const getFirstItem = (collection, cb) => {
  // invoke the callback function and pass the first item from the collection in as an argument
  cb(collection[0]);
};

const getLength = (collection, cb) => {
  // Write a function called getLength that passes the length of the array into the callback
  cb(collection.length);
};

const getLastItem = (collection, cb) => {
  // Write a function called getLastItem which passes the getLastItem item of the array into the callback
  cb(collection[collection.length - 1]);
};

const sumNums = (x, y, cb) => {
  // Write a function called sumNums that adds two numbers and passes the result to the callback
  cb(x + y);
};

const multiplyNums = (x, y, cb) => {
  // Write a function called multiplyNums that multiplies two numbers and passes the result to the callback
  cb(x * y);
};

const contains = (collection, item, cb) => {
  // Write a function called contains that checks if an item is present inside of the given array.
  // Pass true to the callback if it is, otherwise pass false
  cb(collection.includes(item));
};

const removeDuplicates = (collection, cb) => {
  // Write a function called removeDuplicates that removes all duplicate values from the given array.
  // Pass the array to the callback function.  Do not mutate the original array.
  const uniq = (arr) => {
    const result = [];

    for (let i = 0; i < arr.length; i++) {
      if (!result.includes(arr[i])) {
        result.push(arr[i]);
      }
    }

    return result;
  };

  cb(uniq(collection));
};

module.exports = {
  getFirstItem,
  getLength,
  getLastItem,
  sumNums,
  multiplyNums,
  contains,
  removeDuplicates
};