"""Conversation state management and persistence helpers."""

from __future__ import annotations

import json
import os
import tempfile
from dataclasses import dataclass, field
from datetime import datetime, timezone
from pathlib import Path
from typing import ClassVar, Dict, Iterable, List, MutableMapping

DEFAULT_CONVERSATION_ID = "default"


@dataclass
class ConversationState:
    """In-memory representation of a conversation transcript."""

    conversation_id: str
    created_at: str
    updated_at: str
    messages: List[Dict[str, str]] = field(default_factory=list)


class ConversationManager:
    """Load and persist conversation transcripts as JSON files."""

    VALID_ROLES: ClassVar[set[str]] = {"system", "user", "assistant"}

    def __init__(
        self,
        storage_dir: str | Path | None = None,
        conversation_id: str | None = None,
    ) -> None:
        module_root = Path(__file__).resolve().parent
        default_storage = module_root / "data" / "conversations"
        self._storage_dir = Path(storage_dir) if storage_dir else default_storage
        self._storage_dir.mkdir(parents=True, exist_ok=True)

        self._conversation_id = conversation_id or DEFAULT_CONVERSATION_ID
        self._path = self._storage_dir / f"{self._conversation_id}.json"

        self._state = self._load_state()

    # ------------------------------------------------------------------ properties
    @property
    def conversation_id(self) -> str:
        return self._state.conversation_id

    @property
    def messages(self) -> List[Dict[str, str]]:
        return list(self._state.messages)

    @property
    def chat_messages(self) -> List[Dict[str, str]]:
        """Return messages formatted for the Ollama chat API."""
        return [
            {"role": msg["role"], "content": msg["content"]}
            for msg in self._state.messages
        ]

    # ------------------------------------------------------------------ public API
    def append_message(self, role: str, content: str) -> Dict[str, str]:
        """Append a new message and persist the updated transcript."""
        normalized_role = role.lower()
        if normalized_role not in self.VALID_ROLES:
            raise ValueError(f"Invalid role '{role}'. Expected one of {self.VALID_ROLES}.")

        timestamp = datetime.now(timezone.utc).isoformat()
        message = {
            "role": normalized_role,
            "content": content,
            "timestamp": timestamp,
        }

        self._state.messages.append(message)
        self._state.updated_at = timestamp
        self._write_state()
        return message

    def replace_messages(self, messages: Iterable[Dict[str, str]]) -> None:
        """Replace the transcript contents. Useful for loading fixtures."""
        normalized: List[Dict[str, str]] = []
        for item in messages:
            role = item.get("role", "").lower()
            content = item.get("content", "")
            if role not in self.VALID_ROLES:
                continue
            normalized.append(
                {
                    "role": role,
                    "content": content,
                    "timestamp": item.get("timestamp")
                    or datetime.now(timezone.utc).isoformat(),
                }
            )

        now = datetime.now(timezone.utc).isoformat()
        self._state.messages = normalized
        self._state.created_at = self._state.created_at or now
        self._state.updated_at = now
        self._write_state()

    def clear_messages(self) -> None:
        """Clear all messages and reset the conversation state."""
        timestamp = datetime.now(timezone.utc).isoformat()
        self._state = ConversationState(
            conversation_id=self._conversation_id,
            created_at=timestamp,
            updated_at=timestamp,
            messages=[],
        )
        self._write_state()
    
    def trim_to_recent(self, keep_count: int = 20) -> List[Dict[str, str]]:
        """Trim conversation to keep only recent messages, return removed messages.
        
        Args:
            keep_count: Number of recent messages to keep
            
        Returns:
            List of messages that were removed (older messages)
        """
        if len(self._state.messages) <= keep_count:
            return []
        
        # Split messages into old and recent
        removed_messages = self._state.messages[:-keep_count]
        self._state.messages = self._state.messages[-keep_count:]
        
        # Update state and persist
        self._state.updated_at = datetime.now(timezone.utc).isoformat()
        self._write_state()
        
        return removed_messages

    # ------------------------------------------------------------------ persistence
    def _load_state(self) -> ConversationState:
        """Load the transcript from disk or create a fresh default."""
        if self._path.exists():
            try:
                with self._path.open("r", encoding="utf-8") as fh:
                    payload = json.load(fh)
                return self._state_from_payload(payload)
            except (json.JSONDecodeError, OSError):
                pass

        timestamp = datetime.now(timezone.utc).isoformat()
        return ConversationState(
            conversation_id=self._conversation_id,
            created_at=timestamp,
            updated_at=timestamp,
            messages=[],
        )

    def _state_from_payload(self, payload: MutableMapping[str, object]) -> ConversationState:
        """Normalize persisted data into ConversationState instances."""
        conversation_id = str(payload.get("id") or self._conversation_id)
        created_at = str(payload.get("created_at") or datetime.now(timezone.utc).isoformat())
        updated_at = str(payload.get("updated_at") or created_at)

        messages_payload = payload.get("messages", [])
        messages: List[Dict[str, str]] = []
        if isinstance(messages_payload, list):
            for item in messages_payload:
                if not isinstance(item, dict):
                    continue
                role = str(item.get("role", "")).lower()
                content = str(item.get("content", ""))
                if role not in self.VALID_ROLES:
                    continue
                timestamp = str(
                    item.get("timestamp") or datetime.now(timezone.utc).isoformat()
                )
                messages.append({"role": role, "content": content, "timestamp": timestamp})

        return ConversationState(
            conversation_id=conversation_id,
            created_at=created_at,
            updated_at=updated_at,
            messages=messages,
        )

    def _write_state(self) -> None:
        """Persist the conversation state atomically."""
        payload = {
            "id": self._state.conversation_id,
            "created_at": self._state.created_at,
            "updated_at": self._state.updated_at,
            "messages": self._state.messages,
        }

        with tempfile.NamedTemporaryFile(
            "w",
            encoding="utf-8",
            dir=self._storage_dir,
            delete=False,
            prefix=f"{self._conversation_id}.",
            suffix=".tmp",
        ) as tmp_file:
            json.dump(payload, tmp_file, indent=2, ensure_ascii=False)
            tmp_file.flush()
            os.fsync(tmp_file.fileno())

        os.replace(tmp_file.name, self._path)