Store available themes in a dictionary (#139)

src/InteractBase.jl

@@ -78,7 +78,7 @@ export latex, alert, confirm, highlight, notifications, accordion, tabulator, ma
 
 export onchange
 
-export settheme!, resettheme!, gettheme, NativeHTML
+export settheme!, resettheme!, gettheme, availablethemes, NativeHTML
 
 export slap_design!
 

src/backends.jl

@@ -2,6 +2,23 @@ libraries(::WidgetTheme) = [style_css]
 
 Base.@deprecate_binding backend Widgets.backends
 
+const themes = OrderedDict{Symbol, WidgetTheme}(:nativehtml => NativeHTML())
+
+registertheme!(key::Union{Symbol, AbstractString}, val::WidgetTheme) = setindex!(themes, val, Symbol(key))
+
+"""
+`settheme!(s::Union{Symbol, AbstractString})`
+
+Set theme of Interact globally. See `availablethemes()` to know what themes are currently available.
+"""
+function settheme!(s::Union{Symbol, AbstractString})
+    theme = get(themes, Symbol(s)) do
+        error("Theme $s is not available.")
+    end
+    settheme!(theme)
+end
+
 settheme!(b::WidgetTheme) = isa(Widgets.get_backend(), WidgetTheme) && Widgets.set_backend!(b)
 gettheme() = isa(Widgets.get_backend(), WidgetTheme) ? Widgets.get_backend() : nothing
+availablethemes() = sort(collect(keys(themes)))
 resettheme!() = isa(Widgets.get_backend(), WidgetTheme) && Widgets.reset_backend!()

test/test_theme.jl

@@ -1,9 +1,16 @@
 struct MyTheme<:InteractBase.WidgetTheme; end
+InteractBase.registertheme!(:mytheme, MyTheme())
 
 @testset "theme" begin
     @test gettheme() == NativeHTML()
     settheme!(MyTheme())
     @test gettheme() == MyTheme()
     resettheme!()
     @test gettheme() == NativeHTML()
+    settheme!("mytheme")
+    @test gettheme() == MyTheme()
+    settheme!(:nativehtml)
+    @test gettheme() == NativeHTML()
+    @test availablethemes() == [:mytheme, :nativehtml]
+    @test_throws ErrorException settheme!("not a theme")
 end