customizing newtonsoft

json.fs

namespace AlphaFront
module JsonCustomConverters =
 open Newtonsoft.Json
 open Microsoft.FSharp.Reflection
 open System
 open System.IO

 type DuConverter() =
    inherit JsonConverter()

    override __.WriteJson(writer, value, serializer) =
        let unionType = value.GetType()
        let unionCases = FSharpType.GetUnionCases(unionType)
        let case, fields = FSharpValue.GetUnionFields(value, unionType)
              
        let allSingle = unionCases |> Seq.forall (fun c -> c.GetFields() |> Seq.length = 1)

        match allSingle,fields with
        //simplies case no parameters - just like an enumeration
        | _,[||] -> writer.WriteRawValue(sprintf "\"%s\"" case.Name)
        //all single values - discriminate between record types - so we just serialize the record
        | true,[| singleValue |] -> serializer.Serialize(writer,singleValue)
        //diferent types in same discriminated union - write the case and the items as tuples
        | false,values ->
            writer.WriteStartObject()
            writer.WritePropertyName "Case"
            writer.WriteRawValue(sprintf "\"%s\"" case.Name)
            let valuesCount = Seq.length values
            for i in 1 .. valuesCount do
                let itemName = sprintf "Item%i" i
                writer.WritePropertyName itemName
                serializer.Serialize(writer,values.[i-1])
            writer.WriteEndObject()
        | _,_ -> failwith "Handle this new case"




    override __.ReadJson(reader, destinationType, existingValue, serializer) =
        let parts =
            if reader.TokenType <> JsonToken.StartObject then [| (JsonToken.Undefined, obj()), (reader.TokenType, reader.Value) |]
            else
                seq {
                    yield! reader |> Seq.unfold (fun reader ->
                                         if reader.Read() then Some((reader.TokenType, reader.Value), reader)
                                         else None)
                }
                |> Seq.takeWhile(fun (token, _) -> token <> JsonToken.EndObject)
                |> Seq.pairwise
                |> Seq.mapi (fun id value -> id, value)
                |> Seq.filter (fun (id, _) -> id % 2 = 0)
                |> Seq.map snd
                |> Seq.toArray

        //get simplified key value collection
        let fieldsValues =
            parts
                |> Seq.map (fun ((_, fieldName), (fieldType,fieldValue)) -> fieldName,fieldType,fieldValue)
                |> Seq.toArray
        //all cases of the targe discriminated union
        let unionCases = FSharpType.GetUnionCases(destinationType)

        //the first simple case - this DU contains just simple values - as enum - get the value
        let _,_,firstFieldValue = fieldsValues.[0]

        let fieldsCount = fieldsValues |> Seq.length

        let valuesOnly = fieldsValues |> Seq.skip 1 |> Seq.map (fun (_,_,v) -> v) |> Array.ofSeq

        let foundDirectCase = unionCases |> Seq.tryFind (fun uc -> uc.Name = (firstFieldValue.ToString()))

        let jsonToValue valueType value =
            match valueType with
                                | JsonToken.Date ->
                                    let dateTimeValue = Convert.ToDateTime(value :> Object)
                                    dateTimeValue.ToString("o")
                                | _ -> value.ToString()

        match foundDirectCase, fieldsCount with
            //simpliest case - just like an enum
            | Some case, 1 -> FSharpValue.MakeUnion(case,[||])
            //case is specified - just create the case with the values as parameters
            | Some case, n -> FSharpValue.MakeUnion(case,valuesOnly)
            //case not specified - look up the record type which suites the best
            | None, _ ->
                //this is the second case - this disc union is not of simple value - it may be records or multiple values
                let reconstructedJson = (Seq.fold (fun acc (name,valueType,value) -> acc + String.Format("\t\"{0}\":\"{1}\",\n",name,(jsonToValue valueType value))) "{\n" fieldsValues) + "}"

                //if it is a record lets try to find the case by looking at the present fields
                let implicitCase = unionCases |> Seq.tryPick (fun uc ->
                    //if the case of the discriminated union is a record then this case will contain just one field which will be the record
                    let ucDef = uc.GetFields() |> Seq.head
                    //we need the get the record type and look at the fields
                    let recordType = ucDef.PropertyType
                    let recordFields = recordType.GetProperties()
                    let matched = fieldsValues |> Seq.forall ( fun (fieldName,_,fieldValue) ->
                        recordFields |> Array.exists(fun f-> f.Name = (fieldName :?> string))
                    )    
                    //if we have found a match onthe record let's keep the union case and type of the record
                    match matched with
                        | true -> Some (uc,recordType)
                        | false -> None
                )

                match implicitCase with
                    | Some (case,recordType) ->
                        use stringReader = new StringReader(reconstructedJson)
                        use jsonReader = new JsonTextReader(stringReader)
                        //creating the record - Json.NET can handle that already
                        let unionCaseValue = serializer.Deserialize(jsonReader,recordType)
                        //convert the record to the parent discrimianted union
                        let parentDUValue = FSharpValue.MakeUnion(case,[|unionCaseValue|])
                        parentDUValue
                    | None -> failwith "can't find such disc union type"

    override __.CanConvert(objectType) =
        FSharpType.IsUnion objectType &&
        //it seems that both option and list are implemented using discriminated unions, so we tell json.net to ignore them and use different serializer
        not (objectType.IsGenericType  && objectType.GetGenericTypeDefinition() = typedefof<list<_>>) &&
        not (objectType.IsGenericType  && objectType.GetGenericTypeDefinition() = typedefof<option<_>>) &&
        not (FSharpType.IsRecord objectType)


    
 type OptionConverter() =
    inherit JsonConverter()

    override x.CanConvert(t) = 
        t.IsGenericType && t.GetGenericTypeDefinition() = typedefof<option<_>>

    override x.WriteJson(writer, value, serializer) =
        let value = 
            if value = null then null
            else 
                let _,fields = FSharpValue.GetUnionFields(value, value.GetType())
                fields.[0]
        serializer.Serialize(writer, value)

    override x.ReadJson(reader, t, existingValue, serializer) =        
        let innerType = t.GetGenericArguments().[0]
        let innerType = 
            if innerType.IsValueType then (typedefof<Nullable<_>>).MakeGenericType([|innerType|])
            else innerType        
        let value = serializer.Deserialize(reader, innerType)
        let cases = FSharpType.GetUnionCases(t)
        if value = null then FSharpValue.MakeUnion(cases.[0], [||])
        else FSharpValue.MakeUnion(cases.[1], [|value|])

 type DecimalConverter () =
    inherit JsonConverter()
    
    override x.CanRead = false;
      
    override x.CanConvert(objectType) =    
          objectType = typedefof<float> ||
          objectType = typedefof<decimal>
    
    override x.WriteJson(writer,value,serializer) =    
        if value.GetType() = typedefof<float> then 
            let f : float = value :?> float
            writer.WriteValue(f.ToString("0.00"));
        else
            let d : decimal = value :?> decimal
            writer.WriteValue(d.ToString("0.00"));

    override x.ReadJson(reader,objectType,existingValue,serializer) : Object =   
        raise (NotImplementedException())