler(handler)
        logger.level, logger.disabled, logger.propagate = saved
    return _clean({"sent": s._channel.sent, "audit": s.audited,
                   "spawned": s.spawned, "log": handler.lines})


def _message_types() -> list[str]:
    names = {v for k, v in vars(MNP).items() if k.isupper() and isinstance(v, str)}
    return sorted(names | {"client_diag", "no_such_type"})


def _odd_types() -> dict[str, dict]:
    """A `type` field that is not a string, or no `type` at all. msgpack will
    carry any value there, and a dispatch keyed by type has to treat each of
    these as the chain of comparisons did — an unhashable one included."""
    return {
        "<missing>": {},
        "<none>": {"type": None},
        "<int>": {"type": 7},
        "<list>": {"type": [MNP.PING]},
        "<dict>": {"type": {"t": MNP.PING}},
        "<bytes>": {"type": MNP.PING.encode()},
    }


def _shapes(keys: list[str]) -> dict[str, dict]:
    return {
        "bare": {},
        "strings": {k: "x" for k in keys},
        "numbers": {k: 7 for k in keys},
        "lists": {k: ["x"] for k in keys},
    }


def _admin_ops() -> list[str]:
    return sorted(v for k, v in vars(adminop).items()
                  if k.startswith("OP_") and isinstance(v, str))


def _record(keys: list[str]) -> dict:
    out = {"keys": keys, "dispatch": {}, "admin": {}}
    for mtype in _message_types():
        for state in ("fresh", "challenged", "member", "operator"):
            for shape, fields in _shapes(keys).items():
                msg = {**fields, "type": mtype, "req_id": REQ_ID}
                out["dispatch"][f"{mtype} | {state} | {shape}"] = _run(_session(state), msg)
    for label, fields in _odd_types().items():
        for state in ("fresh", "challenged", "member", "operator"):
            msg = {**fields, "req_id": REQ_ID}
            out["dispatch"][f"{label} | {state} | bare"] = _run(_session(state), msg)
    for op in _admin_ops() + ["no_such_op"]:
        s = _session("operator")
        s._admin_ops["the-op"] = {"op": op, "subject": "subject", "nonce": b"\x05" * 32,
                                  "ts": int(time.time()), "payload": {}, "group_id": GROUP}
        out["admin"][op] = _run(s, {"type": MNP.ADMIN_RESPONSE, "op_id": "the-op",
                                    "signature": base64.b64encode(b"\x06" * 64).decode(),
                                    "req_id": REQ_ID})
    s = _session("operator")
    s._admin_ops["old"] = {"op": adminop.OP_FILE_DELETE, "subject": "s", "nonce": b"",
                           "ts": 0, "payload": {}, "group_id": GROUP}
    out["admin"]["<expired>"] = _run(s, {"type": MNP.ADMIN_RESPONSE, "op_id": "old",
                                         "signature": "AAAA", "req_id": REQ_ID})
    s = _session("operator")
    s._admin_ops["bad"] = {"op": adminop.OP_FILE_DELETE, "subject": "s", "nonce": b"",
                           "ts": int(time.time()), "payload": {}, "group_id": GROUP}
    out["admin"]["<bad signature encoding>"] = _run(
        s, {"type": MNP.ADMIN_RESPONSE, "op_id": "bad", "signature": "%%%", "req_id": REQ_ID})
    return out


def test_every_message_is_handled_as_recorded():
    golden = json.loads(GOLDEN.read_text(encoding="utf-8"))
    if os.environ.get("MESHBAY_GOLDEN_WRITE") == "1":
        # The field list is kept from the recording, not re-derived from the
        # handlers: it has to be the same input before and after a change.
        GOLDEN.write_text(json.dumps(_record(golden["keys"]), indent=1, sort_keys=True)
                          + "\n", encoding="utf-8")
        golden = json.loads(GOLDEN.read_text(encoding="utf-8"))
    now = _record(golden["keys"])

    assert sorted(now["dispatch"]) == sorted(golden["dispatch"]), (
        "the set of message types changed; regenerate on purpose if it should")
    differ = [k for k in golden["dispatch"] if now["dispatch"][k] != golden["dispatch"][k]]
    differ += [f"admin {k}" for k in sorted(set(golden["admin"]) | set(now["admin"]))
               if now["admin"].get(k) != golden["admin"].get(k)]
    detail = "\n".join(
        f"  {k}\n    was: {golden['dispatch'].get(k) or golden['admin'].get(k[6:])}\n"
        f"    now: {now['dispatch'].get(k) or now['admin'].get(k[6:])}"
        for k in differ[:10])
    assert not differ, f"{len(differ)} case(s) behave differently:\n{detail}"


def test_the_recording_exercises_the_session():
    """A recording of nothing would hold nothing."""
    golden = json.loads(GOLDEN.read_text(encoding="utf-8"))
    cases = golden["dispatch"].values()
    assert len(golden["keys"]) > 50
    assert sum(1 for c in cases if c["spawned"]) > 100, "no handler was ever started"
    assert sum(1 for c in cases if c["sent"]) > 300, "nothing was ever answered"
    assert all(any(m.get("req_id") == REQ_ID for m in c["sent"])
               for c in cases if c["sent"]), "a reply went out without its req_id"
    spawned = {c["spawned"][0] for c in golden["admin"].values() if c["spawned"]}
    assert len(spawned) == len(_admin_ops()), (
        "some signed operation reaches no executor, or two reach the same one")