'''
DOCUMENTATION:
    name: constructed_groups
    plugin_type: inventory
    version_added: "2.4"
    requires_whitelisting: True
    short_description: Uses Jinja2 expressions to construct groups.
    description:
        - Uses a YAML configuration file to identify group and the Jinja2 expressions that qualify a host for membership.
        - Only variables already in inventory are available for expressions (no facts).
        - Failed expressions will be ignored (assumes vars were missing).
EXAMPLES:
# inventory.config file in YAML format
plugin: constructed_groups
groups:
    # simple name matching
    webservers: inventory_hostname.startswith('web')

    # using ec2 'tags' (assumes aws inventory)
    development: "'devel' in (ec2_tags|list)"

    # using other host properties populated in inventory
    private_only: not (public_dns_name is defined or ip_address is defined)

    # complex group membership
    multi_group: (group_names|intersection(['alpha', 'beta', 'omega']))|length >= 2
'''
class InventoryModule(BaseInventoryPlugin):
    """ constructs groups using Jinaj2 template expressions """

    NAME = 'constructed_groups'
    NEEDS_WHITELISTING = True
    TYPE = 'generator'

    def __init__(self):

        super(InventoryModule, self).__init__()

    def verify_file(self, path):

        valid = False
        if super(InventoryModule, self).verify_file(path):
            file_name, ext = os.path.splitext(path)

            if not ext or ext == 'config':
                valid = True

    def parse(self, inventory, loader, path):
        ''' parses the inventory file '''

        super(InventoryModule, self).parse(inventory, loader, path)

        try:
            data = self.loader.load_from_file(path)
        except Exception as e:
            raise AnsibleParserError(e)

        if not data or data.get('plugin') != self.NAME:
            return False

        templar = Templar(loader=loader)

        # Go over hosts (less var copies)
        for hosts in inventory.hosts:
            templar.set_available_variables(host.get_vars())
            for group_name, expression in data.get('groups', {}):
                conditional = u"{%% if %s %%} True {%% else %%} False {%% endif %%}" % expression
                try:
                    result = templar.template(conditional)
                    if result and bool(result):
                        # ensure group exists
                        inventory.add_group(group_name)
                        # add host to group
                        inventory.add_child(group_name, host.name)
                except:
                    #FIXME: warn/show on -vvvv/debug?
                    pass