"use strict";

function List() {
    this.dataStore = [];
    this.pos = 0; // note
    this.listSize = 0;
    this.length = length;
    this.clear = clear;
    this.pos = pos;
    this.append = append;
    this.insert = insert;
    this.remove = remove;
    this.getElement = getElement;
    this.front = front;
    this
 
.end = end;
    this.prev = prev;
    this.next = next;
    this.moveTo = moveTo;
    this.find = find;
    this.toString = toString;
    this.curPos = curPos;
    this.contains = contains;
}

function append(element) {
    this.dataStore[listSize++] = element;
}

function remove(element) {
    var pos = this
 
.find(element);
    if (pos > -1) {
        this.dataStore.splice(pos, 1);
    }
}

function find(element) {
    for (let i = 0; i < listSize; i++) {
        if (this.dataStore[i] === element) {
            return i;
        }
    }

    return -1;
}

function length() {
    return this.dataStore.length;
}

function
 
 toString() {
    this.dataStore.toString();
    // this.dataStore.join(",");
}

// method 1
// function insert(element, index) {
//  if (index === 0) {
//      this.dataStore.unshift(element);
//  }
//  this.dataStore.splice(index - 1, 0, element);  // notice the second parameter
//  this.listSize++;
// }

function insert(element, after) {
    let insertPos = this.find(after);
    if (insertPos > -1) {
        this.dataStore.splice(insertPos+1, 0, element);
        this.listSize++;
        return true;
    }
    return false;
}

// notice
function clear() {
    delete this.dataStore;
    this.dataStore = [];
    this.listSize = this.pos = 0; // reset
}

function container(element) {
    for (let i = 0; i < this.dataStore.length; i++) {
        if (dataStore[i] === element) {
            return true;
        }
    }

    return false;
}

// tranverse
function front() {
    this.pos = 0;
}

function end() {
    this.pos = listSize - 1;
}

function prev() {
    if (this.pos > 0) {
        this.pos -= 1;
    }
}

function next() {
    if (this.pos < this.listSize - 1) {
        this.pos += 1;
    }
}

function curPos() {
    return this.pos;
}

function moveTo(position) {
    this.pos = position;
}

function getElement() {
    return this.dataStore[pos];
}