MIN() OVER PARTITION resulting in duplicate rows

Question

I have a table that looks like:

consumer_id	product_id	prod_state	date
a	1	wholesale	1
a	1	stock	2
a	1	sold	3
a	1	return	4

I want to transform it such that my states are in the columns, and the value is the date, i.e something like

consumer_id	product_id	wholesale_date	stock_date	sold_date	return_date
a	1	1	2	3	4

(the dates are actual dates, but to create the table easily, I've just put numbers).

So in order to do this, I write the following code

SELECT consumer_id
     , product_id
     , CASE WHEN prod_state = 'wholesale'
          THEN MIN(date) OVER(PARTITION BY consumer_id, product_id, prod_state)
          ELSE NULL 
     END as wholesale_date
     , CASE WHEN prod_state = 'stock'
          THEN MIN(date) OVER(PARTITION BY consumer_id, product_id, prod_state)
          ELSE NULL 
     END as sold_date
     , CASE WHEN prod_state = 'wholesale'
          THEN MIN(date) OVER(PARTITION BY consumer_id, product_id, prod_state)
          ELSE NULL 
       END as sold_date

from table

With a similar case statement used for each state.

However what this ends up doing is creating a table that looks a bit like this

consumer_id	product_id	wholesale_date	stock_date	sold_date	return_date
a	1	1	NULL	NULL	NULL
a	1	NULL	2	NULL	NULL
a	1	NULL	NULL	3	NULL
a	1	NULL	NULL	NULL	4

How do I remove all the duplicate rows and collapse them all into one row?

Even by adding group by's to the bottom of my query doesn't help with this.

Thank you