fullstackopen-notes/parts/4/blogApp/src/utils.js

const reverse = (string) => {
  return string.split("").reverse().join("");
};

const average = (array) => {
  const reducer = (sum, item) => {
    return sum + item;
  };

  return array.length === 0 ? 0 : array.reduce(reducer, 0) / array.length;
};

const listHelper = (posts) => {
  console.log("lol");
  return 1;
};

const totalLikes = (posts) => {
  if (!posts) {
    return 0;
  }

  const likeCount = posts
    .map((post) => post.likes)
    .reduce((cum, value) => cum + value, 0);

  return likeCount;
};

const favoritePost = (posts) => {
  if (!posts || posts.length === 0) {
    return null;
  }

  const highestLikes = posts.reduce(
    (max, post) => (post.likes > max ? (max = post.likes) : max),
    0
  );

  const favoritePost = posts.find((post) => post.likes == highestLikes);

  return favoritePost;
};

const mostPosts = (posts) => {
  if (!posts || posts.length === 0) {
    return null;
  }

  const countMap = posts.reduce((acc, post) => {
    acc[post.author] = (acc[post.author] || 0) + 1;
    return acc;
  }, {});

  const [author, postsCount] = Object.entries(countMap).reduce(
    (max, entry) => (entry[1] > max[1] ? entry : max),
    ['', 0]
  );

  return { author, posts: postsCount };
};

const mostLikes = (posts) => {
    if (!posts || posts.length === 0) {
      return null;
    }
  
    const likesMap = posts.reduce((acc, post) => {
      acc[post.author] = (acc[post.author] || 0) + post.likes;
      return acc;
    }, {});
  
    const [author, likesCount] = Object.entries(likesMap).reduce(
      (max, entry) => (entry[1] > max[1] ? entry : max),
      ['', 0]
    );
  
    return { author, likes: likesCount };
  };

module.exports = {
  reverse,
  average,
  listHelper,
  totalLikes,
  favoritePost,
  mostPosts,
  mostLikes
};