load-state.js

load-state.js

// You and your teammate have been working on a project for two and a half
// weeks. Everything is going well except you notice that one of the functions
// your teammate wrote is failing a test case, which you know to be correct.
// Unfortunately, your teammate is sick today and to make matters worse, you
// realize that you need to demo your project in ten minutes. So you decide
// to try and fix the function. Can you fix it in time for your demo?

////////////////////////////////////////////////////////////////////////////////

const SYMBOLS = [ 'AAPL', 'AMZN', 'MONY', 'PETS', 'PZZA', 'SHOP', 'TSLA', 'WIFI' ];

////////////////////////////////////////////////////////////////////////////////

const readJSON = function()
{
	// Simulate success rate
	if (Math.random() > 0.2)
	{
		// Call was successful
		return Promise.resolve
		({
			version: 1,
			payload: {
				AAPL: 1588773600,
				AMZN: 1588690800,
				MONY: 1588428000,
				PETS: 1588532400,
				SHOP: 1588525200,
				TSLA: 1588608000
			}
		});
	}

	else return Promise.reject ('the file could not be opened for reading');
};

////////////////////////////////////////////////////////////////////////////////

const loadState = function()
{
	// Read the previous state
    const result = readJSON();
    
	return result.then (state =>
	{
		// If state is compliant
		if (state.version !== 1)
		{
			console.warn ('version mismatch with previous state, rebuilding...');
			return { };
		}

		return state.payload;
	}, () => ({}))

	.then (payload =>
	{
		// Populate primary queue data
		for (const symbol of SYMBOLS)
		{
			if (!(symbol in payload))
				payload[symbol] = 0;
		}

		// Oldest entries to the top
		return Object.fromEntries (
			Object.entries (payload)
			.sort ((a, b) => b[1] > a[1])
		);
	});

};

////////////////////////////////////////////////////////////////////////////////

(async () =>
{
    const state = JSON.stringify (await loadState());
	const success = JSON.stringify
	({
        AAPL: 1588773600,
        AMZN: 1588690800,
        MONY: 1588428000,
		PETS: 1588532400,
        PZZA: 0,
		SHOP: 1588525200,
		TSLA: 1588608000,
		WIFI: 0,
    });

	const failure = JSON.stringify
	({
		AAPL: 0,
		AMZN: 0,
		MONY: 0,
		PETS: 0,
		PZZA: 0,
		SHOP: 0,
		TSLA: 0,
		WIFI: 0
	});

	// Perform a poor-mans comparison on result
	if (state !== success && state !== failure)
		throw new Error ('unrecognized result');

})();