from dataclasses import dataclass, field
from uuid import uuid4


@dataclass
class SessionState:
    session_id: str = field(default_factory=lambda: str(uuid4()))
    active_turn_id: int | None = None
    next_turn_id: int = 1
    expected_audio_sequence: int = 0
    closed: bool = False

    def start_turn(self) -> int:
        if self.closed:
            raise RuntimeError("Session is closed.")

        if self.active_turn_id is not None:
            raise RuntimeError("A turn is already active.")

        self.active_turn_id = self.next_turn_id
        self.next_turn_id += 1
        self.expected_audio_sequence = 0

        return self.active_turn_id

    def accept_audio_chunk(
        self,
        turn_id: int,
        sequence_number: int,
        payload_size: int,
    ) -> None:
        if self.closed:
            raise RuntimeError("Session is closed.")

        if self.active_turn_id != turn_id:
            raise ValueError(
                f"Unexpected turn_id={turn_id}; "
                f"active_turn_id={self.active_turn_id}."
            )

        if sequence_number != self.expected_audio_sequence:
            raise ValueError(
                f"Expected sequence_number="
                f"{self.expected_audio_sequence}, "
                f"received={sequence_number}."
            )

        if payload_size == 0:
            raise ValueError("Audio chunk cannot be empty.")

        self.expected_audio_sequence += 1

    def end_turn(self, turn_id: int) -> None:
        if self.active_turn_id != turn_id:
            raise ValueError(
                f"Cannot end turn {turn_id}; "
                f"active_turn_id={self.active_turn_id}."
            )

        self.active_turn_id = None
        self.expected_audio_sequence = 0

    def interrupt(self, turn_id: int) -> None:
        if self.active_turn_id == turn_id:
            self.active_turn_id = None
            self.expected_audio_sequence = 0

    def close(self) -> None:
        self.active_turn_id = None
        self.closed = True