presume median downvote on new post

prisma/migrations/20220922210703_outlaw/migration.sql

@@ -0,0 +1,64 @@
+CREATE OR REPLACE FUNCTION create_item(
+    title TEXT, url TEXT, text TEXT, boost INTEGER,
+    parent_id INTEGER, user_id INTEGER, fwd_user_id INTEGER,
+    has_img_link BOOLEAN, spam_within INTERVAL)
+RETURNS "Item"
+LANGUAGE plpgsql
+AS $$
+DECLARE
+    user_msats INTEGER;
+    cost INTEGER;
+    free_posts INTEGER;
+    free_comments INTEGER;
+    freebie BOOLEAN;
+    item "Item";
+    med_votes INTEGER;
+BEGIN
+    PERFORM ASSERT_SERIALIZED();
+
+    SELECT msats, "freePosts", "freeComments"
+    INTO user_msats, free_posts, free_comments
+    FROM users WHERE id = user_id;
+
+    freebie := (parent_id IS NULL AND free_posts > 0) OR (parent_id IS NOT NULL AND free_comments > 0);
+    cost := 1000 * POWER(10, item_spam(parent_id, user_id, spam_within)) * CASE WHEN has_img_link THEN 10 ELSE 1 END;
+
+    IF NOT freebie AND cost > user_msats THEN
+        RAISE EXCEPTION 'SN_INSUFFICIENT_FUNDS';
+    END IF;
+
+    -- get this user's median item score
+    SELECT COALESCE(percentile_cont(0.5) WITHIN GROUP(ORDER BY "weightedVotes" - "weightedDownVotes"), 0) INTO med_votes FROM "Item" WHERE "userId" = user_id;
+
+    -- if their median votes are positive, start at 0
+    -- if the median votes are negative, start their post with that many down votes
+    -- basically: if their median post is bad, presume this post is too
+    IF med_votes >= 0 THEN
+        med_votes := 0;
+    ELSE
+        med_votes := ABS(med_votes);
+    END IF;
+
+    INSERT INTO "Item" (title, url, text, "userId", "parentId", "fwdUserId", "paidImgLink", "weightedDownVotes", created_at, updated_at)
+    VALUES (title, url, text, user_id, parent_id, fwd_user_id, has_img_link, med_votes, now_utc(), now_utc()) RETURNING * INTO item;
+
+    IF freebie THEN
+        IF parent_id IS NULL THEN
+            UPDATE users SET "freePosts" = "freePosts" - 1 WHERE id = user_id;
+        ELSE
+            UPDATE users SET "freeComments" = "freeComments" - 1 WHERE id = user_id;
+        END IF;
+    ELSE
+        UPDATE users SET msats = msats - cost WHERE id = user_id;
+
+        INSERT INTO "ItemAct" (sats, "itemId", "userId", act, created_at, updated_at)
+        VALUES (cost / 1000, item.id, user_id, 'VOTE', now_utc(), now_utc());
+    END IF;
+
+    IF boost > 0 THEN
+        PERFORM item_act(item.id, user_id, 'BOOST', boost);
+    END IF;
+
+    RETURN item;
+END;
+$$;