list_processing.ts

type Game = {
  name: string
  rating: number
}

const gameList: Game[] = [
  { name: 'call of duty', rating: 4.0 },
  { name: 'assasin creed', rating: 6.4 },
  { name: 'mario', rating: 10.2 },
]

// 1. returns list of name from list of game
const names = (games: Game[]): string[] =>
  games.map(game => game.name)

// 2. returns list of string that has format `<name> [<rating>]`
// eg. `call of duty [7.4]`
const formatGames = (games: Game[]): string[] =>
  games.map(({ name, rating }) => `${name} [${rating}]`)

// 3. get sum of all the ratings in list of game
const totalRatingsOf = (games: Game[]): number =>
  games
    .map(game => game.rating)
    .reduce((a, b) => a + b, 0)

// 4. get average of all the ratings in list of game
const averageRatingsOf = (games: Game[]): number =>
  totalRatingsOf(games) / games.length

// ----

const gamesWithName = (name: string, games: Game[]): Game[] =>
  games.filter(game => game.name === name)

// 5. get total rating by names from list of game
const ratingByName = (name: string, games: Game[]): number =>
  totalRatingsOf(gamesWithName(name, games))

// 6. get total rating by names from list of game
const averageRatingsByName = (name: string, games: Game[]): number =>
  averageRatingsOf(gamesWithName(name, games))

// ---

const updateGameRating = (update: (rating: number) => number) => (game: Game) => ({
  ...game,
  rating: update(game.rating)
})

// 7. increase rating for all games
const increaseRatingBy = (inc: number, games: Game[]): Game[] =>
  games
    .map(updateGameRating(rating => rating + inc))

// 8. decrease rating for game with specific name
const decreaseRatingBy = (
  dec: number,
  name: string,
  games: Game[],
): Game[] =>
  gamesWithName(name, games)
    .map(updateGameRating(rating => rating - dec))

// 9. returns game if the name exist else returns undefined
const findByName = (name: string, games: Game[]): Game =>
  games.find(game => game.name === name)

// games.reduce((found, game) =>
//   found
//     ? found
//     : game.name === name
//       ? game
//       : undefined
// , undefined)

console.log(findByName('call of duty', gameList))

// 10. decrease rating for game that has name in the list
const decreaseRatingForNames = (
  dec: number,
  names: string[],
  games: Game[],
): Game[] =>
  games
    .filter(game => names.includes(game.name))
    .map(updateGameRating(rating => rating - dec))