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.
"""
defmodule UnitRecord do
@moduledoc false
require Record
Record.defrecord(:unit, name: nil, long: nil, short: nil, conversion: nil)
end
defmodule Unit do
@moduledoc false
import UnitRecord
@approx_year unit(name: :approx_year, long: "year", short: "yr", conversion: {12, :approx_month})
@approx_month unit(name: :approx_month, long: "month", short: "mo", conversion: {30, :day})
@day unit(name: :day, long: "day", short: "d", conversion: {24, :hour})
@hour unit(name: :hour, long: "hour", short: "h", conversion: {60, :minute})
@minute unit(name: :minute, long: "minute", short: "m", conversion: {60, :second})
@second unit(name: :second, long: "second", short: "s", conversion: {1000, :millisecond})
@millisecond unit(name: :millisecond, long: "millisecond", short: "ms", conversion: {1000, :microsecond})
@microsecond unit(name: :microsecond, long: "microsecond", short: "us", conversion: {1000, :nanosecond})
@nanosecond unit(name: :nanosecond, long: "nanosecond", short: "ns", conversion: nil)
@units_desc [@approx_year, @approx_month, @day, @hour, @minute, @second, @millisecond, @microsecond, @nanosecond]
@unit_names_desc Enum.map(@units_desc, fn record -> unit(record, :name) end)
@units_asc Enum.reverse(@units_desc)
@unit_names_asc Enum.map(@units_asc, fn record -> unit(record, :name) end)
@unit_map Map.new(@units_desc, fn record -> {unit(record, :name), record} end)
# # #
def conversion(unit_name) when is_atom(unit_name), do: @unit_map[unit_name] |> conversion()
def conversion(unit_record), do: unit(unit_record, :conversion)
def long_name(unit_name) when is_atom(unit_name), do: @unit_map[unit_name] |> long_name()
def long_name(unit_record), do: unit(unit_record, :long)
def multiplier(unit_name) when is_atom(unit_name), do: @unit_map[unit_name] |> multiplier()
def multiplier(unit_record), do: conversion(unit_record) |> elem(0)
def name(unit_name) when is_atom(unit_name), do: unit_name
def name(unit_record), do: unit(unit_record, :name)
def names(:asc), do: @unit_names_asc
def names(:desc), do: @unit_names_desc
def short_name(unit_name) when is_atom(unit_name), do: @unit_map[unit_name] |> short_name()
def short_name(unit_record), do: unit(unit_record, :short)
# # #
def larger(unit_name) when unit_name in @unit_names_desc do
case Enum.find_index(@unit_names_desc, &(&1 == unit_name)) do
0 -> nil
index -> Enum.at(@units_desc, index - 1)
end
end
def larger?(unit_a, unit_b) do
Enum.find_index(@unit_names_desc, &(&1 == unit_a)) < Enum.find_index(@unit_names_desc, &(&1 == unit_b))
end
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`.
See also `from_now/1`.
```elixir
iex> DateTime.utc_now()
...> |> Moar.DateTime.subtract({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, Unit.names(: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(from_duration, to_unit), do: shift(from_duration, to_unit) |> elem(0)
@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_or_transformers_or_suffix \\ nil, transformers_or_suffix \\ nil, suffix \\ nil) do
{style, transformers, suffix} =
[style_or_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 in [:ago, :from_now] end)
acc = put_elem(acc, 1, transformers)
cond do
:ago in transformers -> put_elem(acc, 2, [" ", "ago"])
:from_now in transformers -> put_elem(acc, 2, [" ", "from now"])
true -> acc
end
"" = _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)
:from_now, {_time, _unit} = duration -> duration
:from_now, acc -> from_now(acc)
:humanize, acc -> humanize(acc)
other, _acc -> raise "Unknown transformation: #{other}"
end)
unit_name =
if style == :short,
do: Unit.short_name(unit),
else: [" ", Moar.String.pluralize(time, Unit.long_name(unit), &(&1 <> "s"))]
[Kernel.to_string(time), unit_name, suffix] |> Moar.Enum.compact() |> Kernel.to_string()
end
@doc """
Returns the duration between now and `datetime`, in the largest possible unit.
`datetime` can be an ISO8601-formatted string, a `DateTime`, or a `NaiveDateTime`.
See also `ago/1`.
```elixir
iex> DateTime.utc_now()
...> |> Moar.DateTime.add({121, :minute})
...> |> Moar.Duration.from_now()
...> |> Moar.Duration.approx()
{2, :hour}
```
"""
@spec from_now(date_time_ish()) :: t()
def from_now(datetime) when is_binary(datetime), do: datetime |> Moar.DateTime.from_iso8601!() |> from_now()
def from_now(%module{} = datetime), do: between(module.utc_now(), datetime)
@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, Unit.names(: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({_time, from_unit} = duration, to_unit) when from_unit == to_unit,
do: duration
def shift({_time, from_unit} = duration, to_unit) do
if Unit.larger?(from_unit, to_unit),
do: shift_down(duration) |> shift(to_unit),
else: shift_up(duration) |> shift(to_unit)
end
@doc """
Shifts `duration` to the next smaller unit. Raises if it's already at the smallest unit (nanosecond).
```elixir
iex> Moar.Duration.shift_down({1, :hour})
{60, :minute}
```
"""
@spec shift_down(t()) :: t()
def shift_down({time, from_unit} = duration) do
case Unit.conversion(from_unit) do
nil ->
raise "Cannot shift #{inspect(duration)} to a smaller unit because #{from_unit} is the smallest supported unit."
{conversion_multiplier, conversion_unit} ->
{time * conversion_multiplier, conversion_unit}
end
end
@doc """
Shifts `duration` to the next larger unit. Raises if it's already at the largest unit (approx_year).
Rounds the result towards zero.
> #### Warning {: .warning}
>
> This function is lossy because it rounds down to the nearest whole number.
```elixir
iex> Moar.Duration.shift_up({60, :minute})
{1, :hour}
iex> Moar.Duration.shift_up({125, :minute})
{2, :hour}
```
"""
def shift_up({time, from_unit} = duration) do
case Unit.larger(from_unit) do
nil ->
raise "Cannot shift #{inspect(duration)} to a larger unit because #{from_unit} is the largest supported unit."
larger_unit ->
{div(time, Unit.multiplier(larger_unit)), Unit.name(larger_unit)}
end
end
@doc """
Shortcut to `format(duration, :long)`. See `format/4`.
"""
@spec to_string(t()) :: String.t()
def to_string(duration), do: format(duration, :long)
end