Extract some modules

ui/ops.js

@@ -0,0 +1,44 @@
+import initModule from '../libapi.mjs';
+
+/** @typedef {import('../libapi.mjs').Context} Context */
+
+/** This function should be called once user has selected the camera and other operations can begin. */
+export let start;
+
+let started = new Promise(resolve => {
+  start = resolve;
+});
+
+let queue = (async () => {
+  let { Context } = await initModule();
+  await started;
+  let ctx = await new Context();
+  addEventListener('beforeunload', e => {
+    ctx.delete();
+  });
+  return ctx;
+})();
+
+/** Schedules an exclusive async operation on the global context.
+ * @template T
+ * @param {(ctx: Context) => Promise<T>} op
+ * @returns {Promise<T>}
+ */
+export function scheduleOp(op) {
+  let caughtRes = queue.then(async ctx => {
+    let resultPromise = op(ctx);
+    try {
+      await resultPromise;
+    } catch {}
+    return {
+      ctx,
+      resultPromise
+    };
+  });
+
+  // Queue should ignore result values as well as errors from singular ops.
+  queue = caughtRes.then(res => res.ctx);
+
+  // Result should contain the unwrapped value or error.
+  return caughtRes.then(res => res.resultPromise);
+}