Clarify intention of op.previous

[nikolockenvitz]

In #generateOperation(), the previous property is set for all non-create operations. Based on the name, my first assumption was that it's just a pointer to the previous operation. From the implementation I suppose that it's a pointer to the "relevant" previous operation, i.e.

• for update operations, it points to the last create/update/recover operation
• for recover operations, it points to the last create/recover operation

(so that we can access the relevant private key in generateRequest). Is this understanding correct?

The logic that is implemented there is non-trivial and should either be refactored or explained with a comment IMHO. Also, wouldn't it make more sense to iterate through the array from the end and stop once the relevant operation is found?

ion-tools/src/did.js

Lines 38 to 42 in 02199dd

	if (type !== 'create') {
	op.previous = this.#ops.reduce((last, op) => {
	return op.operation === type || (op.operation === 'recover' && (type === 'deactivate' || type === 'update')) ? op : last;
	}, this.#ops[0]);
	}

If my understanding is correct and you agree, I can open a PR to suggest an improved implementation.