from .exceptions import ConfigError, ConfigNotFound
from .models import ConfigStore
from .signals import config_signal


class ConfigHandler(object):
    """
    An simple object class to wrap the config variables. It is a container
    object. To get a config variable use x = config[...], to set it use
    config[...] = x.
    """
    def __getitem__(self, key):
        try:
            return self._cache[key]
        except KeyError:
            raise ConfigNotFound('The config variable %s was not found.' % key)
        except AttributeError:
            self.setup_cache()
            return self[key]

    def __setitem__(self, key, value):
        # Save the new value to the database
        updated_rows = ConfigStore.objects.filter(key=key).update(value=value)
        if not updated_rows:
            ConfigStore.objects.create(key=key, value=value)

        # Update cache
        try:
            self._cache[key] = value
        except AttributeError:
            # This happens, when a config-var is set, before __getitem__ was
            # called. In this case nothing should happen.
            pass

        # Call on_change callback
        for receiver, config_collection in config_signal.send(sender='set_value'):
            for config_variable in config_collection.variables:
                if config_variable.name == key and config_variable.on_change:
                    config_variable.on_change()
                    break

    def items(self):
        """
        Returns key-value pairs of all config variables.
        """
        if not hasattr(self, '_cache'):
            self.setup_cache()
        return self._cache.items()

    def get_default(self, key):
        """
        Returns the default value for 'key'.
        """
        for receiver, config_collection in config_signal.send(sender='get_default'):
            for config_variable in config_collection.variables:
                if config_variable.name == key:
                    return config_variable.default_value
        raise ConfigNotFound('The config variable %s was not found.' % key)

    def setup_cache(self):
        """
        Loads all config variables from the database by sending a signal to
        save the default to the cache.
        """
        self._cache = {}
        for receiver, config_collection in config_signal.send(sender='setup_cache'):
            for config_variable in config_collection.variables:
                if config_variable.name in self._cache:
                    raise ConfigError('Too many values for config variable %s found.' % config_variable.name)
                self._cache[config_variable.name] = config_variable.default_value
        for config_object in ConfigStore.objects.all():
            self._cache[config_object.key] = config_object.value

    def __contains__(self, key):
        try:
            config[key]
        except ConfigNotFound:
            return False
        else:
            return True

    def get_all_translatable(self):
        """
        Generator to get all config variables as strings when their values are
        intended to be translated.
        """
        for receiver, config_collection in config_signal.send(sender='get_all_translatable'):
            for config_variable in config_collection.variables:
                if config_variable.translatable:
                    yield config_variable.name

config = ConfigHandler()
"""
Final entry point to get an set config variables. To get a config variable
use x = config[...], to set it use config[...] = x.
"""


class ConfigBaseCollection(object):
    """
    An abstract base class for simple and grouped config collections. The
    attributes title and url are required for collections that should be
    shown as a view. The attribute weight is used for the order of the
    links in the submenu of the views. The attribute extra_context can be
    used to insert extra css and js files into the template.
    """
    def __init__(self, title=None, url=None, weight=0, extra_context={}):
        self.title = title
        self.url = url
        self.weight = weight
        self.extra_context = extra_context

    def is_shown(self):
        """
        Returns True if at least one variable of the collection has a form field.
        """
        for variable in self.variables:
            if variable.form_field is not None:
                is_shown = True
                break
        else:
            is_shown = False
        if is_shown and (self.title is None or self.url is None):
            raise ConfigError('The config collection %s must have a title and an url attribute.' % self)
        return is_shown


class ConfigGroupedCollection(ConfigBaseCollection):
    """
    A simple object class for a grouped config collection. Developers have to
    set the groups attribute (tuple). The config variables are available
    via the variables attribute. The collection is shown as a view via the config
    main menu entry if there is at least one variable with a form field.
    """
    def __init__(self, groups, **kwargs):
        self.groups = groups
        super(ConfigGroupedCollection, self).__init__(**kwargs)

    @property
    def variables(self):
        for group in self.groups:
            for variable in group.variables:
                yield variable


class ConfigCollection(ConfigBaseCollection):
    """
    A simple object class for a ungrouped config collection. Developers have
    to set the variables (tuple) directly. The collection is shown as a view via
    the config main menu entry if there is at least one variable with a
    form field.
    """
    def __init__(self, variables, **kwargs):
        self.variables = variables
        super(ConfigCollection, self).__init__(**kwargs)


class ConfigGroup(object):
    """
    A simple object class representing a group of variables (tuple) with
    a special title.
    """

    def __init__(self, title, variables):
        self.title = title
        self.variables = variables

    def get_field_names(self):
        return [variable.name for variable in self.variables if variable.form_field is not None]


class ConfigVariable(object):
    """
    A simple object class to wrap new config variables. The keyword
    arguments 'name' and 'default_value' are required. The keyword
    argument 'form_field' has to be set if the variable should appear
    on the ConfigView. The argument 'on_change' can get a callback
    which is called every time, the variable is changed. If the argument
    'translatable' is set, OpenSlides is able to translate the value during
    setup of the database if the admin uses the respective command line option.
    """
    def __init__(self, name, default_value, form_field=None, on_change=None, translatable=False):
        self.name = name
        self.default_value = default_value
        self.form_field = form_field
        self.on_change = on_change
        self.translatable = translatable