prop/lib/microwaveprop/weather/iem_client.ex

defmodule Microwaveprop.Weather.IemClient do
  @moduledoc false

  @iem_base "https://mesonet.agron.iastate.edu"

  # --- URL builders ---

  def asos_url(station_id, start_dt, end_dt) do
    "#{@iem_base}/cgi-bin/request/asos.py" <>
      "?station=#{station_id}" <>
      "&data=tmpf&data=dwpf&data=relh&data=sknt&data=drct" <>
      "&data=mslp&data=alti&data=skyc1" <>
      "&year1=#{start_dt.year}&month1=#{start_dt.month}&day1=#{start_dt.day}" <>
      "&hour1=#{start_dt.hour}&minute1=0" <>
      "&year2=#{end_dt.year}&month2=#{end_dt.month}&day2=#{end_dt.day}" <>
      "&hour2=#{end_dt.hour}&minute2=59" <>
      "&format=onlycomma&latlon=no&elev=no&missing=null&trace=null&direct=no&report_type=3"
  end

  def raob_url(station_id, dt) do
    ts = format_iem_ts(dt)
    "#{@iem_base}/json/raob.py?ts=#{ts}&station=#{station_id}"
  end

  # --- HTTP fetchers ---

  def fetch_asos(station_id, start_dt, end_dt) do
    url = asos_url(station_id, start_dt, end_dt)

    case Req.get(url) do
      {:ok, %{status: 200, body: body}} ->
        {:ok, parse_asos_csv(body)}

      {:ok, %{status: status}} ->
        {:error, "IEM ASOS HTTP #{status}"}

      {:error, reason} ->
        {:error, reason}
    end
  end

  def fetch_raob(station_id, dt) do
    url = raob_url(station_id, dt)

    case Req.get(url) do
      {:ok, %{status: 200, body: body}} ->
        {:ok, parse_raob_json(body)}

      {:ok, %{status: status}} ->
        {:error, "IEM RAOB HTTP #{status}"}

      {:error, reason} ->
        {:error, reason}
    end
  end

  # --- Parsers ---

  def parse_asos_csv(csv_text) do
    csv_text
    |> String.split("\n")
    |> Enum.reject(fn line ->
      line == "" or String.starts_with?(line, "#") or String.starts_with?(line, "station")
    end)
    |> Enum.map(&parse_asos_row/1)
  end

  def parse_raob_json(json) when is_map(json) do
    json
    |> Map.get("profiles", [])
    |> Enum.map(fn entry ->
      %{
        observed_at: parse_raob_timestamp(entry["valid"]),
        profile: entry["profile"] || []
      }
    end)
  end

  # --- Private ---

  defp parse_asos_row(line) do
    parts = String.split(line, ",")

    %{
      observed_at: parse_asos_timestamp(Enum.at(parts, 1)),
      temp_f: parse_float(Enum.at(parts, 2)),
      dewpoint_f: parse_float(Enum.at(parts, 3)),
      relative_humidity: parse_float(Enum.at(parts, 4)),
      wind_speed_kts: parse_float(Enum.at(parts, 5)),
      wind_direction_deg: parse_int(Enum.at(parts, 6)),
      sea_level_pressure_mb: parse_float(Enum.at(parts, 7)),
      altimeter_setting: parse_float(Enum.at(parts, 8)),
      sky_condition: parse_nullable_string(Enum.at(parts, 9))
    }
  end

  defp parse_asos_timestamp(str) when is_binary(str) do
    # Format: "2026-03-28 18:53"
    case DateTime.from_iso8601(String.trim(str) <> ":00Z") do
      {:ok, dt, _} -> DateTime.truncate(dt, :second)
      _ -> nil
    end
  end

  defp parse_asos_timestamp(_), do: nil

  defp parse_raob_timestamp(str) when is_binary(str) do
    # Format: "2026-03-28 12:00:00+00:00"
    cleaned =
      str
      |> String.trim()
      |> String.replace(~r/\+00:00$/, "Z")
      |> String.replace(" ", "T")

    case DateTime.from_iso8601(cleaned) do
      {:ok, dt, _} -> DateTime.truncate(dt, :second)
      _ -> nil
    end
  end

  defp parse_raob_timestamp(_), do: nil

  defp parse_float(nil), do: nil
  defp parse_float("null"), do: nil

  defp parse_float(str) do
    case Float.parse(String.trim(str)) do
      {val, _} -> val
      :error -> nil
    end
  end

  defp parse_int(nil), do: nil
  defp parse_int("null"), do: nil

  defp parse_int(str) do
    case Integer.parse(String.trim(str)) do
      {val, _} -> val
      :error -> nil
    end
  end

  defp parse_nullable_string(nil), do: nil
  defp parse_nullable_string("null"), do: nil

  defp parse_nullable_string(str) do
    trimmed = String.trim(str)
    if trimmed == "", do: nil, else: trimmed
  end

  defp format_iem_ts(dt) do
    y = Integer.to_string(dt.year)
    mo = dt.month |> Integer.to_string() |> String.pad_leading(2, "0")
    d = dt.day |> Integer.to_string() |> String.pad_leading(2, "0")
    h = dt.hour |> Integer.to_string() |> String.pad_leading(2, "0")
    mi = dt.minute |> Integer.to_string() |> String.pad_leading(2, "0")
    "#{y}#{mo}#{d}#{h}#{mi}"
  end
end