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| // --- beauty begins --- | |
| const createLens = (get, set) => ({ get, set }); | |
| const view = (obj, lens) => lens.get(obj) | |
| const compose = (lenses) => { | |
| return createLens( | |
| (obj) => lenses.reduce(view, obj), | |
| (value, obj) => | |
| lenses.reduceRight((acc, lens, index) => | |
| lens.set(acc, lenses.slice(0, index).reduce(view, obj)), value) | |
| ); | |
| }; | |
| // --- bureaucracy begins --- | |
| const shallowCopy = (obj) => | |
| Array.isArray(obj) | |
| ? obj.slice() | |
| : Object.create(Object.getPrototypeOf(obj), Object.getOwnPropertyDescriptors(obj)) | |
| const prop = (key) => createLens( | |
| (obj) => obj[key], | |
| (value, obj) => { | |
| const nextObj = shallowCopy(obj) | |
| nextObj[key] = value | |
| return nextObj | |
| } | |
| ); | |
| // --- craziness begins --- | |
| const SELECTOR_RESULT = Symbol() | |
| const selectorProxyHandler = { | |
| get: (path, key) => { | |
| if (key === SELECTOR_RESULT) return path | |
| return new Proxy([...path, key], selectorProxyHandler) | |
| }, | |
| } | |
| const selectorProxy = new Proxy([], selectorProxyHandler) | |
| // --- destiny begins --- | |
| const withSelector = (fn, selector) => { | |
| let prev = Symbol() | |
| return (value) => { | |
| const next = selector(value) | |
| if(next !== prev) { | |
| fn(next) | |
| prev = next | |
| } | |
| } | |
| } | |
| const atomMap = new WeakMap() | |
| const getAtomFromCache = (atom, path) => { | |
| // ... | |
| } | |
| const focusAtom = <T, U>(atom: Atom<T>, selector: PropertyKey[] | PropertyKey | ((s: T) => U)) => { | |
| const path = typeof selector === 'function' | |
| ? selector(selectorProxy)[SELECTOR_RESULT] | |
| : typeof selector === 'string' | |
| ? [selector] | |
| : selector | |
| // const maybeCachedAtom = getFocusAtomFromCache(atom, path) | |
| // if(maybeCachedAtom) return maybeCachedAtom | |
| const lens = compose(path.map(prop)) | |
| return { | |
| get: () => selector(atom.get()), | |
| set: (value) => atom.set(lens.set(value, atom.get())), | |
| subscribe: (fn) => atom.subscribe(withSelector(fn, selector)) | |
| } | |
| } | |
| // --- usage --- | |
| const atom = atom({ deeply: { nested: ['hello', 'world'] } }) | |
| const nestedAtom = focusAtom(atom, (s) => s.deeply.nested[1]) | |
| console.log('nestedAtom.get()', nestedAtom.get()) | |
| nestedAtom.set('dunya') | |
| console.log('nestedAtom.set("dunya")', atom.get()) | |
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