"""Single-owner encrypted RPC session; transport cannot bypass this gate."""
from __future__ import annotations

import json
import threading
import time

from .protocol import Handshake, ProtocolError, Reassembler


class RpcError(Exception):
    def __init__(self, code, message):
        self.code, self.message = code, message
        super().__init__(code)


def checked_name(value):
    if not isinstance(value, str) or not value.strip() or len(value) > 40:
        raise RpcError("BAD_REQUEST", "名称须为 1 至 40 个字符")
    if any(ord(char) < 32 or ord(char) == 127 for char in value):
        raise RpcError("BAD_REQUEST", "名称包含不支持的字符")
    return value.strip()


class SessionManager:
    def __init__(self, dispatch, identity, *, clock=time.monotonic):
        self.dispatch = dispatch
        self.identity = identity
        self.clock = clock
        self.lock = threading.RLock()
        self.owner = None
        self.receiver = None
        self.cipher = None
        self.opened = False
        self.client_name = None
        self.last_request = -1
        self.connected_at = self.last_activity = 0
        self.generation = 0
        self.peer_mtu = 23

    def connect(self, owner):
        with self.lock:
            if self.owner is not None:
                return self.owner == owner
            self.owner = owner
            self.receiver = Reassembler(self.clock)
            self.connected_at = self.last_activity = self.clock()
            return True

    def disconnect(self, owner):
        with self.lock:
            if self.owner != owner:
                return
            self.owner = self.receiver = self.cipher = self.client_name = None
            self.opened = False
            self.last_request = -1
            self.peer_mtu = 23
            self.generation += 1

    def expired(self):
        with self.lock:
            if self.owner is None:
                return False
            deadline = self.last_activity + 20 if self.opened else self.connected_at + 10
            return self.clock() >= deadline or (
                self.receiver.pending is not None and self.clock() - self.receiver.started >= 15)

    def status(self):
        with self.lock:
            return dict(connected=self.opened, client_name=self.client_name if self.opened else None,
                        generation=self.generation)

    def accept(self, owner, fragment):
        with self.lock:
            if owner != self.owner or self.expired():
                raise ProtocolError("NOT_READY")
            message = self.receiver.accept(fragment)
            if message is None:
                return None
            kind, payload = message
            if self.cipher is None:
                if kind != 1:
                    raise ProtocolError("NOT_READY")
                handshake = Handshake()
                self.cipher = handshake.finish(payload, server=True)
                return 2, handshake.hello
            if kind != 3:
                raise ProtocolError("BAD_REQUEST")
            from .protocol import json_object
            request = json_object(self.cipher.decrypt(payload))
            request_id = request.get("id")
            if not isinstance(request_id, str) or not 1 <= len(request_id) <= 64 or not request_id.isascii() or not request_id.isdecimal():
                raise ProtocolError("BAD_REQUEST")
            number = int(request_id)
            response = dict(id=request_id)
            try:
                if number <= self.last_request:
                    raise RpcError("CONFLICT", "请求编号已使用")
                self.last_request = number
                method, params = request.get("method"), request.get("params")
                if not isinstance(method, str) or not isinstance(params, dict):
                    raise RpcError("BAD_REQUEST", "请求格式无效")
                if not self.opened:
                    if method != "session.open":
                        raise ProtocolError("NOT_READY")
                    name = checked_name(params.get("client_name"))
                    peer_mtu = params.get('receive_mtu', 23)
                    if type(peer_mtu) is not int or not 23 <= peer_mtu <= 517:
                        raise RpcError('BAD_REQUEST', '接收分片上限无效')
                    result = self.identity()
                    self.peer_mtu = peer_mtu
                    self.client_name = name
                    self.opened = True
                    self.generation += 1
                elif method == "session.ping":
                    result = dict(alive=True)
                elif method == "session.rename":
                    self.client_name = checked_name(params.get("client_name"))
                    result = dict(client_name=self.client_name)
                elif method == "session.open":
                    raise RpcError("CONFLICT", "会话已经建立")
                else:
                    result = self.dispatch(method, params)
                response.update(ok=True, result=result)
                self.last_activity = self.clock()
            except RpcError as error:
                response.update(ok=False, error=dict(code=error.code, message=error.message, retryable=False))
            except ProtocolError:
                raise
            except Exception:
                response.update(ok=False, error=dict(code="DEVICE_ERROR", message="设备操作失败，请刷新状态", retryable=False))
            raw = json.dumps(response, ensure_ascii=False, separators=(",", ":"), allow_nan=False).encode("utf-8")
            return 3, self.cipher.encrypt(raw)