defmodule Cldr.Interval do
  @moduledoc """
  Interval formats allow for software to format intervals like "Jan 10-12, 2008" as a
  shorter and more natural format than "Jan 10, 2008 - Jan 12, 2008". They are designed
  to take a start and end date, time or datetime plus a formatting pattern
  and use that information to produce a localized format.

  The interval functions in the library will determine the calendar
  field with the greatest difference between the two datetimes before using the
  format pattern.

  For example, the greatest difference in "Jan 10-12, 2008" is the day field, while
  the greatest difference in "Jan 10 - Feb 12, 2008" is the month field. This is used to
  pick the exact format pattern to be used.

  ### Interval Formats

  CLDR provides a three-level mapping to a concrete format pattern.

  * The first level determines which fields are included in the
   interval format. This level is called a *format style*.

  * The second level is grouped by *standard formats* (`:long`, `:medium`, `:short`)
    which reflect the length of the specified fields - espeially the
    format length of the `month` field for *dates*.

  * The third level is a format skeleton which can then be resolved to
    a format pattern.

  Here's an example of the format styles, encapsulating standard formats
  the resolve to format skeletons.

  ```elixir
  iex> Cldr.Date.Interval.styles()
  %{
    date: %{long: :yMMMEd, medium: :yMMMd, short: :yMd},
    month: %{long: :MMM, medium: :MMM, short: :M},
    month_and_day: %{long: :MMMEd, medium: :MMMd, short: :Md},
    year_and_month: %{long: :yMMMM, medium: :yMMM, short: :yM}
  }

  # The *time* interval styles are also segments by whether 12-hour
  # or 24-hour time formatting is requested.
  iex> Cldr.Time.Interval.styles()
  %{
    flex: %{h12: %{long: :Bhm, medium: :Bhm, short: :Bh}, h23: %{long: :Bhm, medium: :Bhm, short: :Bh}},
    time: %{h12: %{long: :hm, medium: :hm, short: :h}, h23: %{long: :Hm, medium: :Hm, short: :H}},
    zone: %{h12: %{long: :hmv, medium: :hmv, short: :hv}, h23: %{long: :Hmv, medium: :Hmv, short: :Hv}}
  }
  ```

  Here the format style is the key of the map. For a *date* they
  keys are `:date`, `:month`, `:month_and_day` and `year_and_month`.
  These are then mapped to one of the standard interval formats `:short`,
  `:medium` or `:long` returning a format skeleton.

  ### Interval formats

  In a manner similar to formatting discrete *dates*, *times* and *date_times*,
  standard formats are introduced to simplify common usage. For all intervals the following
  standard formats are:

  * `:short`
  * `:medium` (the default)
  * `:long`

  In each case, the mapping is from a format style to a standard format which then
  resolves to a format skeleton. The format skeleton is then used to resolve
  a format pattern for the interval.

  These maps can be examined as follows where `"en"` is any configured
  locale name and `:gregorian` is the underlying CLDR calendar type. In
  common use the `:gregorian` calendar is the standard.  However other
  calendar types are also supported. For example:

  ```elixir
  iex> Cldr.known_calendars()
  [:buddhist, :chinese, :coptic, :dangi, :ethiopic, :ethiopic_amete_alem,
   :gregorian, :hebrew, :indian, :islamic, :islamic_civil, :islamic_rgsa,
   :islamic_tbla, :islamic_umalqura, :japanese, :persian, :roc]
  ```

  To examine the available interval formats, `Cldr.DateTime.Format.interval_formats/2`
  can be used although its use is primarily internal to the implementation of
  `to_string/3` and would not normally be called directly.

  ```elixir
  Cldr.DateTime.Format.interval_formats(:en, :gregorian)
  => {:ok,
       %{
         Bh: %{
           B: ["h B – ", "h B"],
           h: ["h – ", "h B"]
         },
         Bhm: %{
           B: ["h:mm B – ", "h:mm B"],
           h: ["h:mm – ", "h:mm B"],
           m: ["h:mm – ", "h:mm B"]
         },
         Gy: %{
           G: ["y G – ", "y G"],
           y: ["y – ", "y G"]
         },
         GyM: %{
           G: ["M/y G – ", "M/y G"],
           M: ["M/y – ", "M/y G"],
           y: ["M/y – ", "M/y G"]
         },
         GyMEd: %{
           G: ["E, M/d/y G – ", "E, M/d/y G"],
           M: ["E, M/d/y – ", "E, M/d/y G"],
           d: ["E, M/d/y – ", "E, M/d/y G"],
           y: ["E, M/d/y – ", "E, M/d/y G"]
         },
         ...
       }
     }
  ```

  At this point we can see that the path to resolving a format (using
  the `:en` locale for this example) is:

  * Apply the format style. For *dates*, this is `:date`, returning
    `%{long: :yMMMEd, medium: :yMMMd, short: :yMd}`
  * Apply the standard format. For *dates*, the default is `:medium` returning
    the format skeleton `:yMMMd`.
  * Using the returned format skeleton, resolve the interval formats returning:

  ```elixir
  %{
     d: ["MMM d – ", "d, y"],
     m: ["MMM d – ", "MMM d, y"],
     y: ["MMM d, y – ", "MMM d, y"]
   }
  ```

  ### The field with the greatest difference

  There remains one more choice to make - and that choice is made
  based upon the highest order date field that is different between the
  `from` and `to` *dates*.

  With two *dates* `2020-02-02` and `2021-01-01` the highest order
  difference is `:year`. With `2020-02-02` and `2020-01-01` it is `:month`.

  ### Formatting the interval

  Using this `greatest difference` information we can now resolve the
  final format. With the `:year` field being the greatest difference then
  the format is `y: ["MMM d, y – ", "MMM d, y"]`.

  Finally, formatting can proceed for the `from` *date* being formatted with
  the `"MMM d, y – "` format pattern and the `to` *date* being formatted with the
  `"MMM d, y"` format pattern and the two results then being concatenated to
  form the final string.

  ### Other ways to specify an interval format

  So far we have considered formats that are resolved from standard styles
  and stamdard formats. This is the typical usage and they are specified
  as parameters to the `to_string/3` function. For example:

  ```elixir
  iex> Cldr.Date.Interval.to_string ~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr
  {:ok, "Jan 1 – 12, 2020"}

  iex> Cldr.Date.Interval.to_string ~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr, format: :long
  {:ok, "Wed, Jan 1 – Sun, Jan 12, 2020"}

  iex> Cldr.Date.Interval.to_string ~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr,
  ...> style: :month_and_day
  {:ok, "Jan 1 – 12"}
  ```

  ### Direct use of format skeletons

  It is also possible to directly specify a format skeleton. For example:
  ```elixir
  iex> Cldr.Date.Interval.to_string ~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr, format: :GyMMMd
  {:ok, "Jan 1 – 12, 2020 AD"}
  ```

  ### Using format patterns

  In the unusual situation where one of the standard formats and format skeletons does
  not meet requirements, a format pattern can also be specified. For example:

  ```elixir
  iex> Cldr.Date.Interval.to_string ~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr,
  ...> format: "E, M/d/y – E, M/d/y"
  {:ok, "Wed, 1/1/2020 – Sun, 1/12/2020"}
  ```

  In this case, the steps to formatting are:

  1. Split the format pattern at the point at which the first repeating
     formatting code is detected. In the pattern above it is where the second `E`
     is detected. The result in this case will be `["E, M/d/y – ", "E, M/d/y"]`
     For the purposes of splitting, duplicates are ignored. Therefore
     "EEE, M/d/y – E, M/d/y" will split into `["EEE, M/d/y – ", "E, M/d/y"]`.

  2. Each part of the pattern is parsed.

  3. The two *dates*, *times* or *date_times* are formatted.

  This is a more expensive operation than using the standard formats and styles
  since the underlying formats for these types are precompiled
  into an efficient runtime format.

  ### Configuring precompiled interval formats

  If there is a requirement for repeated use of format strings
  then they can be configured in the backend module so that they are
  precompiled and therefore not suffer a runtime performance penalty.

  In a backend module, configure the required formats as a list under the
  `:precompile_interval_formats` key:

  ```elixir
  defmodule MyApp.Cldr do
    use Cldr,
      locales: ["en", "fr"],
      default_locale: "en",
      precompile_interval_formats: ["E, MMM d/y – d/y"]
  end
  ```

  """

  @typedoc "A Date.Range or CalendarInterval range"
  if Cldr.Code.ensure_compiled?(CalendarInterval) do
    @type range :: Date.Range.t() | CalendarInterval.t()
  else
    @type range :: Date.Range.t()
  end

  @typedoc "Any date, time or datetime"
  @type datetime ::
          Calendar.date()
          | Calendar.datetime()
          | Calendar.naive_datetime()
          | Calendar.time()

  # These are type-detecting patterns to be used
  # in function heads
  import Cldr.Calendar,
    only: [
      date: 0,
      datetime: 0,
      naivedatetime: 0,
      time: 0
    ]

  import Kernel,
    except: [
      to_string: 1
    ]

  # Single argument version.
  # Derive backend and locale

  @doc false
  def to_string(%Date.Range{} = range) do
    {locale, backend} = Cldr.locale_and_backend_from(nil, nil)
    to_string(range, backend, locale: locale)
  end

  if Cldr.Code.ensure_compiled?(CalendarInterval) do
    def to_string(%CalendarInterval{} = interval) do
      {locale, backend} = Cldr.locale_and_backend_from(nil, nil)
      to_string(interval, backend, locale: locale)
    end
  end

  @doc false
  def to_string(unquote(date()) = from, unquote(date()) = to) do
    {locale, backend} = Cldr.locale_and_backend_from(nil, nil)
    to_string(from, to, backend, locale: locale)
  end

  def to_string(unquote(time()) = from, unquote(time()) = to) do
    {locale, backend} = Cldr.locale_and_backend_from(nil, nil)
    to_string(from, to, backend, locale: locale)
  end

  # Dual argument version with backend
  def to_string(%Date.Range{} = range, backend) when is_atom(backend) do
    {locale, backend} = Cldr.locale_and_backend_from(nil, backend)
    to_string(range, backend, locale: locale)
  end

  if Cldr.Code.ensure_compiled?(CalendarInterval) do
    def to_string(%CalendarInterval{} = interval, backend) when is_atom(backend) do
      {locale, backend} = Cldr.locale_and_backend_from(nil, backend)
      to_string(interval, backend, locale: locale)
    end
  end

  @doc false
  def to_string(unquote(date()) = from, unquote(date()) = to, backend) when is_atom(backend) do
    {locale, backend} = Cldr.locale_and_backend_from(nil, backend)
    to_string(from, to, backend, locale: locale)
  end

  def to_string(unquote(time()) = from, unquote(time()) = to, backend) when is_atom(backend) do
    {locale, backend} = Cldr.locale_and_backend_from(nil, backend)
    to_string(from, to, backend, locale: locale)
  end

  # Dual argument version with options
  def to_string(%Date.Range{} = range, options) when is_list(options) do
    {locale, backend} = Cldr.locale_and_backend_from(options)
    to_string(range, backend, locale: Keyword.put_new(options, :locale, locale))
  end

  if Cldr.Code.ensure_compiled?(CalendarInterval) do
    def to_string(%CalendarInterval{} = interval, options) when is_list(options) do
      {locale, backend} = Cldr.locale_and_backend_from(options)
      to_string(interval, backend, Keyword.put_new(options, :locale, locale))
    end
  end

  def to_string(unquote(date()) = from, unquote(date()) = to, options) when is_list(options) do
    {locale, backend} = Cldr.locale_and_backend_from(options)
    options = Keyword.put_new(options, :locale, locale)
    to_string(from, to, backend, options)
  end

  def to_string(unquote(time()) = from, unquote(time()) = to, options) when is_list(options) do
    {locale, backend} = Cldr.locale_and_backend_from(options)
    options = Keyword.put_new(options, :locale, locale)
    to_string(from, to, backend, options)
  end

  @doc """
  Returns a `t:Date.Range.t/0` or `t:CalendarInterval.t/0` as
  a localised string.

  ### Arguments

  * `range` is either a `t:Date.Range.t/0` returned from `Date.range/2`
    or a `CalendarInterval.t`.

  * `backend` is any module that includes `use Cldr` and
    is therefore a `Cldr` backend module

  * `options` is a keyword list of options. The default is
    `[format: :medium, style: :date | :time | nil]`.

  ### Options

  * `:format` is one of `:short`, `:medium` or `:long` or a
    specific format skeleton of format pattern representing an interval
    format. The default is `:medium`.

  * `:style` supports different formatting styles. The valid
    styles depends on whether formatting is for a *date*, *time* or *date_time*.
    Since the functions in this module will make a determination as
    to which formatter to be used based upon the data passed to them
    it is recommended the style option be omitted. If styling is important
    then call `to_string/3` directly on `Cldr.Date.Interval`, `Cldr.Time.Interval`
    or `Cldr.DateTime.Interval`.

    * For a *date* the alternatives are `:date`, `:month_and_day`, `:month`
      and `:year_and_month`. The default is `:date`.

    * For a *time* the alternatives are `:time`, `:zone` and
      `:flex`. The default is `:time`.

    * For a *date_time* there are no style options, the default
      for each of the *date* and *time* parts is used.

  * `locale` is any valid locale name returned by `Cldr.known_locale_names/0`
    or a `t:Cldr.LanguageTag.t/0` struct.  The default is `Cldr.get_locale/0`.

  * `number_system:` a number system into which the formatted date digits should
    be transliterated.

  ### Returns

  * `{:ok, string}` or

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

  ### Notes

  * `to_string/3` will decide which formatter to call based upon
    the arguments provided to it.

    * A `t:Date.Range.t/0` will call `Cldr.Date.Interval.to_string/3`.

    * A `t:CalendarInterval.t/0` will call `Cldr.Date.Interval.to_string/3`
      if its `:precision` is `:year`, `:month` or `:day`. Otherwise
      it will call `Cldr.Time.Interval.to_string/3`.

    * If `from` and `to` both conform to the `t:Calendar.datetime/0`
      type then `Cldr.DateTime.Interval.to_string/3` is called.

    * Otherwise if `from` and `to` conform to the `t:Calendar.date/0`
      type then `Cldr.Date.Interval.to_string/3` is called.

    * Otherwise if `from` and `to` conform to the `t:Calendar.time/0`
      type then `Cldr.Time.Interval.to_string/3` is called.

  * `CalendarInterval` support requires adding the
    dependency [calendar_interval](https://hex.pm/packages/calendar_interval)
    to the `deps` configuration in `mix.exs`.

  * For more information on interval format patterns
    see `Cldr.Interval`.

  * The available format skeletons that can be applied are the
    keys of the map returned by `Cldr.DateTime.Format.interval_formats("en", :gregorian)`
    where `"en"` can be replaced by any configuration locale name and `:gregorian`
    is the underlying CLDR calendar type.

  * In the case where `from` and `to` are equal, a single
    *date*, *time* or *date_time* is formatted instead of an interval.

  ### Examples

      iex> Cldr.Interval.to_string(Date.range(~D[2020-01-01], ~D[2020-01-12]), MyApp.Cldr,
      ...> format: :long)
      {:ok, "Wed, Jan 1 – Sun, Jan 12, 2020"}

      iex> use CalendarInterval
      iex> Cldr.Interval.to_string(~I"2020-01-01/12", MyApp.Cldr,
      ...> format: :long)
      {:ok, "Wed, Jan 1 – Sun, Jan 12, 2020"}

  """
  @spec to_string(range, Cldr.backend(), Keyword.t()) ::
          {:ok, String.t()} | {:error, {module, String.t()}}

  def to_string(%Date.Range{first: first, last: last}, backend, options) do
    Cldr.Date.Interval.to_string(first, last, backend, options)
  end

  if Cldr.Code.ensure_compiled?(CalendarInterval) do
    def to_string(%CalendarInterval{first: from, last: to, precision: precision}, backend, options)
        when precision in [:year, :month, :day] do
      Cldr.Date.Interval.to_string(from, to, backend, options)
    end

    def to_string(%CalendarInterval{first: from, last: to, precision: precision}, backend, options)
        when precision in [:hour, :minute] do
      from = %{from | second: 0, microsecond: {0, 6}}
      to = %{to | second: 0, microsecond: {0, 6}}
      Cldr.DateTime.Interval.to_string(from, to, backend, options)
    end

    def to_string(%CalendarInterval{first: from, last: to, precision: precision}, backend, options)
        when precision in [:second, :microsecond] do
      from = %{from | microsecond: {0, 6}}
      to = %{to | microsecond: {0, 6}}
      Cldr.DateTime.Interval.to_string(from, to, backend, options)
    end
  end

  @doc false
  def to_string(from, to, backend, options \\ [])

  @doc """
  Returns a string representing the formatted
  interval formed by two dates.

  ### Arguments

  * `from` is any map that conforms to the
    any one of the `Calendar` types.

  * `to` is any map that conforms to the
    any one of the `Calendar` types. `to` must
    occur on or after `from`.

  * `backend` is any module that includes `use Cldr` and
    is therefore a `Cldr` backend module.

  * `options` is a keyword list of options. The default is
    `[format: :medium, style: :date | :time | nil]`.

  ### Options

  * `:format` is one of `:short`, `:medium` or `:long` or a
    specific format skeleton or a format pattern representing of an interval
    format. The default is `:medium`.

  * `:style` supports different formatting styles. The valid
    styles depends on whether formatting is for a date, time or datetime.
    Since the functions in this module will make a determination as
    to which formatter to be used based upon the data passed to them
    it is recommended the style option be omitted. If styling is important
    then call `to_string/3` directly on `Cldr.Date.Interval`, `Cldr.Time.Interval`
    or `Cldr.DateTime.Interval`.

    * For a date the alternatives are `:date`, `:month_and_day`, `:month`
      and `:year_and_month`. The default is `:date`.

    * For a time the alternatives are `:time`, `:zone` and
      `:flex`. The default is `:time`.

    * For a datetime there are no style options, the default
      for each of the date and time part is used.

  * `locale` is any valid locale name returned by `Cldr.known_locale_names/0`
    or a `t:Cldr.LanguageTag.t/0` struct.  The default is `Cldr.get_locale/0`.

  * `number_system:` a number system into which the formatted date digits should
    be transliterated.

  ### Returns

  * `{:ok, string}` or

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

  ### Notes

  * `to_string/3` will decide which formatter to call based upon
    the arguments provided to it.

    * A `t:Date.Range.t/0` will call `Cldr.Date.Interval.to_string/3`.

    * A `t:CalendarInterval.t/0` will call `Cldr.Date.Interval.to_string/3`
      if its `:precision` is `:year`, `:month` or `:day`. Otherwise
      it will call `Cldr.Time.Interval.to_string/3`.

    * If `from` and `to` both conform to either of the `t:Calendar.datetime/0` or
      `t:Calendar.naive_datetime/0` types then `Cldr.DateTime.Interval.to_string/3`
      is called.

    * Otherwise if `from` and `to` conform to the `t:Calendar.date/0`
      type then `Cldr.Date.Interval.to_string/3` is called.

    * Otherwise if `from` and `to` conform to the `t:Calendar.time/0`
      type then `Cldr.Time.Interval.to_string/3` is called.

  * `CalendarInterval` support requires adding the
    dependency [calendar_interval](https://hex.pm/packages/calendar_interval)
    to the `deps` configuration in `mix.exs`.

  * For more information on interval format pattern
    see `Cldr.Interval`.

  * The available format skeletons that can be applied are the
    keys of the map returned by `Cldr.DateTime.Format.interval_formats(:en, :gregorian)`
    where `:en` can be replaced by any configuration locale name and `:gregorian`
    is the underlying CLDR calendar type.

  * In the case where `from` and `to` are considered equal, a single
    *date*, *time* or *date_time* is formatted instead of an interval.

  ### Examples

      iex> Cldr.Interval.to_string(~D[2020-01-01], ~D[2020-12-31], MyApp.Cldr)
      {:ok, "Jan 1 – Dec 31, 2020"}

      iex> Cldr.Interval.to_string(~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr)
      {:ok, "Jan 1 – 12, 2020"}

      iex> Cldr.Interval.to_string(~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr,
      ...> format: :long)
      {:ok, "Wed, Jan 1 – Sun, Jan 12, 2020"}

      iex> Cldr.Interval.to_string(~D[2020-01-01], ~D[2020-12-01], MyApp.Cldr,
      ...> format: :long, style: :year_and_month)
      {:ok, "January – December 2020"}

      iex> Cldr.Interval.to_string(~U[2020-01-01 00:00:00.0Z], ~U[2020-12-01 10:05:00.0Z],
      ...> MyApp.Cldr, format: :long)
      {:ok, "January 1, 2020, 12:00:00 AM UTC – December 1, 2020, 10:05:00 AM UTC"}

      iex> Cldr.Interval.to_string(~U[2020-01-01 00:00:00.0Z], ~U[2020-01-01 10:05:00.0Z],
      ...> MyApp.Cldr, format: :long)
      {:ok, "January 1, 2020, 12:00:00 AM UTC – 10:05:00 AM UTC"}

      iex> Cldr.Interval.to_string(~N[2025-10-05 14:50:00], ~N[2025-10-05 16:30:00],
      ...> format: :short)
      {:ok, "10/5/25, 2:50 PM\u2009–\u20094:30 PM"}

      iex> Cldr.Interval.to_string(~N[2025-10-05 14:50:00], ~N[2025-10-05 16:30:00],
      ...> format: :medium)
      {:ok, "Oct 5, 2025, 2:50:00 PM\u2009–\u20094:30:00 PM"}

  """
  @spec to_string(datetime, datetime, Cldr.backend(), Keyword.t()) ::
          {:ok, String.t()} | {:error, {module, String.t()}}

  def to_string(unquote(datetime()) = from, unquote(datetime()) = to, backend, options) do
    Cldr.DateTime.Interval.to_string(from, to, backend, options)
  end

  def to_string(unquote(naivedatetime()) = from, unquote(naivedatetime()) = to, backend, options) do
    Cldr.DateTime.Interval.to_string(from, to, backend, options)
  end

  def to_string(unquote(date()) = from, unquote(date()) = to, backend, options) do
    Cldr.Date.Interval.to_string(from, to, backend, options)
  end

  def to_string(unquote(time()) = from, unquote(time()) = to, backend, options) do
    Cldr.Time.Interval.to_string(from, to, backend, options)
  end

  @doc false
  def to_string!(%Date.Range{} = range, backend) when is_atom(backend) do
    {locale, backend} = Cldr.locale_and_backend_from(nil, backend)
    to_string!(range, backend, locale: locale)
  end

  @doc false
  def to_string!(%Date.Range{} = range, options) when is_list(options) do
    {locale, backend} = Cldr.locale_and_backend_from(options)
    options = Keyword.put_new(options, :locale, locale)
    to_string!(range, backend, options)
  end

  if Cldr.Code.ensure_compiled?(CalendarInterval) do
    @doc false
    def to_string!(%CalendarInterval{} = range, backend) when is_atom(backend) do
      {locale, backend} = Cldr.locale_and_backend_from(nil, backend)
      to_string!(range, backend, locale: locale)
    end

    @doc false
    def to_string!(%CalendarInterval{} = range, options) when is_list(options) do
      {locale, backend} = Cldr.locale_and_backend_from(options)
      options = Keyword.put_new(options, :locale, locale)
      to_string!(range, backend, options)
    end
  end

  @doc """
  Returns a `t:Date.Range.t/0` or `t:CalendarInterval.t/0` as
  a localised string or raises an exception.

  ### Arguments

  * `range` is either a `t:Date.Range.t/0` returned from `Date.range/2`
    or a `CalendarInterval.t`.

  * `backend` is any module that includes `use Cldr` and
    is therefore a `Cldr` backend module.

  * `options` is a keyword list of options. The default is
    `[format: :medium, style: :date | :time | nil]`.

  ### Options

  * `:format` is one of `:short`, `:medium` or `:long` or a
    specific format skeleton or a format pattern representing an interval
    format. The default is `:medium`.

  * `:style` supports different formatting styles. The valid
    styles depends on whether formatting is for a date, time or datetime.
    Since the functions in this module will make a determination as
    to which formatter to be used based upon the data passed to them
    it is recommended the style option be omitted. If styling is important
    then call `to_string/3` directly on `Cldr.Date.Interval`, `Cldr.Time.Interval`
    or `Cldr.DateTime.Interval`.

    * For a *date* the alternatives are `:date`, `:month_and_day`, `:month`
      and `:year_and_month`. The default is `:date`.

    * For a *time* the alternatives are `:time`, `:zone` and
      `:flex`. The default is `:time`.

    * For a *date_time* there are no style options, the default
      for each of the date and time part is used.

  * `locale` is any valid locale name returned by `Cldr.known_locale_names/0`
    or a `t:Cldr.LanguageTag.t/0` struct.  The default is `Cldr.get_locale/0`.

  * `number_system:` a number system into which the formatted date digits should
    be transliterated.

  ### Returns

  * `formatted_string` or

  * raises an exception.

  ### Notes

  * `to_string/3` will decide which formatter to call based upon
    the arguments provided to it.

    * A `t:Date.Range.t/0` will call `Cldr.Date.Interval.to_string/3`.

    * A `t:CalendarInterval.t/0` will call `Cldr.Date.Interval.to_string/3`
      if its `:precision` is `:year`, `:month` or `:day`. Otherwise
      it will call `Cldr.Time.Interval.to_string/3`.

    * If `from` and `to` both conform to either of the `t:Calendar.datetime/0` or
      `t:Calendar.naive_datetime/0` types then `Cldr.DateTime.Interval.to_string/3`
      is called.

    * Otherwise if `from` and `to` conform to the `t:Calendar.date/0`
      type then `Cldr.Date.Interval.to_string/3` is called.

    * Otherwise if `from` and `to` conform to the `t:Calendar.time/0`
      type then `Cldr.Time.Interval.to_string/3` is called.

  * `CalendarInterval` support requires adding the
    dependency [calendar_interval](https://hex.pm/packages/calendar_interval)
    to the `deps` configuration in `mix.exs`.

  * For more information on interval format pattern
    see `Cldr.Interval`.

  * The available format skeletons that can be applied are the
    keys of the map returned by `Cldr.DateTime.Format.interval_formats("en", :gregorian)`
    where `"en"` can be replaced by any configuration locale name and `:gregorian`
    is the underlying CLDR calendar type.

  * In the case where `from` and `to` are equal, a single
    *date*, *time* or *date_time* is formatted instead of an interval.

  ### Examples

      iex> use CalendarInterval
      iex> Cldr.Interval.to_string!(~I"2020-01-01/12", MyApp.Cldr,
      ...> format: :long)
      "Wed, Jan 1 – Sun, Jan 12, 2020"

      iex> Cldr.Interval.to_string!(Date.range(~D[2020-01-01], ~D[2020-01-12]), MyApp.Cldr,
      ...> format: :long)
      "Wed, Jan 1 – Sun, Jan 12, 2020"

  """
  @spec to_string!(range, Cldr.backend(), Keyword.t()) :: String.t() | no_return()

  def to_string!(%Date.Range{} = range, backend, options) do
    case to_string(range, backend, options) do
      {:ok, string} -> string
      {:error, {exception, reason}} -> raise exception, reason
    end
  end

  if Cldr.Code.ensure_compiled?(CalendarInterval) do
    def to_string!(%CalendarInterval{} = range, backend, options) do
      case to_string(range, backend, options) do
        {:ok, string} -> string
        {:error, {exception, reason}} -> raise exception, reason
      end
    end
  end

  @doc """
  Returns a string representing the formatted
  interval formed by two dates or raises an
  exception.

  ### Arguments

  * `from` is any map that conforms to the
    any one of the `Calendar` types.

  * `to` is any map that conforms to the
    any one of the `Calendar` types. `to` must
    occur on or after `from`.

  * `backend` is any module that includes `use Cldr` and
    is therefore a `Cldr` backend module

  * `options` is a keyword list of options. The default is
    `[format: :medium, style: :date | :time | nil]`.

  ### Options

  * `:format` is one of `:short`, `:medium` or `:long` or a
    specific format skeleton or a format pattern representing an interval
    format. The default is `:medium`.

  * `:style` supports different formatting styles. The valid
    styles depends on whether formatting is for a date, time or datetime.
    Since the functions in this module will make a determination as
    to which formatter to be used based upon the data passed to them
    it is recommended the style option be omitted. If styling is important
    then call `to_string/3` directly on `Cldr.Date.Interval`, `Cldr.Time.Interval`
    or `Cldr.DateTime.Interval`.

    * For a *date* the alternatives are `:date`, `:month_and_day`, `:month`
      and `:year_and_month`. The default is `:date`.

    * For a *time* the alternatives are `:time`, `:zone` and
      `:flex`. The default is `:time`.

    * For a *date_time* there are no style options, the default
      for each of the *date* and *time* part is used.

  * `locale` is any valid locale name returned by `Cldr.known_locale_names/0`
    or a `t:Cldr.LanguageTag.t/0` struct.  The default is `Cldr.get_locale/0`.

  * `number_system:` a number system into which the formatted date digits should
    be transliterated.

  ### Returns

  * `formatted_string` or

  * raises an exception.

  ### Notes

  * `to_string!/3` will decide which formatter to call based upon
    the arguments provided to it.

    * A `t:Date.Range.t/0` will call `Cldr.Date.Interval.to_string/3`

    * A `t:CalendarInterval.t/0` will call `Cldr.Date.Interval.to_string/3`
      if its `:precision` is `:year`, `:month` or `:day`. Otherwise
      it will call `Cldr.Time.Interval.to_string/3`.

    * If `from` and `to` both conform to either of the `t:Calendar.datetime/0` or
      `t:Calendar.naive_datetime/0` types then `Cldr.DateTime.Interval.to_string/3`
      is called.

    * Otherwise if `from` and `to` conform to the `t:Calendar.date/0`
      type then `Cldr.Date.Interval.to_string/3` is called.

    * Otherwise if `from` and `to` conform to the `t:Calendar.time/0`
      type then `Cldr.Time.Interval.to_string/3` is called.

  * `CalendarInterval` support requires adding the
    dependency [calendar_interval](https://hex.pm/packages/calendar_interval)
    to the `deps` configuration in `mix.exs`.

  * For more information on interval format pattern
    see `Cldr.Interval`.

  * The available format skeletons that can be applied are the
    keys of the map returned by `Cldr.DateTime.Format.interval_formats("en", :gregorian)`
    where `"en"` can be replaced by any configuration locale name and `:gregorian`
    is the underlying CLDR calendar type.

  * In the case where `from` and `to` are equal, a single
    date, time or datetime is formatted instead of an interval.

  ### Examples

      iex> Cldr.Interval.to_string!(~D[2020-01-01], ~D[2020-12-31], MyApp.Cldr)
      "Jan 1 – Dec 31, 2020"

      iex> Cldr.Interval.to_string!(~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr)
      "Jan 1 – 12, 2020"

      iex> Cldr.Interval.to_string!(~D[2020-01-01], ~D[2020-01-12], MyApp.Cldr,
      ...> format: :long)
      "Wed, Jan 1 – Sun, Jan 12, 2020"

      iex> Cldr.Interval.to_string!(~D[2020-01-01], ~D[2020-12-01], MyApp.Cldr,
      ...> format: :long, style: :year_and_month)
      "January – December 2020"

      iex> Cldr.Interval.to_string!(~U[2020-01-01 00:00:00.0Z], ~U[2020-12-01 10:05:00.0Z],
      ...> MyApp.Cldr, format: :long)
      "January 1, 2020, 12:00:00 AM UTC – December 1, 2020, 10:05:00 AM UTC"

      iex> Cldr.Interval.to_string!(~U[2020-01-01 00:00:00.0Z], ~U[2020-01-01 10:05:00.0Z],
      ...> MyApp.Cldr, format: :long)
      "January 1, 2020, 12:00:00 AM UTC – 10:05:00 AM UTC"

  """
  @spec to_string!(datetime, datetime, Cldr.backend(), Keyword.t()) :: String.t() | no_return()

  def to_string!(from, to, backend, options \\ []) do
    case to_string(from, to, backend, options) do
      {:ok, string} -> string
      {:error, {exception, reason}} -> raise exception, reason
    end
  end
end