new Vue({
  el: '#demo',

  data: {
    sortKey: 'name',
    reverse: false,
    searchName: '',
    searchOperator: '',
    searchAge: '',
    columns: ['name', 'age'],
    newUser: {},
    search: "",
    name: "",
    age: "",

    users: [
      { name: 'John', age: 50 },
      { name: 'Jane', age: 22 },
      { name: 'Paul', age: 34 },
      { name: 'Kate', age: 15 },
      { name: 'Amanda', age: 65 },
      { name: 'Steve', age: 38 },
      { name: 'Keith', age: 21 },
      { name: 'Don', age: 50 },
      { name: 'Susan', age: 21 }
    ]
  },
  methods: {
    sortBy: function (sortKey) {
      this.reverse = (this.sortKey == sortKey) ? !this.reverse : false;

      this.sortKey = sortKey;
    }, 
    filterByName : function(user) {
      // no search, don't filter : 
      if (this.searchName.length === 0) {
        return true;
      }

      return  (user.name.toLowerCase().indexOf(this.searchName.toLowerCase()) > -1);
    }, 
    filterByAge : function (user) {
      // no operator selected or no age typed, don't filter : 
      if (this.searchOperator.length === 0 || this.age.length === 0) {
        return true;
      }

      if (this.searchOperator === '>') {
        return (user.age > this.age); 
      } else  if (this.searchOperator === '<') {
        return (user.age < this.age);
      }      
    }, 
    orderBy : function (userA, userB) {
      let condition = (userA[this.sortKey] > userB[this.sortKey]);
      if (this.reverse) {
        return !condition;
      } else {
        return condition;
      }
    }
  },
  computed: {
    filteredPersons: function () {
      return this.users
      .filter(this.filterByName)
      .filter(this.filterByAge)
      .sort(this.orderBy);
    }
  },  
});