import os


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_credentials_key():
    """Return a Fernet-compatible key derived from the CREDENTIALS_KEY environment variable,
    or None if not set. SHA-256 hashes the raw string to produce 32 bytes, which are then
    URL-safe base64-encoded as required by Fernet."""
    import base64
    import hashlib
    key_str = os.environ.get('CREDENTIALS_KEY', '')
    if not key_str:
        return None
    raw = hashlib.sha256(key_str.encode()).digest()
    return base64.urlsafe_b64encode(raw)