feat(render): accept options to modify rendering behavior

These can be defined both at 'render time' and when the `Diagram` that
is being rendered is constructed. This makes sure `Diagram`s rendered
implicitly, i.e. through `Base.show`, can use these `options` while at
the same allowing these options to be overridden when rendering.

src/Kroki.jl

@@ -128,6 +128,11 @@ UriSafeBase64Payload(diagram::Diagram) = foldl(
 Renders a [`Diagram`](@ref) through a Kroki service to the specified output
 format.
 
+Allows the specification of [diagram
+options](https://docs.kroki.io/kroki/setup/diagram-options) through the
+`options` keyword. The `options` default to those specified on the
+[`Diagram`](@ref).
+
 If the Kroki service responds with an error, throws an
 [`InvalidDiagramSpecificationError`](@ref
 Kroki.Exceptions.InvalidDiagramSpecificationError) or
@@ -140,7 +145,11 @@ _SVG output is supported for all [`Diagram`](@ref) types_. See [Kroki's
 website](https://kroki.io/#support) for an overview of other supported output
 formats per diagram type. Note that this list may not be entirely up-to-date.
 """
-render(diagram::Diagram, output_format::AbstractString) =
+render(
+  diagram::Diagram,
+  output_format::AbstractString;
+  options::Dict{String, String} = diagram.options,
+) =
   try
     getfield(
       request(
@@ -154,6 +163,11 @@ render(diagram::Diagram, output_format::AbstractString) =
           ],
           '/',
         ),
+        # Pass all diagram options as headers to Kroki by prepending the
+        # necessary prefix to all provided `options`. This ensures this package
+        # does not have to be updated whenever new options are added to the
+        # service
+        "Kroki-Diagram-Options-" .* keys(options) .=> values(options),
       ),
       :body,
     )

test/runtests.jl

@@ -130,6 +130,27 @@ end
       # after the render, these should be ignored when matching
       @test endswith(rendered, r"</svg>\s?")
     end
+
+    @testset "takes `options` into account" begin
+      expected_theme_name = "materia"
+      options = Dict{String, String}("theme" => expected_theme_name)
+      diagram = Diagram(:plantuml, "A -> B: C"; options)
+
+      @testset "defaults to `Diagram` options" begin
+        rendered = String(render(diagram, "svg"))
+
+        @test occursin("!theme $(expected_theme_name)", rendered)
+      end
+
+      @testset "allows definition at render-time" begin
+        expected_overridden_theme = "sketchy"
+        rendered = String(
+          render(diagram, "svg"; options = Dict("theme" => expected_overridden_theme)),
+        )
+
+        @test occursin("!theme $(expected_overridden_theme)", rendered)
+      end
+    end
   end
 
   @testset "`Base.show`" begin