import json
import os

_APP_CONFIG_PATH = '/data/app_config.json'
_app_config_cache = None
_app_config_mtime = None


def _load_app_config():
    global _app_config_cache, _app_config_mtime
    try:
        mtime = os.path.getmtime(_APP_CONFIG_PATH)
        if _app_config_cache is not None and mtime == _app_config_mtime:
            return _app_config_cache
        with open(_APP_CONFIG_PATH) as f:
            _app_config_cache = json.load(f)
        _app_config_mtime = mtime
        return _app_config_cache
    except Exception:
        return {}


def product_name():
    return os.environ.get('PRODUCT_NAME', 'routlin')


def web_app_display_name():
    edition = 'Pro' if is_pro() else 'CE'
    return os.environ.get('WEB_APP_DISPLAY_NAME', f'{product_name().capitalize()}-{edition} Dashboard')


def is_production():
    return not os.environ.get('DEV_MODE', '').lower() in ('1', 'true', 'yes')


def routlin_location():
    return os.environ.get('ROUTLIN_LOCATION', '/routlin_location')


def is_pro():
    try:
        return bool(open(f'{routlin_location()}/.license').read().strip())
    except OSError:
        return False


def get_host_utc_offset():
    # Returns signed integer seconds east of UTC (e.g. -21600 for UTC-6, +19800 for UTC+5:30).
    import time
    return time.localtime().tm_gmtoff


def get_client_utc_offset(timezone_str):
    """Return signed integer UTC offset in seconds for the given IANA timezone string."""
    try:
        from zoneinfo import ZoneInfo
        from datetime import datetime
        return int(datetime.now(ZoneInfo(timezone_str)).utcoffset().total_seconds())
    except Exception:
        return get_host_utc_offset()


def get_host_timezone():
    """Return the host timezone name (e.g. 'America/New_York'), or '' if unknown."""
    tz = os.environ.get('TZ', '').strip()
    if tz:
        return tz
    try:
        with open('/etc/timezone') as f:
            return f.read().strip()
    except OSError:
        pass
    return ''


def get_initial_manager_email():
    cfg = _load_app_config()
    return str(cfg.get('initial_manager_email') or os.environ.get('INITIAL_MANAGER_EMAIL', '')).strip().lower()


def is_single_user():
    return 'initial_manager_password' in _load_app_config()


def get_initial_manager_password_hash():
    return _load_app_config().get('initial_manager_password', '')


def get_credentials_key():
    """Return a Fernet-compatible key derived from the credentials_key in app_config.json
    (or CREDENTIALS_KEY env var as fallback), or None if not set. SHA-256 hashes the raw
    string to produce 32 bytes, URL-safe base64-encoded as required by Fernet."""
    import base64
    import hashlib
    cfg     = _load_app_config()
    key_str = str(cfg.get('credentials_key') or os.environ.get('CREDENTIALS_KEY', '')).strip()
    if not key_str:
        return None
    raw = hashlib.sha256(key_str.encode()).digest()
    return base64.urlsafe_b64encode(raw)


def get_smtp_config():
    """Return SMTP settings from app_config.json, falling back to env vars."""
    cfg  = _load_app_config()
    smtp = cfg.get('smtp', {})
    user = str(smtp.get('user') or os.environ.get('SMTP_USER', '')).strip()
    return {
        'host':     str(smtp.get('host')     or os.environ.get('SMTP_HOST', '')).strip(),
        'port':     int(smtp.get('port')     or os.environ.get('SMTP_PORT', 587)),
        'user':     user,
        'password': str(smtp.get('password') or os.environ.get('SMTP_PASSWORD', '')).strip(),
        'from':     str(smtp.get('from')     or os.environ.get('SMTP_FROM', user)).strip(),
    }