Rebuild JSON string to a different structure, parsing specific fields

I receive a JSON like this

{
   "raw_content":"very long string"
   "mode":"ML",
   "user_id":"4000008367",
   "user_description":"John Doe",
   "model":3,
   "dest_contact":"[email protected]",
   "order_details":[
      "ART.:  214883 PELL GRANI 9 ESPR.BAR SKGR 1000        SGOC.:  1000 GR\nVS.ART: 305920132                                     COMPOS. PALLET\n36  COLLI     PEZ.RA:      6  TOT.PEZZI:      216  B: 12  T:  6\nEU C.L.:   24,230\nCO  SCAP- :    16,500    CA  SCAP- :    15,000    CO  SCCP- :     0,000\nCO  SAGV- :     0,00000\nC.N. :    17,200SCAD.MIN.:    25/01/22\nCONDIZIONI PAGAMENTO : 60GG B.B. DT RIC FT FINEMESE ART62\n",
      "ART.:  287047 PELLINI BIO100%ARABICALTGR  250        SGOC.:   250 GR\nVS.ART: 315860176                                     COMPOS. PALLET\n36  COLLI     PEZ.RA:      6  TOT.PEZZI:      216  B: 12  T:  3\nEU C.L.:    8,380\nCO  SCAP- :    16,500    PR  SCAP- :    15,000    CO  SCCP- :     0,000\nCO  SAGV- :     0,00000\nC.N. :     5,950SCAD.MIN.:    25/01/22\nCONDIZIONI PAGAMENTO : 60GG B.B. DT RIC FT FINEMESE ART62\n",
      "ART.: 3137837 CAFFE PELLINI TOP     LTGR  250        SGOC.:   250 GR\nVS.ART: 315850175                                     COMPOS. PALLET\n30  COLLI     PEZ.RA:     12  TOT.PEZZI:      360  B:  6  T:  5\nEU C.L.:    6,810\nCO  SCAP- :    16,500    PR  SCAP- :    12,000    CO  SCCP- :     0,000\nCO  SAGV- :     0,00000\nC.N. :     5,000SCAD.MIN.:    18/08/21\nCONDIZIONI PAGAMENTO : 60GG B.B. DT RIC FT FINEMESE ART62\n",
      "ART.: 7748220 ESPRES.SUP.TRADIZ. MOKPKGR  500        SGOC.:   500 GR\nVS.ART: 315930114                                     COMPOS. PALLET\n80  COLLI     PEZ.RA:     10  TOT.PEZZI:      800  B: 10  T:  6\nEU C.L.:    7,580\nCO  SCAP- :    16,500    PR  SCAP- :    27,750    CO  SCCP- :     0,000\nCO  SAGV- :     0,00000\nC.N. :     4,570SCAD.MIN.:    25/01/22\nCONDIZIONI PAGAMENTO : 60GG B.B. DT RIC FT FINEMESE ART62\n"
   ],
   "order_footer":"\nPALLET DA CM. 80X120\nT O T A L E  C O L L I   182\n\n- EX D.P.R. 322 - 18/05/82 NON SI ACCETTANO TERMINI MINIMI DI\nCONSERVAZIONE INFERIORI A QUELLI INDICATI\n-      CONSEGNA FRANCO BANCHINA, PALLET MONOPRODOTTO\nCOME DA PALLETTIZZAZIONE SPECIFICATA\nCONDIZIONI DI PAGAMENTO : COME DA ACCORDI\n"
}

and I want to reorder it to this

{
    id: "32839ds8a32jjdas93193snkkk32jhds-k2j1", // generated, see my implementation
    rawContent: "very long string",
    parsedContent: {"mode":"ML", "user_id":"4000008367", "user_description":"John Doe", "order_details":[ "....." ], ... } // basically all the fields except raw content
}

How can I do this? I'm trying to work it with maps:

        var output map[string]interface{}
        var message processing.Document // message is of type struct {ID string, Raw string, Parsed string}

        err = json.Unmarshal([]byte(doc), &output)
        if err != nil {
            // error handling
        }

        message.ParsedContent = "{"

        for key, data := range output {
            if key == "raw_content" {
                hash := md5.Sum([]byte(data.(string)))
                message.ID = hex.EncodeToString(hash[:])
                message.RawContent = base64.RawStdEncoding.EncodeToString([]byte(data.(string)))
            } else {
                temp := fmt.Sprintf("\"%s\": \"%s\", ", key, data)
                message.ParsedContent = message.ParsedContent + temp
            }
        }

        message.ParsedContent = message.ParsedContent + "}"
        msg, err := json.Marshal(message)
        if err != nil {
            // error handling
        }

        fmt.Println(string(msg))

There's a few problem with this. If it was only strings it would be ok, but there are integers and the sprintf doesn't work (the output I get, for example on the field "model" is "model": "%!s(float64=3)". I could do an if key == model and parse it as an int, but as I said the fields are not always the same and there are other integers that sometimes are there and sometimes are not there. Also, the field "order_footer" has escaped new lines which are somehow deleted in my parsing, and this breaks the validity of the resulting JSON.

How can I solve this issues?

EDIT: As suggested, hand-parsing JSON is a bad idea. I could parse it into a struct, the field "model" actually tells me which struct to use. The struct for "model": 3 for example is:

type MOD3 struct {
    Raw                     string   `json:"raw_content"`
    Mode                    string   `json:"mode"`
    UserID                  string   `json:"user_id"`
    UserDes                 string   `json:"user_description"`
    Model                   int      `json:"model"`
    Heading                 string   `json:"legal_heading"`
    DestContact             string   `json:"dest_contact"`
    VendorID                string   `json:"vendor_id"`
    VendorLegal             string   `json:"vendor_legal"`
    OrderID                 string   `json:"order_id"`
    OrderDate               int64    `json:"order_date"`
    OrderReference          string   `json:"order_reference"`
    DeliveryDate            int64    `json:"delivery_date"`
    OrderDestination        string   `json:"order_destination"`
    OrderDestinationAddress string   `json:"order_destination_address"`
    Items                   []string `json:"order_details"`
    OrderFooter             string   `json:"order_footer"`
}

At this point, how can I parse specific fields to the output format?