Allow restricting by timestamp or position.

Closes #181.

lib/www/server/lib/db/navdata/get.js

@@ -9,12 +9,76 @@ function fields (obj, keys) {
 	return retval;
 }
 
+/** Perform a restrict (aka select) operation on the relation.
+ *
+ * Recognised queries are:
+ *
+ * - tstamp:i; tolerance:j
+ * - pos:λ,φ; radius: ρ
+ *
+ * Defaults:
+ *
+ * - tolerance: 1000 (ms)
+ * - radius: 1 (m)
+ *
+ * Queries are ANDed together.
+ */
+function restrict (q="") {
+	let sql = [];
+
+	/* This takes in a string of the form:
+	 * "key0=value0;key1=value1;key2=value=2"
+	 * and returns an object like:
+	 * { key0: "value0", key1: "value1", key2: "value=2" }
+	 */
+	const constraints = Object.fromEntries(q.split(/\s*;\s*/).map(i => {
+		const parts = i.split(/(\s*:\s*)/);
+		return [parts[0], parts.slice(2).join("")]
+	}));
+
+	// TODO Consider adding an event_tstamp field, or indexing meta->>tstamp
+	if ("tstamp" in constraints) {
+		const ts = new Date(constraints.tstamp);
+
+		if (isNaN(ts)) {
+			throw new Error("Invalid query");
+		}
+
+		const tolerance = constraints.tolerance ?? 1000;
+		const ts0 = new Date(ts.valueOf()-Number(tolerance));
+		const ts1 = new Date(ts.valueOf()+Number(tolerance));
+		console.log(tolerance, ts, ts0, ts1);
+		console.log(constraints);
+
+		if (!isNaN(ts0) && !isNaN(ts1)) {
+			sql.push(`(meta->>'tstamp')::timestamptz BETWEEN '${ts0.toISOString()}' AND '${ts1.toISOString()}'`);
+		} else {
+			throw new Error("Invalid query");
+		}
+	}
+
+	if ("pos" in constraints) {
+		const [ lon, lat ] = constraints.pos.split(",").map(i => Number(i));
+
+		if (isNaN(lon) || isNaN(lat)) {
+			throw new Error("Invalid query");
+		}
+
+		const radius = constraints.radius ?? 1;
+
+		sql.push(`ST_DistanceSphere(geometry, ST_Point(${lon}, ${lat}, 4326)) <= ${radius}`)
+	}
+
+	return sql.length ? ("WHERE " + sql.join(" AND ")) : "";
+}
+
 async function get (opts = {}) {
 	const client = await pool.connect();
 
 	const text = `
 		SELECT meta
 		FROM real_time_inputs
+		${restrict(opts.q)}
 		ORDER BY tstamp DESC
 		LIMIT $1
 		OFFSET $2
@@ -24,6 +88,7 @@ async function get (opts = {}) {
 
 	const res = await client.query(text, values);
 	client.release();
+	// TODO Must change this to use utils/project instead.
 	return opts.fields
 		? res.rows.map(r => fields(r.meta, opts.fields.split(/[;,\s]+/)))
 		: res.rows.map(r => r.meta);