type levelDBErrors =
  | EncodingError
  | InitializationError
  | LevelUPError
  | NotFoundError
  | OpenError
  | ReadError
  | WriteError;

type leveldown;
type ldb;

[@bs.module]
external levelup: leveldown => ldb = "levelup";

[@bs.module]
external leveldown: string => leveldown = "leveldown";

[@bs.send]
external put : (ldb, string, string) => Js.Promise.t(unit) = "put";

[@bs.send]
external get : (ldb, string) => Js.Promise.t(string) = "get";

let db = levelup(leveldown("./mydb"));
put(db, "sdd", "sdsd")
|> Js.Promise.then_(_ => {
  get(db, "sdd")
  |> Js.Promise.then_(value => {
    let valueStr: string = Buffer.contents(value);
    Js.log(valueStr);
    Js.Promise.resolve(valueStr);
  })
  |> Js.Promise.catch(err => {
    Js.log(err);
    Js.Promise.resolve("Error");
  });
})

/*

 We've found a bug for you!
  /Users/michalmajchrzak/Documents/Reason/bs-leveldb/src/leveldb.re 29:6-34:4

  27 │ |> Js.Promise.then_(_ => {
  28 │   get(db, "sdd")
  29 │   |> Js.Promise.then_(value => {
  30 │     /* I am getting <Buffer 13 32..> here as a value */
   . │ ...
  33 │     Js.Promise.resolve(valueStr);
  34 │   })
  35 │   |> Js.Promise.catch(err => {
  36 │     Js.log(err);

  This has type:
    Js.Promise.t(Buffer.t) => Js.Promise.t(string)
  But somewhere wanted:
    Js.Promise.t(string) => 'a

  The incompatible parts:
    Js.Promise.t(Buffer.t) (defined as Js.Promise.t(Buffer.t))
    vs
    Js.Promise.t(string) (defined as Js.Promise.t(string))

    Further expanded:
      Buffer.t
      vs
      string


*/