leaderboard: paginate API results

src/leaderboard.rs

@@ -10,21 +10,39 @@ use sqlx::PgPool;
 
 use crate::{
     AppState,
-    model::{ActivityCrossing, LeaderboardGroup, LeaderboardRow},
+    model::{ActivityCrossing, LeaderboardGroup, LeaderboardPage, LeaderboardRow},
 };
 
 #[derive(Debug, Deserialize, Default)]
 pub struct LeaderboardQuery {
     pub group_id: Option<i64>,
+    #[serde(default)]
+    pub offset: i64,
+    #[serde(default = "default_page_size")]
+    pub limit: i64,
+}
+
+fn default_page_size() -> i64 {
+    50
 }
 
 pub async fn api(
     State(state): State<AppState>,
     Query(query): Query<LeaderboardQuery>,
-) -> Result<Json<Vec<LeaderboardGroup>>, (axum::http::StatusCode, String)> {
-    build(&state.db, query.group_id)
+) -> Result<Json<LeaderboardPage>, (axum::http::StatusCode, String)> {
+    let offset = query.offset.max(0);
+    let limit = query.limit.clamp(1, 200);
+
+    build(&state.db, query.group_id, offset, limit)
         .await
-        .map(Json)
+        .map(|groups| {
+            let returned = groups.iter().map(|group| group.rows.len() as i64).sum::<i64>();
+            Json(LeaderboardPage {
+                groups,
+                next_offset: offset + returned,
+                has_more: returned == limit,
+            })
+        })
         .map_err(|error| {
             tracing::error!(%error, "leaderboard query failed");
             (
@@ -34,7 +52,7 @@ pub async fn api(
         })
 }
 
-pub async fn build(db: &PgPool, group_id: Option<i64>) -> Result<Vec<LeaderboardGroup>> {
+pub async fn build(db: &PgPool, group_id: Option<i64>, offset: i64, limit: i64) -> Result<Vec<LeaderboardGroup>> {
     let rows = sqlx::query(
         r#"
         WITH bucketed AS (
@@ -114,9 +132,13 @@ pub async fn build(db: &PgPool, group_id: Option<i64>) -> Result<Vec<Leaderboard
             to_county,
             crossing_time,
             rank
+        LIMIT $2
+        OFFSET $3
         "#,
     )
     .bind(group_id)
+    .bind(limit)
+    .bind(offset)
     .fetch_all(db)
     .await?;
 

src/model.rs

@@ -63,6 +63,13 @@ pub struct LeaderboardGroup {
     pub rows: Vec<LeaderboardRow>,
 }
 
+#[derive(Debug, Serialize, Clone)]
+pub struct LeaderboardPage {
+    pub groups: Vec<LeaderboardGroup>,
+    pub next_offset: i64,
+    pub has_more: bool,
+}
+
 #[derive(Debug, Serialize, Clone)]
 pub struct ActivityCrossing {
     pub crossing_time: DateTime<Utc>,