Specific use of “comprar” or “comprando”

Question

I wonder which is correct in this specific context:

1. Has gastado mucho comprando regalos

vs.

2. Has gastado mucho comprar regalos.

I want to say:

You have spent a lot buying presents.

Answer 1

Sentence (1):

1. Has gastado mucho comprando regalos.

is correct.

Instead, sentence (2):

2. Has gastado mucho comprar regalos.

is not grammatical.

It could be made grammatical by adding the preposition "en":

3. Has gastado mucho en comprar regalos.

Sentence (3), though grammatical, is not as idiomatic (or usual) as (1), and could be translated as:

• You have spent a lot of money on the purchase of gifts.

Then, sentence (3) can also be expressed by using a noun instead of the infinitive:

4. Has gastado mucho en la compra de regalos.