"""Numeric derivative of data coming from a source sensor over time."""

from __future__ import annotations

from datetime import datetime, timedelta
from decimal import Decimal, DecimalException, InvalidOperation
import logging

import voluptuous as vol

from homeassistant.components.sensor import (
    ATTR_STATE_CLASS,
    PLATFORM_SCHEMA as SENSOR_PLATFORM_SCHEMA,
    RestoreSensor,
    SensorEntity,
    SensorStateClass,
)
from homeassistant.config_entries import ConfigEntry
from homeassistant.const import (
    ATTR_UNIT_OF_MEASUREMENT,
    CONF_NAME,
    CONF_SOURCE,
    CONF_UNIQUE_ID,
    STATE_UNAVAILABLE,
    STATE_UNKNOWN,
    Platform,
    UnitOfTime,
)
from homeassistant.core import (
    CALLBACK_TYPE,
    Event,
    EventStateChangedData,
    EventStateReportedData,
    HomeAssistant,
    State,
    callback,
)
from homeassistant.helpers import config_validation as cv, entity_registry as er
from homeassistant.helpers.device import async_entity_id_to_device
from homeassistant.helpers.entity_platform import (
    AddConfigEntryEntitiesCallback,
    AddEntitiesCallback,
)
from homeassistant.helpers.event import (
    async_call_later,
    async_track_state_change_event,
    async_track_state_report_event,
)
from homeassistant.helpers.reload import async_setup_reload_service
from homeassistant.helpers.typing import ConfigType, DiscoveryInfoType

from .const import (
    CONF_MAX_SUB_INTERVAL,
    CONF_ROUND_DIGITS,
    CONF_TIME_WINDOW,
    CONF_UNIT,
    CONF_UNIT_PREFIX,
    CONF_UNIT_TIME,
    DOMAIN,
)

_LOGGER = logging.getLogger(__name__)

ATTR_SOURCE_ID = "source"

# SI Metric prefixes
UNIT_PREFIXES = {
    None: 1,
    "n": 1e-9,
    "μ": 1e-6,
    "m": 1e-3,
    "k": 1e3,
    "M": 1e6,
    "G": 1e9,
    "T": 1e12,
}

# SI Time prefixes
UNIT_TIME = {
    UnitOfTime.SECONDS: 1,
    UnitOfTime.MINUTES: 60,
    UnitOfTime.HOURS: 60 * 60,
    UnitOfTime.DAYS: 24 * 60 * 60,
}

DEFAULT_ROUND = 3
DEFAULT_TIME_WINDOW = 0

PLATFORM_SCHEMA = SENSOR_PLATFORM_SCHEMA.extend(
    {
        vol.Optional(CONF_NAME): cv.string,
        vol.Optional(CONF_UNIQUE_ID): cv.string,
        vol.Required(CONF_SOURCE): cv.entity_id,
        vol.Optional(CONF_ROUND_DIGITS, default=DEFAULT_ROUND): vol.Coerce(int),
        vol.Optional(CONF_UNIT_PREFIX, default=None): vol.In(UNIT_PREFIXES),
        vol.Optional(CONF_UNIT_TIME, default=UnitOfTime.HOURS): vol.In(UNIT_TIME),
        vol.Optional(CONF_UNIT): cv.string,
        vol.Optional(CONF_TIME_WINDOW, default=DEFAULT_TIME_WINDOW): cv.time_period,
        vol.Optional(CONF_MAX_SUB_INTERVAL): cv.positive_time_period,
    }
)


def _is_decimal_state(state: str) -> bool:
    try:
        Decimal(state)
    except (InvalidOperation, TypeError):
        return False
    else:
        return True


async def async_setup_entry(
    hass: HomeAssistant,
    config_entry: ConfigEntry,
    async_add_entities: AddConfigEntryEntitiesCallback,
) -> None:
    """Initialize Derivative config entry."""
    registry = er.async_get(hass)
    # Validate + resolve entity registry id to entity_id
    source_entity_id = er.async_validate_entity_id(
        registry, config_entry.options[CONF_SOURCE]
    )

    if max_sub_interval_dict := config_entry.options.get(CONF_MAX_SUB_INTERVAL, None):
        max_sub_interval = cv.time_period(max_sub_interval_dict)
    else:
        max_sub_interval = None

    derivative_sensor = DerivativeSensor(
        hass,
        name=config_entry.title,
        round_digits=int(config_entry.options[CONF_ROUND_DIGITS]),
        source_entity=source_entity_id,
        time_window=cv.time_period_dict(config_entry.options[CONF_TIME_WINDOW]),
        unique_id=config_entry.entry_id,
        unit_of_measurement=None,
        unit_prefix=config_entry.options.get(CONF_UNIT_PREFIX),
        unit_time=config_entry.options[CONF_UNIT_TIME],
        max_sub_interval=max_sub_interval,
    )

    async_add_entities([derivative_sensor])


async def async_setup_platform(
    hass: HomeAssistant,
    config: ConfigType,
    async_add_entities: AddEntitiesCallback,
    discovery_info: DiscoveryInfoType | None = None,
) -> None:
    """Set up the derivative sensor."""
    await async_setup_reload_service(hass, DOMAIN, [Platform.SENSOR])

    derivative = DerivativeSensor(
        hass,
        name=config.get(CONF_NAME),
        round_digits=config[CONF_ROUND_DIGITS],
        source_entity=config[CONF_SOURCE],
        time_window=config[CONF_TIME_WINDOW],
        unit_of_measurement=config.get(CONF_UNIT),
        unit_prefix=config[CONF_UNIT_PREFIX],
        unit_time=config[CONF_UNIT_TIME],
        unique_id=config.get(CONF_UNIQUE_ID),
        max_sub_interval=config.get(CONF_MAX_SUB_INTERVAL),
    )

    async_add_entities([derivative])


class DerivativeSensor(RestoreSensor, SensorEntity):
    """Representation of a derivative sensor."""

    _attr_translation_key = "derivative"
    _attr_should_poll = False

    def __init__(
        self,
        hass: HomeAssistant,
        *,
        name: str | None,
        round_digits: int,
        source_entity: str,
        time_window: timedelta,
        unit_of_measurement: str | None,
        unit_prefix: str | None,
        unit_time: UnitOfTime,
        max_sub_interval: timedelta | None,
        unique_id: str | None,
    ) -> None:
        """Initialize the derivative sensor."""
        self._attr_unique_id = unique_id
        self.device_entry = async_entity_id_to_device(
            hass,
            source_entity,
        )
        self._sensor_source_id = source_entity
        self._round_digits = round_digits
        self._attr_native_value = round(Decimal(0), round_digits)
        # List of tuples with (timestamp_start, timestamp_end, derivative)
        self._state_list: list[tuple[datetime, datetime, Decimal]] = []
        self._last_valid_state_time: tuple[str, datetime] | None = None

        self._attr_name = name if name is not None else f"{source_entity} derivative"
        self._attr_extra_state_attributes = {ATTR_SOURCE_ID: source_entity}
        self._unit_template: str | None = None
        if unit_of_measurement is None:
            final_unit_prefix = "" if unit_prefix is None else unit_prefix
            self._unit_template = f"{final_unit_prefix}{{}}/{unit_time}"
            # we postpone the definition of unit_of_measurement to later
            self._attr_native_unit_of_measurement = None
        else:
            self._attr_native_unit_of_measurement = unit_of_measurement

        self._unit_prefix = UNIT_PREFIXES[unit_prefix]
        self._unit_time = UNIT_TIME[unit_time]
        self._time_window = time_window.total_seconds()
        self._max_sub_interval: timedelta | None = (
            None  # disable time based derivative
            if max_sub_interval is None or max_sub_interval.total_seconds() == 0
            else max_sub_interval
        )
        self._cancel_max_sub_interval_exceeded_callback: CALLBACK_TYPE = (
            lambda *args: None
        )

    def _derive_and_set_attributes_from_state(self, source_state: State | None) -> None:
        if self._unit_template and source_state:
            original_unit = self._attr_native_unit_of_measurement
            source_unit = source_state.attributes.get(ATTR_UNIT_OF_MEASUREMENT)
            self._attr_native_unit_of_measurement = self._unit_template.format(
                "" if source_unit is None else source_unit
            )
            if original_unit != self._attr_native_unit_of_measurement:
                _LOGGER.debug(
                    "%s: Derivative sensor switched UoM from %s to %s, resetting state to 0",
                    self.entity_id,
                    original_unit,
                    self._attr_native_unit_of_measurement,
                )
                self._state_list = []
                self._attr_native_value = round(Decimal(0), self._round_digits)

    def _calc_derivative_from_state_list(self, current_time: datetime) -> Decimal:
        def calculate_weight(start: datetime, end: datetime, now: datetime) -> float:
            window_start = now - timedelta(seconds=self._time_window)
            return (end - max(start, window_start)).total_seconds() / self._time_window

        derivative = Decimal("0.00")
        for start, end, value in self._state_list:
            weight = calculate_weight(start, end, current_time)
            derivative = derivative + (value * Decimal(weight))

        _LOGGER.debug(
            "%s: Calculated new derivative as %f from %d segments",
            self.entity_id,
            derivative,
            len(self._state_list),
        )

        return derivative

    def _prune_state_list(self, current_time: datetime) -> None:
        # filter out all derivatives older than `time_window` from our window list
        old_len = len(self._state_list)
        self._state_list = [
            (time_start, time_end, state)
            for time_start, time_end, state in self._state_list
            if (current_time - time_end).total_seconds() < self._time_window
        ]
        _LOGGER.debug(
            "%s: Pruned %d elements from state list",
            self.entity_id,
            old_len - len(self._state_list),
        )

    def _handle_invalid_source_state(self, state: State | None) -> bool:
        # Check the source state for unknown/unavailable condition. If unusable, write unknown/unavailable state and return false.
        if not state or state.state == STATE_UNAVAILABLE:
            self._attr_available = False
            self.async_write_ha_state()
            return False
        if not _is_decimal_state(state.state):
            self._attr_available = True
            self._write_native_value(None)
            return False
        self._attr_available = True
        return True

    def _write_native_value(self, derivative: Decimal | None) -> None:
        self._attr_native_value = (
            None if derivative is None else round(derivative, self._round_digits)
        )
        self.async_write_ha_state()

    async def _handle_restore(self) -> None:
        restored_data = await self.async_get_last_sensor_data()
        if restored_data:
            if self._attr_native_unit_of_measurement is None:
                # Only restore the unit if it's not assigned from YAML
                self._attr_native_unit_of_measurement = (
                    restored_data.native_unit_of_measurement
                )
            try:
                self._attr_native_value = round(
                    Decimal(restored_data.native_value),  # type: ignore[arg-type]
                    self._round_digits,
                )
            except (InvalidOperation, TypeError):
                self._attr_native_value = None

    async def async_added_to_hass(self) -> None:
        """Handle entity which will be added."""
        await super().async_added_to_hass()
        await self._handle_restore()

        source_state = self.hass.states.get(self._sensor_source_id)
        self._derive_and_set_attributes_from_state(source_state)

        def schedule_max_sub_interval_exceeded(source_state: State | None) -> None:
            """Schedule calculation using the source state and max_sub_interval.

            The callback reference is stored for possible cancellation if the source state
            reports a change before max_sub_interval has passed.
            If the callback is executed, meaning there was no state change reported, the
            source_state is assumed constant and calculation is done using its value.
            """
            if (
                self._max_sub_interval is not None
                and source_state is not None
                and (_is_decimal_state(source_state.state))
            ):

                @callback
                def _calc_derivative_on_max_sub_interval_exceeded_callback(
                    now: datetime,
                ) -> None:
                    """Calculate derivative based on time and reschedule."""

                    _LOGGER.debug(
                        "%s: Recalculating derivative due to max_sub_interval time elapsed",
                        self.entity_id,
                    )
                    self._prune_state_list(now)
                    derivative = self._calc_derivative_from_state_list(now)
                    self._write_native_value(derivative)

                    # If derivative is now zero, don't schedule another timeout callback, as it will have no effect
                    if derivative != 0:
                        schedule_max_sub_interval_exceeded(source_state)

                _LOGGER.debug(
                    "%s: Scheduling max_sub_interval_callback in %s",
                    self.entity_id,
                    self._max_sub_interval,
                )
                self._cancel_max_sub_interval_exceeded_callback = async_call_later(
                    self.hass,
                    self._max_sub_interval,
                    _calc_derivative_on_max_sub_interval_exceeded_callback,
                )

        @callback
        def on_state_reported(event: Event[EventStateReportedData]) -> None:
            """Handle constant sensor state."""
            _LOGGER.debug(
                "%s: New state reported event: %s", self.entity_id, event.data
            )
            self._cancel_max_sub_interval_exceeded_callback()
            new_state = event.data["new_state"]
            if not self._handle_invalid_source_state(new_state):
                return

            assert new_state
            if self._attr_native_value == Decimal(0):
                # If the derivative is zero, and the source sensor hasn't
                # changed state, then we know it will still be zero.
                return
            schedule_max_sub_interval_exceeded(new_state)
            calc_derivative(
                new_state,
                new_state.state,
                event.data["last_reported"],
                event.data["old_last_reported"],
            )

        @callback
        def on_state_changed(event: Event[EventStateChangedData]) -> None:
            """Handle changed sensor state."""
            _LOGGER.debug("%s: New state changed event: %s", self.entity_id, event.data)
            self._cancel_max_sub_interval_exceeded_callback()
            new_state = event.data["new_state"]

            if not self._handle_invalid_source_state(new_state):
                return

            assert new_state

            original_unit = self._attr_native_unit_of_measurement
            self._derive_and_set_attributes_from_state(new_state)
            if original_unit != self._attr_native_unit_of_measurement:
                self.async_write_ha_state()
                return

            schedule_max_sub_interval_exceeded(new_state)
            old_state = event.data["old_state"]
            if old_state is not None:
                calc_derivative(
                    new_state,
                    old_state.state,
                    new_state.last_updated,
                    old_state.last_reported,
                )
            else:
                # On first state change from none, update availability
                self.async_write_ha_state()

        def calc_derivative(
            new_state: State,
            old_value: str,
            new_timestamp: datetime,
            old_timestamp: datetime,
        ) -> None:
            """Handle the sensor state changes."""
            if not _is_decimal_state(old_value):
                if self._last_valid_state_time:
                    old_value = self._last_valid_state_time[0]
                    old_timestamp = self._last_valid_state_time[1]
                else:
                    # Sensor becomes valid for the first time, just keep the restored value
                    self.async_write_ha_state()
                    return

            self._prune_state_list(new_timestamp)

            try:
                elapsed_time = (new_timestamp - old_timestamp).total_seconds()
                delta_value = Decimal(new_state.state) - Decimal(old_value)
                new_derivative = (
                    delta_value
                    / Decimal(elapsed_time)
                    / Decimal(self._unit_prefix)
                    * Decimal(self._unit_time)
                )
                _LOGGER.debug(
                    "%s: Calculated new derivative segment as %f / %f / %f * %f = %f",
                    self.entity_id,
                    delta_value,
                    elapsed_time,
                    self._unit_prefix,
                    self._unit_time,
                    new_derivative,
                )

            except ValueError as err:
                _LOGGER.warning(
                    "%s: While calculating derivative: %s", self.entity_id, err
                )
            except DecimalException as err:
                _LOGGER.warning(
                    "%s: Invalid state (%s > %s): %s",
                    self.entity_id,
                    old_value,
                    new_state.state,
                    err,
                )
            except AssertionError as err:
                _LOGGER.error(
                    "%s: Could not calculate derivative: %s", self.entity_id, err
                )

            # For total inreasing sensors, the value is expected to continuously increase.
            # A negative derivative for a total increasing sensor likely indicates the
            # sensor has been reset. To prevent inaccurate data, discard this sample.
            if (
                new_state.attributes.get(ATTR_STATE_CLASS)
                == SensorStateClass.TOTAL_INCREASING
                and new_derivative < 0
            ):
                _LOGGER.debug(
                    "%s: Dropping sample as source total_increasing sensor decreased",
                    self.entity_id,
                )
                return

            # add latest derivative to the window list
            self._state_list.append((old_timestamp, new_timestamp, new_derivative))
            self._last_valid_state_time = (
                new_state.state,
                new_timestamp,
            )

            # If outside of time window just report derivative (is the same as modeling it in the window),
            # otherwise take the weighted average with the previous derivatives
            if elapsed_time > self._time_window:
                derivative = new_derivative
            else:
                derivative = self._calc_derivative_from_state_list(new_timestamp)
            self._write_native_value(derivative)

        source_state = self.hass.states.get(self._sensor_source_id)
        if source_state is None or source_state.state in [
            STATE_UNAVAILABLE,
            STATE_UNKNOWN,
        ]:
            self._attr_available = False

        if self._max_sub_interval is not None:
            schedule_max_sub_interval_exceeded(source_state)

            @callback
            def on_removed() -> None:
                self._cancel_max_sub_interval_exceeded_callback()

            self.async_on_remove(on_removed)

        self.async_on_remove(
            async_track_state_change_event(
                self.hass, self._sensor_source_id, on_state_changed
            )
        )

        self.async_on_remove(
            async_track_state_report_event(
                self.hass, self._sensor_source_id, on_state_reported
            )
        )
