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'use strict';
function init(list) {
list._idleNext = list;
list._idlePrev = list;
}
// Show the most idle item.
function peek(list) {
if (list._idlePrev === list) return null;
return list._idlePrev;
}
// Remove an item from its list.
function remove(item) {
if (item._idleNext) {
item._idleNext._idlePrev = item._idlePrev;
}
if (item._idlePrev) {
item._idlePrev._idleNext = item._idleNext;
}
item._idleNext = null;
item._idlePrev = null;
}
// Remove an item from its list and place at the end.
function append(list, item) {
if (item._idleNext || item._idlePrev) {
remove(item);
}
// Items are linked with _idleNext -> (older) and _idlePrev -> (newer).
// Note: This linkage (next being older) may seem counter-intuitive at first.
item._idleNext = list._idleNext;
item._idlePrev = list;
// The list _idleNext points to tail (newest) and _idlePrev to head (oldest).
list._idleNext._idlePrev = item;
list._idleNext = item;
}
function isEmpty(list) {
return list._idleNext === list;
}
module.exports = {
init,
peek,
remove,
append,
isEmpty
};
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