module Make (S : Abstract.Storage.STORAGE) = struct
  module Pointer = struct
    type 'a t = {
      addr : S.address;
      loader : S.transaction -> S.address -> ('a, Concepts.Condition.condition) result
    }

    let make loader addr = { addr; loader }
    let address_of { addr; _ } = addr
    let swap { loader; _ } addr = make loader addr
    let deref tx { addr; loader } = loader tx addr
  end

  let as_hash = function
    | S.Hash h -> h
    | _ -> failwith "A label was provided where a hash was expected."

  let to_hum_string = function
    | S.Hash h -> "Hash " ^ (Concepts.Hash.to_hum_string h)
    | S.Label l -> "Label " ^ l

  module Error = struct
    open Concepts.Condition

    let missing_data addr =
      condition "missing-data" "An expected value was not found on the underlying storage. Is your database corrupted?"
        ("address" |=| Concepts.Value.String (to_hum_string addr))
  end

  let finish tx = function
    | Ok value ->
       let open Utilities.Result in
       let* () = S.commit tx in
       Ok value
    | Error condition ->
       let _ = S.abort tx in
       Error condition

  let with_transaction connection body =
    let open Utilities.Result in
    let* tx = S.start connection in
    body tx |> finish tx

  let store_blob tx blob =
    let open Utilities.Result in
    let address = Concepts.Hash.hash_of_blob blob in
    let* () = S.put tx (S.Hash address) blob in
    Ok address

  let get_req tx addr =
    S.get tx addr
    |> Utilities.Result.fmap (Option.to_result ~none:(Error.missing_data addr))

end