"""Utility functions for adaptation commands."""
from collections.abc import AsyncGenerator
from dataclasses import dataclass
from typing import Any

from homeassistant.components.light import (
    ATTR_BRIGHTNESS,
    ATTR_BRIGHTNESS_PCT,
    ATTR_BRIGHTNESS_STEP,
    ATTR_BRIGHTNESS_STEP_PCT,
    ATTR_COLOR_NAME,
    ATTR_COLOR_TEMP_KELVIN,
    ATTR_HS_COLOR,
    ATTR_RGB_COLOR,
    ATTR_TRANSITION,
    ATTR_XY_COLOR,
)
from homeassistant.const import ATTR_ENTITY_ID
from homeassistant.core import Context, HomeAssistant, State

COLOR_ATTRS = {  # Should ATTR_PROFILE be in here?
    ATTR_COLOR_NAME,
    ATTR_COLOR_TEMP_KELVIN,
    ATTR_HS_COLOR,
    ATTR_RGB_COLOR,
    ATTR_XY_COLOR,
}

BRIGHTNESS_ATTRS = {
    ATTR_BRIGHTNESS,
    ATTR_BRIGHTNESS_PCT,
    ATTR_BRIGHTNESS_STEP,
    ATTR_BRIGHTNESS_STEP_PCT,
}

ServiceData = dict[str, Any]


def _split_service_call_data(service_data: ServiceData) -> list[ServiceData]:
    """Splits the service data by the adapted attributes, i.e., into separate data
    items for brightness and color.
    """

    common_attrs = {ATTR_ENTITY_ID}
    common_data = {k: service_data[k] for k in common_attrs if k in service_data}

    attributes_split_sequence = [BRIGHTNESS_ATTRS, COLOR_ATTRS]
    service_datas = []

    for attributes in attributes_split_sequence:
        split_data = {
            attribute: service_data[attribute]
            for attribute in attributes
            if service_data.get(attribute)
        }
        if split_data:
            service_datas.append(common_data | split_data)

    # Distribute the transition duration across all service calls
    if service_datas and (transition := service_data.get(ATTR_TRANSITION)) is not None:
        transition = service_data[ATTR_TRANSITION] / len(service_datas)

        for service_data in service_datas:
            service_data[ATTR_TRANSITION] = transition

    return service_datas


def _filter_service_data(service_data: ServiceData, state: State | None) -> ServiceData:
    """Filter service data by removing attributes that already equal the given state.

    Removes all attributes from service call data whose values are already present
    in the target entity's state."""

    if not state:
        return service_data

    filtered_service_data = {
        k: service_data[k]
        for k in service_data.keys()
        if k not in state.attributes or service_data[k] != state.attributes[k]
    }

    return filtered_service_data


def _has_relevant_service_data_attributes(service_data: ServiceData) -> bool:
    """Determines whether the service data justifies an adaptation service call.

    A service call is not justified for data which does not contain any entries that
    change relevant attributes of an adapting entity, e.g., brightness or color."""
    common_attrs = {ATTR_ENTITY_ID, ATTR_TRANSITION}
    relevant_attrs = set(service_data) - common_attrs

    return bool(relevant_attrs)


async def _create_service_call_data_iterator(
    hass: HomeAssistant,
    service_datas: list[ServiceData],
    filter_by_state: bool = False,
) -> AsyncGenerator[ServiceData, None]:
    """Enumerates and filters a list of service datas on the fly.

    If filtering is enabled, every service data is filtered by the current state of
    the related entity and only returned if it contains relevant data that justifies
    a service call.
    The main advantage of this generator over a list is that it applies the filter
    at the time when the service data is read instead of up front. This gives greater
    flexibility because entity states can change while the items are iterated.
    """

    for service_data in service_datas:
        if filter_by_state and (entity_id := service_data.get(ATTR_ENTITY_ID)):
            current_entity_state = hass.states.get(entity_id)

            # Filter data to remove attributes that equal the current state
            if current_entity_state:
                service_data = _filter_service_data(service_data, current_entity_state)

            # Emit service data if it still contains relevant attributes (else try next)
            if _has_relevant_service_data_attributes(service_data):
                yield service_data
        else:
            yield service_data


@dataclass
class AdaptationData:
    """Holds all data required to execute an adaptation."""

    entity_id: str
    context: Context
    sleep_time: float
    service_call_datas: AsyncGenerator[ServiceData, None]
    initial_sleep: bool = False

    async def next_service_call_data(self) -> ServiceData | None:
        """Return data for the next service call, or none if no more data exists."""
        return await anext(self.service_call_datas, None)


def prepare_adaptation_data(
    hass: HomeAssistant,
    entity_id: str,
    context: Context,
    transition: float | None,
    split_delay: float,
    service_data: ServiceData,
    split: bool,
    filter_by_state: bool,
) -> AdaptationData:
    "Prepares a data object carrying all data required to execute an adaptation."
    service_datas = (
        [service_data] if not split else _split_service_call_data(service_data)
    )

    sleep_time = (
        transition / max(1, len(service_datas)) if transition is not None else 0
    ) + split_delay

    service_data_iterator = _create_service_call_data_iterator(
        hass, service_datas, filter_by_state
    )

    return AdaptationData(entity_id, context, sleep_time, service_data_iterator)