53 lines
1.6 KiB
Elixir
53 lines
1.6 KiB
Elixir
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defmodule Rsh26pool.JST do
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@moduledoc """
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Helpers for converting between UTC (how timestamps are stored) and
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Japan Standard Time (JST, UTC+9) which is what the UI shows and accepts.
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A full time zone database is not configured for this demo, and JST has no
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daylight saving time, so a fixed +9h offset is sufficient and dependency free.
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"""
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@offset_seconds 9 * 3600
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@doc """
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Parses a `datetime-local` form value (e.g. `"2026-07-04T15:30"`), interpreting
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it as wall-clock JST, and returns the corresponding UTC `DateTime`.
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"""
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@spec parse_local(String.t()) :: {:ok, DateTime.t()} | :error
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def parse_local(value) when is_binary(value) do
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with {:ok, naive} <- NaiveDateTime.from_iso8601(ensure_seconds(value)) do
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utc =
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naive
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|> DateTime.from_naive!("Etc/UTC")
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|> DateTime.add(-@offset_seconds, :second)
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|> DateTime.truncate(:second)
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{:ok, utc}
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else
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_ -> :error
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end
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end
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def parse_local(_), do: :error
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@doc "Converts a stored UTC `DateTime` to a JST `DateTime` for display."
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@spec to_local(DateTime.t()) :: DateTime.t()
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def to_local(%DateTime{} = dt), do: DateTime.add(dt, @offset_seconds, :second)
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@doc "Formats a stored UTC `DateTime` as a human friendly JST string."
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@spec format(DateTime.t() | nil) :: String.t()
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def format(nil), do: ""
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def format(%DateTime{} = dt) do
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l = to_local(dt)
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"~4..0B/~2..0B/~2..0B ~2..0B:~2..0B"
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|> :io_lib.format([l.year, l.month, l.day, l.hour, l.minute])
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|> to_string()
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end
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defp ensure_seconds(value) do
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if Regex.match?(~r/T\d{2}:\d{2}$/, value), do: value <> ":00", else: value
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end
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end
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