defmodule Moar.Duration do
# @related [test](/test/duration_test.exs)
@moduledoc """
A duration is a `{time, unit}` tuple.
The time is a number and the unit is one of:
* `:nanosecond`
* `:microsecond`
* `:millisecond`
* `:second`
* `:minute`
* `:hour`
* `:day`
* `:approx_month` (30 days)
* `:approx_year` (360 days)
> #### Note {: .info}
>
> This module is naive and intentionally doesn't account for real-world calendars and all of their complexity,
> such as leap years, leap days, daylight saving time, past and future calendar oddities, etc.
>
> As ["Falsehoods programmers believe about time"](https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b923ca)
> says, "If you think you understand everything about time, you're probably doing it wrong."
>
> See [`Cldr.Calendar.Duration`](https://hexdocs.pm/ex_cldr_calendars/Cldr.Calendar.Duration.html) for one example
> of a full-featured library that is far more likely to be correct.
"""
@seconds_per_minute 60
@seconds_per_hour @seconds_per_minute * 60
@seconds_per_day @seconds_per_hour * 24
@seconds_per_approx_month @seconds_per_day * 30
@seconds_per_approx_year @seconds_per_approx_month * 12
@units_kw_desc [
approx_year: {"yr", "year"},
approx_month: {"mo", "month"},
day: {"d", "day"},
hour: {"h", "hour"},
minute: {"m", "minute"},
second: {"s", "second"},
millisecond: {"ms", "millisecond"},
microsecond: {"us", "microsecond"},
nanosecond: {"ns", "nanosecond"}
]
@units_desc Keyword.keys(@units_kw_desc)
@units_asc @units_desc |> Enum.reverse()
@units_to_short_names Map.new(@units_kw_desc, fn {unit, {short_name, _}} -> {unit, short_name} end)
@units_to_names Map.new(@units_kw_desc, fn {unit, {_, name}} -> {unit, name} end)
@type date_time_ish() :: DateTime.t() | NaiveDateTime.t() | binary()
@type format_style() :: :long | :short
@type format_transformer() :: :ago | :approx | :humanize
@type format_transformers() :: format_transformer() | [format_transformer()]
@type t() :: {time :: number(), unit :: time_unit()}
@type time_unit() ::
:nanosecond
| :microsecond
| :millisecond
| :second
| :minute
| :hour
| :day
| :approx_month
| :approx_year
@doc """
Returns the duration between `datetime` and now, in the largest possible unit.
`datetime` can be an ISO8601-formatted string, a `DateTime`, or a `NaiveDateTime`.
```elixir
iex> DateTime.utc_now() |> Moar.DateTime.add({-121, :minute}) |> Moar.Duration.ago() |> Moar.Duration.shift(:minute)
{121, :minute}
```
"""
@spec ago(date_time_ish()) :: t()
def ago(datetime) when is_binary(datetime), do: datetime |> Moar.DateTime.from_iso8601!() |> ago()
def ago(%module{} = datetime), do: between(datetime, module.utc_now())
@doc """
Shifts `duration` to an approximately equal duration that's simpler. For example, `{121, :second}` would get
shifted to `{2, :minute}`.
> #### Warning {: .warning}
>
> This function is lossy because it intentionally loses precision.
If the time value of the duration is exactly 1, the duration is returned unchanged: `{1, :minute}` => `{1, :minute}`.
Otherwise, the duration is shifted to the highest unit where the time value is >= 2.
```elixir
iex> Moar.Duration.approx({1, :minute})
{1, :minute}
iex> Moar.Duration.approx({7300, :second})
{2, :hour}
```
"""
@spec approx(t()) :: t()
def approx({1, _unit} = duration), do: duration
def approx(duration), do: approx(duration, @units_desc)
defp approx(duration, [head_unit | tail_units] = _units_desc) do
new_duration = {new_time, _new_unit} = shift(duration, head_unit)
if new_time >= 2 || tail_units == [],
do: new_duration,
else: approx(duration, tail_units)
end
@doc """
Returns the duration between `earlier` and `later`, in the largest possible unit.
`earlier` and `later` can be ISO8601-formatted strings, `DateTime`s, or `NaiveDateTime`s.
```elixir
iex> earlier = ~U[2020-01-01T00:00:00.000000Z]
iex> later = ~U[2020-01-01T02:01:00.000000Z]
iex> Moar.Duration.between(earlier, later)
{121, :minute}
```
"""
@spec between(date_time_ish(), date_time_ish()) :: t()
def between(earlier, later), do: {Moar.Difference.diff(later, earlier), :microsecond} |> humanize()
@doc """
Converts a `{duration, time_unit}` tuple into a numeric duration, rounding down to the nearest whole number.
> #### Warning {: .warning}
>
> This function is lossy because it rounds down to the nearest whole number.
Uses `System.convert_time_unit/3` under the hood; see its documentation for more details.
It is similar to `shift/1` but this function returns an integer value, while `shift/1` returns a duration tuple.
```elixir
iex> Moar.Duration.convert({121, :second}, :minute)
2
```
"""
@spec convert(from :: t(), to :: time_unit()) :: number()
def convert({time, :minute}, to_unit), do: convert({time * @seconds_per_minute, :second}, to_unit)
def convert({time, :hour}, to_unit), do: convert({time * @seconds_per_hour, :second}, to_unit)
def convert({time, :day}, to_unit), do: convert({time * @seconds_per_day, :second}, to_unit)
def convert({time, :approx_month}, to_unit), do: convert({time * @seconds_per_approx_month, :second}, to_unit)
def convert({time, :approx_year}, to_unit), do: convert({time * @seconds_per_approx_year, :second}, to_unit)
def convert(duration, :minute), do: convert(duration, :second) |> Integer.floor_div(@seconds_per_minute)
def convert(duration, :hour), do: convert(duration, :second) |> Integer.floor_div(@seconds_per_hour)
def convert(duration, :day), do: convert(duration, :second) |> Integer.floor_div(@seconds_per_day)
def convert(duration, :approx_month), do: convert(duration, :second) |> Integer.floor_div(@seconds_per_approx_month)
def convert(duration, :approx_year), do: convert(duration, :second) |> Integer.floor_div(@seconds_per_approx_year)
def convert({time, from_unit}, to_unit), do: System.convert_time_unit(time, from_unit, to_unit)
@doc """
Formats a duration in either a long or short style, with optional transformers and an optional suffix.
* The first argument is a duration tuple, unless one of the transformers is `:ago`, in which case
it can be a `DateTime`, `NaiveDateTime`, or an ISO8601-formatted string.
* The second argument is optional and is the style, transformer, list of transformers, or suffix.
* The third argument is optional and is the transformer, list of transformers, or suffix.
* The fourth argument is optional and is the suffix.
Styles:
* `:long`, which formats like `"25 seconds"`.
* `:short`, which formats like `"25s"`.
* Defaults to `:long`
Transformers:
* `:ago` transforms via `ago/1`
* `:approx` transforms via `approx/1`
* `:humanize` transforms via `humanize/1`
* If no transformers are specified, no transformations are applied.
Suffix:
* A string that will be appended to the formatted result.
* If the `:ago` transformer is specified and a suffix is not specified, the suffix will default to `"ago"`.
To use the "ago" transformer with no suffix, specify an empty string as the suffix (`nil` will not suffice).
```elixir
iex> Moar.Duration.format({1, :second})
"1 second"
iex> Moar.Duration.format({120, :second})
"120 seconds"
iex> Moar.Duration.format({120, :second}, :long)
"120 seconds"
iex> Moar.Duration.format({120, :second}, :short)
"120s"
iex> Moar.Duration.format({120, :second}, "yonder")
"120 seconds yonder"
iex> Moar.Duration.format({120, :second}, :humanize)
"2 minutes"
iex> Moar.Duration.format({120, :second}, :humanize, "yonder")
"2 minutes yonder"
iex> Moar.Duration.format({310, :second})
"310 seconds"
iex> Moar.Duration.format({310, :second}, :approx)
"5 minutes"
iex> DateTime.utc_now()
...> |> Moar.DateTime.add({-310, :second})
...> |> Moar.Duration.format(:short, [:ago, :approx], "henceforth")
"5m henceforth"
```
"""
@format_styles [:long, :short]
@spec format(
t() | date_time_ish(),
format_style() | format_transformers() | binary() | nil,
format_transformers() | binary() | nil,
binary() | nil
) :: binary()
def format(duration_or_datetime, style_transformers_or_suffix \\ nil, transformers_or_suffix \\ nil, suffix \\ nil) do
{style, transformers, suffix} =
[style_transformers_or_suffix, transformers_or_suffix, suffix]
|> Enum.reduce({nil, nil, nil}, fn
style, acc when style in @format_styles ->
put_elem(acc, 0, style)
transformers, acc when is_list(transformers) or (is_atom(transformers) and not is_nil(transformers)) ->
transformers = List.wrap(transformers) |> Enum.sort(fn a, _b -> a == :ago end)
acc = put_elem(acc, 1, transformers)
if :ago in transformers, do: put_elem(acc, 2, [" ", "ago"]), else: acc
"" = _suffix, acc ->
put_elem(acc, 2, "")
suffix, acc when is_binary(suffix) ->
put_elem(acc, 2, [" ", suffix])
nil, acc ->
acc
end)
{time, unit} =
transformers
|> List.wrap()
|> Enum.reduce(duration_or_datetime, fn
:approx, acc -> approx(acc)
:ago, {_time, _unit} = duration -> duration
:ago, acc -> ago(acc)
:humanize, acc -> humanize(acc)
other, _acc -> raise "Unknown transformation: #{other}"
end)
unit_name =
if style == :short,
do: @units_to_short_names[unit],
else: [" ", Moar.String.pluralize(time, @units_to_names[unit], &(&1 <> "s"))]
[Kernel.to_string(time), unit_name, suffix] |> Moar.Enum.compact() |> Kernel.to_string()
end
@doc """
If possible, shifts `duration` to a higher time unit that is more readable to a human. Returns `duration`
unchanged if it cannot be exactly shifted.
```elixir
iex> Moar.Duration.humanize({60000, :millisecond})
{1, :minute}
iex> Moar.Duration.humanize({48, :hour})
{2, :day}
iex> Moar.Duration.humanize({49, :hour})
{49, :hour}
```
"""
@spec humanize(t()) :: t()
def humanize(duration), do: humanize(duration, @units_asc)
defp humanize({_time, current_unit} = duration, [head_unit | remaining_units] = _units) do
cond do
Enum.empty?(remaining_units) ->
duration
current_unit == head_unit ->
[next_unit | _] = remaining_units
up = shift(duration, next_unit)
down = shift(up, current_unit)
if down == duration,
do: humanize(up, remaining_units),
else: humanize(duration, remaining_units)
true ->
humanize(duration, remaining_units)
end
end
@doc """
Shifts `duration` to `time_unit`. It is similar to `convert/1` but this function returns a duration tuple,
while `convert/1` just returns an integer value.
> #### Warning {: .warning}
>
> This function is lossy because it rounds down to the nearest whole number.
```elixir
iex> Moar.Duration.shift({121, :second}, :minute)
{2, :minute}
```
"""
@spec shift(t(), time_unit()) :: t()
def shift(duration, to_unit), do: {convert(duration, to_unit), to_unit}
@doc """
Shortcut to `format(duration, :long)`. See `format/2`.
"""
@spec to_string(t()) :: String.t()
def to_string(duration), do: format(duration, :long)
@doc """
Returns the list of duration unit names in descending order.
"""
@spec units() :: [time_unit()]
def units, do: @units_desc
end
