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| 'use strict';
|
| const unique = arr => arr.filter((v, i) => arr.lastIndexOf(v) === i);
| const compact = arr => unique(arr).filter(Boolean);
|
| module.exports = (action, data = {}, value = '') => {
| let { past = [], present = '' } = data;
| let rest, prev;
|
| switch (action) {
| case 'prev':
| case 'undo':
| rest = past.slice(0, past.length - 1);
| prev = past[past.length - 1] || '';
| return {
| past: compact([value, ...rest]),
| present: prev
| };
|
| case 'next':
| case 'redo':
| rest = past.slice(1);
| prev = past[0] || '';
| return {
| past: compact([...rest, value]),
| present: prev
| };
|
| case 'save':
| return {
| past: compact([...past, value]),
| present: ''
| };
|
| case 'remove':
| prev = compact(past.filter(v => v !== value));
| present = '';
|
| if (prev.length) {
| present = prev.pop();
| }
|
| return {
| past: prev,
| present
| };
|
| default: {
| throw new Error(`Invalid action: "${action}"`);
| }
| }
| };
|
|
