Hard stool and then normal

Hello I got this problem which is bothering me alot. When i go to the WC first time in the day - the start of the first stool its first very hard very lump, very dark and i see alot of mucus on it, and then in the same stool it becomes normal. Its like 20% hard, lumpy, dark and mucus and then 80% its normal with normal color. Can somebody please explain me this?