to_json.mbt

pub trait ToJson {
  write_json_string(Self, Buffer) -> Unit
}

fn ToJson::write_json_string(self : Int, buf : Buffer) -> Unit {
  buf.write_string(self.to_string())
}

fn ToJson::write_json_string(self : Bool, buf : Buffer) -> Unit {
  buf.write_string(self.to_string())
}

fn ToJson::write_json_string(self : String, buf : Buffer) -> Unit {
  buf.write_string(self.to_string())
}

fn ToJson::write_json_string[T : ToJson](self : Array[T], buf : Buffer) -> Unit {
  buf.write_string("[")
  self.iteri(
    fn(i, item) {
      item.write_json_string(buf)
      if i < self.length() - 1 {
        buf.write_string(", ")
      }
    },
  )
  buf.write_string("]")
}

fn ToJson::write_json_string[T : ToJson](
  self : @map.Map[String, T],
  buf : Buffer
) -> Unit {
  buf.write_string("{")
  self.iteri(
    fn(i, key, val) {
      buf.write_string(key)
      buf.write_string(": ")
      val.write_json_string(buf)
      buf.write_string(", ")
      if i < self.size() - 1 {
        buf.write_string(", ")
      }
    },
  )
  buf.write_string("}")
}

pub fn to_json[X : ToJson](x : X) -> String {
  let buf = Buffer::make(10)
  x.write_json_string(buf)
  buf.to_string()
}

struct Data {
  x : Int
  y : Bool
  z : String
} derive(Debug, Show)

// NOTE: this is imperfect. I need to get members by refrection
fn to_members(self : Data) -> Array[(String, ToJson)] {
  [("x", self.x), ("y", self.y), ("z", self.z)]
}

fn Data::write_json_string(self : Data, buf : Buffer) -> Unit {
  let members = to_members(self)
  buf.write_string("{")
  members.iteri(
    fn(i, item) {
      let (key, val) = item
      buf.write_string(key)
      buf.write_string(": ")
      val.write_json_string(buf)
      if i < members.length() - 1 {
        buf.write_string(", ")
      }
    },
  )
  buf.write_string("}")
}

fn main {
  // array
  let x = [1, 2, 3]
  println(to_json(x))
  // map
  let map : @map.Map[String, Int] = @map.Map::[("a", 1), ("b", 2), ("c", 3)]
  println(to_json(map))
  // custom data     
  let data : Data = { x: 1, y: true, z: "hello" }
  let res3 = to_json(data)
  println(res3)
}