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Add DateTime/NaiveDateTime.beginning_of_day and DateTime/NaiveDateTime.end_of_day #12443

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merged 6 commits into from Mar 5, 2023
Merged

Add DateTime/NaiveDateTime.beginning_of_day and DateTime/NaiveDateTime.end_of_day #12443

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6fb2605
Add beginning_of_day/1 and end_of_day/1
thiamsantos Mar 3, 2023
c044ff5
Remove functions from datetime
thiamsantos Mar 5, 2023
b0d229c
Test precision
thiamsantos Mar 5, 2023
9324c24
Add documentation on how to use with datetimes
thiamsantos Mar 5, 2023
fdcfc7c
Fix type reference in documentation
thiamsantos Mar 5, 2023
d74435e
Apply suggestions from code review
josevalim Mar 5, 2023
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12 changes: 12 additions & 0 deletions lib/elixir/lib/calendar.ex
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Expand Up @@ -326,6 +326,18 @@ defmodule Calendar do
{:ok, {year, month, day, hour, minute, second, microsecond}, utc_offset}
| {:error, atom}

@doc """
Converts the given `t:iso_days/0` to the first moment of the day.
"""
@doc since: "1.15.0"
@callback iso_days_to_beginning_of_day(iso_days) :: iso_days

@doc """
Converts the given `t:iso_days/0` to the last moment of the day.
"""
@doc since: "1.15.0"
@callback iso_days_to_end_of_day(iso_days) :: iso_days

# General Helpers

@doc """
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40 changes: 40 additions & 0 deletions lib/elixir/lib/calendar/iso.ex
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Expand Up @@ -1401,6 +1401,46 @@ defmodule Calendar.ISO do
"-" <> zero_pad(-val, count)
end

@doc """
Converts the `t:Calendar.iso_days/0` to the first moment of the day.

## Examples

iex> Calendar.ISO.iso_days_to_beginning_of_day({0, {0, 86400000000}})
{0, {0, 86400000000}}
iex> Calendar.ISO.iso_days_to_beginning_of_day({730485, {43200000000, 86400000000}})
{730485, {0, 86400000000}}
iex> Calendar.ISO.iso_days_to_beginning_of_day({730485, {46800000000, 86400000000}})
{730485, {0, 86400000000}}

"""
@doc since: "1.15.0"
@impl true
@spec iso_days_to_beginning_of_day(Calendar.iso_days()) :: Calendar.iso_days()
def iso_days_to_beginning_of_day({days, _day_fraction}) do
{days, {0, @parts_per_day}}
end

@doc """
Converts the `t:Calendar.iso_days/0` to the last moment of the day.

## Examples

iex> Calendar.ISO.iso_days_to_end_of_day({0, {0, 86400000000}})
{0, {86399999999, 86400000000}}
iex> Calendar.ISO.iso_days_to_end_of_day({730485, {43200000000, 86400000000}})
{730485, {86399999999, 86400000000}}
iex> Calendar.ISO.iso_days_to_end_of_day({730485, {46800000000, 86400000000}})
{730485, {86399999999, 86400000000}}

"""
@doc since: "1.15.0"
@impl true
@spec iso_days_to_end_of_day(Calendar.iso_days()) :: Calendar.iso_days()
def iso_days_to_end_of_day({days, _day_fraction}) do
{days, {@parts_per_day - 1, @parts_per_day}}
end

## Helpers

@doc false
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54 changes: 54 additions & 0 deletions lib/elixir/lib/calendar/naive_datetime.ex
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Expand Up @@ -1169,6 +1169,60 @@ defmodule NaiveDateTime do
end
end

@doc """
Calculates a `NaiveDateTime` that is the first moment for the given `NaiveDateTime`.

To calculate the beginning of day of a `DateTime`, call this function, then convert back to a `DateTime`:

datetime
|> NaiveDateTime.beginning_of_day()
|> DateTime.from_naive(datetime.timezone)
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Note that the beginning of the day may not exist or be ambiguous
in a given timezone, so you must handle those cases accordingly.

## Examples

iex> NaiveDateTime.beginning_of_day(~N[2000-01-01 23:00:07.123456])
~N[2000-01-01 00:00:00.000000]

"""
@doc since: "1.15.0"
@spec beginning_of_day(Calendar.naive_datetime()) :: t
def beginning_of_day(%{calendar: calendar, microsecond: {_, precision}} = naive_datetime) do
naive_datetime
|> to_iso_days()
|> calendar.iso_days_to_beginning_of_day()
|> from_iso_days(calendar, precision)
end

@doc """
Calculates a `NaiveDateTime` that is the last moment for the given `NaiveDateTime`.

To calculate the end of day of a `DateTime`, call this function, then convert back to a `DateTime`:

datetime
|> NaiveDateTime.beginning_of_day()
|> DateTime.from_naive(datetime.timezone)
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Note that the end of the day may not exist or be ambiguous
in a given timezone, so you must handle those cases accordingly.

## Examples

iex> NaiveDateTime.end_of_day(~N[2000-01-01 23:00:07.123456])
~N[2000-01-01 23:59:59.999999]

"""
@doc since: "1.15.0"
@spec end_of_day(Calendar.naive_datetime()) :: t
def end_of_day(%{calendar: calendar, microsecond: {_, precision}} = naive_datetime) do
naive_datetime
|> to_iso_days()
|> calendar.iso_days_to_end_of_day()
|> from_iso_days(calendar, precision)
end

## Helpers

defp seconds_from_day_fraction({parts_in_day, @seconds_per_day}),
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6 changes: 6 additions & 0 deletions lib/elixir/test/elixir/calendar/holocene.exs
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Expand Up @@ -148,4 +148,10 @@ defmodule Calendar.Holocene do

@impl true
defdelegate valid_time?(hour, minute, second, microsecond), to: Calendar.ISO

@impl true
defdelegate iso_days_to_beginning_of_day(iso_days), to: Calendar.ISO

@impl true
defdelegate iso_days_to_end_of_day(iso_days), to: Calendar.ISO
end
35 changes: 35 additions & 0 deletions lib/elixir/test/elixir/calendar/naive_datetime_test.exs
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Expand Up @@ -348,4 +348,39 @@ defmodule NaiveDateTimeTest do
assert catch_error(NaiveDateTime.to_time(~T[00:00:00.000000]))
end
end

describe "beginning_of_day/1" do
test "precision" do
assert NaiveDateTime.beginning_of_day(~N[2000-01-01 23:00:07.123]) ==
~N[2000-01-01 00:00:00.000]

assert NaiveDateTime.beginning_of_day(~N[2000-01-01 23:00:07]) == ~N[2000-01-01 00:00:00]
end
end

describe "end_of_day/1" do
test "precision" do
assert NaiveDateTime.end_of_day(~N[2000-01-01 23:00:07.123]) == %NaiveDateTime{
calendar: Calendar.ISO,
day: 1,
hour: 23,
microsecond: {999_999, 3},
minute: 59,
month: 1,
second: 59,
year: 2000
}

assert NaiveDateTime.end_of_day(~N[2000-01-01 23:00:07]) == %NaiveDateTime{
calendar: Calendar.ISO,
day: 1,
hour: 23,
microsecond: {999_999, 0},
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the fact it's {999_999, 0} might lead to surprising behaviour:

import ExUnit.Assertions
start = ~N[2023-01-01 00:00:00]
assert NaiveDateTime.end_of_day(start) == 
       start |> NaiveDateTime.add(1, :day) |> NaiveDateTime.add(-1, :second)
** (ExUnit.AssertionError)

Assertion with == failed
code:  assert NaiveDateTime.end_of_day(start) ==
              start |> NaiveDateTime.add(1, :day) |> NaiveDateTime.add(-1, :second)
left:  ~N[2023-01-01 23:59:59]
right: ~N[2023-01-01 23:59:59]

the difference is:

iex> NaiveDateTime.end_of_day(start).microsecond
{999999, 0}

iex> start |> NaiveDateTime.add(1, :day) |> NaiveDateTime.add(-1, :second) |> Map.fetch!(:microsecond)
{0, 0}

We'd see similar behaviour for different precisions e.g. milliseconds.

I'm honestly not sure what should be the behaviour here.

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one way to look at it is we should be able to write the assertion under question using just sigils:

assert NaiveDateTime.end_of_day(~N[2000-01-01 23:00:07]) == ~N[2000-01-01 23:59:59]

and the fact we can't is a reason to revisit this?

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I created a new issue. We should probably truncate it based on the precision: {(10 ** precision) - 1, precision}

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I just opened a PR to fix this #12450.

minute: 59,
month: 1,
second: 59,
year: 2000
}
end
end
end