feat(NewtonsoftJson): Upconvert from Case that should be a string

[bartelink]

Provide an upconversion that lets you write the updated form per TypeSafeEnumConverter, but also accept mangled versions that predate impl of #96

i.e. read:

"items": [
        {
          "serviceId": "5c8795be52e34e82883d61babed19513",
          "serviceKind": {
            "Case": "ProductA"
          }
        },
        {
          "serviceId": "8a55ebbf0d404485b50da95bdb53f7b3",
          "serviceKind": {
            "Case": "ProductB"
          }
        }
      ]
    },

but write:

"items": [
                            {
                                "serviceId": "5c8795be52e34e82883d61babed19513",
                                "serviceKind": "ProductB"
                            },
                            {
                                "serviceId": "8a55ebbf0d404485b50da95bdb53f7b3",
                                "serviceKind": "ProductA"
                            }
                        ]

related: JamesNK/Newtonsoft.Json#1662 (comment)

[deviousasti]

What's the use-case? Someone might have persisted this to their DB without checking what it actually serializes as?

[bartelink]

Exactly - DUs in particular are notorious; the standard encoding is sensitive to reordering of fields etc, and more, as mentioned in the linked json.net issue.

The most common thing IME is that people use random SCDUs and typesafe enums declared in common files in serialised structs. And then, once it's in the database, you're tied to that representation forever unless you're prepared to roundtrip e.g. all the events in your event store to 'fix' them, and life is short!

[bartelink]

Poor man's impl:

and ScduProxy = { Case: string; Fields: string[] }
and private EmailAddressNsjConverter() =
    inherit FsCodec.NewtonsoftJson.JsonIsomorphism<EmailAddress, string>()
    override this.Pickle(v) = v.ToString()
    override this.UnPickle(input) = input |> EmailAddress
    override this.Read(reader, serializer) =
        if reader.TokenType = Newtonsoft.Json.JsonToken.String then base.Read(reader, serializer)
        elif reader.TokenType = Newtonsoft.Json.JsonToken.StartObject then
            // UNPACK { "Case": "EmailAddress", "Fields": [ "abc@def.com" ] }
            let p = serializer.Deserialize<ScduProxy>(reader)
            match p.Case, p.Fields with
            | "EmailAddress", [| x |] -> this.UnPickle x
            | _ -> failwith $"unexpected %A{p}"
        else failwith $"unexpected {reader.TokenType}"