implemented progressive message fetching on scroll

db/init.sql

@@ -46,7 +46,7 @@ CREATE TABLE IF NOT EXISTS room_invite_ (
 
 CREATE TABLE IF NOT EXISTS message_ (
   id BIGSERIAL PRIMARY KEY,
-  -- uuid UUID NOT NULL,
+  uuid UUID NOT NULL,
   sender INT REFERENCES user_(id) NOT NULL,
   room INT REFERENCES room_(id) NOT NULL,
   message_type VARCHAR(32) NOT NULL,

db/mock_data.sql

@@ -14,13 +14,13 @@ INSERT INTO membership_ (user_id, room) VALUES
 (3, 1),  -- Carol in General Discussion
 (1, 3);  -- Alice in Random Memes
 
-INSERT INTO message_ (sender, room, message_type, content) VALUES
-(1, 1, 'text', 'Hey everyone, hows it going?'),
-(2, 1, 'text', 'All good! Just trying to get through some work.'),
-(3, 1, 'text', 'Hello! How are you guys?'),
-(2, 2, 'text', 'Anyone seen the new tech updates?'),
-(1, 3, 'image', 'Heres a funny meme I found!'),
-(3, 1, 'text', 'I love how active this room is!');
+INSERT INTO message_ (sender, room, message_type, content, uuid) VALUES
+(1, 1, 'text', 'Hey everyone, hows it going?', '3ae85002-8a82-479f-b1c9-6faa3dceb2f3'),
+(2, 1, 'text', 'All good! Just trying to get through some work.', '8e60aa27-9eef-4f1c-a913-47ac6ea1229b'),
+(3, 1, 'text', 'Hello! How are you guys?', 'f2b688f8-6678-465c-8092-9636a9ae2f16'),
+(2, 2, 'text', 'Anyone seen the new tech updates?', '20c6b5d4-c8b1-4afe-844c-339e128fc344'),
+(1, 3, 'image', 'Heres a funny meme I found!', '7dd79706-9187-47a5-b4f0-86e07cbb4564'),
+(3, 1, 'text', 'I love how active this room is!', '9024823f-1b0c-436b-b81d-08dc06ac34df');
 
 INSERT INTO friendship_ (user_first, user_second) VALUES
 (1, 3),  -- Alice and Carol

src/routes/messages.rs

@@ -1,6 +1,6 @@
 use axum::{
     Extension, Json, Router,
-    extract::Path,
+    extract::{Path, Query},
     http::{HeaderMap, StatusCode},
     routing::{get, post},
 };
@@ -15,6 +15,7 @@ use crate::{
 
 #[derive(sqlx::FromRow, serde::Serialize, Debug)]
 pub struct MessageRow {
+    pub uuid: Uuid,
     pub sender: String,
     pub message_type: String,
     pub content: String,
@@ -36,6 +37,12 @@ pub struct NewMessagePayload {
     pub content: String,
 }
 
+#[derive(serde::Deserialize)]
+struct MessageFetchQuery {
+    limit: Option<i32>,
+    before: Option<Uuid>,
+}
+
 pub fn routes() -> Router {
     Router::new()
         .route("/messages/{room_uuid}", get(list_messages))
@@ -44,6 +51,7 @@ pub fn routes() -> Router {
 
 async fn list_messages(
     Path(room_uuid): Path<Uuid>,
+    Query(query): Query<MessageFetchQuery>,
     headers: HeaderMap,
     Extension(db): Extension<PgPool>,
 ) -> Result<Json<Vec<Message>>, (StatusCode, String)> {
@@ -59,9 +67,12 @@ async fn list_messages(
         ));
     }
 
+    let limit: i32 = query.limit.unwrap_or(30).abs().min(80);
+
     let messages = sqlx::query_as::<_, MessageRow>(
         r#"
         SELECT
+            m.uuid,
             u.username AS sender,
             r.uuid AS room,
             m.message_type,
@@ -71,23 +82,27 @@ async fn list_messages(
         JOIN user_ u ON u.id = m.sender
         JOIN room_ r ON r.id = m.room
         WHERE m.room = $1
-    ORDER BY m.id
+        AND ($2::uuid IS NULL OR m.id < (SELECT id FROM message_ WHERE uuid = $2))
+        ORDER BY m.id DESC
+        LIMIT $3
         "#,
     )
     .bind(room_id)
+    .bind(query.before)
+    .bind(limit)
     .fetch_all(&db)
     .await
-    .map_err(|_| {
+    .map_err(|e| {
         (
             StatusCode::INTERNAL_SERVER_ERROR,
-            "Failed to list messages".into(),
+            format!("Failed to list messages: {e}"),
         )
     })?;
 
-    let messages: Vec<Message> = messages
+    let mut messages: Vec<Message> = messages
         .into_iter()
         .map(|m| Message {
-            uuid: uuid::Uuid::now_v7(),
+            uuid: m.uuid,
             sender: m.sender,
             message_type: m.message_type,
             content: m.content,
@@ -95,6 +110,8 @@ async fn list_messages(
         })
         .collect();
 
+    messages.reverse();
+
     Ok(Json(messages))
 }
 
@@ -117,14 +134,17 @@ async fn create_message(
         ));
     }
 
+    let uuid = Uuid::now_v7();
+
     let sent_at: chrono::NaiveDateTime = sqlx::query_scalar(
-        "INSERT INTO message_ (sender, room, message_type, content)
-        VALUES ($1, $2, $3, $4) RETURNING sent_at",
+        "INSERT INTO message_ (sender, room, message_type, content, uuid)
+        VALUES ($1, $2, $3, $4, $5) RETURNING sent_at",
     )
     .bind(user_id)
     .bind(room_id)
     .bind(&payload.message_type)
     .bind(&payload.content)
+    .bind(&uuid)
     .fetch_one(&db)
     .await
     .map_err(|_| (StatusCode::BAD_REQUEST, "Could not create message".into()))?;
@@ -132,7 +152,7 @@ async fn create_message(
     let sender_name = username_from_uuid(&db, claims.sub).await?;
 
     let message = Message {
-        uuid: uuid::Uuid::now_v7(),
+        uuid: uuid,
         sender: sender_name,
         message_type: payload.message_type,
         content: payload.content,