Expose a JavaScript command API for the browser app (#1713)

Thanks @olup.

apps/solidcraft-web/src/api.rs

@@ -0,0 +1,131 @@
+//! Promise-based access to the running app's existing control channel.
+
+use std::cell::RefCell;
+use std::rc::Rc;
+use std::sync::mpsc::{Receiver, Sender, TryRecvError};
+use std::time::Duration;
+
+use serde_json::{Value, json};
+use solidcraft_ui_egui::ControlRequest;
+use wasm_bindgen::{JsValue, closure::Closure};
+
+const MAX_PENDING: usize = 256;
+const MAX_JSON_BYTES: usize = 16 * 1024 * 1024;
+
+struct Pending {
+    reply: Receiver<Value>,
+    resolve: js_sys::Function,
+    reject: js_sys::Function,
+}
+
+#[derive(Clone)]
+pub struct Api {
+    sender: Sender<ControlRequest>,
+    pending: Rc<RefCell<Vec<Pending>>>,
+    ctx: egui::Context,
+}
+
+fn params(value: &JsValue) -> Result<Value, String> {
+    if value.is_undefined() || value.is_null() {
+        return Ok(json!({}));
+    }
+    let text = js_sys::JSON::stringify(value).ok().and_then(|v| v.as_string()).ok_or("params must be JSON serializable")?;
+    if text.len() > MAX_JSON_BYTES {
+        return Err("params exceed 16 MiB".into());
+    }
+    serde_json::from_str(&text).map_err(|e| format!("invalid params: {e}"))
+}
+
+fn error(message: &str) -> JsValue {
+    js_sys::Error::new(message).into()
+}
+
+impl Api {
+    pub fn install(sender: Sender<ControlRequest>, ctx: egui::Context) -> Result<Self, JsValue> {
+        let api = Self { sender, pending: Rc::default(), ctx };
+        let object = js_sys::Object::new();
+        let request = api.clone();
+        let execute = api.clone();
+        let commands = api.clone();
+        let inspect = api.clone();
+        for (name, function) in [
+            (
+                "request",
+                Closure::<dyn Fn(String, JsValue) -> js_sys::Promise>::new(move |method: String, value: JsValue| {
+                    request.request(&method, params(&value))
+                })
+                .into_js_value(),
+            ),
+            (
+                "execute",
+                Closure::<dyn Fn(String, JsValue) -> js_sys::Promise>::new(move |command: String, value: JsValue| {
+                    execute.request("engine.execute", params(&value).map(|p| json!({"command": command, "params": p})))
+                })
+                .into_js_value(),
+            ),
+            ("commands", Closure::<dyn Fn() -> js_sys::Promise>::new(move || commands.request("engine.commands", Ok(json!({})))).into_js_value()),
+            (
+                "inspect",
+                Closure::<dyn Fn(JsValue) -> js_sys::Promise>::new(move |value: JsValue| inspect.request("document.inspect", params(&value)))
+                    .into_js_value(),
+            ),
+        ] {
+            js_sys::Reflect::set(&object, &name.into(), &function)?;
+        }
+        let window = web_sys::window().ok_or_else(|| error("no window"))?;
+        js_sys::Reflect::set(&window, &"solidcraft".into(), &object)?;
+        Ok(api)
+    }
+
+    fn request(&self, method: &str, params: Result<Value, String>) -> js_sys::Promise {
+        let params = match params {
+            Ok(params) => params,
+            Err(message) => return js_sys::Promise::reject(&error(&message)),
+        };
+        if self.pending.borrow().len() >= MAX_PENDING {
+            return js_sys::Promise::reject(&error("too many pending SolidCraft requests (maximum 256)"));
+        }
+        js_sys::Promise::new(&mut |resolve, reject| {
+            let (request, reply) = ControlRequest::new(method, params.clone());
+            if self.sender.send(request).is_err() {
+                let _ = reject.call1(&JsValue::UNDEFINED, &error("SolidCraft is not running"));
+                return;
+            }
+            self.pending.borrow_mut().push(Pending { reply, resolve, reject });
+            self.ctx.request_repaint();
+        })
+    }
+
+    pub fn poll(&self) {
+        let mut completed = Vec::new();
+        self.pending.borrow_mut().retain_mut(|pending| {
+            let result = match pending.reply.try_recv() {
+                Ok(reply) => {
+                    if reply.get("ok").and_then(Value::as_bool) == Some(true) {
+                        js_sys::JSON::parse(&reply.get("result").unwrap_or(&Value::Null).to_string())
+                    } else {
+                        Err(error(reply.get("error").and_then(Value::as_str).unwrap_or("SolidCraft request failed")))
+                    }
+                }
+                Err(TryRecvError::Empty) => return true,
+                Err(TryRecvError::Disconnected) => Err(error("SolidCraft request dropped")),
+            };
+            completed.push((pending.resolve.clone(), pending.reject.clone(), result));
+            false
+        });
+        // Release the queue before calling JavaScript, which can submit another request.
+        for (resolve, reject, result) in completed {
+            match result {
+                Ok(value) => {
+                    let _ = resolve.call1(&JsValue::UNDEFINED, &value);
+                }
+                Err(error) => {
+                    let _ = reject.call1(&JsValue::UNDEFINED, &error);
+                }
+            }
+        }
+        if !self.pending.borrow().is_empty() {
+            self.ctx.request_repaint_after(Duration::from_millis(16));
+        }
+    }
+}