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