full frontend refactor

lib/mound_hunters/mound_parser.ex

@@ -266,4 +266,70 @@ defmodule MoundHunters.MoundParser do
       end
     end
   end
+
+  @doc """
+  Converts Web Mercator coordinates (EPSG:3857) to WGS84 lat/lng (EPSG:4326).
+
+  Web Mercator uses meters from origin, this converts back to decimal degrees.
+
+  ## Examples
+
+      iex> MoundHunters.MoundParser.web_mercator_to_latlon(0, 0)
+      {0.0, 0.0}
+      
+      iex> MoundHunters.MoundParser.web_mercator_to_latlon(1113194.91, 5009377.09)
+      {10.0, 40.0}
+  """
+  @spec web_mercator_to_latlon(float(), float()) :: {lat :: float(), lon :: float()}
+  def web_mercator_to_latlon(x, y) do
+    # Web Mercator origin offset (meters)
+    origin_shift = :math.pi() * 6_378_137.0
+
+    # Convert x to longitude
+    lon = x / origin_shift * 180.0
+
+    # Convert y to latitude
+    lat = y / origin_shift * 180.0
+
+    lat =
+      180.0 / :math.pi() *
+        (2.0 * :math.atan(:math.exp(lat * :math.pi() / 180.0)) - :math.pi() / 2.0)
+
+    {lat, lon}
+  end
+
+  @doc """
+  Converts a bounding box from Web Mercator to lat/lng.
+
+  Returns a map with min/max lat/lng values.
+
+  ## Examples
+
+      iex> MoundHunters.MoundParser.bounds_web_mercator_to_latlon(
+      ...>   %{min_x: -9_000_000, max_x: -8_900_000, min_y: 4_900_000, max_y: 5_000_000}
+      ...> )
+      %{min_lat: ..., max_lat: ..., min_lng: ..., max_lng: ...}
+  """
+  @spec bounds_web_mercator_to_latlon(%{
+          min_x: float(),
+          max_x: float(),
+          min_y: float(),
+          max_y: float()
+        }) :: %{
+          min_lat: float(),
+          max_lat: float(),
+          min_lng: float(),
+          max_lng: float()
+        }
+  def bounds_web_mercator_to_latlon(%{min_x: min_x, max_x: max_x, min_y: min_y, max_y: max_y}) do
+    {min_lat, min_lng} = web_mercator_to_latlon(min_x, min_y)
+    {max_lat, max_lng} = web_mercator_to_latlon(max_x, max_y)
+
+    %{
+      min_lat: min_lat,
+      max_lat: max_lat,
+      min_lng: min_lng,
+      max_lng: max_lng
+    }
+  end
 end