"""
Authentication for Art DAG L2 Server.

User registration, login, and JWT tokens.
"""

import json
import os
import secrets
from datetime import datetime, timezone, timedelta
from pathlib import Path
from typing import Optional

import bcrypt
from jose import JWTError, jwt
from pydantic import BaseModel

# JWT settings
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_DAYS = 30


def load_jwt_secret() -> str:
    """Load JWT secret from Docker secret, env var, or generate."""
    # Try Docker secret first
    secret_path = Path("/run/secrets/jwt_secret")
    if secret_path.exists():
        return secret_path.read_text().strip()

    # Try environment variable
    if os.environ.get("JWT_SECRET"):
        return os.environ["JWT_SECRET"]

    # Generate one (tokens won't persist across restarts!)
    print("WARNING: No JWT_SECRET configured. Tokens will be invalidated on restart.")
    return secrets.token_hex(32)


SECRET_KEY = load_jwt_secret()


class User(BaseModel):
    """A registered user."""
    username: str
    password_hash: str
    created_at: str
    email: Optional[str] = None


class UserCreate(BaseModel):
    """Request to register a user."""
    username: str
    password: str
    email: Optional[str] = None


class UserLogin(BaseModel):
    """Request to login."""
    username: str
    password: str


class Token(BaseModel):
    """JWT token response."""
    access_token: str
    token_type: str = "bearer"
    username: str
    expires_at: str


def get_users_path(data_dir: Path) -> Path:
    """Get users file path."""
    return data_dir / "users.json"


def load_users(data_dir: Path) -> dict[str, dict]:
    """Load users from disk."""
    path = get_users_path(data_dir)
    if path.exists():
        with open(path) as f:
            return json.load(f)
    return {}


def save_users(data_dir: Path, users: dict[str, dict]):
    """Save users to disk."""
    path = get_users_path(data_dir)
    with open(path, "w") as f:
        json.dump(users, f, indent=2)


def hash_password(password: str) -> str:
    """Hash a password (truncate to 72 bytes for bcrypt)."""
    # Truncate to 72 bytes (bcrypt limit)
    pw_bytes = password.encode('utf-8')[:72]
    return bcrypt.hashpw(pw_bytes, bcrypt.gensalt()).decode('utf-8')


def verify_password(plain_password: str, hashed_password: str) -> bool:
    """Verify a password against its hash."""
    pw_bytes = plain_password.encode('utf-8')[:72]
    return bcrypt.checkpw(pw_bytes, hashed_password.encode('utf-8'))


def create_user(data_dir: Path, username: str, password: str, email: Optional[str] = None) -> User:
    """Create a new user."""
    users = load_users(data_dir)

    if username in users:
        raise ValueError(f"Username already exists: {username}")

    user = User(
        username=username,
        password_hash=hash_password(password),
        created_at=datetime.now(timezone.utc).isoformat(),
        email=email
    )

    users[username] = user.model_dump()
    save_users(data_dir, users)

    return user


def authenticate_user(data_dir: Path, username: str, password: str) -> Optional[User]:
    """Authenticate a user by username and password."""
    users = load_users(data_dir)

    if username not in users:
        return None

    user_data = users[username]
    if not verify_password(password, user_data["password_hash"]):
        return None

    return User(**user_data)


def create_access_token(username: str) -> Token:
    """Create a JWT access token."""
    expires = datetime.now(timezone.utc) + timedelta(days=ACCESS_TOKEN_EXPIRE_DAYS)

    payload = {
        "sub": username,
        "exp": expires,
        "iat": datetime.now(timezone.utc)
    }

    token = jwt.encode(payload, SECRET_KEY, algorithm=ALGORITHM)

    return Token(
        access_token=token,
        username=username,
        expires_at=expires.isoformat()
    )


def verify_token(token: str) -> Optional[str]:
    """Verify a JWT token, return username if valid."""
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        username = payload.get("sub")
        return username
    except JWTError:
        return None


def get_current_user(data_dir: Path, token: str) -> Optional[User]:
    """Get current user from token."""
    username = verify_token(token)
    if not username:
        return None

    users = load_users(data_dir)
    if username not in users:
        return None

    return User(**users[username])