index.js

'use strict';
const isObject = require('is-obj');

const disallowedKeys = new Set([
	'__proto__',
	'prototype',
	'constructor'
]);

const digits = new Set('0123456789');

function getPathSegments(path) {
	const parts = [];
	let currentSegment = '';
	let currentPart = 'start';
	let isIgnoring = false;

	for (const character of path) {
		switch (character) {
			case '\\':
				if (currentPart === 'index') {
					throw new Error('Invalid character in an index');
				}

				if (currentPart === 'indexEnd') {
					throw new Error('Invalid character after an index');
				}

				if (isIgnoring) {
					currentSegment += character;
				}

				currentPart = 'property';
				isIgnoring = !isIgnoring;
				break;

			case '.':
				if (currentPart === 'index') {
					throw new Error('Invalid character in an index');
				}

				if (currentPart === 'indexEnd') {
					currentPart = 'property';
					break;
				}

				if (isIgnoring) {
					isIgnoring = false;
					currentSegment += character;
					break;
				}

				if (disallowedKeys.has(currentSegment)) {
					return [];
				}

				parts.push(currentSegment);
				currentSegment = '';
				currentPart = 'property';
				break;

			case '[':
				if (currentPart === 'index') {
					throw new Error('Invalid character in an index');
				}

				if (currentPart === 'indexEnd') {
					currentPart = 'index';
					break;
				}

				if (isIgnoring) {
					isIgnoring = false;
					currentSegment += character;
					break;
				}

				if (currentPart === 'property') {
					if (disallowedKeys.has(currentSegment)) {
						return [];
					}

					parts.push(currentSegment);
					currentSegment = '';
				}

				currentPart = 'index';
				break;

			case ']':
				if (currentPart === 'index') {
					parts.push(Number.parseInt(currentSegment, 10));
					currentSegment = '';
					currentPart = 'indexEnd';
					break;
				}

				if (currentPart === 'indexEnd') {
					throw new Error('Invalid character after an index');
				}

				// Falls through

			default:
				if (currentPart === 'index' && !digits.has(character)) {
					throw new Error('Invalid character in an index');
				}

				if (currentPart === 'indexEnd') {
					throw new Error('Invalid character after an index');
				}

				if (currentPart === 'start') {
					currentPart = 'property';
				}

				if (isIgnoring) {
					isIgnoring = false;
					currentSegment += '\\';
				}

				currentSegment += character;
		}
	}

	if (isIgnoring) {
		currentSegment += '\\';
	}

	if (currentPart === 'property') {
		if (disallowedKeys.has(currentSegment)) {
			return [];
		}

		parts.push(currentSegment);
	} else if (currentPart === 'index') {
		throw new Error('Index was not closed');
	} else if (currentPart === 'start') {
		parts.push('');
	}

	return parts;
}

function isStringIndex(object, key) {
	if (typeof key !== 'number' && Array.isArray(object)) {
		const index = Number.parseInt(key, 10);
		return Number.isInteger(index) && object[index] === object[key];
	}

	return false;
}

function assertNotStringIndex(object, key) {
	if (isStringIndex(object, key)) {
		throw new Error('Cannot use string index');
	}
}

module.exports = {
	get(object, path, value) {
		if (!isObject(object) || typeof path !== 'string') {
			return value === undefined ? object : value;
		}

		const pathArray = getPathSegments(path);
		if (pathArray.length === 0) {
			return value;
		}

		for (let i = 0; i < pathArray.length; i++) {
			const key = pathArray[i];

			if (isStringIndex(object, key)) {
				object = i === pathArray.length - 1 ? undefined : null;
			} else {
				object = object[key];
			}

			if (object === undefined || object === null) {
				// `object` is either `undefined` or `null` so we want to stop the loop, and
				// if this is not the last bit of the path, and
				// if it didn't return `undefined`
				// it would return `null` if `object` is `null`
				// but we want `get({foo: null}, 'foo.bar')` to equal `undefined`, or the supplied value, not `null`
				if (i !== pathArray.length - 1) {
					return value;
				}

				break;
			}
		}

		return object === undefined ? value : object;
	},

	set(object, path, value) {
		if (!isObject(object) || typeof path !== 'string') {
			return object;
		}

		const root = object;
		const pathArray = getPathSegments(path);

		for (let i = 0; i < pathArray.length; i++) {
			const p = pathArray[i];
			assertNotStringIndex(object, p);

			if (!isObject(object[p])) {
				object[p] = Number.isInteger(pathArray[i + 1]) ? [] : {};
			}

			if (i === pathArray.length - 1) {
				object[p] = value;
			}

			object = object[p];
		}

		return root;
	},

	delete(object, path) {
		if (!isObject(object) || typeof path !== 'string') {
			return false;
		}

		const pathArray = getPathSegments(path);

		for (let i = 0; i < pathArray.length; i++) {
			const p = pathArray[i];
			assertNotStringIndex(object, p);

			if (i === pathArray.length - 1) {
				delete object[p];
				return true;
			}

			object = object[p];

			if (!isObject(object)) {
				return false;
			}
		}
	},

	has(object, path) {
		if (!isObject(object) || typeof path !== 'string') {
			return false;
		}

		const pathArray = getPathSegments(path);
		if (pathArray.length === 0) {
			return false;
		}

		// eslint-disable-next-line unicorn/no-for-loop
		for (let i = 0; i < pathArray.length; i++) {
			if (isObject(object)) {
				if (!(pathArray[i] in object && !isStringIndex(object, pathArray[i]))) {
					return false;
				}

				object = object[pathArray[i]];
			} else {
				return false;
			}
		}

		return true;
	}
};