add endpoint for earliest saved meal

.sqlx/query-66fcef790324f9eedc03ad052acc67111c50d82f56471df1c9adba498be0d543.json

@@ -0,0 +1,20 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "SELECT MIN(date) AS \"date!\" FROM meals WHERE is_latest = TRUE;",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "date!",
+        "type_info": "Date"
+      }
+    ],
+    "parameters": {
+      "Left": []
+    },
+    "nullable": [
+      null
+    ]
+  },
+  "hash": "66fcef790324f9eedc03ad052acc67111c50d82f56471df1c9adba498be0d543"
+}

web-api/src/endpoints/metadata.rs

@@ -0,0 +1,47 @@
+use std::sync::OnceLock;
+
+use actix_web::{
+    get,
+    web::{self, ServiceConfig},
+    HttpResponse, Responder,
+};
+use chrono::NaiveDate;
+use serde_json::json;
+use sqlx::PgPool;
+
+pub fn configure(cfg: &mut ServiceConfig) {
+    cfg.service(web::scope("/metadata").service(earliest_meal_date));
+}
+
+static EARLIEST_MEAL_DATE: OnceLock<NaiveDate> = OnceLock::new();
+
+#[get("/earliest-meal-date")]
+async fn earliest_meal_date(db: web::Data<PgPool>) -> impl Responder {
+    if let Some(earliest_date) = EARLIEST_MEAL_DATE.get() {
+        earliest_meal_date_ok_response(*earliest_date)
+    } else {
+        match sqlx::query_scalar!(
+            r#"SELECT MIN(date) AS "date!" FROM meals WHERE is_latest = TRUE;"#
+        )
+        .fetch_one(db.as_ref())
+        .await
+        {
+            Ok(date) => {
+                EARLIEST_MEAL_DATE.set(date).ok();
+                earliest_meal_date_ok_response(date)
+            }
+            Err(err) => {
+                tracing::error!("Failed to query datebase: {err}");
+                HttpResponse::InternalServerError().json(json!({
+                    "error": "Failed to query database"
+                }))
+            }
+        }
+    }
+}
+
+fn earliest_meal_date_ok_response(date: NaiveDate) -> HttpResponse {
+    HttpResponse::Ok().json(json!({
+        "date": date,
+    }))
+}

web-api/src/endpoints/mod.rs

@@ -5,11 +5,13 @@ use shared::Canteen;
 use strum::IntoEnumIterator as _;
 
 mod menu;
+mod metadata;
 mod nutrition;
 mod price_history;
 
 pub fn configure(cfg: &mut ServiceConfig) {
     cfg.service(index)
+        .configure(metadata::configure)
         .configure(menu::configure)
         .configure(nutrition::configure)
         .configure(price_history::configure);