externals/npm/node_modules/linked-list/_source/linked-list.js

'use strict';

/**
 * Constants.
 */

var errorMessage;

errorMessage = 'An argument without append, prepend, ' +
    'or detach methods was given to `List';

/**
 * Creates a new List: A linked list is a bit like an Array, but
 * knows nothing about how many items are in it, and knows only about its
 * first (`head`) and last (`tail`) items. Each item (e.g. `head`, `tail`,
 * &c.) knows which item comes before or after it (its more like the
 * implementation of the DOM in JavaScript).
 * @global
 * @private
 * @constructor
 * @class Represents an instance of List.
 */

function List(/*items...*/) {
    if (arguments.length) {
        return List.from(arguments);
    }
}

var ListPrototype;

ListPrototype = List.prototype;

/**
 * Creates a new list from the arguments (each a list item) passed in.
 * @name List.of
 * @param {...ListItem} [items] - Zero or more items to attach.
 * @returns {list} - A new instance of List.
 */

List.of = function (/*items...*/) {
    return List.from.call(this, arguments);
};

/**
 * Creates a new list from the given array-like object (each a list item)
 * passed in.
 * @name List.from
 * @param {ListItem[]} [items] - The items to append.
 * @returns {list} - A new instance of List.
 */
List.from = function (items) {
    var list = new this(), length, iterator, item;

    if (items && (length = items.length)) {
        iterator = -1;

        while (++iterator < length) {
            item = items[iterator];

            if (item !== null && item !== undefined) {
                list.append(item);
            }
        }
    }

    return list;
};

/**
 * List#head
 * Default to `null`.
 */
ListPrototype.head = null;

/**
 * List#tail
 * Default to `null`.
 */
ListPrototype.tail = null;

/**
 * Returns the list's items as an array. This does *not* detach the items.
 * @name List#toArray
 * @returns {ListItem[]} - An array of (still attached) ListItems.
 */
ListPrototype.toArray = function () {
    var item = this.head,
        result = [];

    while (item) {
        result.push(item);
        item = item.next;
    }

    return result;
};

/**
 * Prepends the given item to the list: Item will be the new first item
 * (`head`).
 * @name List#prepend
 * @param {ListItem} item - The item to prepend.
 * @returns {ListItem} - An instance of ListItem (the given item).
 */
ListPrototype.prepend = function (item) {
    if (!item) {
        return false;
    }

    if (!item.append || !item.prepend || !item.detach) {
        throw new Error(errorMessage + '#prepend`.');
    }

    var self, head;

    // Cache self.
    self = this;

    // If self has a first item, defer prepend to the first items prepend
    // method, and return the result.
    head = self.head;

    if (head) {
        return head.prepend(item);
    }

    // ...otherwise, there is no `head` (or `tail`) item yet.

    // Detach the prependee.
    item.detach();

    // Set the prependees parent list to reference self.
    item.list = self;

    // Set self's first item to the prependee, and return the item.
    self.head = item;

    return item;
};

/**
 * Appends the given item to the list: Item will be the new last item (`tail`)
 * if the list had a first item, and its first item (`head`) otherwise.
 * @name List#append
 * @param {ListItem} item - The item to append.
 * @returns {ListItem} - An instance of ListItem (the given item).
 */

ListPrototype.append = function (item) {
    if (!item) {
        return false;
    }

    if (!item.append || !item.prepend || !item.detach) {
        throw new Error(errorMessage + '#append`.');
    }

    var self, head, tail;

    // Cache self.
    self = this;

    // If self has a last item, defer appending to the last items append
    // method, and return the result.
    tail = self.tail;

    if (tail) {
        return tail.append(item);
    }

    // If self has a first item, defer appending to the first items append
    // method, and return the result.
    head = self.head;

    if (head) {
        return head.append(item);
    }

    // ...otherwise, there is no `tail` or `head` item yet.

    // Detach the appendee.
    item.detach();

    // Set the appendees parent list to reference self.
    item.list = self;

    // Set self's first item to the appendee, and return the item.
    self.head = item;

    return item;
};

/**
 * Creates a new ListItem: A linked list item is a bit like DOM node:
 * It knows only about its "parent" (`list`), the item before it (`prev`),
 * and the item after it (`next`).
 * @global
 * @private
 * @constructor
 * @class Represents an instance of ListItem.
 */

function ListItem() {}

List.Item = ListItem;

var ListItemPrototype = ListItem.prototype;

ListItemPrototype.next = null;

ListItemPrototype.prev = null;

ListItemPrototype.list = null;

/**
 * Detaches the item operated on from its parent list.
 * @name ListItem#detach
 * @returns {ListItem} - The item operated on.
 */
ListItemPrototype.detach = function () {
    // Cache self, the parent list, and the previous and next items.
    var self = this,
        list = self.list,
        prev = self.prev,
        next = self.next;

    // If the item is already detached, return self.
    if (!list) {
        return self;
    }

    // If self is the last item in the parent list, link the lists last item
    // to the previous item.
    if (list.tail === self) {
        list.tail = prev;
    }

    // If self is the first item in the parent list, link the lists first item
    // to the next item.
    if (list.head === self) {
        list.head = next;
    }

    // If both the last and first items in the parent list are the same,
    // remove the link to the last item.
    if (list.tail === list.head) {
        list.tail = null;
    }

    // If a previous item exists, link its next item to selfs next item.
    if (prev) {
        prev.next = next;
    }

    // If a next item exists, link its previous item to selfs previous item.
    if (next) {
        next.prev = prev;
    }

    // Remove links from self to both the next and previous items, and to the
    // parent list.
    self.prev = self.next = self.list = null;

    // Return self.
    return self;
};

/**
 * Prepends the given item *before* the item operated on.
 * @name ListItem#prepend
 * @param {ListItem} item - The item to prepend.
 * @returns {ListItem} - The item operated on, or false when that item is not
 * attached.
 */
ListItemPrototype.prepend = function (item) {
    if (!item || !item.append || !item.prepend || !item.detach) {
        throw new Error(errorMessage + 'Item#prepend`.');
    }

    // Cache self, the parent list, and the previous item.
    var self = this,
        list = self.list,
        prev = self.prev;

    // If self is detached, return false.
    if (!list) {
        return false;
    }

    // Detach the prependee.
    item.detach();

    // If self has a previous item...
    if (prev) {
        // ...link the prependees previous item, to selfs previous item.
        item.prev = prev;

        // ...link the previous items next item, to self.
        prev.next = item;
    }

    // Set the prependees next item to self.
    item.next = self;

    // Set the prependees parent list to selfs parent list.
    item.list = list;

    // Set the previous item of self to the prependee.
    self.prev = item;

    // If self is the first item in the parent list, link the lists first item
    // to the prependee.
    if (self === list.head) {
        list.head = item;
    }

    // If the the parent list has no last item, link the lists last item to
    // self.
    if (!list.tail) {
        list.tail = self;
    }

    // Return the prependee.
    return item;
};

/**
 * Appends the given item *after* the item operated on.
 * @name ListItem#append
 * @param {ListItem} item - The item to append.
 * @returns {ListItem} - The item operated on, or false when that item is not
 * attached.
 */
ListItemPrototype.append = function (item) {
    // If item is falsey, return false.
    if (!item || !item.append || !item.prepend || !item.detach) {
        throw new Error(errorMessage + 'Item#append`.');
    }

    // Cache self, the parent list, and the next item.
    var self = this,
        list = self.list,
        next = self.next;

    // If self is detached, return false.
    if (!list) {
        return false;
    }

    // Detach the appendee.
    item.detach();

    // If self has a next item...
    if (next) {
        // ...link the appendees next item, to selfs next item.
        item.next = next;

        // ...link the next items previous item, to the appendee.
        next.prev = item;
    }

    // Set the appendees previous item to self.
    item.prev = self;

    // Set the appendees parent list to selfs parent list.
    item.list = list;

    // Set the next item of self to the appendee.
    self.next = item;

    // If the the parent list has no last item or if self is the parent lists
    // last item, link the lists last item to the appendee.
    if (self === list.tail || !list.tail) {
        list.tail = item;
    }

    // Return the appendee.
    return item;
};

/**
 * Expose `List`.
 */

module.exports = List;