# -*- coding: utf-8 -*-

#    Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

import collections

from debtcollector import removals
import prettytable
import six

from automaton import exceptions as excp


def _orderedkeys(data, sort=True):
    if sort:
        return sorted(six.iterkeys(data))
    else:
        return list(six.iterkeys(data))


class _Jump(object):
    """A FSM transition tracks this data while jumping."""
    def __init__(self, name, on_enter, on_exit):
        self.name = name
        self.on_enter = on_enter
        self.on_exit = on_exit


class FiniteMachine(object):
    """A finite state machine.

    This state machine can be used to automatically run a given set of
    transitions and states in response to events (either from callbacks or from
    generator/iterator send() values, see PEP 342). On each triggered event, a
    ``on_enter`` and ``on_exit`` callback can also be provided which will be
    called to perform some type of action on leaving a prior state and before
    entering a new state.

    NOTE(harlowja): reactions will *only* be called when the generator/iterator
    from ``runner.run_iter()`` does *not* send back a new event (they will
    always be called if the ``runner.run()`` method is used). This allows for
    two unique ways (these ways can also be intermixed) to use this state
    machine when using ``runner.run_iter()``; one where *external* events
    trigger the next state transition and one where *internal* reaction
    callbacks trigger the next state transition. The other way to use this
    state machine is to skip using ``runner.run()`` or ``runner.run_iter()``
    completely and use the ``process_event()`` method explicitly and trigger
    the events via some *external* functionality/triggers...
    """

    # Result of processing an event (cause and effect...)
    _Effect = collections.namedtuple('_Effect', 'reaction,terminal')

    @classmethod
    def _effect_builder(cls, new_state, event):
        return cls._Effect(new_state['reactions'].get(event),
                           new_state["terminal"])

    @removals.removed_kwarg('default_start_state',
                            message="The usage of 'default_start_state' via"
                            " the machine constructor is deprecated and will"
                            " be removed in a future version; usage of"
                            " the 'default_start_state' property setter is"
                            " recommended.")
    def __init__(self, default_start_state=None):
        self._transitions = {}
        self._states = collections.OrderedDict()
        self._default_start_state = default_start_state
        self._current = None
        self.frozen = False

    @property
    def default_start_state(self):
        return self._default_start_state

    @default_start_state.setter
    def default_start_state(self, state):
        """Sets the *default* start state that the machine should use.

        NOTE(harlowja): this will be used by ``initialize`` but only if that
        function is not given its own ``start_state`` that overrides this
        default.
        """
        if self.frozen:
            raise excp.FrozenMachine()
        if state not in self._states:
            raise excp.NotFound("Can not set the default start state to"
                                " undefined state '%s'" % (state))
        self._default_start_state = state

    @property
    def current_state(self):
        if self._current is not None:
            return self._current.name
        return None

    @property
    def terminated(self):
        """Returns whether the state machine is in a terminal state."""
        if self._current is None:
            return False
        return self._states[self._current.name]['terminal']

    def add_state(self, state, terminal=False, on_enter=None, on_exit=None):
        """Adds a given state to the state machine.

        The on_enter and on_exit callbacks, if provided will be expected to
        take two positional parameters, these being the state being exited (for
        on_exit) or the state being entered (for on_enter) and a second
        parameter which is the event that is being processed that caused the
        state transition.
        """
        if self.frozen:
            raise excp.FrozenMachine()
        if state in self._states:
            raise excp.Duplicate("State '%s' already defined" % state)
        if on_enter is not None:
            if not six.callable(on_enter):
                raise ValueError("On enter callback must be callable")
        if on_exit is not None:
            if not six.callable(on_exit):
                raise ValueError("On exit callback must be callable")
        self._states[state] = {
            'terminal': bool(terminal),
            'reactions': {},
            'on_enter': on_enter,
            'on_exit': on_exit,
        }
        self._transitions[state] = collections.OrderedDict()

    def add_reaction(self, state, event, reaction, *args, **kwargs):
        """Adds a reaction that may get triggered by the given event & state.

        Reaction callbacks may (depending on how the state machine is ran) be
        used after an event is processed (and a transition occurs) to cause the
        machine to react to the newly arrived at stable state.

        These callbacks are expected to accept three default positional
        parameters (although more can be passed in via *args and **kwargs,
        these will automatically get provided to the callback when it is
        activated *ontop* of the three default). The three default parameters
        are the last stable state, the new stable state and the event that
        caused the transition to this new stable state to be arrived at.

        The expected result of a callback is expected to be a new event that
        the callback wants the state machine to react to. This new event
        may (depending on how the state machine is ran) get processed (and
        this process typically repeats) until the state machine reaches a
        terminal state.
        """
        if self.frozen:
            raise excp.FrozenMachine()
        if state not in self._states:
            raise excp.NotFound("Can not add a reaction to event '%s' for an"
                                " undefined state '%s'" % (event, state))
        if not six.callable(reaction):
            raise ValueError("Reaction callback must be callable")
        if event not in self._states[state]['reactions']:
            self._states[state]['reactions'][event] = (reaction, args, kwargs)
        else:
            raise excp.Duplicate("State '%s' reaction to event '%s'"
                                 " already defined" % (state, event))

    def add_transition(self, start, end, event):
        """Adds an allowed transition from start -> end for the given event."""
        if self.frozen:
            raise excp.FrozenMachine()
        if start not in self._states:
            raise excp.NotFound("Can not add a transition on event '%s' that"
                                " starts in a undefined state '%s'"
                                % (event, start))
        if end not in self._states:
            raise excp.NotFound("Can not add a transition on event '%s' that"
                                " ends in a undefined state '%s'"
                                % (event, end))
        self._transitions[start][event] = _Jump(end,
                                                self._states[end]['on_enter'],
                                                self._states[start]['on_exit'])

    def _pre_process_event(self, event):
        current = self._current
        if current is None:
            raise excp.NotInitialized("Can not process event '%s'; the state"
                                      " machine hasn't been initialized"
                                      % event)
        if self._states[current.name]['terminal']:
            raise excp.InvalidState("Can not transition from terminal"
                                    " state '%s' on event '%s'"
                                    % (current.name, event))
        if event not in self._transitions[current.name]:
            raise excp.NotFound("Can not transition from state '%s' on"
                                " event '%s' (no defined transition)"
                                % (current.name, event))

    def _post_process_event(self, event, result):
        return result

    def process_event(self, event):
        """Trigger a state change in response to the provided event."""
        self._pre_process_event(event)
        current = self._current
        replacement = self._transitions[current.name][event]
        if current.on_exit is not None:
            current.on_exit(current.name, event)
        if replacement.on_enter is not None:
            replacement.on_enter(replacement.name, event)
        self._current = replacement
        result = self._effect_builder(self._states[replacement.name], event)
        return self._post_process_event(event, result)

    def initialize(self, start_state=None):
        """Sets up the state machine (sets current state to start state...)."""
        if start_state is None:
            start_state = self._default_start_state
        if start_state not in self._states:
            raise excp.NotFound("Can not start from a undefined"
                                " state '%s'" % (start_state))
        if self._states[start_state]['terminal']:
            raise excp.InvalidState("Can not start from a terminal"
                                    " state '%s'" % (start_state))
        # No on enter will be called, since we are priming the state machine
        # and have not really transitioned from anything to get here, we will
        # though allow on_exit to be called on the event that causes this
        # to be moved from...
        self._current = _Jump(start_state, None,
                              self._states[start_state]['on_exit'])

    def copy(self, shallow=False, unfreeze=False):
        """Copies the current state machine.

        NOTE(harlowja): the copy will be left in an *uninitialized* state.

        NOTE(harlowja): when a shallow copy is requested the copy will share
                        the same transition table and state table as the
                        source; this can be advantageous if you have a machine
                        and transitions + states that is defined somewhere
                        and want to use copies to run with (the copies have
                        the current state that is different between machines).
        """
        c = type(self)()
        c._default_start_state = self._default_start_state
        if unfreeze and self.frozen:
            c.frozen = False
        else:
            c.frozen = self.frozen
        if not shallow:
            for state, data in six.iteritems(self._states):
                copied_data = data.copy()
                copied_data['reactions'] = copied_data['reactions'].copy()
                c._states[state] = copied_data
            for state, data in six.iteritems(self._transitions):
                c._transitions[state] = data.copy()
        else:
            c._transitions = self._transitions
            c._states = self._states
        return c

    def __contains__(self, state):
        """Returns if this state exists in the machines known states."""
        return state in self._states

    def freeze(self):
        """Freezes & stops addition of states, transitions, reactions..."""
        self.frozen = True

    @property
    def states(self):
        """Returns the state names."""
        return list(six.iterkeys(self._states))

    @property
    def events(self):
        """Returns how many events exist."""
        c = 0
        for state in six.iterkeys(self._states):
            c += len(self._transitions[state])
        return c

    def __iter__(self):
        """Iterates over (start, event, end) transition tuples."""
        for state in six.iterkeys(self._states):
            for event, target in six.iteritems(self._transitions[state]):
                yield (state, event, target.name)

    def pformat(self, sort=True, empty='.'):
        """Pretty formats the state + transition table into a string.

        NOTE(harlowja): the sort parameter can be provided to sort the states
        and transitions by sort order; with it being provided as false the rows
        will be iterated in addition order instead.
        """
        tbl = prettytable.PrettyTable(["Start", "Event", "End",
                                       "On Enter", "On Exit"])
        for state in _orderedkeys(self._states, sort=sort):
            prefix_markings = []
            if self.current_state == state:
                prefix_markings.append("@")
            postfix_markings = []
            if self.default_start_state == state:
                postfix_markings.append("^")
            if self._states[state]['terminal']:
                postfix_markings.append("$")
            pretty_state = "%s%s" % ("".join(prefix_markings), state)
            if postfix_markings:
                pretty_state += "[%s]" % "".join(postfix_markings)
            if self._transitions[state]:
                for event in _orderedkeys(self._transitions[state],
                                          sort=sort):
                    target = self._transitions[state][event]
                    row = [pretty_state, event, target.name]
                    if target.on_enter is not None:
                        try:
                            row.append(target.on_enter.__name__)
                        except AttributeError:
                            row.append(target.on_enter)
                    else:
                        row.append(empty)
                    if target.on_exit is not None:
                        try:
                            row.append(target.on_exit.__name__)
                        except AttributeError:
                            row.append(target.on_exit)
                    else:
                        row.append(empty)
                    tbl.add_row(row)
            else:
                tbl.add_row([pretty_state, empty, empty, empty, empty])
        return tbl.get_string()


class HierarchicalFiniteMachine(FiniteMachine):
    """A fsm that understands how to run in a hierarchical mode."""

    # Result of processing an event (cause and effect...)
    _Effect = collections.namedtuple('_Effect',
                                     'reaction,terminal,machine')

    def __init__(self, default_start_state=None):
        super(HierarchicalFiniteMachine, self).__init__(
            default_start_state=default_start_state)
        self._nested_machines = {}

    @classmethod
    def _effect_builder(cls, new_state, event):
        return cls._Effect(new_state['reactions'].get(event),
                           new_state["terminal"], new_state.get('machine'))

    def add_state(self, state,
                  terminal=False, on_enter=None, on_exit=None, machine=None):
        if machine is not None and not isinstance(machine, FiniteMachine):
            raise ValueError(
                "Nested state machines must themselves be state machines")
        super(HierarchicalFiniteMachine, self).add_state(
            state, terminal=terminal, on_enter=on_enter, on_exit=on_exit)
        if machine is not None:
            self._states[state]['machine'] = machine
            self._nested_machines[state] = machine

    def copy(self, shallow=False, unfreeze=False):
        c = super(HierarchicalFiniteMachine, self).copy(shallow=shallow,
                                                        unfreeze=unfreeze)
        if shallow:
            c._nested_machines = self._nested_machines
        else:
            c._nested_machines = self._nested_machines.copy()
        return c

    def initialize(self, start_state=None):
        super(HierarchicalFiniteMachine, self).initialize(
            start_state=start_state)
        for data in six.itervalues(self._states):
            if 'machine' in data:
                data['machine'].initialize()

    @property
    def nested_machines(self):
        return self._nested_machines
