#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-3.0-or-later
"""In-memory transport double for Phase-1.0W policy tests only."""

from __future__ import annotations

from typing import Any


class FakeTransportError(RuntimeError):
    """Synthetic sequence error."""


class FakeTransport:
    """Record one synthetic session without any network primitives."""

    def __init__(self, inbound_chunks: list[bytes]) -> None:
        self._inbound = list(inbound_chunks)
        self._plan: Any = None
        self._command_index = 0
        self._opened_once = False
        self._closed = False
        self.events: list[str] = []

    def open_once(self, plan: Any) -> None:
        if self._opened_once:
            raise FakeTransportError("fake transport already opened")
        self._opened_once = True
        self._plan = plan
        self.events.append("OPEN")

    def send_command_token(self, command: str) -> None:
        if not self._opened_once or self._closed or self._plan is None:
            raise FakeTransportError("fake transport is not open")
        if self._command_index >= len(self._plan.commands) or \
                command != self._plan.commands[self._command_index]:
            raise FakeTransportError("unexpected synthetic command")
        self._command_index += 1
        self.events.append(f"COMMAND_{command.upper()}")

    def receive_chunk(self) -> bytes | None:
        if not self._opened_once or self._closed:
            raise FakeTransportError("fake transport is not open")
        if not self._inbound:
            return None
        self.events.append("RECEIVE")
        return self._inbound.pop(0)

    def close_once(self) -> None:
        if not self._opened_once or self._closed:
            raise FakeTransportError("fake transport cannot close")
        self._closed = True
        self.events.append("CLOSE")