"""
Utility function for django-analytical.
"""

from django.conf import settings


HTML_COMMENT = "<!-- %(service)s disabled on internal IP " \
        "address\n%(html)s\n-->"


def get_required_setting(setting, value_re, invalid_msg):
    """
    Return a constant from ``django.conf.settings``.  The `setting`
    argument is the constant name, the `value_re` argument is a regular
    expression used to validate the setting value and the `invalid_msg`
    argument is used as exception message if the value is not valid.
    """
    try:
        value = getattr(settings, setting)
    except AttributeError:
        raise AnalyticalException("%s setting: not found" % setting)
    value = str(value)
    if not value_re.search(value):
        raise AnalyticalException("%s setting: %s: '%s'"
                % (setting, invalid_msg, value))
    return value


def get_identity(context, prefix=None, identity_func=None):
    """
    Get the identity of a logged in user from a template context.

    The `prefix` argument is used to provide different identities to
    different analytics services.  The `identity_func` argument is a
    function that returns the identity of the user; by default the
    identity is the username.
    """
    if prefix is not None:
        try:
            return context['%s_identity' % prefix]
        except KeyError:
            pass
    try:
        return context['analytical_identity']
    except KeyError:
        pass
    if getattr(settings, 'ANALYTICAL_AUTO_IDENTIFY', True):
        try:
            try:
                user = context['user']
            except KeyError:
                request = context['request']
                user = request.user
            if user.is_authenticated():
                if identity_func is not None:
                    return identity_func(user)
                else:
                    return user.username
        except (KeyError, AttributeError):
            pass
    return None


def is_internal_ip(context, prefix=None):
    """
    Return whether the visitor is coming from an internal IP address,
    based on information from the template context.

    The prefix is used to allow different analytics services to have
    different notions of internal addresses.
    """
    try:
        request = context['request']
        remote_ip = request.META.get('HTTP_X_FORWARDED_FOR', '')
        if not remote_ip:
            remote_ip = request.META.get('REMOTE_ADDR', '')
        if not remote_ip:
            return False

        internal_ips = ''
        if prefix is not None:
            internal_ips = getattr(settings, '%s_INTERNAL_IPS' % prefix, '')
        if not internal_ips:
            internal_ips = getattr(settings, 'ANALYTICAL_INTERNAL_IPS', '')
        if not internal_ips:
            internal_ips = getattr(settings, 'INTERNAL_IPS', '')

        return remote_ip in internal_ips
    except (KeyError, AttributeError):
        return False


def disable_html(html, service):
    """
    Disable HTML code by commenting it out.

    The `service` argument is used to display a friendly message.
    """
    return HTML_COMMENT % {'html': html, 'service': service}


class AnalyticalException(Exception):
    """
    Raised when an exception occurs in any django-analytical code that should
    be silenced in templates.
    """
    silent_variable_failure = True