use gadts for layer, clean code

src/layer.ml

@@ -1,23 +1,89 @@
-type t = Jv.t
+type _ t =
+  | Basic : Jv.t -> [> `Basic ] t
+  | Geojson : Jv.t -> [> `Geojson ] t
+  | Marker : Jv.t -> [> `Marker ] t
+  | Tile : Jv.t -> [> `Tile ] t
 
-let add_to map layer = ignore @@ Jv.call layer "addTo" [| Map.to_jv_t map |]
+(** Basic layers *)
 
-let remove layer = ignore @@ Jv.call layer "remove" [||]
+let add_to : type kind. Map.t -> kind t -> unit =
+ fun map -> function
+  | Basic l | Geojson l | Marker l | Tile l ->
+    let (_ : Jv.t) = Jv.call l "addTo" [| Map.to_jv map |] in
+    ()
 
-let remove_from map layer =
-  ignore @@ Jv.call layer "removeFrom" [| Map.to_jv_t map |]
+let remove : type kind. kind t -> unit = function
+  | Basic l | Geojson l | Marker l | Tile l ->
+    let (_ : Jv.t) = Jv.call l "remove" [||] in
+    ()
 
-let bind_popup el layer =
-  ignore @@ Jv.call layer "bindPopup" [| Brr.El.to_jv el |]
+let remove_from : type kind. Map.t -> kind t -> unit =
+ fun map -> function
+  | Basic l | Geojson l | Marker l | Tile l ->
+    let (_ : Jv.t) = Jv.call l "removeFrom" [| Map.to_jv map |] in
+    ()
 
-let unbind_popup layer = ignore @@ Jv.call layer "unbindPopup" [||]
+let bind_popup : type kind. Brr.El.t -> kind t -> unit =
+ fun el -> function
+  | Basic l | Geojson l | Marker l | Tile l ->
+    let (_ : Jv.t) = Jv.call l "bindPopup" [| Brr.El.to_jv el |] in
+    ()
 
-let open_popup layer = ignore @@ Jv.call layer "openPopup" [||]
+let unbind_popup : type kind. kind t -> unit = function
+  | Basic l | Geojson l | Marker l | Tile l ->
+    let (_ : Jv.t) = Jv.call l "unbindPopup" [||] in
+    ()
 
-let close_popup layer = ignore @@ Jv.call layer "closePopup" [||]
+let open_popup : type kind. kind t -> unit = function
+  | Basic l | Geojson l | Marker l | Tile l ->
+    let (_ : Jv.t) = Jv.call l "openPopup" [||] in
+    ()
 
-let get_popup layer = Popup.of_jv_t @@ Jv.call layer "getPopup" [||]
+let close_popup : type kind. kind t -> unit = function
+  | Basic l | Geojson l | Marker l | Tile l ->
+    let (_ : Jv.t) = Jv.call l "closePopup" [||] in
+    ()
 
-let of_jv_t = Fun.id
+let get_popup : type kind. kind t -> Popup.t = function
+  | Basic l | Geojson l | Marker l | Tile l ->
+    Jv.call l "getPopup" [||] |> Popup.of_jv
 
-let to_jv_t = Fun.id
+let to_jv : type kind. kind t -> Jv.t = function
+  | Basic l | Geojson l | Marker l | Tile l -> l
+
+(** Geojson layers *)
+
+let create_geojson : ?options:Jv.t -> Jv.t -> [ `Geojson ] t =
+ fun ?(options = Jv.null) geojson ->
+  let jv_t = Jv.call Global.leaflet "geoJSON" [| geojson; options |] in
+  Geojson jv_t
+
+(** Marker layers *)
+
+let create_marker : Latlng.t -> [ `Marker ] t =
+ fun latlng ->
+  let jv_t = Jv.call Global.leaflet "marker" [| Latlng.to_jv latlng |] in
+  Marker jv_t
+
+(** Tile layers *)
+
+let create_tile_osm : string option -> [ `Tile ] t =
+ fun url ->
+  (* see https://wiki.openstreetmap.org/wiki/Tile_servers *)
+  let url =
+    Option.value url
+      ~default:"https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
+  in
+  let jv_t =
+    Jv.call Global.leaflet "tileLayer"
+      [| Jv.of_string url
+       ; Jv.obj
+           [| ( "attribution"
+              , Jv.of_string
+                  "&copy; <a \
+                   href=\"https://www.openstreetmap.org/copyright\">OpenStreetMap</a> \
+                   contributors" )
+           |]
+      |]
+  in
+  Tile jv_t