Extract CaptureButton; allow non-singletone connections

ui/capture-button.js

@@ -0,0 +1,33 @@
+import { h, Component, Fragment } from 'preact';
+
+/** @extends Component<{ getFile: () => Promise<File> }, { inProgress: boolean }> */
+export class CaptureButton extends Component {
+  state = { inProgress: false };
+
+  handleCapture = async () => {
+    this.setState({ inProgress: true });
+    let file = await this.props.getFile();
+    let url = URL.createObjectURL(file);
+    Object.assign(document.createElement('a'), {
+      download: file.name,
+      href: url
+    }).click();
+    URL.revokeObjectURL(url);
+    this.setState({ inProgress: false });
+  };
+
+  render() {
+    return h(
+      Fragment,
+      null,
+      h('input', {
+        type: 'button',
+        id: 'capture',
+        class:
+          'pure-button' + (this.state.inProgress ? ' pure-button-active' : ''),
+        onclick: this.handleCapture,
+        value: `${this.state.inProgress ? '⌛' : '📷'} Capture image`
+      })
+    );
+  }
+}

ui/index.js

@@ -1,10 +1,12 @@
-import { h, render, Component, Fragment } from 'preact';
-import { scheduleOp, start } from './ops.js';
+import { h, render, Component } from 'preact';
+import { CaptureButton } from './capture-button.js';
+import { connect } from './ops.js';
 import { Preview } from './preview.js';
 import { Widget } from './widget.js';
 
 /** @typedef {import('../libapi.mjs').Context} Context */
 /** @typedef {import('../libapi.mjs').Config} Config */
+/** @typedef {import('./ops').Connection} Connection */
 
 let isDebug = new URLSearchParams(location.search).has('debug');
 
@@ -13,38 +15,6 @@ if (isDebug) {
   await import('preact/debug');
 }
 
-/** @extends Component<null, { inProgress: boolean }> */
-class CaptureButton extends Component {
-  state = { inProgress: false };
-
-  handleCapture = async () => {
-    this.setState({ inProgress: true });
-    let file = await scheduleOp(context => context.captureImageAsFile());
-    let url = URL.createObjectURL(file);
-    Object.assign(document.createElement('a'), {
-      download: file.name,
-      href: url
-    }).click();
-    URL.revokeObjectURL(url);
-    this.setState({ inProgress: false });
-  };
-
-  render() {
-    return h(
-      Fragment,
-      null,
-      h('input', {
-        type: 'button',
-        id: 'capture',
-        class:
-          'pure-button' + (this.state.inProgress ? ' pure-button-active' : ''),
-        onclick: this.handleCapture,
-        value: `${this.state.inProgress ? '⌛' : '📷'} Capture image`
-      })
-    );
-  }
-}
-
 /** @typedef {{ type: 'CameraPicker' } | { type: 'Status', message: string } | { type: 'Config', config: Config }} AppState */
 
 const INTERFACE_CLASS = 6; // PTP
@@ -52,37 +22,28 @@ const INTERFACE_SUBCLASS = 1; // MTP
 
 /** @extends Component<null, AppState> */
 class App extends Component {
-  state = /** @type {AppState} */ ({
-    type: 'Status',
-    message: 'Looking for cameras...'
-  });
+  /** @type {Connection} */
+  connection;
 
-  constructor(...args) {
-    super(...args);
-    // @ts-ignore
-    navigator.usb.getDevices().then(devices => {
-      for (let dev of devices) {
-        for (let conf of dev.configurations) {
-          for (let intf of conf.interfaces) {
-            for (let alt of intf.alternates) {
-              if (
-                alt.interfaceClass === INTERFACE_CLASS &&
-                alt.interfaceSubclass === INTERFACE_SUBCLASS
-              ) {
-                return this.connectToCamera();
-              }
-            }
-          }
-        }
-      }
-      this.setState({ type: 'CameraPicker' });
-    });
-    addEventListener('error', ({ message }) => {
+  componentDidMount() {
+    addEventListener('error', ({ message }) =>
       this.setState({
         type: 'Status',
         message: `⚠ ${message}`
-      });
-    });
+      })
+    );
+    addEventListener(
+      'beforeunload',
+      () => {
+        if (!this.connection) return;
+        this.connection.disconnect();
+        this.connection = undefined;
+      },
+      { once: true }
+    );
+    // Try to connect to camera at startup.
+    // If none is found among saved connections, it will fallback to a picker.
+    this.tryToConnectToCamera();
   }
 
   selectDevice = async () => {
@@ -95,22 +56,23 @@ class App extends Component {
         }
       ]
     });
-    this.connectToCamera();
+    await this.tryToConnectToCamera();
   };
 
-  connectToCamera() {
-    start();
+  async tryToConnectToCamera() {
     this.setState({ type: 'Status', message: 'Connecting...' });
-    (async () => {
-      while (true) {
-        await this.refreshConfig();
-        await new Promise(resolve => setTimeout(resolve, 100));
+    try {
+      this.connection = await connect();
+    } catch (e) {
+      console.warn(e);
+      this.setState({ type: 'CameraPicker' });
+      return;
     }
-    })();
-  }
-
-  async refreshConfig() {
-    let config = await scheduleOp(context => context.configToJS());
+    // We should reach this only once.
+    while (this.connection) {
+      let config = await this.connection.schedule(context =>
+        context.configToJS()
+      );
       if (!isDebug) {
         delete config.children.other;
       }
@@ -118,6 +80,8 @@ class App extends Component {
         type: 'Config',
         config
       });
+      await new Promise(resolve => setTimeout(resolve, 100));
+    }
   }
 
   /**
@@ -128,7 +92,7 @@ class App extends Component {
   setValue = async (name, value) => {
     /** @type {Promise<void>} */
     let uiTimeout;
-    await scheduleOp(context => {
+    await this.connection.schedule(context => {
       // This is terrible, yes... but some configs return too quickly before they're actually updated.
       // We want to wait some time before updating the UI in that case, but not block subsequent ops.
       uiTimeout = new Promise(resolve => setTimeout(resolve, 800));
@@ -137,6 +101,12 @@ class App extends Component {
     await uiTimeout;
   };
 
+  capturePreview = () =>
+    this.connection.schedule(context => context.capturePreviewAsBlob());
+
+  captureImage = () =>
+    this.connection.schedule(context => context.captureImageAsFile());
+
   render(/** @type {App['props']} */ props, /** @type {App['state']} */ state) {
     switch (state.type) {
       case 'CameraPicker':
@@ -164,8 +134,7 @@ class App extends Component {
             'div',
             { class: 'pure-u-2-3' },
             h(Preview, {
-              getPreview: () =>
-                scheduleOp(context => context.capturePreviewAsBlob())
+              getPreview: this.capturePreview
             })
           ),
           h(
@@ -174,7 +143,7 @@ class App extends Component {
             h(
               'form',
               { class: 'pure-form pure-form-aligned' },
-              h(CaptureButton, null),
+              h(CaptureButton, { getFile: this.captureImage }),
               h(Widget, { config: state.config, setValue: this.setValue })
             )
           )

ui/ops.js

@@ -2,43 +2,39 @@ 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;
+const ContextPromise = initModule().then(Module => Module.Context);
 
-let started = new Promise(resolve => {
-  start = resolve;
-});
+export async function connect() {
+  let Context = await ContextPromise;
 
-let queue = (async () => {
-  let { Context } = await initModule();
-  await started;
-  let ctx = await new Context();
-  addEventListener('beforeunload', e => {
-    ctx.delete();
-  });
-  return ctx;
-})();
+  let context = await new Context();
 
-/** Schedules an exclusive async operation on the global context.
+  let queue = Promise.resolve();
+
+  /** 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
-    };
-  });
+  function schedule(op) {
+    let res = queue.then(() => op(context));
 
     // Queue should ignore result values as well as errors from singular ops.
-  queue = caughtRes.then(res => res.ctx);
+    queue = res.then(
+      () => {},
+      () => {}
+    );
 
     // Result should contain the unwrapped value or error.
-  return caughtRes.then(res => res.resultPromise);
+    return res;
+  }
+
+  return {
+    schedule,
+    disconnect() {
+      context.delete();
+    }
+  };
 }
+
+/** @typedef {ReturnType<typeof connect> extends Promise<infer Connection> ? Connection : never} Connection */