const flattenArray = (array = []) => {
	let queue = [...array]
	let output = []

	while (queue.length) {
		const element = queue.shift()

		if (Number.isInteger(element)) {
			output.push(element)
		} else if (Array.isArray(element)) {
			queue.unshift(...element)
		} else if (!Number.isNaN(element % 1)) {
			// typeof would report the generic 'number', so create a special case to clarify
			// modulus 1 returns NaN for non-numbers, and we know element is not an integer
			throw new Error(`Undefined behavior for element of type: (non-integer) number`)
		} else {
			throw new Error(`Undefined behavior for element of type: ${typeof element}`)
		}
	}

	return output
}

module.exports = flattenArray