add: great post average

crates/core/src/database/posts.rs

@@ -510,6 +510,80 @@ impl DataManager {
         Ok(res.unwrap())
     }
 
+    /// Calculate the GPA (great post average) of a given user.
+    ///
+    /// To be considered a "great post", a post must have a score ((likes - dislikes) / (likes + dislikes))
+    /// of at least 0.6.
+    ///
+    /// GPA is calculated based on the user's last 250 posts.
+    pub async fn calculate_user_gpa(&self, id: usize) -> usize {
+        // just for note, this is SUPER bad for performance... which is why we
+        // only calculate this when it expires in the cache (every week)
+        if let Some(cached) = self.0.1.get(format!("atto.user.gpa:{}", id)).await {
+            if let Ok(c) = cached.parse() {
+                return c;
+            }
+        }
+
+        // ...
+        let conn = match self.0.connect().await {
+            Ok(c) => c,
+            Err(_) => return 0,
+        };
+
+        let res = query_rows!(
+            &conn,
+            &format!("SELECT * FROM posts WHERE owner = $1 ORDER BY created DESC LIMIT 250",),
+            &[&(id as i64)],
+            |x| { Self::get_post_from_row(x) }
+        );
+
+        if res.is_err() {
+            return 0;
+        }
+
+        // ...
+        let mut real_posts_count: usize = 0; // posts which can be scored
+        let mut good_posts: usize = 0;
+        // let mut bad_posts: usize = 0;
+
+        let posts = res.unwrap();
+
+        for post in posts {
+            if post.likes == 0 && post.dislikes == 0 {
+                // post has no likes or dislikes... doesn't count
+                continue;
+            }
+
+            real_posts_count += 1;
+
+            // likes percentage / total likes
+            let score: f32 = (post.likes as f32 - post.dislikes as f32)
+                / (post.likes as f32 + post.dislikes as f32);
+
+            if score.is_sign_negative() {
+                // bad_posts += 1;
+                continue;
+            }
+
+            if score > 0.6 {
+                good_posts += 1;
+            }
+            // } else {
+            //     bad_posts += 1;
+            // }
+        }
+
+        let gpa = ((good_posts as f32 / real_posts_count as f32) * 4.0).round() as usize;
+
+        self.0
+            .1
+            .set(format!("atto.user.gpa:{}", id), gpa.to_string())
+            .await;
+
+        gpa
+    }
+
     /// Get all replies from the given user (from most recent).
     ///
     /// # Arguments