export type UserId = string
export type Name = string

export type User = {
  id: string,
  name: string,
  active: boolean
}

export error UserMissing = { id: string }
export error StoreUnavailable = { message: string }

export service Users {
  find(id: UserId): Option<User> fails StoreUnavailable
  save(user: User): void fails StoreUnavailable
  all(): User[] fails StoreUnavailable
}

export const getUser = (id: UserId): User
  fails UserMissing | StoreUnavailable
  uses Users.find =>
  match Users.find(id) {
    Some(user) => user,
    None => fail(UserMissing({ id }))
  }

export const rename = (id: UserId, name: Name): User
  fails UserMissing | StoreUnavailable
  uses Users.find | Users.save => {
  const user = getUser(id)
  const renamed = { ...user, name }
  Users.save(renamed)
  renamed
}

export const displayName = (id: UserId): Name
  fails StoreUnavailable
  uses Users.find =>
  try {
    getUser(id).name
  } catch {
    UserMissing(error) => "Guest"
  }

export const activeNames = (): Name[]
  fails StoreUnavailable
  uses Users.all =>
  Users.all()
    |> filter(user => user.active)
    |> map(user => user.name)