defmodule Fast.Ecto.TimeZoneQuery do
  # -- Imports
  import Ecto.Query, warn: false

  @doc """
  Converts a timestamp to the specified timezone.
  Ensures proper timezone conversion by:
  1. Converting the timestamp to UTC
  2. Converting to the target timezone
  3. Converting back to timestamptz
  """
  defmacro at_time_zone(timestamp_expr, tz_field) do
    quote do
      fragment(
        "((?)::timestamp AT TIME ZONE 'UTC' AT TIME ZONE (?))::timestamptz",
        unquote(timestamp_expr),
        iana_tz(unquote(tz_field))
      )
    end
  end

  @doc """
  Converts US timezone names to IANA timezone names for PostgreSQL compatibility.
  """
  defmacro iana_tz(tz_field) do
    quote do
      fragment(
        """
        CASE ?
          WHEN 'America/Puerto_Rico' THEN 'America/Puerto_Rico'
          WHEN 'US/Alaska' THEN 'America/Anchorage'
          WHEN 'US/Aleutian' THEN 'America/Adak'
          WHEN 'US/Arizona' THEN 'America/Phoenix'
          WHEN 'US/Central' THEN 'America/Chicago'
          WHEN 'US/East-Indiana' THEN 'America/Indiana/Indianapolis'
          WHEN 'US/Eastern' THEN 'America/New_York'
          WHEN 'US/Hawaii' THEN 'Pacific/Honolulu'
          WHEN 'US/Indiana-Starke' THEN 'America/Indiana/Knox'
          WHEN 'US/Michigan' THEN 'America/Detroit'
          WHEN 'US/Mountain' THEN 'America/Denver'
          WHEN 'US/Pacific' THEN 'America/Los_Angeles'
          WHEN 'US/Samoa' THEN 'Pacific/Pago_Pago'
          ELSE ?
        END
        """,
        unquote(tz_field),
        unquote(tz_field)
      )
    end
  end
end