"""Validate Telegram Web App initData and extract user username."""

import hashlib
import hmac
import json
import time
from urllib.parse import unquote

# Telegram algorithm: https://core.telegram.org/bots/webapps#validating-data-received-via-the-mini-app
# Data-check string: sorted key=value with URL-decoded values, then HMAC-SHA256(WebAppData, token) as secret.


def validate_init_data(
    init_data: str,
    bot_token: str,
    max_age_seconds: int | None = None,
) -> str | None:
    """Validate initData and return username; see validate_init_data_with_reason for failure reason."""
    username, _ = validate_init_data_with_reason(init_data, bot_token, max_age_seconds)
    return username


def validate_init_data_with_reason(
    init_data: str,
    bot_token: str,
    max_age_seconds: int | None = None,
) -> tuple[str | None, str]:
    """
    Validate initData signature and return (username, None) or (None, reason).
    reason is one of: "ok", "empty", "no_hash", "hash_mismatch", "auth_date_expired", "no_user", "user_invalid", "no_username".
    """
    if not init_data or not bot_token:
        return (None, "empty")
    init_data = init_data.strip()
    params = {}
    for part in init_data.split("&"):
        if "=" not in part:
            continue
        key, _, value = part.partition("=")
        if not key:
            continue
        params[key] = value
    hash_val = params.pop("hash", None)
    if not hash_val:
        return (None, "no_hash")
    data_pairs = sorted(params.items())
    # Data-check string: key=value with URL-decoded values (per Telegram example)
    data_string = "\n".join(f"{k}={unquote(v)}" for k, v in data_pairs)
    # HMAC-SHA256(key=WebAppData, message=bot_token) per reference implementations
    secret_key = hmac.new(
        b"WebAppData",
        msg=bot_token.encode(),
        digestmod=hashlib.sha256,
    ).digest()
    computed = hmac.new(
        secret_key,
        msg=data_string.encode(),
        digestmod=hashlib.sha256,
    ).hexdigest()
    if not hmac.compare_digest(computed.lower(), hash_val.lower()):
        return (None, "hash_mismatch")
    if max_age_seconds is not None and max_age_seconds > 0:
        auth_date_raw = params.get("auth_date")
        if not auth_date_raw:
            return (None, "auth_date_expired")
        try:
            auth_date = int(float(auth_date_raw))
        except (ValueError, TypeError):
            return (None, "auth_date_expired")
        if time.time() - auth_date > max_age_seconds:
            return (None, "auth_date_expired")
    user_raw = params.get("user")
    if not user_raw:
        return (None, "no_user")
    try:
        user = json.loads(unquote(user_raw))
    except (json.JSONDecodeError, TypeError):
        return (None, "user_invalid")
    if not isinstance(user, dict):
        return (None, "user_invalid")
    username = user.get("username")
    if not username or not isinstance(username, str):
        return (None, "no_username")
    return (username.strip().lstrip("@").lower(), "ok")