Add the Luchtmeetnet provider

Also introduce the providers module.

Cargo.toml

@@ -8,5 +8,5 @@ chrono = "0.4.19"
 color-eyre = "0.5.6"
 geocoding = "0.3.1"
 image = "0.24.0"
-reqwest = "0.11.9"
+reqwest = { version = "0.11.9", features = ["json"] }
 rocket = { version = "0.5.0-rc.1", features = ["json"] }

src/main.rs

@@ -21,8 +21,10 @@ use rocket::tokio::{self, select};
 use rocket::{get, routes, FromFormField, State};
 
 use self::maps::{Maps, MapsHandle};
+use self::providers::luchtmeetnet::Item as LuchtmeetnetItem;
 
-mod maps;
+pub(crate) mod maps;
+pub(crate) mod providers;
 
 /// The current for a specific location.
 ///

src/providers.rs

@@ -0,0 +1,5 @@
+//! All supported metric data providers.
+//!
+//! Data is either provided via a direct (JSON) API or via looking up values on maps.
+
+pub(crate) mod luchtmeetnet;

src/providers/luchtmeetnet.rs

@@ -0,0 +1,64 @@
+//! The Luchtmeetnet open data provider.
+//!
+//! For more information about Luchtmeetnet, see: <https://www.luchtmeetnet.nl/contact>.
+
+use chrono::serde::ts_seconds;
+use chrono::{DateTime, Utc};
+use rocket::serde::{Deserialize, Serialize};
+
+use crate::Metric;
+
+/// The base URL for the Luchtmeetnet API.
+const LUCHTMEETNET_BASE_URL: &str = "https://api.luchtmeetnet.nl/open_api/concentrations";
+
+/// The Luchtmeetnet API data container.
+///
+/// This is only used temporarily during deserialization.
+#[derive(Debug, Deserialize)]
+#[serde(crate = "rocket::serde")]
+struct Container {
+    data: Vec<Item>,
+}
+
+/// The Luchtmeetnet API data item.
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(crate = "rocket::serde")]
+pub(crate) struct Item {
+    /// The time for when the value is forecast.
+    #[serde(
+        rename(deserialize = "timestamp_measured"),
+        serialize_with = "ts_seconds::serialize"
+    )]
+    time: DateTime<Utc>,
+    /// The forecasted value.
+    ///
+    /// The unit depends on the selected [metric](Metric).
+    value: f32,
+}
+
+/// Retrieves the Luchtmeetnet forecasted items for the provided position and metric.
+///
+/// Returns [`None`] if retrieval or deserialization fails, or if the metric is not supported by
+/// this provider.
+pub(crate) async fn get(lat: f64, lon: f64, metric: Metric) -> Option<Vec<Item>> {
+    let formula = match metric {
+        Metric::AQI => "lki",
+        Metric::NO2 => "no2",
+        Metric::O3 => "o3",
+        Metric::PM10 => "pm10",
+        _ => return None, // Unsupported metric
+    };
+    let url = format!(
+        "{LUCHTMEETNET_BASE_URL}?formula={formula}&latitude={:.05}&longitude={:.05}",
+        lat, lon
+    );
+
+    println!("▶️  Retrieving Luchtmeetnet data from {url}");
+    let response = reqwest::get(&url).await.ok()?;
+    let root: Container = match response.error_for_status() {
+        Ok(res) => res.json().await.ok()?,
+        Err(_err) => return None,
+    };
+
+    Some(root.data)
+}