import os
import select
import sys
import time
from importlib import import_module
from pathlib import Path
from threading import Event, Lock, Thread
from typing import Optional, Type

from agent import Agent, SimpleAgent
from telnetclient import TelnetClient


class SessionState:
    """Share Telnet session state safely across threads."""

    def __init__(self) -> None:
        self._send_lock = Lock()
        self._output_lock = Lock()
        self._output_event = Event()
        self._last_output = ""
        self._last_agent_send = 0.0

    def send(self, client: TelnetClient, message: str) -> None:
        with self._send_lock:
            client.send(message)

    def agent_send(
        self,
        client: TelnetClient,
        message: str,
        *,
        min_interval: float,
        stop_event: Event,
    ) -> bool:
        """Send on behalf of the agent while respecting a minimum cadence."""
        while not stop_event.is_set():
            with self._send_lock:
                now = time.time()
                elapsed = now - self._last_agent_send
                if elapsed >= min_interval:
                    client.send(message)
                    self._last_agent_send = now
                    return True
                wait_time = min_interval - elapsed
            if wait_time <= 0:
                continue
            if stop_event.wait(wait_time):
                break
        return False

    def update_output(self, text: str) -> None:
        if not text:
            return
        with self._output_lock:
            self._last_output = text
        self._output_event.set()

    def snapshot_output(self) -> str:
        with self._output_lock:
            return self._last_output

    def wait_for_output(self, timeout: float) -> bool:
        return self._output_event.wait(timeout)

    def clear_output_event(self) -> None:
        self._output_event.clear()


def run_agent_loop(
    client: TelnetClient,
    state: SessionState,
    agent: Agent,
    stop_event: Event,
    *,
    idle_delay: float = 0.5,
    min_send_interval: float = 1.0,
) -> None:
    """Invoke *agent* whenever new output arrives and send its response."""
    while not stop_event.is_set():
        triggered = state.wait_for_output(timeout=idle_delay)
        if stop_event.is_set():
            break
        if not triggered:
            continue
        state.clear_output_event()
        last_output = state.snapshot_output()
        if not last_output:
            continue
        try:
            agent.observe(last_output)
            command = agent.decide()
        except Exception as exc:  # pragma: no cover - defensive logging
            print(f"Agent failed: {exc}", file=sys.stderr)
            continue
        if not command:
            continue
        sent = state.agent_send(
            client,
            command,
            min_interval=min_send_interval,
            stop_event=stop_event,
        )
        if not sent:
            break


def load_env_file(path: str = ".env") -> None:
    """Populate ``os.environ`` with key/value pairs from a dotenv file."""
    env_path = Path(path)
    if not env_path.exists():
        return
    for line in env_path.read_text().splitlines():
        stripped = line.strip()
        if not stripped or stripped.startswith("#"):
            continue
        if "=" not in stripped:
            continue
        key, value = stripped.split("=", 1)
        key = key.strip()
        value = value.strip().strip('"').strip("'")
        if key and key not in os.environ:
            os.environ[key] = value


def require_env(key: str) -> str:
    value = os.environ.get(key)
    if value is None:
        raise RuntimeError(f"Missing required environment variable: {key}")
    return value


def build_agent(agent_spec: str) -> Agent:
    """Instantiate an agent based on ``MISTLE_AGENT`` contents."""
    normalized = agent_spec.strip()
    if not normalized:
        return SimpleAgent()

    key = normalized.lower()
    if key == "simple":
        return SimpleAgent()

    if key == "explore":
        try:
            module = import_module("agent")
            agent_cls = getattr(module, "ExploreAgent")
        except AttributeError as exc:  # pragma: no cover - optional dependency
            raise RuntimeError("ExploreAgent is not available in agent module") from exc
        return _instantiate_agent(agent_cls, normalized)

    if ":" in normalized:
        module_name, class_name = normalized.split(":", 1)
        if not module_name or not class_name:
            raise RuntimeError("MISTLE_AGENT must be in 'module:ClassName' format")
        module = import_module(module_name)
        agent_cls = getattr(module, class_name)
        return _instantiate_agent(agent_cls, normalized)

    raise RuntimeError(f"Unknown agent spec '{agent_spec}'.")


def _instantiate_agent(agent_cls: Type[Agent], agent_spec: str) -> Agent:
    if not issubclass(agent_cls, Agent):
        raise RuntimeError(f"{agent_spec} is not an Agent subclass")
    try:
        return agent_cls()
    except TypeError as exc:
        raise RuntimeError(f"Failed to instantiate {agent_spec}: {exc}") from exc


def login(
    client: TelnetClient,
    *,
    user: str,
    password: str,
    login_prompt: str,
    banner_timeout: float = 10.0,
    response_timeout: float = 2.0,
    state: Optional[SessionState] = None,
) -> None:
    """Handle the banner/prompt exchange and send credentials."""
    if login_prompt:
        banner = client.read_until(login_prompt, timeout=banner_timeout)
    else:
        banner = client.receive(timeout=response_timeout)
    if banner:
        print(banner, end="" if banner.endswith("\n") else "\n")
        if state:
            state.update_output(banner)

    if user:
        client.send(user)
        time.sleep(0.2)
    if password:
        client.send(password)

    response = client.receive(timeout=response_timeout)
    if response:
        print(response, end="" if response.endswith("\n") else "\n")
        if state:
            state.update_output(response)


def interactive_session(
    client: TelnetClient,
    state: SessionState,
    stop_event: Event,
    *,
    poll_interval: float = 0.2,
    receive_timeout: float = 0.2,
    exit_command: str,
) -> None:
    """Keep the Telnet session running, proxying input/output until interrupted."""
    if exit_command:
        print(f"Connected. Press Ctrl-C to exit (will send {exit_command!r}).")
    else:
        print("Connected. Press Ctrl-C to exit.")

    while not stop_event.is_set():
        incoming = client.receive(timeout=receive_timeout)
        if incoming:
            print(incoming, end="" if incoming.endswith("\n") else "\n")
            state.update_output(incoming)

        readable, _, _ = select.select([sys.stdin], [], [], poll_interval)
        if sys.stdin in readable:
            line = sys.stdin.readline()
            if line == "":
                stop_event.set()
                break
            line = line.rstrip("\r\n")
            if not line:
                continue
            state.send(client, line)


def graceful_shutdown(
    client: TelnetClient,
    exit_command: str,
    *,
    state: Optional[SessionState] = None,
) -> None:
    if not exit_command:
        return
    try:
        if state:
            state.send(client, exit_command)
        else:
            client.send(exit_command)
        farewell = client.receive(timeout=2.0)
        if farewell:
            print(farewell, end="" if farewell.endswith("\n") else "\n")
            if state:
                state.update_output(farewell)
    except Exception as exc:  # pragma: no cover - best effort logging
        print(f"Failed to send exit command: {exc}", file=sys.stderr)


def main() -> int:
    load_env_file()

    host = require_env("MISTLE_HOST")

    port_raw = require_env("MISTLE_PORT")
    try:
        port = int(port_raw)
    except ValueError as exc:
        raise RuntimeError("MISTLE_PORT must be an integer") from exc

    user = os.environ.get("MISTLE_USER", "")
    password = os.environ.get("MISTLE_PASSWORD", "")
    login_prompt = os.environ.get("MISTLE_LOGIN_PROMPT", "")
    exit_command = os.environ.get("MISTLE_EXIT_COMMAND", "")
    agent_mode = os.environ.get("MISTLE_AGENT_MODE", "").lower() in {"1", "true", "yes", "on"}
    agent_spec = os.environ.get("MISTLE_AGENT", "")

    state = SessionState()
    stop_event = Event()
    agent_thread: Optional[Thread] = None
    agent: Optional[Agent] = None

    with TelnetClient(host=host, port=port, timeout=10.0) as client:
        login(
            client,
            user=user,
            password=password,
            login_prompt=login_prompt,
            state=state,
        )

        if agent_mode:
            agent = build_agent(agent_spec)
            agent_thread = Thread(
                target=run_agent_loop,
                args=(client, state, agent, stop_event),
                kwargs={"min_send_interval": 1.0},
                daemon=True,
            )
            agent_thread.start()

        interrupted = False
        try:
            interactive_session(
                client,
                state=state,
                stop_event=stop_event,
                exit_command=exit_command,
            )
        except KeyboardInterrupt:
            print()
            interrupted = True
        finally:
            stop_event.set()
            if agent_thread:
                agent_thread.join(timeout=1.0)

        if interrupted:
            graceful_shutdown(client, exit_command, state=state)

    return 0


if __name__ == "__main__":
    raise SystemExit(main())