# Copyright 2015 Canonical Ltd.
# This file is part of cloud-init.  See LICENCE file for license information.
#
# vi: ts=4 expandtab
"""
cloud-init reporting framework

The reporting framework is intended to allow all parts of cloud-init to
report events in a structured manner.
"""

from ..registry import DictRegistry
from ..reporting.handlers import available_handlers


FINISH_EVENT_TYPE = 'finish'
START_EVENT_TYPE = 'start'

DEFAULT_CONFIG = {
    'logging': {'type': 'log'},
}


class _nameset(set):
    def __getattr__(self, name):
        if name in self:
            return name
        raise AttributeError("%s not a valid value" % name)


status = _nameset(("SUCCESS", "WARN", "FAIL"))


class ReportingEvent(object):
    """Encapsulation of event formatting."""

    def __init__(self, event_type, name, description):
        self.event_type = event_type
        self.name = name
        self.description = description

    def as_string(self):
        """The event represented as a string."""
        return '{0}: {1}: {2}'.format(
            self.event_type, self.name, self.description)

    def as_dict(self):
        """The event represented as a dictionary."""
        return {'name': self.name, 'description': self.description,
                'event_type': self.event_type}


class FinishReportingEvent(ReportingEvent):

    def __init__(self, name, description, result=status.SUCCESS):
        super(FinishReportingEvent, self).__init__(
            FINISH_EVENT_TYPE, name, description)
        self.result = result
        if result not in status:
            raise ValueError("Invalid result: %s" % result)

    def as_string(self):
        return '{0}: {1}: {2}: {3}'.format(
            self.event_type, self.name, self.result, self.description)

    def as_dict(self):
        """The event represented as json friendly."""
        data = super(FinishReportingEvent, self).as_dict()
        data['result'] = self.result
        return data


def update_configuration(config):
    """Update the instanciated_handler_registry.

    :param config:
        The dictionary containing changes to apply.  If a key is given
        with a False-ish value, the registered handler matching that name
        will be unregistered.
    """
    for handler_name, handler_config in config.items():
        if not handler_config:
            instantiated_handler_registry.unregister_item(
                handler_name, force=True)
            continue
        handler_config = handler_config.copy()
        cls = available_handlers.registered_items[handler_config.pop('type')]
        instantiated_handler_registry.unregister_item(handler_name)
        instance = cls(**handler_config)
        instantiated_handler_registry.register_item(handler_name, instance)


def report_event(event):
    """Report an event to all registered event handlers.

    This should generally be called via one of the other functions in
    the reporting module.

    :param event_type:
        The type of the event; this should be a constant from the
        reporting module.
    """
    for _, handler in instantiated_handler_registry.registered_items.items():
        handler.publish_event(event)


def report_finish_event(event_name, event_description,
                        result=status.SUCCESS):
    """Report a "finish" event.

    See :py:func:`.report_event` for parameter details.
    """
    event = FinishReportingEvent(event_name, event_description, result)
    return report_event(event)


def report_start_event(event_name, event_description):
    """Report a "start" event.

    :param event_name:
        The name of the event; this should be a topic which events would
        share (e.g. it will be the same for start and finish events).

    :param event_description:
        A human-readable description of the event that has occurred.
    """
    event = ReportingEvent(START_EVENT_TYPE, event_name, event_description)
    return report_event(event)


class ReportEventStack(object):
    """Context Manager for using :py:func:`report_event`

    This enables calling :py:func:`report_start_event` and
    :py:func:`report_finish_event` through a context manager.

    :param name:
        the name of the event

    :param description:
        the event's description, passed on to :py:func:`report_start_event`

    :param message:
        the description to use for the finish event. defaults to
        :param:description.

    :param parent:
    :type parent: :py:class:ReportEventStack or None
        The parent of this event.  The parent is populated with
        results of all its children.  The name used in reporting
        is <parent.name>/<name>

    :param reporting_enabled:
        Indicates if reporting events should be generated.
        If not provided, defaults to the parent's value, or True if no parent
        is provided.

    :param result_on_exception:
        The result value to set if an exception is caught. default
        value is FAIL.
    """
    def __init__(self, name, description, message=None, parent=None,
                 reporting_enabled=None, result_on_exception=status.FAIL):
        self.parent = parent
        self.name = name
        self.description = description
        self.message = message
        self.result_on_exception = result_on_exception
        self.result = status.SUCCESS

        # use parents reporting value if not provided
        if reporting_enabled is None:
            if parent:
                reporting_enabled = parent.reporting_enabled
            else:
                reporting_enabled = True
        self.reporting_enabled = reporting_enabled

        if parent:
            self.fullname = '/'.join((parent.fullname, name,))
        else:
            self.fullname = self.name
        self.children = {}

    def __repr__(self):
        return ("ReportEventStack(%s, %s, reporting_enabled=%s)" %
                (self.name, self.description, self.reporting_enabled))

    def __enter__(self):
        self.result = status.SUCCESS
        if self.reporting_enabled:
            report_start_event(self.fullname, self.description)
        if self.parent:
            self.parent.children[self.name] = (None, None)
        return self

    def _childrens_finish_info(self):
        for cand_result in (status.FAIL, status.WARN):
            for name, (value, msg) in self.children.items():
                if value == cand_result:
                    return (value, self.message)
        return (self.result, self.message)

    @property
    def result(self):
        return self._result

    @result.setter
    def result(self, value):
        if value not in status:
            raise ValueError("'%s' not a valid result" % value)
        self._result = value

    @property
    def message(self):
        if self._message is not None:
            return self._message
        return self.description

    @message.setter
    def message(self, value):
        self._message = value

    def _finish_info(self, exc):
        # return tuple of description, and value
        if exc:
            return (self.result_on_exception, self.message)
        return self._childrens_finish_info()

    def __exit__(self, exc_type, exc_value, traceback):
        (result, msg) = self._finish_info(exc_value)
        if self.parent:
            self.parent.children[self.name] = (result, msg)
        if self.reporting_enabled:
            report_finish_event(self.fullname, msg, result)


instantiated_handler_registry = DictRegistry()
update_configuration(DEFAULT_CONFIG)