import { DefaultMap } from "./util.js";

// The registry ensures that we never accidentally create more than one JS object for the same function type.
// It is a cheap workaround for JS lacking customizable hash-functions and equality-testing-functions.
// This same pattern is repeated throughout the code for all non-nullary type constructors (list, sum, product, ...)
const fnTypeRegistry = new DefaultMap(inType => new DefaultMap(outType => ({ in: inType, out: outType })));

// type constructor for function types
export const fnType = ({ in: inType, out: outType }) => fnTypeRegistry.getdefault(inType, true).getdefault(outType, true);

export const Type = Symbol('Type');
export const Function = Symbol('Function');

// Implementation of 'in' and 'out' functions,
// to get input/output type of a function signature:
export const getIn = fn => fn.in;
export const getOut = fn => fn.out;

// a module is just a set of typed objects
// each 'typed object' is implicitly an instance of TypeLink (defined below)
export const ModuleMetaCircular = {l:[  
  // TODO? maybe follow Lean so
  //    Type.{0} : Type.{1}
  //    Type.{1} : Type.{2}
  //    ...
  // see: https://lean-lang.org/functional_programming_in_lean/functor-applicative-monad/universes.html

  // Type : Type
  {i: Type, t: Type},

  // Function : Type
  {i: Function, t: Type},

  // (Function -> Type) : Function
  {i: fnType({in: Function, out: Type}), t: Function},

  {i: getIn , t: fnType({in: Function, out: Type})},
  {i: getOut, t: fnType({in: Function, out: Type})},
]};


// Wrapper around function below.
export const typedFnType = (instance, callback) => {
  const [t, typesOfFns] = typedFnType2(callback);
  const res = [
    { i: instance, t },
    ...typesOfFns,
  ];
  return res;
};

// Create a function type, and also create Type-links for the function type (being typed by Function) and for all the nested function types. Saves a lot of code writing.
export const typedFnType2 = callback => {
  const fnTs = [];
  const wrappedFnType = ({ in: inType, out: outType }) => {
    console.log('wrappedFnType called');
    const fnT = fnType({ in: inType, out: outType });
    fnTs.push(fnT);
    return fnT;
  };
  const t = callback(wrappedFnType); // force evaluation
  return [
    t,
    fnTs.map(fnT => ({ i: fnT, t: Function })),
  ];
};