Implement `top_tags`.

1 files changed, 38 insertions, 0 deletions

diff --git a/src/database.rs b/src/database.rs
index db33117..bd195f2 100644
--- a/src/database.rs
+++ b/src/database.rs
@@ -254,6 +254,24 @@ impl TagDatabase {
             limit: None,
         })
     }
+
+    pub fn top_tags(&self, n: i64) -> Result<Vec<(i64, String)>> {
+        Ok(self
+            .0
+            .prepare(
+                "SELECT tags.name, COUNT(mapping.tag) AS tag_count
+                 FROM mapping
+                 INNER JOIN tags ON tags.id = mapping.tag
+                 GROUP BY tag
+                 ORDER BY tag_count DESC
+                 LIMIT ?",
+            )?
+            .query_map(params![n], |row| -> rusqlite::Result<(i64, String)> {
+                Ok((row.get(1)?, row.get(0)?))
+            })?
+            .filter_map(|s| s.ok())
+            .collect())
+    }
 }
 
 /// The result of an image query in бирка-тян's tag database.
@@ -357,4 +375,24 @@ mod tests {
         assert_eq!(tb.images_by_tags(&["2"]).unwrap().len(), 2);
         assert_eq!(tb.images_by_tags(&["1", "2"]).unwrap().len(), 1);
     }
+
+    #[test]
+    fn top_tags() {
+        let tb = TagDatabase::new_mem().unwrap();
+        let ids: Vec<i64> = (1..4)
+            .map(|i| {
+                let i = i.to_string();
+                tb.import_image(Path::new(&i), &i).unwrap()
+            })
+            .collect();
+        tb.add_tag("1").unwrap();
+        tb.add_tag("2").unwrap();
+        tb.tag_image(ids[0], "1").unwrap();
+        tb.tag_image(ids[1], "2").unwrap();
+        tb.tag_image(ids[2], "1").unwrap();
+        tb.tag_image(ids[2], "2").unwrap();
+        assert_eq!(tb.top_tags(2).unwrap().len(), 2);
+        assert_eq!(tb.top_tags(2).unwrap()[0].0, 2);
+        assert_eq!(tb.top_tags(2).unwrap()[1].0, 2);
+    }
 }