"""
Authentication & security helpers — JWT issuance/verification + password hashing.

- Passwords are hashed with PBKDF2-HMAC-SHA256 (Python stdlib, no native build deps).
  Legacy plaintext passwords still verify (and are upgraded to a hash on next login),
  so existing accounts keep working.
- JWTs are signed with HS256. Set a strong JWT_SECRET as an HF Space secret in prod.
"""

import os
import time
import base64
import hmac
import hashlib
import secrets
import logging

import jwt  # PyJWT
from fastapi import Depends, HTTPException
from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials

logger = logging.getLogger(__name__)

JWT_SECRET    = os.getenv("JWT_SECRET", "botboss-dev-secret-change-me")
JWT_ALGO      = "HS256"
JWT_TTL_HOURS = int(os.getenv("JWT_TTL_HOURS", "168"))  # 7 days

# ── Password hashing (PBKDF2, stdlib) ────────────────────────────────────────
_PBKDF2_ROUNDS = 200_000


def hash_password(password: str) -> str:
    salt = secrets.token_bytes(16)
    dk = hashlib.pbkdf2_hmac("sha256", (password or "").encode(), salt, _PBKDF2_ROUNDS)
    return "pbkdf2$" + base64.b64encode(salt).decode() + "$" + base64.b64encode(dk).decode()


def verify_password(password: str, stored: str) -> bool:
    if not stored:
        return False
    if stored.startswith("pbkdf2$"):
        try:
            _, salt_b64, dk_b64 = stored.split("$")
            salt = base64.b64decode(salt_b64)
            expected = base64.b64decode(dk_b64)
            dk = hashlib.pbkdf2_hmac("sha256", (password or "").encode(), salt, _PBKDF2_ROUNDS)
            return hmac.compare_digest(dk, expected)
        except Exception:
            return False
    # Legacy plaintext account (pre-hashing) — compare directly.
    return hmac.compare_digest(password or "", stored)


def is_hashed(stored: str) -> bool:
    return bool(stored) and stored.startswith("pbkdf2$")


# ── JWT ──────────────────────────────────────────────────────────────────────
def create_token(user: dict) -> str:
    now = int(time.time())
    payload = {
        "sub":   user.get("id"),
        "email": user.get("email"),
        "type":  user.get("type"),
        "name":  user.get("name"),
        "iat":   now,
        "exp":   now + JWT_TTL_HOURS * 3600,
    }
    return jwt.encode(payload, JWT_SECRET, algorithm=JWT_ALGO)


def decode_token(token: str):
    try:
        return jwt.decode(token, JWT_SECRET, algorithms=[JWT_ALGO])
    except Exception:
        return None


# ── FastAPI dependencies ─────────────────────────────────────────────────────
_bearer = HTTPBearer(auto_error=False)


def get_current_user(creds: HTTPAuthorizationCredentials = Depends(_bearer)):
    """Require a valid JWT. Returns the token payload {sub,email,type,name}."""
    if not creds or not creds.credentials:
        raise HTTPException(status_code=401, detail="Authentication required")
    payload = decode_token(creds.credentials)
    if not payload:
        raise HTTPException(status_code=401, detail="Invalid or expired token")
    return payload


def get_optional_user(creds: HTTPAuthorizationCredentials = Depends(_bearer)):
    """Return the token payload if present/valid, else None (for adaptive endpoints)."""
    if not creds or not creds.credentials:
        return None
    return decode_token(creds.credentials)