open Utf8Json
open Utf8Json.Resolvers
open Utf8Json.FSharp

CompositeResolver.RegisterAndSetAsDefault(
  FSharpResolver.Instance,
  EnumResolver.UnderlyingValue,
  StandardResolver.Default
)

type ENUM = A = 0 | B = 1

[<JsonFormatter(typeof<DUFormatter>)>]
type DU = A | B | C
and DUFormatter() =
    interface IJsonFormatter<DU> with
        override x.Serialize(writer : byref<JsonWriter>, value:DU, resolver : IJsonFormatterResolver) =
            writer.WriteString(value.ToString())

        override x.Deserialize(reader : byref<JsonReader>, resolver : IJsonFormatterResolver) =
            let str = reader.ReadString()
            match str with
            | "A" -> A
            | "B" -> B
            | "C" -> C
            | _ -> failwithf "This is not the case of DU union: %A" str

type SUBRECORD = {
    subField: float
}

type RECORD = {
    field : int
    field2 : string
    field3 : SUBRECORD
}

[<EntryPoint>]
let main argv =
    let a = Some "Hello world"
    let r = {
        field = 10
        field2 = "Hello"
        field3 = {
            subField = 42.0
        }
    }

    let s = JsonSerializer.ToJsonString ENUM.B
    let s2 = JsonSerializer.ToJsonString DU.B
    let s3 = JsonSerializer.ToJsonString a
    let s4 = JsonSerializer.ToJsonString r

    let zz = JsonSerializer.Deserialize<DU> s2
    printfn "%A" zz

    printfn "%s %s %s %s" s s2 s3 s4
    0