"""
Provide pre-made queries on top of the recorder component.

For more details about this component, please refer to the documentation at
https://home-assistant.io/components/history/
"""
import re
from collections import defaultdict
from datetime import timedelta
from itertools import groupby

import homeassistant.util.dt as dt_util
from homeassistant.components import recorder, script
from homeassistant.components.http import HomeAssistantView

DOMAIN = 'history'
DEPENDENCIES = ['recorder', 'http']

SIGNIFICANT_DOMAINS = ('thermostat',)
IGNORE_DOMAINS = ('zone', 'scene',)

URL_HISTORY_PERIOD = re.compile(
    r'/api/history/period(?:/(?P<date>\d{4}-\d{1,2}-\d{1,2})|)')


def last_5_states(entity_id):
    """Return the last 5 states for entity_id."""
    entity_id = entity_id.lower()

    states = recorder.get_model('States')
    return recorder.execute(
        recorder.query('States').filter(
            (states.entity_id == entity_id) &
            (states.last_changed == states.last_updated)
        ).order_by(states.state_id.desc()).limit(5))


def get_significant_states(start_time, end_time=None, entity_id=None):
    """
    Return states changes during UTC period start_time - end_time.

    Significant states are all states where there is a state change,
    as well as all states from certain domains (for instance
    thermostat so that we get current temperature in our graphs).
    """
    states = recorder.get_model('States')
    query = recorder.query('States').filter(
        (states.domain.in_(SIGNIFICANT_DOMAINS) |
         (states.last_changed == states.last_updated)) &
        ((~states.domain.in_(IGNORE_DOMAINS)) &
         (states.last_updated > start_time)))

    if end_time is not None:
        query = query.filter(states.last_updated < end_time)

    if entity_id is not None:
        query = query.filter_by(entity_id=entity_id.lower())

    states = (
        state for state in recorder.execute(
            query.order_by(states.entity_id, states.last_updated))
        if _is_significant(state))

    return states_to_json(states, start_time, entity_id)


def state_changes_during_period(start_time, end_time=None, entity_id=None):
    """Return states changes during UTC period start_time - end_time."""
    states = recorder.get_model('States')
    query = recorder.query('States').filter(
        (states.last_changed == states.last_updated) &
        (states.last_changed > start_time))

    if end_time is not None:
        query = query.filter(states.last_updated < end_time)

    if entity_id is not None:
        query = query.filter_by(entity_id=entity_id.lower())

    states = recorder.execute(
        query.order_by(states.entity_id, states.last_updated))

    return states_to_json(states, start_time, entity_id)


def get_states(utc_point_in_time, entity_ids=None, run=None):
    """Return the states at a specific point in time."""
    if run is None:
        run = recorder.run_information(utc_point_in_time)

        # History did not run before utc_point_in_time
        if run is None:
            return []

    from sqlalchemy import and_, func

    states = recorder.get_model('States')
    most_recent_state_ids = recorder.query(
        func.max(states.state_id).label('max_state_id')
    ).filter(
        (states.created >= run.start) &
        (states.created < utc_point_in_time)
    )

    if entity_ids is not None:
        most_recent_state_ids = most_recent_state_ids.filter(
            states.entity_id.in_(entity_ids))

    most_recent_state_ids = most_recent_state_ids.group_by(
        states.entity_id).subquery()

    query = recorder.query('States').join(most_recent_state_ids, and_(
        states.state_id == most_recent_state_ids.c.max_state_id))

    return recorder.execute(query)


def states_to_json(states, start_time, entity_id):
    """Convert SQL results into JSON friendly data structure.

    This takes our state list and turns it into a JSON friendly data
    structure {'entity_id': [list of states], 'entity_id2': [list of states]}

    We also need to go back and create a synthetic zero data point for
    each list of states, otherwise our graphs won't start on the Y
    axis correctly.
    """
    result = defaultdict(list)

    entity_ids = [entity_id] if entity_id is not None else None

    # Get the states at the start time
    for state in get_states(start_time, entity_ids):
        state.last_changed = start_time
        state.last_updated = start_time
        result[state.entity_id].append(state)

    # Append all changes to it
    for entity_id, group in groupby(states, lambda state: state.entity_id):
        result[entity_id].extend(group)
    return result


def get_state(utc_point_in_time, entity_id, run=None):
    """Return a state at a specific point in time."""
    states = get_states(utc_point_in_time, (entity_id,), run)

    return states[0] if states else None


# pylint: disable=unused-argument
def setup(hass, config):
    """Setup the history hooks."""
    hass.wsgi.register_view(Last5StatesView)
    hass.wsgi.register_view(HistoryPeriodView)

    return True


class Last5StatesView(HomeAssistantView):
    """Handle last 5 state view requests."""

    url = '/api/history/entity/<entity:entity_id>/recent_states'
    name = 'api:history:entity-recent-states'

    def get(self, request, entity_id):
        """Retrieve last 5 states of entity."""
        return self.json(last_5_states(entity_id))


class HistoryPeriodView(HomeAssistantView):
    """Handle history period requests."""

    url = '/api/history/period'
    name = 'api:history:view-period'
    extra_urls = ['/api/history/period/<date:date>']

    def get(self, request, date=None):
        """Return history over a period of time."""
        one_day = timedelta(days=1)

        if date:
            start_time = dt_util.as_utc(dt_util.start_of_local_day(date))
        else:
            start_time = dt_util.utcnow() - one_day

        end_time = start_time + one_day
        entity_id = request.args.get('filter_entity_id')

        return self.json(
            get_significant_states(start_time, end_time, entity_id).values())


def _is_significant(state):
    """Test if state is significant for history charts.

    Will only test for things that are not filtered out in SQL.
    """
    # scripts that are not cancellable will never change state
    return (state.domain != 'script' or
            state.attributes.get(script.ATTR_CAN_CANCEL))
