"""TurnQueue — a thread-safe FIFO of prompts to run as the next turn(s).

This is the agent-side queue that unifies message queueing across CLI, TUI
gateway, desktop, and messaging platforms.  It lives on the AIAgent instance,
alongside the existing ``_pending_steer`` mechanism.

Unlike steer (which injects into the *current* turn's tool results), queued
prompts become the *next* user turn after the current one finishes.  The
drain point is the agent-loop / gateway-runner tail — wherever the current
turn ends and ``running`` flips to False.

Thread-safety: all mutations go through ``self._lock``.  Safe to call from
gateway threads, CLI process_loop, and the agent execution thread.
"""

from __future__ import annotations

import threading
import time
import uuid
from dataclasses import dataclass, field
from typing import Any, Optional


@dataclass
class QueuedTurn:
    """A single queued prompt entry."""

    id: str
    text: str
    transport: Any = None  # pinned transport for the drained turn
    queued_at: float = field(default_factory=time.time)
    # Where the entry came from: "queue" (explicit session.queue.add — the
    # client shows it in a queue panel, not the transcript) or "busy_submit"
    # (a prompt.submit that landed mid-turn — the client already echoed it
    # as an optimistic user message). Lets drain events tell clients whether
    # the text still needs painting.
    source: str = "queue"

    def to_dict(self) -> dict:
        """Serialise for RPC / event emission (no transport internals)."""
        return {
            "id": self.id,
            "text": self.text,
            "queued_at": self.queued_at,
            "source": self.source,
        }


class TurnQueue:
    """Thread-safe FIFO of prompts waiting to become the next turn.

    Replaces the ad-hoc ``session["queued_prompt"]`` dict slot in the TUI
    gateway and the ``localStorage``-backed queue in the desktop renderer.
    The queue lives in the agent process so it drains even when no client
    window is open.
    """

    def __init__(self) -> None:
        self._entries: list[QueuedTurn] = []
        self._lock = threading.Lock()

    # ── enqueue ──────────────────────────────────────────────

    def enqueue(
        self,
        text: str,
        transport: Any = None,
        source: str = "queue",
    ) -> QueuedTurn:
        """Add a prompt to the back of the queue.

        Consecutive text entries are *not* merged here — the gateway's
        ``_handle_busy_submit`` still does merge if it wants to (mirroring
        ``repair_message_sequence``).  Callers that want merge semantics
        should check ``peek()`` first.

        Returns the created :class:`QueuedTurn`.
        """
        entry = QueuedTurn(
            id=str(uuid.uuid4()),
            text=text,
            transport=transport,
            source=source,
        )
        with self._lock:
            self._entries.append(entry)
        return entry

    def requeue_front(self, entry: QueuedTurn) -> QueuedTurn:
        """Put a drained entry back at the *front* of the queue.

        Used by the gateway when the turn dispatch for a drained entry raises
        — the pop already happened, so the entry (same id, so client mirrors
        stay consistent) is restored to the head for the next drain attempt
        instead of being silently lost.
        """
        with self._lock:
            self._entries.insert(0, entry)
        return entry

    # ── drain ────────────────────────────────────────────────

    def drain(self) -> Optional[QueuedTurn]:
        """Pop and return the head entry, or None if the queue is empty."""
        with self._lock:
            if not self._entries:
                return None
            return self._entries.pop(0)

    # ── peek / inspect ───────────────────────────────────────

    def peek(self) -> list[QueuedTurn]:
        """Return a snapshot copy of pending entries (for UI sync)."""
        with self._lock:
            return list(self._entries)

    def is_empty(self) -> bool:
        with self._lock:
            return len(self._entries) == 0

    def __len__(self) -> int:
        with self._lock:
            return len(self._entries)

    def __bool__(self) -> bool:
        return len(self) > 0

    # ── mutate ───────────────────────────────────────────────

    def remove(self, entry_id: str) -> bool:
        """Remove a specific entry by id. Returns True if found."""
        with self._lock:
            before = len(self._entries)
            self._entries = [e for e in self._entries if e.id != entry_id]
            return len(self._entries) < before

    def promote(self, entry_id: str) -> bool:
        """Move an entry to the front of the queue. Returns True if found."""
        with self._lock:
            idx = None
            for i, e in enumerate(self._entries):
                if e.id == entry_id:
                    idx = i
                    break
            if idx is None or idx == 0:
                return False
            entry = self._entries.pop(idx)
            self._entries.insert(0, entry)
            return True

    def update_text(self, entry_id: str, text: str) -> bool:
        """Update the text of a queued entry. Returns True if found."""
        with self._lock:
            for e in self._entries:
                if e.id == entry_id:
                    e.text = text
                    return True
            return False

    def clear(self) -> int:
        """Clear all entries. Returns the number removed."""
        with self._lock:
            n = len(self._entries)
            self._entries.clear()
            return n

    # ── serialisation ────────────────────────────────────────

    def to_list(self) -> list[dict]:
        """Return a list of plain dicts for RPC / event emission."""
        with self._lock:
            return [e.to_dict() for e in self._entries]