const curry = require("ramda").curry;
const reduce = require("ramda").reduce;
const compose = require("ramda").compose;
const concat = require("ramda").concat;

const Maybe = require("@mostly-adequate/support").Maybe;

// the 'maybe' function returns an error message when the given Maybe isNothing,
//   or the result of applying a given fn to the value in the Maybe.
// maybe :: b -> (a -> b) -> Maybe a -> b
const maybe = curry((alt, fn, aMaybe) => aMaybe.isNothing ? alt : fn(aMaybe.$value));

const prependString = curry((str, val) => `${str} ${val}`);

// wraps a value in a function, used in places where a function is needed,
//   but you want the value given to the function.
const returnTheValue = val => val;

// Allows dot notation instead of array segments as in Ramda's 'path' function
const elvis = curry((path, object) =>
  path ? reduce((value, key) =>
    value && value[key], object, path.split(".")) : object
);

// Wraps elvis in a Maybe Monad so they can't harm him
const safeElvis = curry((path, object) => Maybe.of(elvis(path, object)));

const getHeightWrongly = safeElvis("metadata.attributes.BLAH.value");
const getHeight = safeElvis("metadata.attributes.height.value");

// composeSuccessMessage :: Maybe m -> string b
const composeSuccessMessage = compose(prependString("Found a person's height:"), returnTheValue);

const person = {
  name: 'I am second',
  metadata: {
    attributes: {
      height: {
        value: 23
      }
    }
  }
};

const result1 = maybe("Wrong path!", returnTheValue, getHeightWrongly(person)); // Nothing as "Wrong path!"
const result2 = maybe("Wrong path!", composeSuccessMessage, getHeight(person)); // Just(23) as "Found a person's height: 23"

console.log(result1);
console.log(result2);