import { struct, Layout } from "buffer-layout";
import { rustEnum } from "@project-serum/borsh";

// Simplified since we only use the SetBuffer variant.
export type IdlInstruction =
  | Create
  | CreateBuffer
  | Write
  | SetBuffer
  | SetAuthority;

type Create = {};
type CreateBuffer = {};
type Write = {};
type SetBuffer = {};
type SetAuthority = {};

const IDL_INSTRUCTION_LAYOUT: Layout<IdlInstruction> = rustEnum([
  struct([], "create"),
  struct([], "createBuffer"),
  struct([], "write"),
  struct([], "setBuffer"),
  struct([], "setAuthority"),
]);

export function encodeInstruction(i: IdlInstruction): Buffer {
  const buffer = Buffer.alloc(1000); // TODO: use a tighter buffer.
  const len = IDL_INSTRUCTION_LAYOUT.encode(i, buffer);
  return Buffer.concat([IDL_TAG, buffer.slice(0, len)]);
}

// Reverse for little endian.
export const IDL_TAG = Buffer.from("0a69e9a778bcf440", "hex").reverse();