import { hkdf } from './crypto'

/**
 * LT Hash is a summation based hash algorithm that maintains the integrity of a piece of data
 * over a series of mutations. You can add/remove mutations and it'll return a hash equal to 
 * if the same series of mutations was made sequentially.
 */

const o = 128;

class d {

	salt: string

	constructor(e: string) {
		this.salt = e
	}
	add(e, t) {
		var r = this;
		for(const item of t) {
			e = r._addSingle(e, item)
		}
		return e
	}
	subtract(e, t) {
		var r = this;
		for(const item of t) {
			e = r._subtractSingle(e, item)
		}
		return e
	}
	subtractThenAdd(e, t, r) {
		var n = this;
		return n.add(n.subtract(e, r), t)
	}
	_addSingle(e, t) {
		var r = this;
		const n = new Uint8Array(hkdf(Buffer.from(t), o, { info: r.salt })).buffer;
		return r.performPointwiseWithOverflow(e, n, ((e,t)=>e + t))
	}
	_subtractSingle(e, t) {
		var r = this;

		const n = new Uint8Array(hkdf(Buffer.from(t), o, { info: r.salt })).buffer;
		return r.performPointwiseWithOverflow(e, n, ((e,t)=>e - t))
	}
	performPointwiseWithOverflow(e, t, r) {
		const n = new DataView(e)
		  , i = new DataView(t)
		  , a = new ArrayBuffer(n.byteLength)
		  , s = new DataView(a);
		for (let e = 0; e < n.byteLength; e += 2)
			s.setUint16(e, r(n.getUint16(e, !0), i.getUint16(e, !0)), !0);
		return a
	}
}
export const LT_HASH_ANTI_TAMPERING = new d('WhatsApp Patch Integrity')