Refactor conditionals to use multi-clause pattern matching

Replace case/cond/if blocks with multi-clause function dispatch
and pattern matching in function heads across 9 modules:
- WeatherUnits: case to multi-clause unit_system/1, unit_labels via do_unit_labels/1
- PacketUtils: if to pattern match on %{"id" => id}, multi-clause threshold/callsign
- SetLocale: case to multi-clause extract_locale/1
- IPGeolocation: if/cond to pattern match on conn, binary prefix matching for private_ip?
- DeviceIdentification: cond to extracted pattern_matches?/2
- MobileChannel: cond to multi-clause do_callsign_match/2
- PacketProcessor: cond to dispatch_visibility/6 on {in_bounds, has_marker} tuple
- PacketManager: destructure packet_state in heads, multi-clause maybe_cleanup/3
- AprsSymbol: case/if to multi-clause get_table_id/1, normalize_symbol_code/1

lib/aprsme/device_identification.ex

@@ -221,28 +221,23 @@ defmodule Aprsme.DeviceIdentification do
       end
 
     Enum.find(devices, fn device ->
-      pattern = device.identifier
-
-      cond do
-        String.contains?(pattern, "?") ->
-          try do
-            regex = wildcard_pattern_to_regex(pattern)
-            Regex.match?(regex, identifier)
-          rescue
-            _e in Regex.CompileError ->
-              false
-          end
-
-        String.contains?(pattern, "*") ->
-          # Compare literally if pattern contains * but not ?
-          pattern == identifier
-
-        true ->
-          pattern == identifier
-      end
+      pattern_matches?(device.identifier, identifier)
     end)
   end
 
+  defp pattern_matches?(pattern, identifier) do
+    if String.contains?(pattern, "?") do
+      try do
+        regex = wildcard_pattern_to_regex(pattern)
+        Regex.match?(regex, identifier)
+      rescue
+        _e in Regex.CompileError -> false
+      end
+    else
+      pattern == identifier
+    end
+  end
+
   # Converts a pattern with ? wildcards to a regex
   defp wildcard_pattern_to_regex(pattern) when is_binary(pattern) do
     # Replace ? with a placeholder, escape all regex metacharacters except the placeholder,

lib/aprsme_web/aprs_symbol.ex

@@ -31,38 +31,37 @@ defmodule AprsmeWeb.AprsSymbol do
           background_size: String.t()
         }
   def get_sprite_info(symbol_table, symbol_code) do
-    # For overlay symbols (A-Z, 0-9), display the base symbol with overlay
-    if symbol_table && String.match?(symbol_table, ~r/^[A-Z0-9]$/) do
-      # Use the base symbol from the overlay table, not the overlay character itself
-      get_overlay_base_symbol_info(symbol_code)
-    else
-      # Normal symbol table processing
-      symbol_table = normalize_symbol_table(symbol_table)
-      symbol_code = normalize_symbol_code(symbol_code)
+    compute_sprite_info(overlay_symbol?(symbol_table), symbol_table, symbol_code)
+  end
 
-      # Map symbol table to sprite file ID
-      table_id = get_table_id(symbol_table)
+  defp overlay_symbol?(table) when is_binary(table), do: String.match?(table, ~r/^[A-Z0-9]$/)
+  defp overlay_symbol?(_), do: false
 
-      sprite_file = "/aprs-symbols/aprs-symbols-128-#{table_id}@2x.png"
+  defp compute_sprite_info(true, _symbol_table, symbol_code) do
+    get_overlay_base_symbol_info(symbol_code)
+  end
 
-      # Get symbol position using ASCII-based calculation
-      symbol_code_ord = get_symbol_code_ord(symbol_code)
+  defp compute_sprite_info(false, symbol_table, symbol_code) do
+    symbol_table = normalize_symbol_table(symbol_table)
+    symbol_code = normalize_symbol_code(symbol_code)
 
-      index = symbol_code_ord - 33
-      safe_index = max(0, min(index, 93))
+    table_id = get_table_id(symbol_table)
+    sprite_file = "/aprs-symbols/aprs-symbols-128-#{table_id}@2x.png"
 
-      # Calculate positioning for 16-column grid
-      column = rem(safe_index, 16)
-      row = div(safe_index, 16)
-      x = -column * 128
-      y = -row * 128
+    symbol_code_ord = get_symbol_code_ord(symbol_code)
+    index = symbol_code_ord - 33
+    safe_index = max(0, min(index, 93))
 
-      %{
-        sprite_file: sprite_file,
-        background_position: "#{x / 4}px #{y / 4}px",
-        background_size: "512px 192px"
-      }
-    end
+    column = rem(safe_index, 16)
+    row = div(safe_index, 16)
+    x = -column * 128
+    y = -row * 128
+
+    %{
+      sprite_file: sprite_file,
+      background_position: "#{x / 4}px #{y / 4}px",
+      background_size: "512px 192px"
+    }
   end
 
   @doc """
@@ -188,9 +187,9 @@ defmodule AprsmeWeb.AprsSymbol do
       ">"
   """
   @spec normalize_symbol_code(String.t() | nil) :: String.t()
-  def normalize_symbol_code(symbol_code) do
-    if symbol_code && symbol_code != "", do: symbol_code, else: ">"
-  end
+  def normalize_symbol_code(nil), do: ">"
+  def normalize_symbol_code(""), do: ">"
+  def normalize_symbol_code(symbol_code), do: symbol_code
 
   @doc """
   Maps a symbol table to its sprite file ID.
@@ -207,18 +206,10 @@ defmodule AprsmeWeb.AprsSymbol do
       "2"
   """
   @spec get_table_id(String.t()) :: String.t()
-  def get_table_id(symbol_table) do
-    case symbol_table do
-      # Primary table
-      "/" -> "0"
-      # Alternate table
-      "\\" -> "1"
-      # Overlay table (A-Z, 0-9)
-      "]" -> "2"
-      # Default to primary table
-      _ -> "0"
-    end
-  end
+  def get_table_id("/"), do: "0"
+  def get_table_id("\\"), do: "1"
+  def get_table_id("]"), do: "2"
+  def get_table_id(_), do: "0"
 
   @doc """
   Renders an APRS symbol as HTML for use in Leaflet markers.

lib/aprsme_web/channels/mobile_channel.ex

@@ -478,27 +478,19 @@ defmodule AprsmeWeb.MobileChannel do
   end
 
   defp callsign_matches?(packet_callsign, tracked_callsign) do
-    # Normalize both to uppercase
-    packet_callsign = String.upcase(packet_callsign)
-    tracked_callsign = String.upcase(tracked_callsign)
+    normalized_packet = String.upcase(packet_callsign)
+    normalized_tracked = String.upcase(tracked_callsign)
+    do_callsign_match(normalized_packet, normalized_tracked)
+  end
 
-    cond do
-      # Exact match
-      packet_callsign == tracked_callsign ->
-        true
+  defp do_callsign_match(callsign, callsign), do: true
 
-      # Wildcard match (e.g., "W5ISP*" matches "W5ISP-9")
-      String.contains?(tracked_callsign, "*") ->
-        pattern = String.replace(tracked_callsign, "*", "")
-        String.starts_with?(packet_callsign, pattern)
-
-      # Base callsign match (e.g., "W5ISP" matches "W5ISP-9")
-      String.starts_with?(packet_callsign, tracked_callsign <> "-") ->
-        true
-
-      # No match
-      true ->
-        false
+  defp do_callsign_match(packet_callsign, tracked_callsign) do
+    if String.contains?(tracked_callsign, "*") do
+      pattern = String.replace(tracked_callsign, "*", "")
+      String.starts_with?(packet_callsign, pattern)
+    else
+      String.starts_with?(packet_callsign, tracked_callsign <> "-")
     end
   end
 

lib/aprsme_web/live/map_live/packet_manager.ex

@@ -35,55 +35,43 @@ defmodule AprsmeWeb.MapLive.PacketManager do
   Add packets to visible storage with memory management.
   Returns updated state and packet IDs for broadcasting.
   """
-  def add_visible_packets(packet_state, packets) when is_list(packets) do
-    # Store packets and get IDs
+  def add_visible_packets(%{visible_packet_ids: visible_ids, packet_count: packet_count} = packet_state, packets)
+      when is_list(packets) do
     packet_ids = PacketStore.store_packets(packets)
+    new_visible_ids = packet_ids ++ visible_ids
 
-    # Update visible packet tracking
-    new_visible_ids = packet_ids ++ packet_state.visible_packet_ids
-
-    # Apply memory management
     {managed_ids, cleanup_needed} = apply_memory_limits(new_visible_ids, @max_visible_packets)
 
     updated_state = %{
       packet_state
       | visible_packet_ids: managed_ids,
-        packet_count: Map.put(packet_state.packet_count, :visible, length(managed_ids))
+        packet_count: Map.put(packet_count, :visible, length(managed_ids))
     }
 
-    # Clean up if needed
-    final_state =
-      if cleanup_needed do
-        perform_cleanup(updated_state, :visible)
-      else
-        updated_state
-      end
-
+    final_state = maybe_cleanup(updated_state, cleanup_needed, :visible)
     {final_state, packet_ids}
   end
 
   @doc """
   Add packets to historical storage with sliding window management.
   """
-  def add_historical_packets(packet_state, packets) when is_list(packets) do
+  def add_historical_packets(
+        %{historical_packet_ids: historical_ids, packet_count: packet_count} = packet_state,
+        packets
+      )
+      when is_list(packets) do
     packet_ids = PacketStore.store_packets(packets)
+    new_historical_ids = packet_ids ++ historical_ids
 
-    new_historical_ids = packet_ids ++ packet_state.historical_packet_ids
     {managed_ids, cleanup_needed} = apply_memory_limits(new_historical_ids, @max_historical_packets)
 
     updated_state = %{
       packet_state
       | historical_packet_ids: managed_ids,
-        packet_count: Map.put(packet_state.packet_count, :historical, length(managed_ids))
+        packet_count: Map.put(packet_count, :historical, length(managed_ids))
     }
 
-    final_state =
-      if cleanup_needed do
-        perform_cleanup(updated_state, :historical)
-      else
-        updated_state
-      end
-
+    final_state = maybe_cleanup(updated_state, cleanup_needed, :historical)
     {final_state, packet_ids}
   end
 
@@ -165,15 +153,15 @@ defmodule AprsmeWeb.MapLive.PacketManager do
     end
   end
 
-  defp perform_cleanup(packet_state, _type) do
+  defp maybe_cleanup(state, false, _type), do: state
+
+  defp maybe_cleanup(%{last_cleanup: last_cleanup} = state, true, _type) do
     current_time = System.monotonic_time(:millisecond)
 
-    # Only cleanup if enough time has passed to avoid excessive cleanup
-    # 30 seconds
-    if current_time - packet_state.last_cleanup > 30_000 do
-      %{packet_state | last_cleanup: current_time}
+    if current_time - last_cleanup > 30_000 do
+      %{state | last_cleanup: current_time}
     else
-      packet_state
+      state
     end
   end
 

lib/aprsme_web/live/map_live/packet_processor.ex

@@ -51,35 +51,40 @@ defmodule AprsmeWeb.MapLive.PacketProcessor do
   """
   @spec handle_packet_visibility(map(), number() | nil, number() | nil, binary(), Socket.t()) :: Socket.t()
   def handle_packet_visibility(packet, lat, lon, callsign_key, socket) do
-    cond do
-      should_remove_marker?(lat, lon, callsign_key, socket) ->
-        remove_marker_from_map(callsign_key, socket)
+    visibility_action(packet, lat, lon, callsign_key, socket)
+  end
 
-      should_add_marker?(lat, lon, callsign_key, socket) ->
-        handle_valid_postgres_packet(packet, lat, lon, socket)
+  defp visibility_action(packet, lat, lon, callsign_key, socket) when not is_nil(lat) and not is_nil(lon) do
+    in_bounds = within_bounds?(%{lat: lat, lon: lon}, socket.assigns.map_bounds)
+    has_marker = Map.has_key?(socket.assigns.visible_packets, callsign_key)
+    dispatch_visibility({in_bounds, has_marker}, packet, lat, lon, callsign_key, socket)
+  end
 
-      should_update_marker?(lat, lon, callsign_key, socket) ->
-        # Marker exists and is within bounds - check if there's significant movement
-        existing_packet = socket.assigns.visible_packets[callsign_key]
-        {existing_lat, existing_lon, _} = CoordinateUtils.get_coordinates(existing_packet)
+  defp visibility_action(_packet, _lat, _lon, _callsign_key, socket), do: socket
 
-        # Check if we have valid existing coordinates
-        if is_number(existing_lat) and is_number(existing_lon) and
-             GeoUtils.significant_movement?(existing_lat, existing_lon, lat, lon, 50) do
-          # Significant movement detected (more than 50 meters), update the marker
-          handle_valid_postgres_packet(packet, lat, lon, socket)
-        else
-          # Just GPS drift (less than 50 meters) or invalid coordinates,
-          # update the packet data but don't send visual update
-          new_visible_packets = Map.put(socket.assigns.visible_packets, callsign_key, packet)
-          assign(socket, :visible_packets, new_visible_packets)
-        end
+  defp dispatch_visibility({false, true}, _packet, _lat, _lon, callsign_key, socket) do
+    remove_marker_from_map(callsign_key, socket)
+  end
 
-      true ->
-        socket
+  defp dispatch_visibility({true, false}, packet, lat, lon, _callsign_key, socket) do
+    handle_valid_postgres_packet(packet, lat, lon, socket)
+  end
+
+  defp dispatch_visibility({true, true}, packet, lat, lon, callsign_key, socket) do
+    existing_packet = socket.assigns.visible_packets[callsign_key]
+    {existing_lat, existing_lon, _} = CoordinateUtils.get_coordinates(existing_packet)
+
+    if is_number(existing_lat) and is_number(existing_lon) and
+         GeoUtils.significant_movement?(existing_lat, existing_lon, lat, lon, 50) do
+      handle_valid_postgres_packet(packet, lat, lon, socket)
+    else
+      new_visible_packets = Map.put(socket.assigns.visible_packets, callsign_key, packet)
+      assign(socket, :visible_packets, new_visible_packets)
     end
   end
 
+  defp dispatch_visibility(_, _packet, _lat, _lon, _callsign_key, socket), do: socket
+
   @doc """
   Handle valid postgres packet by adding it to visible packets and displaying it.
   """
@@ -128,24 +133,6 @@ defmodule AprsmeWeb.MapLive.PacketProcessor do
 
   # Private helper functions
 
-  defp should_remove_marker?(lat, lon, callsign_key, socket) do
-    !is_nil(lat) and !is_nil(lon) and
-      Map.has_key?(socket.assigns.visible_packets, callsign_key) and
-      not within_bounds?(%{lat: lat, lon: lon}, socket.assigns.map_bounds)
-  end
-
-  defp should_add_marker?(lat, lon, callsign_key, socket) do
-    !is_nil(lat) and !is_nil(lon) and
-      not Map.has_key?(socket.assigns.visible_packets, callsign_key) and
-      within_bounds?(%{lat: lat, lon: lon}, socket.assigns.map_bounds)
-  end
-
-  defp should_update_marker?(lat, lon, callsign_key, socket) do
-    !is_nil(lat) and !is_nil(lon) and
-      Map.has_key?(socket.assigns.visible_packets, callsign_key) and
-      within_bounds?(%{lat: lat, lon: lon}, socket.assigns.map_bounds)
-  end
-
   # Use shared bounds utility
   defp within_bounds?(coords, bounds) do
     BoundsUtils.within_bounds?(coords, bounds)

lib/aprsme_web/live/shared/packet_utils.ex

@@ -10,11 +10,8 @@ defmodule AprsmeWeb.Live.Shared.PacketUtils do
   Get unique callsign key from packet.
   """
   @spec get_callsign_key(map()) :: binary()
-  def get_callsign_key(packet) do
-    if Map.has_key?(packet, "id"),
-      do: to_string(packet["id"]),
-      else: [:positive] |> System.unique_integer() |> to_string()
-  end
+  def get_callsign_key(%{"id" => id}), do: to_string(id)
+  def get_callsign_key(_packet), do: [:positive] |> System.unique_integer() |> to_string()
 
   @doc """
   Prune oldest packets from a map to enforce memory limits.
@@ -155,18 +152,13 @@ defmodule AprsmeWeb.Live.Shared.PacketUtils do
   Check if a packet is within the time threshold (not too old).
   """
   @spec packet_within_time_threshold?(struct(), any()) :: boolean()
-  def packet_within_time_threshold?(packet, threshold) do
-    case packet do
-      %{received_at: received_at} when not is_nil(received_at) ->
-        threshold_dt = convert_threshold_to_datetime(threshold)
-        DateTime.compare(received_at, threshold_dt) in [:gt, :eq]
-
-      _ ->
-        # If no timestamp, treat as current
-        true
-    end
+  def packet_within_time_threshold?(%{received_at: received_at}, threshold) when not is_nil(received_at) do
+    threshold_dt = convert_threshold_to_datetime(threshold)
+    DateTime.compare(received_at, threshold_dt) in [:gt, :eq]
   end
 
+  def packet_within_time_threshold?(_packet, _threshold), do: true
+
   defp convert_threshold_to_datetime(threshold) when is_integer(threshold) do
     # Assume seconds since epoch
     DateTime.from_unix!(threshold)
@@ -228,11 +220,10 @@ defmodule AprsmeWeb.Live.Shared.PacketUtils do
   def generate_callsign(packet) do
     base_callsign = get_packet_field(packet, :base_callsign, "")
     ssid = get_packet_field(packet, :ssid, nil)
-
-    if ssid != nil and ssid != "" do
-      "#{base_callsign}-#{ssid}"
-    else
-      base_callsign
-    end
+    format_callsign_with_ssid(base_callsign, ssid)
   end
+
+  defp format_callsign_with_ssid(base_callsign, nil), do: base_callsign
+  defp format_callsign_with_ssid(base_callsign, ""), do: base_callsign
+  defp format_callsign_with_ssid(base_callsign, ssid), do: "#{base_callsign}-#{ssid}"
 end

lib/aprsme_web/plugs/ip_geolocation.ex

@@ -13,23 +13,17 @@ defmodule AprsmeWeb.Plugs.IPGeolocation do
   def init(opts), do: opts
 
   @impl true
-  def call(conn, _opts) do
-    # Only run for the main map page
-    if conn.request_path == "/" && conn.method == "GET" do
-      case get_session(conn, :ip_geolocation) do
-        nil ->
-          # No cached geolocation, fetch it
-          perform_geolocation(conn)
-
-        _cached ->
-          # Already have geolocation in session
-          conn
-      end
-    else
-      conn
-    end
+  def call(%{request_path: "/", method: "GET"} = conn, _opts) do
+    conn
+    |> get_session(:ip_geolocation)
+    |> handle_geolocation(conn)
   end
 
+  def call(conn, _opts), do: conn
+
+  defp handle_geolocation(nil, conn), do: perform_geolocation(conn)
+  defp handle_geolocation(_cached, conn), do: conn
+
   defp perform_geolocation(conn) do
     ip = get_client_ip(conn)
     Logger.info("IP geolocation: Starting lookup for IP #{ip}")
@@ -133,16 +127,12 @@ defmodule AprsmeWeb.Plugs.IPGeolocation do
 
   defp valid_ip_for_geolocation?(_), do: false
 
-  defp private_ip?(ip) do
-    cond do
-      String.starts_with?(ip, "127.") -> true
-      String.starts_with?(ip, "::1") -> true
-      String.starts_with?(ip, "10.") -> true
-      String.starts_with?(ip, "192.168.") -> true
-      String.starts_with?(ip, "172.") -> in_172_private_range?(ip)
-      true -> false
-    end
-  end
+  defp private_ip?("127." <> _), do: true
+  defp private_ip?("::1" <> _), do: true
+  defp private_ip?("10." <> _), do: true
+  defp private_ip?("192.168." <> _), do: true
+  defp private_ip?("172." <> _ = ip), do: in_172_private_range?(ip)
+  defp private_ip?(_), do: false
 
   # Check if IP is in 172.16.0.0/12 range (172.16.0.0 - 172.31.255.255)
   defp in_172_private_range?(ip) do

lib/aprsme_web/plugs/set_locale.ex

@@ -17,15 +17,14 @@ defmodule AprsmeWeb.Plugs.SetLocale do
   end
 
   defp get_locale_from_header(conn) do
-    case get_req_header(conn, "accept-language") do
-      [accept_language | _] ->
-        parse_accept_language(accept_language)
-
-      _ ->
-        nil
-    end
+    conn
+    |> get_req_header("accept-language")
+    |> extract_locale()
   end
 
+  defp extract_locale([accept_language | _]), do: parse_accept_language(accept_language)
+  defp extract_locale(_), do: nil
+
   defp parse_accept_language(accept_language) do
     accept_language
     |> String.split(",")

lib/aprsme_web/weather_units.ex

@@ -11,21 +11,11 @@ defmodule AprsmeWeb.WeatherUnits do
   Returns :imperial for US, :metric for most other countries.
   """
   @spec unit_system(String.t() | nil | any()) :: :imperial | :metric
-  def unit_system(locale) when is_binary(locale) do
-    case locale do
-      # Default to imperial for English
-      "en" -> :imperial
-      # Spanish-speaking countries mostly use metric
-      "es" -> :metric
-      # Germany uses metric
-      "de" -> :metric
-      # France uses metric
-      "fr" -> :metric
-      # Default to metric for unknown locales
-      _ -> :metric
-    end
-  end
-
+  def unit_system("en"), do: :imperial
+  def unit_system("es"), do: :metric
+  def unit_system("de"), do: :metric
+  def unit_system("fr"), do: :metric
+  def unit_system(locale) when is_binary(locale), do: :metric
   def unit_system(nil), do: :imperial
   def unit_system(_), do: :imperial
 
@@ -34,12 +24,8 @@ defmodule AprsmeWeb.WeatherUnits do
   Returns the temperature in the appropriate unit for the locale.
   """
   @spec format_temperature(number() | any(), String.t()) :: {number() | any(), String.t()}
-  def format_temperature(temp, locale) when is_number(temp) do
-    case unit_system(locale) do
-      :imperial -> {temp, "°F"}
-      :metric -> {Convert.f_to_c(temp), "°C"}
-    end
-  end
+  def format_temperature(temp, locale) when is_number(temp),
+    do: format_by_unit(temp, locale, &Convert.f_to_c/1, "°F", "°C")
 
   def format_temperature(temp, _locale), do: {temp, "°F"}
 
@@ -48,12 +34,8 @@ defmodule AprsmeWeb.WeatherUnits do
   Returns the wind speed in the appropriate unit for the locale.
   """
   @spec format_wind_speed(number() | any(), String.t()) :: {number() | any(), String.t()}
-  def format_wind_speed(speed, locale) when is_number(speed) do
-    case unit_system(locale) do
-      :imperial -> {speed, "mph"}
-      :metric -> {Convert.mph_to_kph(speed), "km/h"}
-    end
-  end
+  def format_wind_speed(speed, locale) when is_number(speed),
+    do: format_by_unit(speed, locale, &Convert.mph_to_kph/1, "mph", "km/h")
 
   def format_wind_speed(speed, _locale), do: {speed, "mph"}
 
@@ -62,12 +44,8 @@ defmodule AprsmeWeb.WeatherUnits do
   Returns the rain amount in the appropriate unit for the locale.
   """
   @spec format_rain(number() | any(), String.t()) :: {number() | any(), String.t()}
-  def format_rain(rain, locale) when is_number(rain) do
-    case unit_system(locale) do
-      :imperial -> {rain, "in"}
-      :metric -> {Convert.inches_to_mm(rain), "mm"}
-    end
-  end
+  def format_rain(rain, locale) when is_number(rain),
+    do: format_by_unit(rain, locale, &Convert.inches_to_mm/1, "in", "mm")
 
   def format_rain(rain, _locale), do: {rain, "in"}
 
@@ -75,10 +53,7 @@ defmodule AprsmeWeb.WeatherUnits do
   Formats pressure (keeps hPa for all locales as it's standard).
   """
   @spec format_pressure(number() | any(), any()) :: {number() | any(), String.t()}
-  def format_pressure(pressure, _locale) when is_number(pressure) do
-    {pressure, "hPa"}
-  end
-
+  def format_pressure(pressure, _locale) when is_number(pressure), do: {pressure, "hPa"}
   def format_pressure(pressure, _locale), do: {pressure, "hPa"}
 
   @doc """
@@ -90,23 +65,30 @@ defmodule AprsmeWeb.WeatherUnits do
           rain: String.t(),
           pressure: String.t()
         }
-  def unit_labels(locale) do
-    case unit_system(locale) do
-      :imperial ->
-        %{
-          temperature: "°F",
-          wind_speed: "mph",
-          rain: "in",
-          pressure: "hPa"
-        }
+  def unit_labels(locale), do: do_unit_labels(unit_system(locale))
 
-      :metric ->
-        %{
-          temperature: "°C",
-          wind_speed: "km/h",
-          rain: "mm",
-          pressure: "hPa"
-        }
+  defp do_unit_labels(:imperial) do
+    %{
+      temperature: "°F",
+      wind_speed: "mph",
+      rain: "in",
+      pressure: "hPa"
+    }
+  end
+
+  defp do_unit_labels(:metric) do
+    %{
+      temperature: "°C",
+      wind_speed: "km/h",
+      rain: "mm",
+      pressure: "hPa"
+    }
+  end
+
+  defp format_by_unit(value, locale, converter, imperial_unit, metric_unit) do
+    case unit_system(locale) do
+      :imperial -> {value, imperial_unit}
+      :metric -> {converter.(value), metric_unit}
     end
   end
 end