honor minimal zoom when rendering map preview

assets/js/map.js

@@ -582,6 +582,7 @@ function setup() {
     center: initial.slice(0, 2),
     zoom: initial[2],
     fitBoundsOptions: fitBoundsOpt,
+    // keep in sync with basemap/constants.ex
     minZoom: 9,
     maxZoom: 19,
     style: style,

lib/basemap/constants.ex

@@ -1,3 +1,12 @@
 defmodule Basemap.Constants do
-  def bounds_fitting_max_zoom, do: 17
+  # keep in sync with map.js
+  def min_zoom, do: 9
+
+  @max_zoom 19
+  def max_zoom, do: @max_zoom
+
+  @bounds_fitting_max_zoom 17
+  def bounds_fitting_max_zoom, do: @bounds_fitting_max_zoom
+
+  if @bounds_fitting_max_zoom > @max_zoom, do: raise("invalid config")
 end

lib/basemap/static/runner.ex

@@ -35,12 +35,17 @@ defmodule Basemap.Static.Runner do
   @spec render(render_task(), non_neg_integer()) ::
           {:ok, content_type :: binary(), image :: binary()} | {:error, reason :: binary()}
   def render(task, timeout \\ 5000) do
+    zoom =
+      task.zoom
+      |> max(Basemap.Constants.min_zoom())
+      |> min(Basemap.Constants.bounds_fitting_max_zoom())
+
     line =
       Enum.join(
         [
           task.lon,
           task.lat,
-          task.zoom,
+          zoom,
           task.pixelRatio,
           task.width,
           task.height,

lib/veloroute_web/components/various_helpers.ex

@@ -100,7 +100,12 @@ defmodule VelorouteWeb.VariousHelpers do
   """
   def to_string_center_zoom(bounds) do
     cz = Geo.CheapRuler.bounds_to_center_zoom(bounds)
-    zoom = min(Basemap.Constants.bounds_fitting_max_zoom(), round(cz.zoom))
+
+    zoom =
+      round(cz.zoom)
+      |> max(Basemap.Constants.min_zoom())
+      |> min(Basemap.Constants.bounds_fitting_max_zoom())
+
     Enum.join([cz.lon, cz.lat, zoom], ",")
   end
 end