import logging
import os
from datetime import datetime, timezone
from typing import Any, Dict, Optional, List
from app.core.settings import settings

import pymongo
from pymongo import IndexModel, ASCENDING
from pymongo.errors import PyMongoError, ServerSelectionTimeoutError

# Configure logging
logger = logging.getLogger(__name__)

class DatabaseManager:
    """
    Manages MongoDB operations for the AI system.
    Handles persistent storage of solved problems and connection management.
    """

    def __init__(self, mongo_uri: Optional[str] = None, client: Optional[pymongo.MongoClient] = None):
        """
        Initialize the DatabaseManager.

        Args:
            mongo_uri: MongoDB connection string.
            client: Existing PyMongo client (shared pool).
        """
        self.mongo_uri = mongo_uri or settings.MONGO_URI
        self.client = None
        self.db = None
        self.collection = None
        
        try:
            if client:
                self.client = client
            else:
                # Create new client with specific pool settings if not provided
                self.client = pymongo.MongoClient(
                    self.mongo_uri, 
                    serverSelectionTimeoutMS=5000,
                    minPoolSize=1,  # Keep at least one connection open
                    maxPoolSize=50  # Limit max connections
                )
            
            # Force a call to check if the server is available
            self.client.server_info()
            
            # Setup DB and collection
            db_name = settings.MONGO_DB_NAME
            try:
                # If URI contains a DB name, it will override the setting default
                parsed_uri = pymongo.uri_parser.parse_uri(self.mongo_uri)
                uri_db = parsed_uri.get('database')
                if uri_db:
                    db_name = uri_db
            except Exception:
                pass

            self.db = self.client[db_name]
            self.collection = self.db["solved_problems"]
            self.sessions_collection = self.db["chat_sessions"]
            self.users_collection = self.db["users"]
            
            # Ensure indexes
            self.collection.create_index([("hash", ASCENDING)], name="hash_index")
            self.sessions_collection.create_index([("user_id", ASCENDING)], name="user_id_index")
            self.sessions_collection.create_index([("session_id", ASCENDING)], name="session_id_index", unique=True)
            self.users_collection.create_index([("email", ASCENDING)], name="email_index", unique=True)
            self.users_collection.create_index([("user_id", ASCENDING)], name="user_id_index", unique=True)
            
            logger.info(f"Successfully connected to MongoDB at {self.mongo_uri} (DB: {db_name})")
            
        except (PyMongoError, ServerSelectionTimeoutError) as e:
            logger.error(f"Failed to connect to MongoDB: {e}")
            self.client = None
            self.db = None
            self.collection = None

    # _connect is merged into __init__

    def find_by_hash(self, problem_hash: str) -> Optional[Dict[str, Any]]:
        """
        Retrieve a solved problem by its hash.

        Args:
            problem_hash: The hash generated for the problem text.

        Returns:
            Optional[Dict[str, Any]]: The document if found, else None.
        """
        if self.collection is None:
            logger.warning("MongoDB collection not available. Skipping lookup.")
            return None

        try:
            doc = self.collection.find_one({"hash": problem_hash})
            return doc
        except PyMongoError as e:
            logger.error(f"Error finding problem by hash {problem_hash}: {e}")
            return None

    def save_problem(self, problem_dict: Dict[str, Any], answer_dict: Dict[str, Any]) -> bool:
        """
        Save a solved problem and its answer to the database.

        Args:
            problem_dict: Dictionary containing problem details.
                          Must contain 'hash' if not in answer_dict? 
                          Ideally we assume one of them or we merge them.
                          The user requested save_problem(problem_dict, answer_dict).
            answer_dict: Dictionary containing the answer details.

        Returns:
            bool: True if successful, False otherwise.
        """
        if self.collection is None:
            logger.warning("MongoDB collection not available. Skipping save.")
            return False

        try:
            # Construct the document
            # Expecting 'hash' to be somewhere. If not provided, we can't index it effectively 
            # for 'find_by_hash'. I will assume it is passed in problem_dict or we generate/extract it.
            # But the signature didn't ask for hash arg.
            # I will assume problem_dict contains the 'hash' key.
            
            document = {
                "problem": problem_dict,
                "answer": answer_dict,
                "created_at": datetime.now(timezone.utc),
                # Lift hash to top level for easier indexing/querying if present in problem_dict
            }
            
            problem_hash = problem_dict.get("hash")
            if problem_hash:
                document["hash"] = problem_hash

            result = self.collection.insert_one(document)
            logger.info(f"Saved problem with ID: {result.inserted_id}")
            return True
        except PyMongoError as e:
            logger.error(f"Failed to save problem: {e}")
            return False

    def create_session(self, user_id: str, session_id: str, title: str = "New Chat") -> bool:
        """
        Create a new chat session for a user.
        Uses upsert with $setOnInsert to be idempotent.
        """
        if self.sessions_collection is None:
            return False
        try:
            self.sessions_collection.update_one(
                {"session_id": session_id},
                {
                    "$setOnInsert": {
                        "session_id": session_id,
                        "user_id": user_id,
                        "title": title,
                        "created_at": datetime.now(timezone.utc),
                        "messages": []
                    }
                },
                upsert=True
            )
            return True
        except Exception as e:
            # If it's a duplicate key error, it means another thread just inserted it.
            # That's fine, we consider the session "created" or at least existing.
            if "E11000" in str(e) or "duplicate key" in str(e).lower():
                return True
            logger.error(f"Failed to create session {session_id} for user {user_id}: {e}")
            return False

    def list_sessions(self, user_id: str) -> List[Dict[str, Any]]:
        """
        Retrieve all sessions for a specific user.
        """
        if self.sessions_collection is None:
            return []
        try:
            cursor = self.sessions_collection.find(
                {"user_id": user_id},
                {"session_id": 1, "title": 1, "created_at": 1, "_id": 0}
            ).sort("created_at", -1)
            return list(cursor)
        except PyMongoError as e:
            logger.error(f"Failed to list sessions for user {user_id}: {e}")
            return []

    def get_chat_history(self, user_id: str, session_id: str, limit: int = 50) -> Optional[List[Dict[str, Any]]]:
        """
        Retrieve recent messages for a session, ensuring it belongs to the user.
        Returns None if session not found or not owned by user.
        """
        if self.sessions_collection is None:
            return None
        try:
            doc = self.sessions_collection.find_one(
                {"session_id": session_id, "user_id": user_id},
                {"messages": {"$slice": -limit}, "_id": 0}
            )
            if doc is not None:
                return doc.get("messages", [])
            return None
        except PyMongoError as e:
            logger.error(f"Failed to get history for {session_id} (user: {user_id}): {e}")
            return None

    def save_chat_message(self, user_id: str, session_id: str, role: str, content: str, **kwargs) -> bool:
        """
        Append a message to the session history.
        Only succeeds if the session belongs to the user_id.
        """
        if self.sessions_collection is None:
            return False
        try:
            # logic to update title if it's currently "New Chat" and this is a user message
            if role == "user":
                session = self.sessions_collection.find_one({"session_id": session_id, "user_id": user_id})
                if session and (session.get("title") == "New Chat" or session.get("title") == "New Session" or session.get("title") == "Untitled"):
                    new_title = content[:50] + "..." if len(content) > 50 else content
                    self.sessions_collection.update_one(
                        {"session_id": session_id, "user_id": user_id},
                        {"$set": {"title": new_title}}
                    )

            # Push the new message
            msg = {
                "role": role, 
                "content": content, 
                "timestamp": datetime.now(timezone.utc)
            }
            msg.update(kwargs)
            
            result = self.sessions_collection.update_one(
                {"session_id": session_id, "user_id": user_id},
                {"$push": {"messages": msg}}
            )
            # return True if we found the document to update
            return result.matched_count > 0
        except PyMongoError as e:
            logger.error(f"Failed to save message to {session_id} for user {user_id}: {e}")
            return False

    def delete_session(self, user_id: str, session_id: str) -> bool:
        """
        Delete a session belonging to a user.
        """
        if self.sessions_collection is None:
            return False
        try:
            result = self.sessions_collection.delete_one({"session_id": session_id, "user_id": user_id})
            return result.deleted_count > 0
        except PyMongoError as e:
            logger.error(f"Failed to delete session {session_id} for user {user_id}: {e}")
            return False

    def rename_session(self, user_id: str, session_id: str, new_title: str) -> bool:
        """
        Rename a session belonging to a user.
        """
        if self.sessions_collection is None:
            return False
        try:
            result = self.sessions_collection.update_one(
                {"session_id": session_id, "user_id": user_id},
                {"$set": {"title": new_title}}
            )
            # return True if we found the document to update (even if title was same)
            return result.matched_count > 0
        except PyMongoError as e:
            logger.error(f"Failed to rename session {session_id} for user {user_id}: {e}")
            return False

    # -------------------------------------------------------------------------
    # User Profile Management
    # -------------------------------------------------------------------------
    def create_user(self, user_data: Dict[str, Any]) -> bool:
        """
        Create a new user in the database.
        """
        if self.users_collection is None:
            return False
        try:
            self.users_collection.insert_one(user_data)
            return True
        except PyMongoError as e:
            logger.error(f"Failed to create user: {e}")
            return False

    def get_user_by_email(self, email: str) -> Optional[Dict[str, Any]]:
        """
        Retrieve a user by email.
        """
        if self.users_collection is None:
            return None
        try:
            return self.users_collection.find_one({"email": email})
        except PyMongoError as e:
            logger.error(f"Failed to get user by email {email}: {e}")
            return None

    def get_user_profile(self, user_id: str) -> Optional[Dict[str, Any]]:
        """
        Retrieve user profile by ID (Firebase UID or local UID).
        """
        if self.users_collection is None:
            return None
        try:
            return self.users_collection.find_one({"user_id": user_id})
        except PyMongoError as e:
            logger.error(f"Failed to get profile for {user_id}: {e}")
            return None

    def update_user_profile(self, user_id: str, data: Dict[str, Any]) -> bool:
        """
        Update or create user profile.
        """
        if self.users_collection is None:
            return False
        try:
            self.users_collection.update_one(
                {"user_id": user_id},
                {"$set": {**data, "updated_at": datetime.now(timezone.utc)}},
                upsert=True
            )
            return True
        except PyMongoError as e:
            logger.error(f"Failed to update profile for {user_id}: {e}")
            return False