astro

defmodule Astro do
  @moduledoc """
  High-level API for common astronomical observations.

  This module is the primary public interface for the Astro library.
  It provides functions for sunrise/sunset, moonrise/moonset,
  equinoxes and solstices, lunar phases, and sun/moon position.
  All functions accept standard Elixir `Date` or `DateTime` structs
  and return `{:ok, value}` or `{:error, reason}` tuples.

  For lower-level access see `Astro.Solar`, `Astro.Lunar`,
  `Astro.Time`, `Astro.Earth` and `Astro.Ephemeris`.

  ## Specifying a location

  Location is specified as a `{longitude, latitude}` tuple (note
  the order, matching `Geo.Point`), a `Geo.Point.t` struct, or a
  `Geo.PointZ.t` struct that includes elevation in meters.

  * Longitude is `+` for east, `-` for west, in degrees.
  * Latitude is `+` for north, `-` for south, in degrees.

  ## Time zone resolution

  Rise/set functions (`sunrise/3`, `sunset/3`, `moonrise/3`,
  `moonset/3`) return a `DateTime` in the local time zone of the
  given location. By default the time zone is resolved via
  `TzWorld` (if configured). This can be overridden with the
  following options:

  * `:time_zone` — a zone name string, `:utc`, or `:default`
    (resolve from coordinates via `TzWorld`).
  * `:time_zone_database` — the time zone database module
    (e.g. Tz.TimeZoneDatabase).
  * `:time_zone_resolver` — a custom 1-arity function
    `(%Geo.Point{}) → {:ok, String.t()}`.

  ## Function groups

  ### Solar

  * `sunrise/3`, `sunset/3` — local sunrise and sunset times
  * `solar_noon/2` — UTC solar noon for a location and date
  * `hours_of_daylight/2` — duration of daylight
  * `sun_position_at/1` — right ascension, declination and distance
  * `sun_azimuth_elevation/2` — azimuth and altitude at a datetime
  * `sun_apparent_longitude/1` — apparent ecliptic longitude

  ### Lunar

  * `moonrise/3`, `moonset/3` — local moonrise and moonset times
  * `moon_position_at/1` — right ascension, declination and distance
  * `illuminated_fraction_of_moon_at/1` — fraction of the Moon illuminated
  * `lunar_phase_at/1` — phase angle (0–360°)
  * `lunar_phase_emoji/1` — Unicode emoji for a phase angle

  ### New moon search

  * `date_time_new_moon_before/1`, `date_time_new_moon_at_or_after/1`
  * `date_time_new_moon_nearest/1`

  ### Phase search

  * `date_time_lunar_phase_at_or_before/2`
  * `date_time_lunar_phase_at_or_after/2`

  ### Crescent visibility

  * `new_visible_crescent/3` — predict visibility of the new crescent moon

  ### Equinoxes and solstices

  * `equinox/2` — March or September equinox
  * `solstice/2` — June or December solstice

  """

  alias Astro.{Solar, Lunar, Location, Time, Math, Guards}

  import Astro.Math,
    only: [
      sin: 1,
      cos: 1,
      mod: 2,
      to_degrees: 1
    ]

  @type longitude :: float()
  @type latitude :: float()
  @type altitude :: float()
  @type degrees :: float()
  @type radians :: float()

  @type angle() :: number()
  @type meters() :: number()
  @type astronomical_units() :: number()
  @type kilometers() :: number()
  @type phase() :: angle()

  @type location :: {longitude, latitude} | Geo.Point.t() | Geo.PointZ.t()
  @type date :: Calendar.date() | Calendar.datetime()
  @type options :: keyword()

  @seconds_per_day 86_400

  # Selects the preferred time zone database at compile time based on which
  # optional dependency (`:tzdata` or `:tz`) is available. The `:elixir`
  # `:time_zone_database` application config still takes precedence at
  # runtime — see `default_options/0`.
  @compile_time_time_zone_db (cond do
                                Code.ensure_loaded?(Tzdata.TimeZoneDatabase) ->
                                  Tzdata.TimeZoneDatabase

                                Code.ensure_loaded?(Tz.TimeZoneDatabase) ->
                                  Tz.TimeZoneDatabase

                                true ->
                                  nil
                              end)

  defguard is_lunar_phase(phase) when phase >= 0.0 and phase <= 360.0

  @doc """
  Returns a tuple `{azimuth, altitude}` for a given
  date time and location.

  ### Arguments

  * `location` is the latitude, longitude and
    optionally elevation for the desired sunrise
    azimuth and altitude. It can be expressed as:

    * `{lng, lat}` - a tuple with longitude and latitude
      as floating point numbers. **Note** the order of the
      arguments.
    * a `Geo.Point.t` struct to represent a location without elevation
    * a `Geo.PointZ.t` struct to represent a location and elevation

  * `date_time` is a `t:DateTime.t/0` or a `t:Date.t/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  ### Returns

  * a tuple of the format `{azimith, altitude}` which are
    expressed in float degrees.

  ### Example

      iex> {:ok, date_time} = DateTime.new(~D[2023-05-17], ~T[12:47:00], "Australia/Sydney")
      iex> location = {151.1637781, -33.5145852}
      iex> {_azimuth, _altitude} = Astro.sun_azimuth_elevation(location, date_time)

  """

  # Use https://midcdmz.nrel.gov/solpos/spa.html for validation
  # current implementation is approx 1 degree at variance with
  # that calculator.

  @doc since: "0.11.0"
  @spec sun_azimuth_elevation(location(), Calendar.datetime()) ::
          {azimuth :: float, altitude :: float}

  def sun_azimuth_elevation(location, unquote(Guards.datetime()) = date_time) do
    _ = calendar

    %Geo.PointZ{coordinates: {right_ascension, declination, _distance}} =
      sun_position_at(date_time)

    %Geo.PointZ{coordinates: {_longitude, latitude, _altitude}} =
      Location.normalize_location(location)

    local_sidereal_time =
      Time.local_sidereal_time(location, date_time)

    hour_angle =
      mod(local_sidereal_time - right_ascension, 360.0)

    altitude =
      :math.asin(
        sin(declination) * sin(latitude) + cos(declination) * cos(latitude) * cos(hour_angle)
      )
      |> to_degrees

    a =
      :math.acos(
        (sin(declination) - sin(altitude) * sin(latitude)) / (cos(altitude) * cos(latitude))
      )
      |> to_degrees()

    azimuth =
      if sin(hour_angle) < 0.0, do: a, else: 360.0 - a

    {azimuth, altitude}
  end

  @doc """
  Returns a `t:Geo.PointZ` containing
  the right ascension and declination of
  the sun at a given date or date time.

  ### Arguments

  * `date_time` is a `t:DateTime.t/0` or a `t:Date/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  ### Returns

  * a `t:Geo.PointZ.t/0` struct with coordinates
    `{right_ascension, declination, distance}` with properties
    `%{reference: :celestial, object: :sun}`.
    `distance` is in meters.

  ### Example

      iex> Astro.sun_position_at(~D[1992-10-13])
      %Geo.PointZ{
        coordinates: {-161.61854343627374, -7.785324796344723, 149169604737.93973},
        properties: %{object: :sun, reference: :celestial},
        srid: nil
      }

  """
  @doc since: "0.6.0"
  @spec sun_position_at(date()) :: Geo.PointZ.t()

  def sun_position_at(unquote(Guards.datetime()) = date_time) do
    _ = calendar

    date_time
    |> Time.date_time_to_moment()
    |> Solar.solar_position()
    |> convert_distance_to_m()
    |> Location.normalize_location()
    |> Map.put(:properties, %{reference: :celestial, object: :sun})
  end

  def sun_position_at(unquote(Guards.date()) = date) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> Solar.solar_position()
    |> convert_distance_to_m()
    |> Location.normalize_location()
    |> Map.put(:properties, %{reference: :celestial, object: :sun})
  end

  defp convert_distance_to_m({lng, lat, alt}) do
    {lng, lat, Math.au_to_m(alt)}
  end

  @doc """
  Returns a `t:Geo.PointZ` containing
  the right ascension and declination of
  the moon at a given date or date time.

  ### Arguments

  * `date_time` is a `t:DateTime.t/0` or a `t:Date.t/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  ### Returns

  * a `t:Geo.PointZ` struct with coordinates
    `{right_ascension, declination, distance}` with properties
    `%{reference: :celestial, object: :moon}`
    `distance` is in meters.

  ### Example

      iex> Astro.moon_position_at(~D[1992-04-12]) |> Astro.Location.round(6)
      %Geo.PointZ{
        coordinates: {134.69343, 13.766512, 368409007.322444},
        properties: %{object: :moon, reference: :celestial},
        srid: nil
      }

  """
  @doc since: "0.6.0"
  @spec moon_position_at(date()) :: Geo.PointZ.t()

  def moon_position_at(unquote(Guards.datetime()) = date_time) do
    _ = calendar

    date_time
    |> Time.date_time_to_moment()
    |> moon_position_at_moment()
  end

  def moon_position_at(unquote(Guards.date()) = date) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> moon_position_at_moment()
  end

  defp moon_position_at_moment(moment) do
    moment
    |> Lunar.lunar_position()
    # |> convert_distance_to_m()
    |> Location.normalize_location()
    |> Map.put(:properties, %{reference: :celestial, object: :moon})
  end

  @doc """
  Returns the illumination of the moon
  as a float for a given date or date time.

  ### Arguments

  * `date_time` is a `t:DateTime.t/0` or a `t:Date.t/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  ### Returns

  * a `float` value between `0.0` and `1.0`
    representing the fractional illumination of
    the moon.

  ### Example

      iex> fraction = Astro.illuminated_fraction_of_moon_at(~D[2017-03-16])
      iex> Float.round(fraction, 4)
      0.8884

      iex> fraction = Astro.illuminated_fraction_of_moon_at(~D[1992-04-12])
      iex> Float.round(fraction, 4)
      0.6786

  """
  @doc since: "0.6.0"
  @spec illuminated_fraction_of_moon_at(date()) :: number()

  def illuminated_fraction_of_moon_at(unquote(Guards.datetime()) = date_time) do
    _ = calendar

    date_time
    |> Time.date_time_to_moment()
    |> Lunar.illuminated_fraction_of_moon()
  end

  def illuminated_fraction_of_moon_at(unquote(Guards.date()) = date) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> Lunar.illuminated_fraction_of_moon()
  end

  @doc """
  Returns the date time of the new
  moon before a given date or date time.

  ### Arguments

  * `date_time` is a `t:DateTime.t/0` or a `t:Date.t/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  ### Returns

  * `{:ok, date_time}` at which the new moon occurs or

  * `{:error, {module, reason}}`

  ### Example

      iex> Astro.date_time_new_moon_before(~D[2021-08-23])
      {:ok, ~U[2021-08-08 13:50:07.634598Z]}

  """
  @doc since: "0.5.0"
  @spec(
    date_time_new_moon_before(date()) ::
      {:ok, Calendar.datetime()},
    {:error, {module(), String.t()}}
  )

  def date_time_new_moon_at_or_before(unquote(Guards.datetime()) = date_time) do
    _ = calendar

    date_time
    |> Time.date_time_to_moment()
    |> Lunar.date_time_new_moon_before()
    |> Time.date_time_from_moment()
  end

  def date_time_new_moon_before(unquote(Guards.date()) = date) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> Lunar.date_time_new_moon_before()
    |> Time.date_time_from_moment()
  end

  @doc """
  Returns the date time of the new
  moon nearest to a given date or date time.

  ### Arguments

  * `date_time` is a `t:DateTime.t/0` or a `t:Date.t/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  ### Returns

  * `{:ok, date_time}` at which the new moon occurs or

  * `{:error, {module, reason}}`

  ### Example

      iex> Astro.date_time_new_moon_nearest(~D[2021-08-23])
      {:ok, ~U[2021-08-08 13:50:07.490242Z]}

  """
  @doc since: "2.0.0"
  @spec(
    date_time_new_moon_nearest(date()) ::
      {:ok, Calendar.datetime()},
    {:error, {module(), String.t()}}
  )

  def date_time_new_moon_nearest(unquote(Guards.datetime()) = date_time) do
    _ = calendar

    date_time
    |> Time.date_time_to_moment()
    |> Lunar.date_time_new_moon_nearest()
    |> Time.date_time_from_moment()
  end

  def date_time_new_moon_nearest(unquote(Guards.date()) = date) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> Lunar.date_time_new_moon_nearest()
    |> Time.date_time_from_moment()
  end

  @doc """
  Returns the date time of the new
  moon at or after a given date or
  date time.

  ### Arguments

  * `date_time` is a `DateTime` or a `Date` or
    any struct that meets the requirements of
    `t:Calendar.date` or `t:Calendar.datetime`.

  ### Returns

  * `{:ok, date_time}` at which the new moon occurs or

  * `{:error, {module, reason}}`

  ### Example

      iex> Astro.date_time_new_moon_at_or_after(~D[2021-08-23])
      {:ok, ~U[2021-09-07 00:51:44.267320Z]}

  """
  @doc since: "0.5.0"
  @spec(
    date_time_new_moon_at_or_after(date) ::
      {:ok, Calendar.datetime()},
    {:error, {module(), String.t()}}
  )

  def date_time_new_moon_at_or_after(unquote(Guards.datetime()) = datetime) do
    _ = calendar

    datetime
    |> Time.date_time_to_moment()
    |> Lunar.date_time_new_moon_at_or_after()
    |> Time.date_time_from_moment()
  end

  def date_time_new_moon_at_or_after(unquote(Guards.date()) = date) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> Lunar.date_time_new_moon_at_or_after()
    |> Time.date_time_from_moment()
  end

  @doc """
  Returns the lunar phase as a
  float number of degrees at a given
  date or date time.

  ### Arguments

  * `date_time` is a `t:DateTime.t/0` or a `t:Date.t/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  ### Returns

  * the lunar phase as a float number of
    degrees.

  ### Example

      iex> Astro.lunar_phase_at ~U[2021-08-22 12:02:02.816534Z]
      180.00004404669988

      iex> Astro.lunar_phase_at(~U[2021-07-10 01:16:34.022607Z])
      3.6600909621461326e-6

  """

  @doc since: "0.5.0"
  @spec lunar_phase_at(date()) :: phase()

  def lunar_phase_at(unquote(Guards.datetime()) = date_time) do
    _ = calendar

    date_time
    |> Time.date_time_to_moment()
    |> Lunar.lunar_phase_at()
  end

  def lunar_phase_at(unquote(Guards.date()) = date) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> Lunar.lunar_phase_at()
  end

  @doc """
  Returns the moon phase as a UTF8 binary
  representing an emoji of the moon phase.

  ### Arguments

  * `phase` is a moon phase between `0.0` and `360.0`.

  ### Returns

  * A single grapheme string representing the [Unicode
    moon phase emoji](https://unicode-table.com/en/sets/moon/).

  ### Examples

      iex> Astro.lunar_phase_emoji 0
      "🌑"
      iex> Astro.lunar_phase_emoji 45
      "🌒"
      iex> Astro.lunar_phase_emoji 90
      "🌓"
      iex> Astro.lunar_phase_emoji 135
      "🌔"
      iex> Astro.lunar_phase_emoji 180
      "🌕"
      iex> Astro.lunar_phase_emoji 245
      "🌖"
      iex> Astro.lunar_phase_emoji 270
      "🌗"
      iex> Astro.lunar_phase_emoji 320
      "🌘"
      iex> Astro.lunar_phase_emoji 360
      "🌑"

      iex> ~U[2021-08-22 12:02:02.816534Z]
      ...> |> Astro.lunar_phase_at()
      ...> |> Astro.lunar_phase_emoji()
      "🌕"

  """
  @emoji_base 0x1F310
  @emoji_phase_count 8
  @emoji_phase 360.0 / @emoji_phase_count

  @spec lunar_phase_emoji(phase()) :: String.t()
  def lunar_phase_emoji(360) do
    lunar_phase_emoji(0)
  end

  def lunar_phase_emoji(phase) when is_lunar_phase(phase) do
    offset = ceil(phase / @emoji_phase + 0.5)
    :unicode.characters_to_binary([offset + @emoji_base])
  end

  @doc """
  Returns the date time of a given
  lunar phase at or before a given
  date time or date.

  ### Arguments

  * `date_time` is a `t:DateTime.t/0` or a `t:Date.t/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  * `phase` is the required lunar phase expressed
    as a float number of degrees between `0.0` and
    `3660.0`.

  ### Returns

  * `{:ok, date_time}` at which the phase occurs or

  * `{:error, {module, reason}}`

  ### Example

      iex> Astro.date_time_lunar_phase_at_or_before(~D[2021-08-01], Astro.Lunar.new_moon_phase())
      {:ok, ~U[2021-07-10 01:16:34.022607Z]}

  """

  @doc since: "0.5.0"
  @spec(
    date_time_lunar_phase_at_or_before(date(), Astro.phase()) ::
      {:ok, Calendar.datetime()},
    {:error, {module(), String.t()}}
  )

  def date_time_lunar_phase_at_or_before(unquote(Guards.datetime()) = date_time, phase) do
    _ = calendar

    date_time
    |> Time.date_time_to_moment()
    |> Lunar.date_time_lunar_phase_at_or_before(phase)
    |> Time.date_time_from_moment()
  end

  def date_time_lunar_phase_at_or_before(unquote(Guards.date()) = date, phase) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> Lunar.date_time_lunar_phase_at_or_before(phase)
    |> Time.date_time_from_moment()
  end

  @doc """
  Returns the date time of a given
  lunar phase at or after a given
  date time or date.

  ### Arguments

  * `date_time` is a `t:DateTime.t/0` or a `t:Date.t/0` or
    any struct that meets the requirements of
    `t:Calendar.date/0` or `t:Calendar.datetime/0`.

  * `phase` is the required lunar phase expressed
    as a float number of degrees between `0.0` and
    `360.0`.

  ### Returns

  * `{:ok, date_time}` at which the phase occurs or

  * `{:error, {module, reason}}`

  ### Example

      iex> Astro.date_time_lunar_phase_at_or_after(~D[2021-08-01], Astro.Lunar.full_moon_phase())
      {:ok, ~U[2021-08-22 12:02:02.816534Z]}

  """

  @doc since: "0.5.0"
  @spec(
    date_time_lunar_phase_at_or_after(date(), Astro.phase()) ::
      {:ok, Calendar.datetime()},
    {:error, {module(), String.t()}}
  )

  def date_time_lunar_phase_at_or_after(unquote(Guards.datetime()) = date_time, phase) do
    _ = calendar

    date_time
    |> Time.date_time_to_moment()
    |> Lunar.date_time_lunar_phase_at_or_after(phase)
    |> Time.date_time_from_moment()
  end

  def date_time_lunar_phase_at_or_after(unquote(Guards.date()) = date, phase) do
    _ = calendar

    date
    |> Time.date_time_to_moment()
    |> Lunar.date_time_lunar_phase_at_or_after(phase)
    |> Time.date_time_from_moment()
  end

  @doc """
  Calculates the sunrise for a given location and date.

  Sunrise is the moment when the upper limb of
  the sun appears on the horizon in the morning.

  ### Arguments

  * `location` is the latitude, longitude and
    optionally elevation for the desired sunrise
    time. It can be expressed as:

    * `{lng, lat}` - a tuple with longitude and latitude
      as floating point numbers. **Note** the order of the
      arguments.
    * a `t:Geo.Point.t/0` struct to represent a location without elevation
    * a `t:Geo.PointZ.t/0` struct to represent a location and elevation

  * `date` is a `t:Date.t/0`, `t:NaiveDateTime.t/0` or `t:DateTime.t/0`
    to indicate the date of the year in which
    the sunrise time is required.

  * `options` is a keyword list of options.

  ### Options

  * `solar_elevation` represents the type of sunrise
    required. The default is `:geometric` which equates to
    a solar elevation of 90°. In this case the calculation
    also accounts for refraction and elevation to return a
    result which accords with the eye's perception. Other
    solar elevations are:

      * `:civil` representing a solar elevation of 96.0°. At this
        point the sun is just below the horizon so there is
        generally enough natural light to carry out most
        outdoor activities.

      * `:nautical` representing a solar elevation of 102.0°
        This is the point at which the horizon is just barely visible
        and the moon and stars can still be used for navigation.

      * `:astronomical` representing a solar elevation of 108.0°.
        This is the point beyond which astronomical observation
        becomes impractical.

      * Any floating point number representing the desired
        solar elevation.

  * `:time_zone` is the time zone in which the sunrise
    is requested. The default is `:default` in which
    the sunrise time is reported in the time zone of
    the requested location. `:utc` can be specified or any
    other time zone name supported by the option
    `:time_zone_database` is acceptabe.

  * `:time_zone_database` represents the module that
    implements the `Calendar.TimeZoneDatabase` behaviour.
    The default is the configured Elixir time zone database or
    one of Tzdata.TimeZoneDatabase or Tz.TimeZoneDatabase
    depending upon which dependency is configured.

  * `:time_zone_resolver` is a 1-arity function that resolves the
    time zone name for a given location. The function will receive
    a `%Geo.Point{cordinates: {lng, lat}}` struct and is expected to
    return either `{:ok, time_zone_name}` or `{:error, :time_zone_not_found}`.
    The default is `TzWorld.timezone_at/1` if `:tz_world` is
    configured.

  ### Returns

  * a `t:DateTime.t/0` representing the time of sunrise in the
    requested time zone at the requested location.

  * `{:error, :time_zone_not_found}` if the requested
    time zone is unknown.

  * `{:error, :time_zone_not_resolved}` if it is not possible
    to resolve a time zone name from the location. This can happen
    if `:tz_world` is not configured as a dependency and no
    `:time_zone_resolver` option is specified.

  * `{:error, :no_time}` if for the requested date
    and location there is no sunrise. This can occur at
    very high and very low latitudes during summer and winter.

  ### Notes

  * If the resolved UTC date time is ambiguous because of a daylight savings
    transition, the second of the two possibilities is applied. See
    the `DateTime.from_naive/3` for more information.

  ### Examples

      # Sunrise in Sydney, Australia
      Astro.sunrise({151.20666584, -33.8559799094}, ~D[2019-12-04])
      {:ok, #DateTime<2019-12-04 05:37:00.000000+11:00 AEDT Australia/Sydney>}

      # Sunrise in Alert, Nanavut, Canada
      Astro.sunrise({-62.3481, 82.5018}, ~D[2019-12-04])
      {:error, :no_time}

  """
  @spec sunrise(location, date, options) ::
          {:ok, DateTime.t()}
          | {:error, :time_zone_not_found | :time_zone_not_resolved | :no_time}

  def sunrise(location, date, options \\ []) when is_list(options) do
    Solar.SunRiseSet.sunrise(location, date_to_moment(date), options)
  end

  @doc """
  Calculates the sunset for a given location and date.

  Sunset is the moment when the upper limb of
  the sun disappears below the horizon in the evening.

  ### Arguments

  * `location` is the latitude, longitude and
    optionally elevation for the desired sunrise
    time. It can be expressed as:

    * `{lng, lat}` - a tuple with longitude and latitude
      as floating point numbers. **Note** the order of the
      arguments.
    * a `Geo.Point.t` struct to represent a location without elevation
    * a `Geo.PointZ.t` struct to represent a location and elevation

  * `date` is a `t:Date.t/0`, `t:NaiveDateTime.t/0` or `t:DateTime.t/0`
    to indicate the date of the year in which
    the sunset time is required.

  * `options` is a keyword list of options.

  ### Options

  * `solar_elevation` represents the type of sunset
    required. The default is `:geometric` which equates to
    a solar elevation of 90°. In this case the calulation
    also accounts for refraction and elevation to return a
    result which accords with the eyes perception. Other
    solar elevations are:

      * `:civil` representing a solar elevation of 96.0°. At this
        point the sun is just below the horizon so there is
        generally enough natural light to carry out most
        outdoor activities.

      * `:nautical` representing a solar elevation of 102.0°
        This is the point at which the horizon is just barely visible
        and the moon and stars can still be used for navigation.

      * `:astronomical`representing a solar elevation of 108.0°.
        This is the point beyond which astronomical observation
        becomes impractical.

      * Any floating point number representing the desired
        solar elevation.

  * `:time_zone` is the time zone in which the sunset
    is requested. The default is `:default` in which
    the sunrise time is reported in the time zone of
    the requested location. `:utc` can be specified or any
    other time zone name supported by the option
    `:time_zone_database` is acceptabe.

  * `:time_zone_database` represents the module that
    implements the `Calendar.TimeZoneDatabase` behaviour.
    The default is the configured Elixir time zone database or
    one of Tzdata.TimeZoneDatabase or Tz.TimeZoneDatabase
    depending upon which dependency is configured.

  * `:time_zone_resolver` is a 1-arity function that resolves the
    time zone name for a given location. The function will receive
    a `%Geo.Point{cordinates: {lng, lat}}` struct and is expected to
    return either `{:ok, time_zone_name}` or `{:error, :time_zone_not_found}`.
    The default is `TzWorld.timezone_at/1` if `:tz_world` is
    configured.

  ### Returns

  * a `t:DateTime.t/0` representing the time of sunset in the
    requested time zone at the requested location.

  * `{:error, :time_zone_not_found}` if the requested
    time zone is unknown.

  * `{:error, :time_zone_not_resolved}` if it is not possible
    to resolve a time zone name from the location. This can happen
    if `:tz_world` is not configured as a dependency and no
    `:time_zone_resolver` option is specified.

  * `{:error, :no_time}` if for the requested date
    and location there is no sunset. This can occur at
    very high and very low latitudes during summer and winter.

  ### Notes

  * If the resolved UTC date time is ambiguous because of a daylight savings
    transition, the second of the two possibilities is applied. See
    the `DateTime.from_naive/3` for more information.

  ### Examples

      # Sunset in Sydney, Australia
      Astro.sunset({151.20666584, -33.8559799094}, ~D[2019-12-04])
      {:ok, #DateTime<2019-12-04 19:53:00.000000+11:00 AEDT Australia/Sydney>}

      # Sunset in Alert, Nanavut, Canada
      Astro.sunset({-62.3481, 82.5018}, ~D[2019-12-04])
      {:error, :no_time}

  """
  @spec sunset(location, date, options) ::
          {:ok, DateTime.t()}
          | {:error, :time_zone_not_found | :time_zone_not_resolved | :no_time}

  def sunset(location, date, options \\ []) when is_list(options) do
    Solar.SunRiseSet.sunset(location, date_to_moment(date), options)
  end

  @doc """
  Returns the datetime of moonrise for a given location and date.

  Uses the JPL DE440s ephemeris with fully topocentric correction
  to compute the Moon's altitude zero-crossing via scan-and-bisect.

  ### Arguments

  * `location` is the location as a `{longitude, latitude}` tuple,
    a `Geo.Point.t` or a `Geo.PointZ.t`.

  * `date` is a `t:Date.t/0` or `t:DateTime.t/0`.

  * `options` is a keyword list of options.

  ### Options

  * `:time_zone` is the time zone in which the sunrise
    is requested. The default is `:default` in which
    the sunrise time is reported in the time zone of
    the requested location. `:utc` can be specified or any
    other time zone name supported by the option
    `:time_zone_database` is acceptabe.

  * `:time_zone_database` represents the module that
    implements the `Calendar.TimeZoneDatabase` behaviour.
    The default is the configured Elixir time zone database or
    one of Tzdata.TimeZoneDatabase or Tz.TimeZoneDatabase
    depending upon which dependency is configured.

  * `:time_zone_resolver` is a 1-arity function that resolves the
    time zone name for a given location. The function will receive
    a `%Geo.Point{cordinates: {lng, lat}}` struct and is expected to
    return either `{:ok, time_zone_name}` or `{:error, :time_zone_not_found}`.
    The default is `TzWorld.timezone_at/1` if `:tz_world` is
    configured.

  ### Returns

  * `{:ok, date_time}` with the local time of moonrise, or

  * `{:error, :moon_always_below_horizon}` if the Moon does not
    rise on the given date at the given location.

  """
  @doc since: "2.0.0"
  @spec moonrise(location, date, options) ::
          {:ok, DateTime.t()} | {:error, :moon_always_below_horizon}

  def moonrise(location, date, options \\ default_options())

  def moonrise(location, date, options) when is_list(options) do
    Lunar.MoonRiseSet.moonrise(location, date_to_moment(date), options)
  end

  @doc """
  Returns the datetime of moonset for a given location and date.

  Uses the JPL DE440s ephemeris with fully topocentric correction
  to compute the Moon's altitude zero-crossing via scan-and-bisect.

  ### Arguments

  * `location` is the location as a `{longitude, latitude}` tuple,
    a `Geo.Point.t` or a `Geo.PointZ.t`.

  * `date` is a `t:Date.t/0` or `t:DateTime.t/0`.

  * `options` is a keyword list of options.

  ### Options

  * `:time_zone` is the time zone in which the sunrise
    is requested. The default is `:default` in which
    the sunrise time is reported in the time zone of
    the requested location. `:utc` can be specified or any
    other time zone name supported by the option
    `:time_zone_database` is acceptabe.

  * `:time_zone_database` represents the module that
    implements the `Calendar.TimeZoneDatabase` behaviour.
    The default is the configured Elixir time zone database or
    one of Tzdata.TimeZoneDatabase or Tz.TimeZoneDatabase
    depending upon which dependency is configured.

  * `:time_zone_resolver` is a 1-arity function that resolves the
    time zone name for a given location. The function will receive
    a `%Geo.Point{cordinates: {lng, lat}}` struct and is expected to
    return either `{:ok, time_zone_name}` or `{:error, :time_zone_not_found}`.
    The default is `TzWorld.timezone_at/1` if `:tz_world` is
    configured.

  ### Returns

  * `{:ok, date_time}` with the local time of moonset, or

  * `{:error, :moon_always_above_horizon}` if the Moon does not
    set on the given date at the given location.

  """
  @doc since: "2.0.0"
  @spec moonset(location, date, options) ::
          {:ok, DateTime.t()} | {:error, :moon_always_above_horizon}

  def moonset(location, date, options \\ default_options())

  def moonset(location, date, options) when is_list(options) do
    Lunar.MoonRiseSet.moonset(location, date_to_moment(date), options)
  end

  @doc """
  Predicts the visibility of the new crescent moon at a given location
  on a given date using one of three published criteria.

  At the optimal observation time after sunset, the function evaluates
  the geometric and photometric conditions to classify the crescent
  into one of five visibility categories.

  ### Arguments

  * `location` is the latitude, longitude and optionally elevation for
    the observation site. It can be expressed as:

    * `{lng, lat}` - a tuple with longitude and latitude as floating
      point numbers. **Note** the order of the arguments.

    * a `t:Geo.Point.t/0` struct to represent a location without elevation.

    * a `t:Geo.PointZ.t/0` struct to represent a location and elevation.

  * `date` is a `t:Date.t/0` or `t:DateTime.t/0` indicating the evening
    on which crescent visibility is to be evaluated.

  * `method` selects the prediction criterion. Default `:odeh`.

    * `:odeh` — Odeh (2006). Empirical criterion based on 737 observations.
      Uses topocentric ARCV with a Danjon limit of 6.4°. The most widely
      used modern criterion.

    * `:yallop` — Yallop (1997). Empirical criterion based on 295
      observations. Uses geocentric ARCV. The original single-parameter
      approach that Odeh later refined.

    * `:schaefer` — Schaefer (1988/2000). Physics-based model computing
      the contrast between crescent brightness and twilight sky brightness
      against the human contrast detection threshold. The best observation
      time is found by scanning from sunset to moonset.

  ### Options

  When `method` is `:schaefer`, the following options are accepted as
  an optional fourth argument (a keyword list):

  * `:extinction` — V-band zenith extinction coefficient. Default `0.172`
    (clean sea-level site). Typical values: `0.12` (high mountain),
    `0.17` (sea level), `0.25` (hazy conditions).

  ### Returns

  * `{:ok, visibility}` where `visibility` is one of:

    * `:A` — Visible to the naked eye.

    * `:B` — Visible with optical aid.

    * `:C` — May need optical aid.

    * `:D` — Not visible with optical aid.

    * `:E` — Not visible.

  * `{:error, :no_sunset}` if no sunset occurs on the given date at
    the given location (e.g. polar day).

  * `{:error, :not_found}` if the date is outside the range covered
    by the installed ephemeris.

  ### Method comparison

  | Aspect | Yallop (1997) | Odeh (2006) | Schaefer (1988/2000) |
  |--------|---------------|-------------|----------------------|
  | Basis | Empirical polynomial | Empirical polynomial | Physical model |
  | Observations | 295 | 737 | N/A (theory) |
  | ARCV type | Geocentric | Topocentric | N/A |
  | Best time | Sunset + 4/9 lag | Sunset + 4/9 lag | Scanned (max Rs) |
  | Atmosphere | Not modelled | Not modelled | Extinction coefficient |

  ### Examples

      iex> location = {-0.1275, 51.5072}
      iex> Astro.new_visible_crescent(location, ~D[2025-03-31])
      {:ok, :A}

      iex> location = {-0.1275, 51.5072}
      iex> Astro.new_visible_crescent(location, ~D[2025-03-31], :yallop)
      {:ok, :A}

  """
  @doc since: "2.1.0"
  @type method :: :odeh | :yallop | :schaefer

  @spec new_visible_crescent(location(), date(), method()) ::
          {:ok, Lunar.CrescentVisibility.visibility()} | {:error, :no_sunset | :not_found}

  def new_visible_crescent(location, date, method \\ :odeh)

  def new_visible_crescent(location, date, :yallop) do
    moment = Time.date_time_to_moment(date)
    normalized = Location.normalize_location(location)
    Lunar.CrescentVisibility.yallop_new_visible_crescent(normalized, moment)
  end

  def new_visible_crescent(location, date, :odeh) do
    moment = Time.date_time_to_moment(date)
    normalized = Location.normalize_location(location)
    Lunar.CrescentVisibility.odeh_new_visible_crescent(normalized, moment)
  end

  def new_visible_crescent(location, date, :schaefer) do
    moment = Time.date_time_to_moment(date)
    normalized = Location.normalize_location(location)
    Lunar.CrescentVisibility.schaefer_new_visible_crescent(normalized, moment)
  end

  @doc """
  Same as `new_visible_crescent/3` with `method: :schaefer` but
  accepts additional atmospheric options.

  See `new_visible_crescent/3` for full documentation.

  ### Options

  * `:extinction` — V-band zenith extinction coefficient. Default `0.172`.

  ### Example

      iex> location = {39.8579, 21.3891}
      iex> {:ok, visibility} = Astro.new_visible_crescent(location, ~D[2025-03-31], :schaefer, extinction: 0.25)
      iex> visibility in [:A, :B, :C, :D, :E]
      true

  """
  @doc since: "2.1.0"
  @spec new_visible_crescent(location(), date(), :schaefer, keyword()) ::
          {:ok, Lunar.CrescentVisibility.visibility()} | {:error, :no_sunset | :not_found}

  def new_visible_crescent(location, date, :schaefer, options) when is_list(options) do
    moment = Time.date_time_to_moment(date)
    normalized = Location.normalize_location(location)
    Lunar.CrescentVisibility.schaefer_new_visible_crescent(normalized, moment, options)
  end

  @doc """
  Returns the datetime in UTC for either the
  March or September equinox.

  ### Arguments

  * `year` is the gregorian year for which the equinox is
    to be calculated.

  * `event` is either `:march` or `:september` indicating
    which of the two annual equinox datetimes is required.

  ### Returns

  * `{:ok, datetime}` representing the UTC datetime of
    the equinox.

  * `{:error, :year_out_of_range}` if `year` is outside the
    supported range of 1000 CE to 3000 CE.

  ### Examples

      iex> {:ok, dt} = Astro.equinox 2019, :march
      iex> DateTime.truncate(dt, :second)
      ~U[2019-03-20 21:58:28Z]
      iex> {:ok, dt} = Astro.equinox 2019, :september
      iex> DateTime.truncate(dt, :second)
      ~U[2019-09-23 07:49:52Z]
      iex> Astro.equinox 900, :march
      {:error, :year_out_of_range}

  ### Notes

  This equinox calculation is expected to be accurate
  to within 2 minutes for the years 1000 CE to 3000 CE.

  An equinox is commonly regarded as the instant of
  time when the plane of earth's equator passes through
  the center of the Sun. This occurs twice each year:
  around 20 March and 23 September.

  In other words, it is the moment at which the
  center of the visible sun is directly above the equator.

  """
  @spec equinox(Calendar.year(), :march | :september) ::
          {:ok, DateTime.t()} | {:error, :year_out_of_range}
  def equinox(year, event) when event in [:march, :september] and year in 1000..3000 do
    Solar.equinox_and_solstice(year, event)
  end

  # The calculation is accurate to within 2 minutes only for 1000 CE to
  # 3000 CE; outside that span return an error rather than raising a
  # FunctionClauseError at the caller.
  def equinox(year, event) when event in [:march, :september] and is_integer(year) do
    {:error, :year_out_of_range}
  end

  @doc """
  Returns the datetime in UTC for either the
  June or December solstice.

  ### Arguments

  * `year` is the gregorian year for which the solstice is
    to be calculated.

  * `event` is either `:june` or `:december` indicating
    which of the two annual solstice datetimes is required.

  ### Returns

  * `{:ok, datetime}` representing the UTC datetime of
    the solstice.

  * `{:error, :year_out_of_range}` if `year` is outside the
    supported range of 1000 CE to 3000 CE.

  ### Examples

      iex> {:ok, dt} = Astro.solstice 2019, :december
      iex> DateTime.truncate(dt, :second)
      ~U[2019-12-22 04:19:19Z]
      iex> {:ok, dt} = Astro.solstice 2019, :june
      iex> DateTime.truncate(dt, :second)
      ~U[2019-06-21 15:54:07Z]
      iex> Astro.solstice 3500, :june
      {:error, :year_out_of_range}

  ### Notes

  This solstice calculation is expected to be accurate
  to within 2 minutes for the years 1000 CE to 3000 CE.

  A solstice is an event occurring when the Sun appears
  to reach its most northerly or southerly excursion
  relative to the celestial equator on the celestial
  sphere. Two solstices occur annually, around June 21
  and December 21.

  The seasons of the year are determined by
  reference to both the solstices and the equinoxes.

  The day of a solstice in either hemisphere has either the most
  sunlight of the year (summer solstice) or the least
  sunlight of the year (winter solstice) for any place
  other than the Equator.

  Alternative terms, with no ambiguity as to which
  hemisphere is the context, are "June solstice" and
  "December solstice", referring to the months in
  which they take place every year.

  """
  @spec solstice(Calendar.year(), :june | :december) ::
          {:ok, DateTime.t()} | {:error, :year_out_of_range}
  def solstice(year, event) when event in [:june, :december] and year in 1000..3000 do
    Solar.equinox_and_solstice(year, event)
  end

  # The calculation is accurate to within 2 minutes only for 1000 CE to
  # 3000 CE; outside that span return an error rather than raising a
  # FunctionClauseError at the caller.
  def solstice(year, event) when event in [:june, :december] and is_integer(year) do
    {:error, :year_out_of_range}
  end

  @doc """
  Returns solar noon for a
  given date and location as
  a UTC datetime

  ### Arguments

  * `location` is the latitude, longitude and
    optionally elevation for the desired solar noon
    time. It can be expressed as:

    * `{lng, lat}` - a tuple with longitude and latitude
      as floating point numbers. **Note** the order of the
      arguments.
    * a `Geo.Point.t` struct to represent a location without elevation.
    * a `Geo.PointZ.t` struct to represent a location and elevation.

  * `date` is any `t:Date.t/0` in the Gregorian
    calendar (for example, `Calendar.ISO`).

  ### Returns

  * a UTC datetime representing solar noon
    at the given location for the given date.

  ### Example

      iex> Astro.solar_noon {151.20666584, -33.8559799094}, ~D[2019-12-06]
      {:ok, ~U[2019-12-06 01:45:42Z]}

  ### Notes

  Solar noon is the moment when the sun passes a
  location's meridian and reaches its highest position
  in the sky. In most cases, it doesn't happen at 12 o'clock.

  At solar noon, the Sun reaches its
  highest position in the sky as it passes the
  local meridian.

  """
  @spec solar_noon(Astro.location(), Calendar.date()) :: {:ok, DateTime.t()}
  def solar_noon(location, date) do
    %Geo.PointZ{coordinates: {longitude, _, _}} = Location.normalize_location(location)

    julian_day = Time.julian_day_from_date(date)
    julian_centuries = Time.julian_centuries_from_julian_day(julian_day)

    julian_centuries
    |> Solar.solar_noon_utc(-longitude)
    |> Time.date_time_from_date_and_minutes(date)
  end

  @doc """
  Returns solar longitude for a
  given date. Solar longitude is used
  to identify the seasons.

  ### Arguments

  * `date` is any `t:Date.t/0` in the Gregorian
    calendar (for example, `Calendar.ISO`).

  ### Returns

  * a `float` number of degrees between 0 and
    360 representing the solar longitude
    on `date`.

  ### Examples

      iex> Astro.sun_apparent_longitude ~D[2019-03-21]
      0.08035853207991295
      iex> Astro.sun_apparent_longitude ~D[2019-06-22]
      90.32130455695378
      iex> Astro.sun_apparent_longitude ~D[2019-09-23]
      179.68691978440197
      iex> Astro.sun_apparent_longitude ~D[2019-12-23]
      270.83941087483504

  ### Notes

  Solar longitude (the ecliptic longitude of the sun)
  in effect describes the position of the earth in its
  orbit, being zero at the moment of the March
  equinox.

  Since it is based on how far the earth has moved
  in its orbit since the equinox, it is a measure of
  what time of the tropical year (the year of seasons)
  we are in, but without the inaccuracies of a calendar
  date, which is perturbed by leap years and calendar
  imperfections.

  """
  @spec sun_apparent_longitude(Calendar.date()) :: degrees()
  def sun_apparent_longitude(date) do
    date
    |> Time.julian_day_from_date()
    |> Time.julian_centuries_from_julian_day()
    |> Solar.sun_apparent_longitude()
  end

  @doc """
  Returns the number of hours of daylight for a given
  location on a given date.

  On Elixir 1.17+, the function `duration_of_daylight/2`
  is recommended over this function since it returns a
  `t:Duration.t/0` which can represent a full 24 hours
  of daylight.

  ### Arguments

  * `location` is the latitude, longitude and
    optionally elevation for the desired hours of
    daylight. It can be expressed as:

    * `{lng, lat}` - a tuple with longitude and latitude
      as floating point numbers. **Note** the order of the
      arguments.
    * a `Geo.Point.t` struct to represent a location without elevation
    * a `Geo.PointZ.t` struct to represent a location and elevation.

  * `date` is any `t:Date.t/0` in the Gregorian
    calendar (for example, `Calendar.ISO`).

  ### Returns

  * `{:ok, time}` where `time` is a `Time.t()`. The maximum value is
    `~T[23:59:59]`, representing 24 hours of daylight (a `Time.t()`
    cannot hold `24:00:00`).

  * `{:error, reason}` if the time zone for the location cannot be
    resolved.

  ### Examples

      iex> Astro.hours_of_daylight({151.20666584, -33.8559799094}, ~D[2019-12-10])
      {:ok, ~T[14:20:51]}

      # No sunset in summer
      iex> Astro.hours_of_daylight({-62.3481, 82.5018}, ~D[2019-06-07])
      {:ok, ~T[23:59:59]}

      # No sunrise in winter
      iex> Astro.hours_of_daylight({-62.3481, 82.5018}, ~D[2019-12-07])
      {:ok, ~T[00:00:00]}

  ### Notes

  Daylight is measured as the total time the Sun is above the horizon
  during the local calendar day, so the result is correct regardless of
  whether sunrise precedes sunset.

  In latitudes above the polar circles (approximately +/- 66.5631
  degrees) there will be no hours of daylight in winter and 24 hours of
  daylight in summer. Just below the polar circles, near the solstice,
  a single calendar day can contain a sunset (shortly after midnight)
  followed by a sunrise (a few hours later); such days are handled
  correctly and report close to, but less than, 24 hours.

  """
  @spec hours_of_daylight(Astro.location(), Calendar.date()) ::
          {:ok, Elixir.Time.t()} | {:error, atom()}
  def hours_of_daylight(location, date) do
    case daylight_seconds(location, date) do
      {:ok, seconds} when seconds >= @seconds_per_day ->
        # 24 hours of daylight (polar day). A `Time.t/0` cannot represent
        # 24:00:00, so it is reported one second short. Use
        # `duration_of_daylight/2` for an uncapped `Duration.t/0`.
        Elixir.Time.new(23, 59, 59)

      {:ok, seconds} ->
        Elixir.Time.new(div(seconds, 3600), div(rem(seconds, 3600), 60), rem(seconds, 60))

      {:error, reason} ->
        {:error, reason}
    end
  end

  if Code.ensure_loaded?(Duration) do
    @doc """
    Returns the duration of daylight for a given location on a
    given date as a `t:Duration.t/0`.

    This is the same calculation as `hours_of_daylight/2` but,
    because a `t:Duration.t/0` is not bounded like a `t:Time.t/0`,
    it can represent a full 24 hours of daylight (returned as
    `%Duration{hour: 24}`) during the polar summer rather than
    capping at `~T[23:59:59]`.

    This function is only defined when running on Elixir 1.17 or
    later, where the `Duration` module is available.

    ### Arguments

    * `location` is the latitude, longitude and optionally
      elevation for the desired duration of daylight. It can be
      expressed as:

      * `{lng, lat}` - a tuple with longitude and latitude
        as floating point numbers. **Note** the order of the
        arguments.
      * a `Geo.Point.t` struct to represent a location without elevation.
      * a `Geo.PointZ.t` struct to represent a location and elevation.

    * `date` is any `t:Date.t/0` in the Gregorian calendar
      (for example, `Calendar.ISO`).

    ### Returns

    * `{:ok, duration}` where `duration` is a `t:Duration.t/0`
      between `%Duration{}` (no daylight) and `%Duration{hour: 24}`
      (24 hours of daylight).

    * `{:error, reason}` if the time zone for the location cannot
      be resolved.

    ### Examples

        iex> Astro.duration_of_daylight({151.20666584, -33.8559799094}, ~D[2019-12-10])
        {:ok, %Duration{hour: 14, minute: 20, second: 51}}

        # 24 hours of daylight in the polar summer, uncapped
        iex> Astro.duration_of_daylight({-62.3481, 82.5018}, ~D[2019-06-07])
        {:ok, %Duration{hour: 24}}

        # No daylight in the polar winter
        iex> Astro.duration_of_daylight({-62.3481, 82.5018}, ~D[2019-12-07])
        {:ok, %Duration{}}

    """
    @doc since: "2.3.0"
    @spec duration_of_daylight(Astro.location(), Calendar.date()) ::
            {:ok, Duration.t()} | {:error, atom()}
    def duration_of_daylight(location, date) do
      case daylight_seconds(location, date) do
        {:ok, seconds} ->
          {:ok,
           Duration.new!(
             hour: div(seconds, 3600),
             minute: div(rem(seconds, 3600), 60),
             second: rem(seconds, 60)
           )}

        {:error, reason} ->
          {:error, reason}
      end
    end
  end

  # Total seconds the Sun is above the horizon during the local calendar day,
  # in the range 0..86_400. Rather than subtracting sunrise from sunset (which
  # breaks at sub-polar latitudes near the solstice, where the Sun can set just
  # after local midnight and rise again hours later, so sunset precedes
  # sunrise), the daylight is derived from which events fall within the day:
  #
  #   * both events present  → normal day (rise then set) is set − rise; a
  #     reversed day (set then rise) is the whole day minus the night between.
  #   * only sunrise present → Sun rises and stays up to end of day.
  #   * only sunset present  → Sun is up at midnight and sets during the day.
  #   * neither present      → polar day (24h) or polar night (0h).
  #
  defp daylight_seconds(location, date) do
    case {sunrise(location, date), sunset(location, date)} do
      {{:ok, sunrise}, {:ok, sunset}} ->
        {:ok, daylight_between(sunrise, sunset)}

      {{:error, :no_time}, {:ok, sunset}} ->
        {:ok, seconds_since_midnight(sunset)}

      {{:ok, sunrise}, {:error, :no_time}} ->
        {:ok, @seconds_per_day - seconds_since_midnight(sunrise)}

      {{:error, :no_time}, {:error, :no_time}} ->
        if Solar.SunRiseSet.sun_above_horizon?(location, date_to_moment(date)) do
          {:ok, @seconds_per_day}
        else
          {:ok, 0}
        end

      {{:error, reason}, _} ->
        {:error, reason}

      {_, {:error, reason}} ->
        {:error, reason}
    end
  end

  # When sunset precedes sunrise on the same calendar day the Sun was already
  # up at local midnight, set briefly, then rose again — daylight is the whole
  # day less the night between the two events (`DateTime.diff` is negative).
  defp daylight_between(sunrise, sunset) do
    case DateTime.diff(sunset, sunrise) do
      seconds when seconds >= 0 -> seconds
      night -> @seconds_per_day + night
    end
  end

  defp seconds_since_midnight(%DateTime{hour: hour, minute: minute, second: second}) do
    hour * 3600 + minute * 60 + second
  end

  @doc false
  def default_options do
    default_time_zone_db =
      Application.get_env(:elixir, :time_zone_database) || @compile_time_time_zone_db

    [
      solar_elevation: Solar.solar_elevation(:geometric),
      time_zone: :default,
      time_zone_database: default_time_zone_db
    ]
  end

  # Convert a Date, DateTime or NaiveDateTime to a moment
  # (integer Gregorian days representing UTC midnight).
  defp date_to_moment(date) do
    Time.date_time_to_moment(date)
  end
end