"""
Debugger API — pause / resume / step an in-flight pipeline.

The engine is set by main.py on startup via `set_engine(...)`. If no
engine is registered (e.g. when running the mock server), endpoints
return a structured error rather than crashing.
"""

from fastapi import APIRouter
from typing import Any, Dict, Optional
import threading

router = APIRouter(prefix="/debugger", tags=["debugger"])

# F-15: guards for module-level mutable state used from async handlers.
# Multiple WS clients can call pause/resume/step concurrently.
_engine_lock = threading.Lock()
_state_lock = threading.Lock()

# Single in-memory engine reference (set by main.py)
_ENGINE: Optional[Any] = None
_DEBUG_STATE: Dict[str, Any] = {
    "paused": False,
    "current_step": 0,
    "history": [],
}


def set_engine(engine: Any) -> None:
    global _ENGINE
    with _engine_lock:
        _ENGINE = engine


def get_engine() -> Optional[Any]:
    with _engine_lock:
        return _ENGINE


# -----------------------------
# RESUME
# -----------------------------
@router.post("/resume")
def resume() -> Dict[str, Any]:
    with _state_lock:
        _DEBUG_STATE["paused"] = False
    eng = get_engine()
    if eng and hasattr(eng, "resume"):
        eng.resume()
    return {"state": "running"}


# -----------------------------
# PAUSE
# -----------------------------
@router.post("/pause")
def pause() -> Dict[str, Any]:
    with _state_lock:
        _DEBUG_STATE["paused"] = True
    eng = get_engine()
    if eng and hasattr(eng, "pause"):
        eng.pause()
    return {"state": "paused"}


# -----------------------------
# STEP
# -----------------------------
@router.post("/step")
def step() -> Dict[str, Any]:
    eng = get_engine()
    if eng and hasattr(eng, "step"):
        eng.step()
    with _state_lock:
        _DEBUG_STATE["current_step"] += 1
        step_n = _DEBUG_STATE["current_step"]
    return {"state": "stepped", "step": step_n}


# -----------------------------
# STEP BACK (replay-only)
# -----------------------------
@router.post("/step-back")
def step_back() -> Dict[str, Any]:
    with _state_lock:
        if _DEBUG_STATE["current_step"] > 0:
            _DEBUG_STATE["current_step"] -= 1
        step_n = _DEBUG_STATE["current_step"]
    return {"state": "stepped_back", "step": step_n}


# -----------------------------
# STATE
# -----------------------------
@router.get("/state")
def state() -> Dict[str, Any]:
    eng = get_engine()
    active = bool(eng and hasattr(eng, "is_active") and eng.is_active())
    with _state_lock:
        snapshot = {
            "paused": _DEBUG_STATE["paused"],
            "current_step": _DEBUG_STATE["current_step"],
            "engine_attached": eng is not None,
            "engine_active": active,
        }
    return snapshot


# -----------------------------
# Legacy wrapper for api.py facade
# -----------------------------
def debugger_endpoint(session_id: str, registry: Any = None, bus: Any = None) -> Dict[str, Any]:
    """Legacy — return current debugger state for a session."""
    with _state_lock:
        return {
            "session_id": session_id,
            "paused": _DEBUG_STATE["paused"],
            "current_step": _DEBUG_STATE["current_step"],
            "engine_attached": _ENGINE is not None,
        }