'use strict';

function Transaction() {}

Transaction.start = (data) => {

console.log('\nstart transaction');

const events = {

commit: [],

rollback: [],

timeout: [],

change: [],

};

let delta = {};

const emit = (name) => {

const event = events[name];

for (const listener of event) listener(data);

};

const methods = {

commit: () => {

Object.assign(data, delta);

delta = {};

emit('commit');

},

rollback: () => {

delta = {};

emit('rollback');

},

clone: () => {

const cloned = Transaction.start(data);

Object.assign(cloned.delta, delta);

return cloned;

},

on: (name, callback) => {

const event = events[name];

if (event) event.push(callback);

},

};

return new Proxy(data, {

get(target, key) {

if (key === 'delta') return delta;

if (Object.hasOwn(methods, key)) return methods[key];

if (Object.hasOwn(delta, key)) return delta[key];

return target[key];

},

getOwnPropertyDescriptor: (target, key) =>

Object.getOwnPropertyDescriptor(

Object.hasOwn(delta, key) ? delta : target,

key,

),

ownKeys() {

const changes = Object.keys(delta);

const keys = Object.keys(data).concat(changes);

return keys.filter((x, i, a) => a.indexOf(x) === i);

},

set(target, key, val) {

console.log('set', key, val);

if (target[key] === val) delete delta[key];

else delta[key] = val;

return true;

},

});

};

// Usage

const data = { name: 'Marcus Aurelius', born: 121 };

const transaction = Transaction.start(data);

transaction.on('commit', () => {

console.log('\ncommit transaction');

});

transaction.on('rollback', () => {

console.log('\nrollback transaction');

});

transaction.city = 'Shaoshan';

transaction.rollback();

transaction.city = 'Shaoshan';

transaction.commit();

console.dir({ data });