From 49fcae9b281d0124013ab9b6b8b50eeb96875a88 Mon Sep 17 00:00:00 2001
From: Kevin Schneider <schneider.kev@outlook.de>
Date: Thu, 4 Feb 2021 10:46:47 +0100
Subject: [PATCH] Enable callback evaluation for boxed IConvertible sequences
 aswell

---
 dev/Program.fs                |  4 ++--
 src/Dash.NET/Callback.fs      | 31 +++++++++++++++++++++++++++++--
 src/Dash.NET/DynamicInvoke.fs | 17 +++++++++++++++++
 3 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/dev/Program.fs b/dev/Program.fs
index b810972..1dcc54e 100644
--- a/dev/Program.fs
+++ b/dev/Program.fs
@@ -74,8 +74,8 @@ let callbackArrayInput =
         ],
         (fun (inputs:float []) (nclicks:float) ->
             [
-                "output-1" @. Children => (Array.last inputs) * nclicks * 1.
-                "output-2" @. Children => (Array.last inputs) * nclicks * 2.
+               (Array.last inputs) * nclicks * 1.
+               (Array.last inputs) * nclicks * 2.
             ]
         ),
         State = [
diff --git a/src/Dash.NET/Callback.fs b/src/Dash.NET/Callback.fs
index d3d32d2..2b49344 100644
--- a/src/Dash.NET/Callback.fs
+++ b/src/Dash.NET/Callback.fs
@@ -367,9 +367,12 @@ type Callback<'Function>
 
                 match r with
                 | :? seq<CallbackResultBinding> as bindings -> 
+                // The result is a sequence of boxed CallbackResultBindings
+
                     CallbackResponse.multiOut(bindings)
 
                 | :? seq<obj> as boxedResults -> 
+                // The result of the multioutput is a sequence of boxed types
 
                     let outputs = 
                         handler?outputDependencies 
@@ -381,13 +384,37 @@ type Callback<'Function>
                             outputs
                             |> Seq.zip boxedResults
                             |> Seq.map (fun (boxedRes, output) -> output.Id, output.Property, boxedRes)
-
                         )
 
                     else
                         failwithf "amount of multi callback outputs did not match to the actual callback binding (expected %i but got %i)" (Seq.length outputs) (Seq.length boxedResults)
 
-                | _ -> failwithf "multi callback result %O was not a collection." r
+                | r when (isIConvertibleSeq (r.GetType())) ->
+                // The result of the multioutput is a boxed sequence of IConvertibles, e.g.
+                // [2;3;4], [|"1";"2"|]; seq{2.;3.}
+                
+                    let primitiveSeq = 
+                        r 
+                        |> unbox<System.Collections.IEnumerable> 
+                        |> Seq.cast<IConvertible>
+
+                    let outputs = 
+                        handler?outputDependencies 
+                        |> unbox<seq<CallbackOutput>>
+
+                    if (Seq.length outputs) = (Seq.length primitiveSeq) then
+
+                        CallbackResponse.multiOut(
+                            outputs
+                            |> Seq.zip primitiveSeq
+                            |> Seq.map (fun (result, output) -> output.Id, output.Property, (box result))
+
+                        )
+
+                    else
+                        failwithf "The amount of multi callback outputs returned by the callback function did not match to the amount of outputs defined by the callback dependency (expected %i vs %i). Make sure that the callback function returns a collection of results of length %i" (Seq.length primitiveSeq) (Seq.length outputs) (Seq.length outputs)
+
+                | _ -> failwithf "multi callback result %O of type %O was not a supported collection (supported: seq<IConvertible>, seq<obj>, seq<CallbackResultBinding>). You might be able to circumvent this problem by boxing the return values of your results to generate a seq<obj>." r (r.GetType())
 
             else
                 
diff --git a/src/Dash.NET/DynamicInvoke.fs b/src/Dash.NET/DynamicInvoke.fs
index 8015e18..2377d24 100644
--- a/src/Dash.NET/DynamicInvoke.fs
+++ b/src/Dash.NET/DynamicInvoke.fs
@@ -31,6 +31,23 @@ module DynamicInvoke =
                 f
         loop t
 
+    let isIConvertible (t:Type) =
+        t.GetInterfaces()
+        |> Array.exists (fun t -> t = typeof<IConvertible>)
+
+    let isSeq (t:Type) =
+        t.GetInterfaces()
+        |> Array.exists (fun t -> t = typeof<System.Collections.IEnumerable>)
+
+    let isIConvertibleSeq (t:Type) =
+        if isSeq t then
+            let genericArgs = t.GetGenericArguments()
+            if genericArgs.Length > 0 then
+                isIConvertible genericArgs.[0]
+            else
+                false
+        else
+            false
 
     //This function is (as far as i see it) a 'necessary evil' for solving the problem of callbacks having arbitrary amounts of parameters.
     //However, just like DynamicObj in Plotly.NET, it is definately usable when correctly encapsulated to prevent direct usage.