"""
State Machine Model für den NSCT Research Orchestrator.

Definiert die Lebenszyklus-Zustände eines Research-Run und validiert
erlaubte Zustandübergänge entlang der Pipeline.
"""

from __future__ import annotations

import logging
from enum import Enum
from typing import ClassVar, FrozenSet

logger = logging.getLogger(__name__)


class ResearchRunState(str, Enum):
    """Mögliche Zustände eines Research-Laufs entlang der Pipeline."""

    # --- Initialisierung ---
    CREATED = "created"

    # --- Pipeline-Schritte ---
    PLANNING = "planning"
    SEARCHING = "searching"
    FETCHING = "fetching"
    EXTRACTING = "extracting"
    ANALYZING = "analyzing"
    EXPANDING = "expanding"
    COMPARING = "comparing"
    SYNTHESIZING = "synthesizing"

    # --- Endzustände ---
    COMPLETED = "completed"
    FAILED = "failed"
    CANCELLED = "cancelled"


# Übergangsmatrix: Quelle -> zulässige Ziele (frozenset für Immutable)
_VALID_TRANSITIONS: dict[ResearchRunState, FrozenSet[ResearchRunState]] = {
    ResearchRunState.CREATED: frozenset(
        (ResearchRunState.PLANNING, ResearchRunState.FAILED)
    ),
    ResearchRunState.PLANNING: frozenset(
        (ResearchRunState.SEARCHING, ResearchRunState.FAILED)
    ),
    ResearchRunState.SEARCHING: frozenset(
        (ResearchRunState.FETCHING, ResearchRunState.FAILED)
    ),
    ResearchRunState.FETCHING: frozenset(
        (ResearchRunState.EXTRACTING, ResearchRunState.FAILED)
    ),
    ResearchRunState.EXTRACTING: frozenset(
        (ResearchRunState.ANALYZING, ResearchRunState.FAILED)
    ),
    ResearchRunState.ANALYZING: frozenset(
        (
            ResearchRunState.EXPANDING,
            ResearchRunState.COMPARING,
            ResearchRunState.FAILED,
        )
    ),
    ResearchRunState.EXPANDING: frozenset(
        (
            ResearchRunState.ANALYZING,  # zurück zur Analyse nach Expansion
            ResearchRunState.COMPARING,
            ResearchRunState.FAILED,
        )
    ),
    ResearchRunState.COMPARING: frozenset(
        (ResearchRunState.SYNTHESIZING, ResearchRunState.FAILED)
    ),
    ResearchRunState.SYNTHESIZING: frozenset(
        (ResearchRunState.COMPLETED, ResearchRunState.FAILED)
    ),
    # Terminal-States: keine ausgehenden Übergänge.
    ResearchRunState.COMPLETED: frozenset(),
    ResearchRunState.FAILED: frozenset(),
    ResearchRunState.CANCELLED: frozenset(),
}


class StateMachine:
    """Endlicher Automat für den Lebenszyklus eines Research-Runs.

    Parameters
    ----------
    initial_state : ResearchRunState
        Der Startzustand der Maschine (default: CREATED).

    Attributes
    ----------
    current_state : ResearchRunState
        Der aktuell eingestellte Zustand.
    """

    # Die erlaubten Übergänge sind klassengebunden und typstarr.
    _TRANSITIONS: ClassVar[dict[ResearchRunState, FrozenSet[ResearchRunState]]] = _VALID_TRANSITIONS

    def __init__(self, initial_state: ResearchRunState = ResearchRunState.CREATED) -> None:
        self.current_state: ResearchRunState = initial_state

    def transition(self, new_state: str) -> bool:
        """Führt einen Zustandübergang aus, wenn er erlaubt ist.

        Parameters
        ----------
        new_state : str
            Der gewünschte Zielzustand als String (z. B. ``"planning"``).

        Returns
        -------
        bool
            ``True`` wenn der Übergang erfolgreich war, ``False`` sonst
            (z. B. bei einem unerlaubten Übergang oder Terminal-State).
        """
        target: ResearchRunState | None = None
        try:
            target = ResearchRunState(new_state)
        except ValueError:
            logger.info(
                "Unknown state '%s' — transition %s -> %s rejected",
                self.current_state.value,
                new_state,
            )
            return False

        return self._apply(self.current_state, target)

    def is_terminal(self) -> bool:
        """Prüft, ob die Maschine sich in einem Terminal-State befindet."""
        return self.current_state in (
            ResearchRunState.COMPLETED,
            ResearchRunState.FAILED,
            ResearchRunState.CANCELLED,
        )

    def reset(self, state: ResearchRunState | None = None) -> None:
        """Setzt die Maschine zurück (z. B. vor einem neuen Run).

        Parameters
        ----------
        state : ResearchRunState | None
            Zielzustand; default: CREATED.
        """
        self.current_state = state or ResearchRunState.CREATED

    def _apply(self, from_state: ResearchRunState, to_state: ResearchRunState) -> bool:
        """Interne Übergangslogik mit Logging.

        Parameters
        ----------
        from_state : ResearchRunState
            Der aktuelle Zustand (zur Validierung).
        to_state : ResearchRunState
            Der gewünschte neue Zustand.

        Returns
        -------
        bool
            ``True`` wenn der Übergang ausgeführt wurde, ``False`` sonst.
        """
        allowed: FrozenSet[ResearchRunState] = _VALID_TRANSITIONS.get(from_state)
        if allowed is None:
            raise ValueError(
                f"No outgoing transitions defined for state {from_state.value!r}"
            )

        # Terminal-States blockieren jeglichen Ausgang
        if from_state in (
            ResearchRunState.COMPLETED,
            ResearchRunState.FAILED,
            ResearchRunState.CANCELLED,
        ):
            logger.info(
                "Terminal state %s reached — transition %s -> %s rejected",
                from_state.value,
                from_state.value,
                to_state.value,
            )
            return False

        # Selber-Stehen ist kein Fehler
        if from_state == to_state:
            logger.info(
                "No-op: state already %s — skipping transition",
                from_state.value,
            )
            return False

        if to_state not in allowed:
            logger.info(
                "Transition %s -> %s rejected — not allowed",
                from_state.value,
                to_state.value,
            )
            return False

        # Erlaubt: tatsächlich durchführen
        self.current_state = to_state  # type: ignore[assignment]  # instance attr
        logger.info(
            "Transition %s -> %s accepted",
            from_state.value,
            to_state.value,
        )
        return True