module C = struct
  open Ctypes
  open PosixTypes
  open Foreign

  let mdb_result_of_int = function 0 -> Ok () | x -> Error x
  let int_of_mdb_result = function Ok _ -> 0 | Error x -> x
  let mdb_mode_t = mode_t
  let mdb_result = view ~read:mdb_result_of_int ~write:int_of_mdb_result int

  type mdb_env

  let mdb_env : mdb_env structure typ = structure "mdb_env"

  type mdb_dbi = Unsigned.uint

  let mdb_dbi : mdb_dbi typ = uint

  type mdb_txn

  let mdb_txn : mdb_txn structure typ = structure "mdb_txn"

  type mdb_val

  let mdb_val : mdb_val structure typ = structure "mdb_val"
  let mv_size = field mdb_val "mv_size" size_t
  let mv_data = field mdb_val "mv_data" (ptr void)
  let () = seal mdb_val

  let with_output_pointer output_type default body =
    let open Utilities.Result in
    let output_ptr = allocate output_type default in
    let* () = body output_ptr in
    Ok !@output_ptr

  let mdb_env_create = foreign "mdb_env_create" (ptr (ptr mdb_env) @-> returning mdb_result)

  let mdb_env_create' () =
    with_output_pointer (ptr mdb_env) (from_voidp mdb_env null) mdb_env_create

  let mdb_env_open =
    foreign "mdb_env_open" (ptr mdb_env @-> string @-> uint @-> mdb_mode_t @-> returning mdb_result)

  let mdb_env_close = foreign "mdb_env_close" (ptr mdb_env @-> returning void)

  let mdb_dbi_open =
    foreign "mdb_dbi_open"
      (ptr mdb_txn @-> ptr char @-> uint @-> ptr mdb_dbi @-> returning mdb_result)

  let mdb_dbi_open' txn flags =
    with_output_pointer mdb_dbi (Unsigned.UInt.of_int 0)
      (mdb_dbi_open txn (from_voidp char null) flags)

  let mdb_txn_begin =
    foreign "mdb_txn_begin"
      (ptr mdb_env @-> ptr mdb_txn @-> uint @-> ptr (ptr mdb_txn) @-> returning mdb_result)

  let mdb_txn_begin' env parent flags = with_output_pointer
                                          (ptr mdb_txn)
                                          (from_voidp mdb_txn null)
                                          (mdb_txn_begin env parent flags)
  [@@ocamlformat "disable"]

  let mdb_txn_commit = foreign "mdb_txn_commit" (ptr mdb_txn @-> returning mdb_result)
  let mdb_txn_abort = foreign "mdb_txn_abort" (ptr mdb_txn @-> returning mdb_result)

  (* TODO: make it so that we do not need to copy bytes to a separate array *)
  let carray_of_bytes (b : bytes) =
    let buffer = CArray.make char (Bytes.length b) in
    Bytes.iteri (CArray.set buffer) b;
    buffer

  let bytes_of_carray arr =
    let buffer = Bytes.make (CArray.length arr) (Char.chr 0) in
    CArray.iteri (Bytes.set buffer) arr;
    buffer

  let mdb_val_ptr_of_bytes (b : bytes) =
    let buf = carray_of_bytes b in
    let s = make mdb_val in
    setf s mv_size (Unsigned.Size_t.of_int (Bytes.length b));
    setf s mv_data (to_voidp (CArray.start buf));
    addr s

  let bytes_of_mdb_val (s : mdb_val structure) =
    let buf =
      CArray.from_ptr (from_voidp char (getf s mv_data)) (Unsigned.Size_t.to_int (getf s mv_size))
    in
    bytes_of_carray buf

  let mdb_get =
    foreign "mdb_get"
      (ptr mdb_txn @-> mdb_dbi @-> ptr mdb_val @-> ptr mdb_val @-> returning mdb_result)

  let mdb_get' txn dbi key =
    with_output_pointer mdb_val (make mdb_val) (mdb_get txn dbi (mdb_val_ptr_of_bytes key))
    |> Result.map bytes_of_mdb_val

  let mdb_put =
    foreign "mdb_put"
      (ptr mdb_txn @-> mdb_dbi @-> ptr mdb_val @-> ptr mdb_val @-> uint @-> returning mdb_result)

  let mdb_put' txn dbi key data flags =
    mdb_put txn dbi (mdb_val_ptr_of_bytes key) (mdb_val_ptr_of_bytes data) flags

  let mdb_strerror = foreign "mdb_strerror" (int @-> returning string)

  type mdb_env_ptr = mdb_env structure ptr
  type mdb_txn_ptr = mdb_txn structure ptr

  let null_txn = from_voidp mdb_txn null

  module Errors = struct
    let mdb_notfound = -30798
  end
end

module Error = struct
  open Concepts.Condition

  let lmdb_error code =
    condition "lmdb-error" (C.mdb_strerror code) ("code" |=| Concepts.Value.Integer code)
end

type connection = {env: C.mdb_env_ptr; dbi: C.mdb_dbi}
type transaction = {tx: C.mdb_txn_ptr; dbi: C.mdb_dbi}

let connect (_ : Concepts.Configuration.configuration) =
  begin
    let open Utilities.Result in
    let* env = C.mdb_env_create' () in
    (* TODO: make the path, POSIX mode a config parameter *)
    match C.mdb_env_open env "/tmp/sakura.db" Unsigned.UInt.zero (PosixTypes.Mode.of_int 420) with
    | Error x -> C.mdb_env_close env; Error x
    | Ok () ->
        let* tx = C.mdb_txn_begin' env C.null_txn Unsigned.UInt.zero in
        let* dbi = C.mdb_dbi_open' tx Unsigned.UInt.zero in
        let* () = C.mdb_txn_commit tx in
        Ok {env; dbi}
  end
  |> Result.map_error Error.lmdb_error

let start ({env; dbi} : connection) =
  C.mdb_txn_begin' env C.null_txn Unsigned.UInt.zero
  |> Result.map (fun tx -> {tx; dbi})
  |> Result.map_error Error.lmdb_error

let commit ({tx; _} : transaction) = C.mdb_txn_commit tx |> Result.map_error Error.lmdb_error
let abort ({tx; _} : transaction) = C.mdb_txn_abort tx |> Result.map_error Error.lmdb_error

(*
 * FIXME: `blob_of_bytes` and `bytes_of_blob` should not exist.
 * Rather, the FFI should know how to serialize a blob directly. This
 * makes it so that we do not depend on the OCaml `bytes` type and
 * opens the path for avoiding a copy on the FFI boundary later on
 *)

let get ({tx; dbi} : transaction) (h : Concepts.Hash.hash) =
  begin match C.mdb_get' tx dbi (Concepts.Hash.bytes_of_hash h) with
  | Ok x -> Ok (Some (Concepts.Representation.blob_of_bytes x))
  | Error e when e = C.Errors.mdb_notfound -> Ok None
  | Error e -> Error e
  end
  |> Result.map_error Error.lmdb_error

let put ({tx; dbi} : transaction) (h : Concepts.Hash.hash) (b : Concepts.Representation.blob) =
  C.mdb_put' tx dbi (Concepts.Hash.bytes_of_hash h)
    (Concepts.Representation.bytes_of_blob b)
    Unsigned.UInt.zero
  |> Result.map_error Error.lmdb_error