const C1 = 0xcc9e2d51;
const C2 = 0x1b873593;

/**
 * Tiny helper to perform a multiply that's slightly safer to use for hashing.
 *
 * @param a -
 * @param b -
 * @returns a * b
 */
function safeishMultiply(a: number, b: number) {
	return ((a & 0xffff) * b) + ((((a >>> 16) * b) & 0xffff) << 16);
}

/**
 * Utility for calculating stable hashcodes for keys used in a cache.
 *
 * @param obj -
 *   object to hash
 * @param seed -
 *   seed to hash with
 * @returns
 *   hash code
 */
export function hashcode(obj: string | number | boolean | null, seed = 0) {
	switch(typeof obj) {
		case 'string':
		{
			let hash = seed;
			const n = obj.length & ~0x3;
			for(let i = 0; i < n; i += 4) {
				let k1 = ((obj.charCodeAt(i) & 0xffff)) |
					((obj.charCodeAt(i + 1) & 0xffff) << 8) |
					((obj.charCodeAt(i + 2) & 0xffff) << 16) |
					((obj.charCodeAt(i + 3) & 0xffff) << 24);

				k1 = safeishMultiply(k1, C1);
				k1 = (k1 << 15) | (k1 >>> 17);
				k1 = safeishMultiply(k1, C2);

				hash ^= k1;
				hash = (hash << 13) | (hash >>> 19);
				hash = (hash * 5) + 0xe6546b64;
			}

			{
				let k1 = 0;
				switch(obj.length & 3) {
					case 3:
						k1 ^= (obj.charCodeAt(n + 2) & 0xffff) << 16;
					// eslint-disable-next-line no-fallthrough
					case 2:
						k1 ^= (obj.charCodeAt(n + 1) & 0xffff) << 8;
					// eslint-disable-next-line no-fallthrough
					case 1:
						k1 ^= (obj.charCodeAt(n) & 0xffff);

						k1 = safeishMultiply(k1, C1);
						k1 = (k1 << 15) | (k1 >>> 17);
						k1 = safeishMultiply(k1, C2);

						hash ^= k1;
				}
			}

			hash ^= obj.length;

			hash ^= hash >>> 16;
			hash = safeishMultiply(hash, 0x85ebca6b);
			hash ^= hash >>> 13;
			hash = safeishMultiply(hash, 0xc2b2ae35);
			hash ^= hash >>> 16;

			return hash >>> 0;
		}
		case 'number':
		{
			let hash = obj;

			hash = safeishMultiply(hash, C1);
			hash = (hash << 15) | (hash >>> 17);
			hash = safeishMultiply(hash, C2);

			hash = (hash << 13) | (hash >>> 19);
			hash = (hash * 5) + 0xe6546b64;

			hash ^= hash >>> 16;
			hash = safeishMultiply(hash, 0x85ebca6b);
			hash ^= hash >>> 13;
			hash = safeishMultiply(hash, 0xc2b2ae35);
			hash ^= hash >>> 16;

			hash ^= 1;

			return hash >>> 0;
		}
		case 'boolean':
		{
			return obj ? 1231 : 1237;
		}
		case 'undefined':
			return 0;
		default:
			throw new Error('The given value can not be used as a key in a cache, value was: ' + String(obj));
	}
}