// Serialization (std.ser, §9): the binary format (protobuf 3 wire encoding), canonical JSON, schema evolution.
use std.ser { encode, decode, hex, toJson, fromJson, EncodeError, DecodeError }

enum Status { New = 1, Paid = 2, Shipped = 3 }

data Item {
  sku: str
  qty: i32
}

// version 1 of an order
data OrderV1 {
  id: i64
  status: Status
  items: List<Item>
}

// version 2 adds an optional field and a field with a default: old readers skip them, old writers need not send them
data OrderV2 {
  id: i64
  status: Status
  items: List<Item>
  note: str?
  priority: i32 = 3
}

fn main() io {
  let order = OrderV1{ id: 7, status: Status.Paid, items: [Item{ sku: "a-1", qty: 2 }] }
  match encode(&order) {
    bytes wire => {
      print("wire: {hex(&wire)}")
      match decode<OrderV2>(&wire) {
        OrderV2 v2 => print("as v2: id={v2.id} note={v2.note} priority={v2.priority}")
        DecodeError e => print("decode error {e}")
      }
    }
    EncodeError e => print("encode error {e}")
  }
  match toJson(&order) {
    str json => {
      print("json: {json}")
      match fromJson<OrderV1>(json) {
        OrderV1 back => print("back: {back.items.len()} item(s), status {back.status}")
        DecodeError e => print("decode error {e}")
      }
    }
    EncodeError e => print("encode error {e}")
  }
}