1 files changed, 58 insertions, 2 deletions

diff --git a/src/db/mod.rs b/src/db/mod.rs
index cd71e9e..c1d5ab0 100644
--- a/src/db/mod.rs
+++ b/src/db/mod.rs
@@ -13,6 +13,7 @@ use diesel::{
     prelude::*,
     r2d2::{ConnectionManager, ManageConnection},
 };
+use postgres::Connection as RawPgConn;
 use r2d2_postgres::{
     PostgresConnectionManager as RawPgConnMgr,
     TlsMode,
@@ -32,17 +33,22 @@ lazy_static! {
     static ref RAW_CONN_MGR: RawPgConnMgr = RawPgConnMgr::new(DB_URL.clone(), TlsMode::None).unwrap();
 }
 
+#[inline]
 pub fn connection() -> Result<PgConnection> {
     CONN_MGR.connect().map_err(Error::from)
 }
 
+#[inline]
+fn raw_connection() -> Result<RawPgConn> {
+    RAW_CONN_MGR.connect().map_err(Error::from)
+}
+
 pub fn find_meme<T: AsRef<str>>(conn: &PgConnection, search: T) -> Result<Meme> {
     use diesel::dsl::sql;
     use diesel::sql_types::Text;
 
     let search = search.as_ref();
 
-    // TODO: check for injection
     let mut meme = memes::table
         .filter(memes::title.eq(search))
         .limit(1)
@@ -111,6 +117,56 @@ pub fn delete_meme<T: AsRef<str>>(conn: &PgConnection, search: T, deleted_by: u6
     })
 }
 
+pub fn rare_meme(conn: &PgConnection, audio: bool) -> Result<Meme> {
+    use rand::prelude::*;
+    use failure::err_msg;
+
+    let raw_conn = raw_connection()?;
+
+    let rows = raw_conn.query(r#"
+    SELECT agg.meme_id, (agg.time_diff / agg.ct) AS play_prop, agg.ct FROM (
+        SELECT meme_count.meme_id AS meme_id, meme_count.ct AS ct, EXTRACT(EPOCH FROM (now() - metadata.created)) AS time_diff FROM (
+          SELECT meme_id, COUNT(*) AS ct FROM invocation_records GROUP BY meme_id
+        ) AS meme_count
+          INNER JOIN memes ON memes.id = meme_count.meme_id
+          INNER JOIN metadata ON metadata.id = memes.metadata_id
+        WHERE ((memes.audio_id IS NOT NULL) = $1) OR $2
+    ) AS agg
+    ORDER BY play_prop DESC
+    LIMIT 100;
+    "#, &[&audio, &!audio])?;
+
+    let elems = rows.iter()
+        .map(|row| (row.get::<_, i32>(0), row.get::<_, f64>(1), row.get::<_, i64>(2) as usize))
+        .collect::<Vec<_>>();
+
+    if elems.len() == 0 {
+        return Err(err_msg("no rare memes found"));
+    }
+
+    let total_probability_mass: f64 = elems.iter().map(|(_, prob, _)| prob).sum();
+
+    if total_probability_mass == 0. {
+        return Err(err_msg("rare meme probability mass was 0"))
+    }
+
+    let mut rng = thread_rng();
+    let target_prob = rng.gen_range(0., total_probability_mass);
+
+    let mut cur_prob_acc = 0.;
+    let mut meme_id = elems.last().unwrap().0;
+
+    for &(m_id, prob, _) in elems.iter() {
+        cur_prob_acc += prob;
+        if cur_prob_acc > target_prob {
+            meme_id = m_id;
+            break;
+        }
+    }
+
+    Meme::find(conn, meme_id)
+}
+
 pub fn rand_meme(conn: &PgConnection, audio: bool) -> Result<Meme> {
     use rand::{thread_rng, seq::SliceRandom};
     use failure::err_msg;
@@ -273,7 +329,7 @@ pub fn stats(conn: &PgConnection) -> Result<Stats> {
         .first(conn)
         .map_err(Error::from)?;
 
-    let raw_conn = RAW_CONN_MGR.connect().map_err(Error::from)?;
+    let raw_conn = raw_connection()?;
 
     let rows = raw_conn.query(r#"
     SELECT DATE(time) as dt, COUNT(*) FROM invocation_records