Make `Command` implementations platform-specific

This allows us to introduce a platform-specific `Action` to both `iced_native`
and `iced_web` and remove the `Clipboard` from `Application::update` to maintain
purity.

Additionally, this should let us implement further actions to let users query
and modify the shell environment (e.g. window, clipboard, and more!)

4 files changed, 125 insertions, 40 deletions

diff --git a/web/src/clipboard.rs b/web/src/clipboard.rs
deleted file mode 100644
index 167a1e53..00000000
--- a/web/src/clipboard.rs
+++ /dev/null
@@ -1,21 +0,0 @@
-/// A buffer for short-term storage and transfer within and between
-/// applications.
-#[derive(Debug, Clone, Copy)]
-pub struct Clipboard;
-
-impl Clipboard {
-    /// Creates a new [`Clipboard`].
-    pub fn new() -> Self {
-        Self
-    }
-
-    /// Reads the current content of the [`Clipboard`] as text.
-    pub fn read(&self) -> Option<String> {
-        unimplemented! {}
-    }
-
-    /// Writes the given text contents to the [`Clipboard`].
-    pub fn write(&mut self, _contents: String) {
-        unimplemented! {}
-    }
-}
diff --git a/web/src/command.rs b/web/src/command.rs
new file mode 100644
index 00000000..606097de
--- /dev/null
+++ b/web/src/command.rs
@@ -0,0 +1,77 @@
+mod action;
+
+pub use action::Action;
+
+#[cfg(target_arch = "wasm32")]
+use std::future::Future;
+
+/// A set of asynchronous actions to be performed by some runtime.
+pub enum Command<T> {
+    None,
+    Single(Action<T>),
+    Batch(Vec<Action<T>>),
+}
+
+impl<T> Command<T> {
+    /// Creates an empty [`Command`].
+    ///
+    /// In other words, a [`Command`] that does nothing.
+    pub fn none() -> Self {
+        Self::None
+    }
+
+    /// Creates a [`Command`] that performs the action of the given future.
+    #[cfg(target_arch = "wasm32")]
+    pub fn perform<A>(
+        future: impl Future<Output = T> + 'static,
+        f: impl Fn(T) -> A + 'static + Send,
+    ) -> Command<A> {
+        use iced_futures::futures::FutureExt;
+
+        Command::Single(Action::Future(Box::pin(future.map(f))))
+    }
+
+    /// Applies a transformation to the result of a [`Command`].
+    #[cfg(target_arch = "wasm32")]
+    pub fn map<A>(mut self, f: impl Fn(T) -> A + 'static + Clone) -> Command<A>
+    where
+        T: 'static,
+    {
+        match self {
+            Self::None => Command::None,
+            Self::Single(action) => Command::Single(action.map(f)),
+            Self::Batch(batch) => Command::Batch(
+                batch
+                    .into_iter()
+                    .map(|action| action.map(f.clone()))
+                    .collect(),
+            ),
+        }
+    }
+
+    /// Creates a [`Command`] that performs the actions of all the given
+    /// commands.
+    ///
+    /// Once this command is run, all the commands will be executed at once.
+    pub fn batch(commands: impl IntoIterator<Item = Command<T>>) -> Self {
+        let mut batch = Vec::new();
+
+        for command in commands {
+            match command {
+                Self::None => {}
+                Self::Single(command) => batch.push(command),
+                Self::Batch(commands) => batch.extend(commands),
+            }
+        }
+
+        Self::Batch(batch)
+    }
+
+    pub fn actions(self) -> Vec<Action<T>> {
+        match self {
+            Self::None => Vec::new(),
+            Self::Single(action) => vec![action],
+            Self::Batch(batch) => batch,
+        }
+    }
+}
diff --git a/web/src/command/action.rs b/web/src/command/action.rs
new file mode 100644
index 00000000..cf384f07
--- /dev/null
+++ b/web/src/command/action.rs
@@ -0,0 +1,18 @@
+pub enum Action<T> {
+    Future(iced_futures::BoxFuture<T>),
+}
+
+impl<T> Action<T> {
+    /// Applies a transformation to the result of a [`Command`].
+    #[cfg(target_arch = "wasm32")]
+    pub fn map<A>(self, f: impl Fn(T) -> A + 'static) -> Action<A>
+    where
+        T: 'static,
+    {
+        use iced_futures::futures::FutureExt;
+
+        match self {
+            Self::Future(future) => Action::Future(Box::pin(future.map(f))),
+        }
+    }
+}
diff --git a/web/src/lib.rs b/web/src/lib.rs
index bb09bb0d..ec2bd178 100644
--- a/web/src/lib.rs
+++ b/web/src/lib.rs
@@ -50,8 +50,8 @@
 //! [`wasm-pack`]: https://github.com/rustwasm/wasm-pack
 //! [`wasm-bindgen`]: https://github.com/rustwasm/wasm-bindgen
 //! [`tour` example]: https://github.com/hecrj/iced/tree/0.3/examples/tour
-#![deny(missing_docs)]
-#![deny(missing_debug_implementations)]
+//#![deny(missing_docs)]
+//#![deny(missing_debug_implementations)]
 #![deny(unused_results)]
 #![forbid(unsafe_code)]
 #![forbid(rust_2018_idioms)]
@@ -59,7 +59,7 @@ use dodrio::bumpalo;
 use std::{cell::RefCell, rc::Rc};
 
 mod bus;
-mod clipboard;
+mod command;
 mod element;
 mod hasher;
 
@@ -68,7 +68,7 @@ pub mod subscription;
 pub mod widget;
 
 pub use bus::Bus;
-pub use clipboard::Clipboard;
+pub use command::Command;
 pub use css::Css;
 pub use dodrio;
 pub use element::Element;
@@ -77,7 +77,7 @@ pub use iced_core::{
     keyboard, menu, mouse, Align, Background, Color, Font, HorizontalAlignment,
     Length, Menu, Padding, Point, Rectangle, Size, Vector, VerticalAlignment,
 };
-pub use iced_futures::{executor, futures, Command};
+pub use iced_futures::{executor, futures};
 pub use subscription::Subscription;
 
 #[doc(no_inline)]
@@ -128,11 +128,7 @@ pub trait Application {
     /// this method.
     ///
     /// Any [`Command`] returned will be executed immediately in the background.
-    fn update(
-        &mut self,
-        message: Self::Message,
-        clipboard: &mut Clipboard,
-    ) -> Command<Self::Message>;
+    fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
 
     /// Returns the widgets to display in the [`Application`].
     ///
@@ -162,8 +158,6 @@ pub trait Application {
         let document = window.document().unwrap();
         let body = document.body().unwrap();
 
-        let mut clipboard = Clipboard::new();
-
         let (sender, receiver) =
             iced_futures::futures::channel::mpsc::unbounded();
 
@@ -177,7 +171,7 @@ pub trait Application {
         let mut title = app.title();
         document.set_title(&title);
 
-        runtime.spawn(command);
+        run_command(command, &mut runtime);
 
         let application = Rc::new(RefCell::new(app));
 
@@ -190,8 +184,7 @@ pub trait Application {
 
         let event_loop = receiver.for_each(move |message| {
             let (command, subscription) = runtime.enter(|| {
-                let command =
-                    application.borrow_mut().update(message, &mut clipboard);
+                let command = application.borrow_mut().update(message);
                 let subscription = application.borrow().subscription();
 
                 (command, subscription)
@@ -199,7 +192,7 @@ pub trait Application {
 
             let new_title = application.borrow().title();
 
-            runtime.spawn(command);
+            run_command(command, &mut runtime);
             runtime.track(subscription);
 
             if title != new_title {
@@ -350,8 +343,7 @@ pub trait Embedded {
         );
 
         let (app, command) = runtime.enter(|| Self::new(flags));
-
-        runtime.spawn(command);
+        run_command(command, &mut runtime);
 
         let application = Rc::new(RefCell::new(app));
 
@@ -370,7 +362,7 @@ pub trait Embedded {
                 (command, subscription)
             });
 
-            runtime.spawn(command);
+            run_command(command, &mut runtime);
             runtime.track(subscription);
 
             vdom.weak().schedule_render();
@@ -382,6 +374,25 @@ pub trait Embedded {
     }
 }
 
+fn run_command<Message: 'static + Send, E: Executor>(
+    command: Command<Message>,
+    runtime: &mut iced_futures::Runtime<
+        Hasher,
+        (),
+        E,
+        iced_futures::futures::channel::mpsc::UnboundedSender<Message>,
+        Message,
+    >,
+) {
+    for action in command.actions() {
+        match action {
+            command::Action::Future(future) => {
+                runtime.spawn(future);
+            }
+        }
+    }
+}
+
 struct EmbeddedInstance<A: Embedded> {
     application: Rc<RefCell<A>>,
     bus: Bus<A::Message>,