Count the active businesses that has an attribute of Wi-Fi with medium review count.
active business refers to active = 'true'; 'Wi-Fi' is the attribute_name; medium review count refers to review_count = 'Medium'
SELECT COUNT(T1.business_id) FROM Business AS T1 INNER JOIN Business_Attributes AS T2 ON T1.business_id = T2.business_id INNER JOIN Attributes AS T3 ON T2.attribute_id = T3.attribute_id WHERE T3.attribute_name LIKE 'Wi-Fi' AND T1.active LIKE 'TRUE' AND T1.review_count LIKE 'Medium'