Improve download_progress example (#283)

* Add advanced download example

* Rename to task fields and variables

* Cargo fmt advanced_download/src/download.rs

* Add progress bar for advanced download example

* Merge two download examples to single one

* Apply great review suggestions

* Change to url::Url instead of plain String

* Simplify `download_progress` example

* Update `README` of `download_progress` example

Co-authored-by: Héctor Ramón Jiménez <hector0193@gmail.com>

4 files changed, 168 insertions, 81 deletions

diff --git a/examples/download_progress/Cargo.toml b/examples/download_progress/Cargo.toml
index 4b05e7dc..d3c578b1 100644
--- a/examples/download_progress/Cargo.toml
+++ b/examples/download_progress/Cargo.toml
@@ -1,12 +1,12 @@
 [package]
 name = "download_progress"
 version = "0.1.0"
-authors = ["Songtronix <contact@songtronix.com>"]
+authors = ["Songtronix <contact@songtronix.com>", "Folyd <lyshuhow@gmail.com>"]
 edition = "2018"
 publish = false
 
 [dependencies]
-iced = { path = "../..", features = ["tokio_old"] }
+iced = { path = "../..", features = ["tokio"] }
 iced_native = { path = "../../native" }
 iced_futures = { path = "../../futures" }
-reqwest = "0.10"
+reqwest = "0.11"
diff --git a/examples/download_progress/README.md b/examples/download_progress/README.md
index c606c5f9..7999ce94 100644
--- a/examples/download_progress/README.md
+++ b/examples/download_progress/README.md
@@ -1,6 +1,6 @@
 ## Download progress
 
-A basic application that asynchronously downloads a dummy file of 100 MB and tracks the download progress.
+A basic application that asynchronously downloads multiple dummy files of 100 MB and tracks the download progress.
 
 The example implements a custom `Subscription` in the __[`download`](src/download.rs)__ module. This subscription downloads and produces messages that can be used to keep track of its progress.
 
diff --git a/examples/download_progress/src/download.rs b/examples/download_progress/src/download.rs
index f46a01f7..08805f13 100644
--- a/examples/download_progress/src/download.rs
+++ b/examples/download_progress/src/download.rs
@@ -1,37 +1,46 @@
 use iced_futures::futures;
+use std::hash::{Hash, Hasher};
 
 // Just a little utility function
-pub fn file<T: ToString>(url: T) -> iced::Subscription<Progress> {
+pub fn file<I: 'static + Hash + Copy + Send, T: ToString>(
+    id: I,
+    url: T,
+) -> iced::Subscription<(I, Progress)> {
     iced::Subscription::from_recipe(Download {
+        id,
         url: url.to_string(),
     })
 }
 
-pub struct Download {
+pub struct Download<I> {
+    id: I,
     url: String,
 }
 
 // Make sure iced can use our download stream
-impl<H, I> iced_native::subscription::Recipe<H, I> for Download
+impl<H, I, T> iced_native::subscription::Recipe<H, I> for Download<T>
 where
-    H: std::hash::Hasher,
+    T: 'static + Hash + Copy + Send,
+    H: Hasher,
 {
-    type Output = Progress;
+    type Output = (T, Progress);
 
     fn hash(&self, state: &mut H) {
-        use std::hash::Hash;
+        struct Marker;
+        std::any::TypeId::of::<Marker>().hash(state);
 
-        std::any::TypeId::of::<Self>().hash(state);
-        self.url.hash(state);
+        self.id.hash(state);
     }
 
     fn stream(
         self: Box<Self>,
         _input: futures::stream::BoxStream<'static, I>,
     ) -> futures::stream::BoxStream<'static, Self::Output> {
+        let id = self.id;
+
         Box::pin(futures::stream::unfold(
             State::Ready(self.url),
-            |state| async move {
+            move |state| async move {
                 match state {
                     State::Ready(url) => {
                         let response = reqwest::get(&url).await;
@@ -40,7 +49,7 @@ where
                             Ok(response) => {
                                 if let Some(total) = response.content_length() {
                                     Some((
-                                        Progress::Started,
+                                        (id, Progress::Started),
                                         State::Downloading {
                                             response,
                                             total,
@@ -48,11 +57,14 @@ where
                                         },
                                     ))
                                 } else {
-                                    Some((Progress::Errored, State::Finished))
+                                    Some((
+                                        (id, Progress::Errored),
+                                        State::Finished,
+                                    ))
                                 }
                             }
                             Err(_) => {
-                                Some((Progress::Errored, State::Finished))
+                                Some(((id, Progress::Errored), State::Finished))
                             }
                         }
                     }
@@ -68,7 +80,7 @@ where
                                 (downloaded as f32 / total as f32) * 100.0;
 
                             Some((
-                                Progress::Advanced(percentage),
+                                (id, Progress::Advanced(percentage)),
                                 State::Downloading {
                                     response,
                                     total,
@@ -76,8 +88,12 @@ where
                                 },
                             ))
                         }
-                        Ok(None) => Some((Progress::Finished, State::Finished)),
-                        Err(_) => Some((Progress::Errored, State::Finished)),
+                        Ok(None) => {
+                            Some(((id, Progress::Finished), State::Finished))
+                        }
+                        Err(_) => {
+                            Some(((id, Progress::Errored), State::Finished))
+                        }
                     },
                     State::Finished => {
                         // We do not let the stream die, as it would start a
diff --git a/examples/download_progress/src/main.rs b/examples/download_progress/src/main.rs
index 77b01354..cd024926 100644
--- a/examples/download_progress/src/main.rs
+++ b/examples/download_progress/src/main.rs
@@ -10,17 +10,17 @@ pub fn main() -> iced::Result {
 }
 
 #[derive(Debug)]
-enum Example {
-    Idle { button: button::State },
-    Downloading { progress: f32 },
-    Finished { button: button::State },
-    Errored { button: button::State },
+struct Example {
+    downloads: Vec<Download>,
+    last_id: usize,
+    add: button::State,
 }
 
 #[derive(Debug, Clone)]
 pub enum Message {
-    Download,
-    DownloadProgressed(download::Progress),
+    Add,
+    Download(usize),
+    DownloadProgressed((usize, download::Progress)),
 }
 
 impl Application for Example {
@@ -30,8 +30,10 @@ impl Application for Example {
 
     fn new(_flags: ()) -> (Example, Command<Message>) {
         (
-            Example::Idle {
-                button: button::State::new(),
+            Example {
+                downloads: vec![Download::new(0)],
+                last_id: 0,
+                add: button::State::new(),
             },
             Command::none(),
         )
@@ -43,102 +45,171 @@ impl Application for Example {
 
     fn update(&mut self, message: Message) -> Command<Message> {
         match message {
-            Message::Download => match self {
-                Example::Idle { .. }
-                | Example::Finished { .. }
-                | Example::Errored { .. } => {
-                    *self = Example::Downloading { progress: 0.0 };
+            Message::Add => {
+                self.last_id = self.last_id + 1;
+
+                self.downloads.push(Download::new(self.last_id));
+            }
+            Message::Download(index) => {
+                if let Some(download) = self.downloads.get_mut(index) {
+                    download.start();
                 }
-                _ => {}
-            },
-            Message::DownloadProgressed(message) => match self {
-                Example::Downloading { progress } => match message {
-                    download::Progress::Started => {
-                        *progress = 0.0;
-                    }
-                    download::Progress::Advanced(percentage) => {
-                        *progress = percentage;
-                    }
-                    download::Progress::Finished => {
-                        *self = Example::Finished {
-                            button: button::State::new(),
-                        }
-                    }
-                    download::Progress::Errored => {
-                        *self = Example::Errored {
-                            button: button::State::new(),
-                        };
-                    }
-                },
-                _ => {}
-            },
+            }
+            Message::DownloadProgressed((id, progress)) => {
+                if let Some(download) =
+                    self.downloads.iter_mut().find(|download| download.id == id)
+                {
+                    download.progress(progress);
+                }
+            }
         };
 
         Command::none()
     }
 
     fn subscription(&self) -> Subscription<Message> {
-        match self {
-            Example::Downloading { .. } => {
-                download::file("https://speed.hetzner.de/100MB.bin")
+        Subscription::batch(self.downloads.iter().map(Download::subscription))
+    }
+
+    fn view(&mut self) -> Element<Message> {
+        let downloads = self
+            .downloads
+            .iter_mut()
+            .fold(Column::new().spacing(20), |column, download| {
+                column.push(download.view())
+            })
+            .push(
+                Button::new(&mut self.add, Text::new("Add another download"))
+                    .on_press(Message::Add)
+                    .padding(10),
+            )
+            .align_items(Align::End);
+
+        Container::new(downloads)
+            .width(Length::Fill)
+            .height(Length::Fill)
+            .center_x()
+            .center_y()
+            .padding(20)
+            .into()
+    }
+}
+
+#[derive(Debug)]
+struct Download {
+    id: usize,
+    state: State,
+}
+
+#[derive(Debug)]
+enum State {
+    Idle { button: button::State },
+    Downloading { progress: f32 },
+    Finished { button: button::State },
+    Errored { button: button::State },
+}
+
+impl Download {
+    pub fn new(id: usize) -> Self {
+        Download {
+            id,
+            state: State::Idle {
+                button: button::State::new(),
+            },
+        }
+    }
+
+    pub fn start(&mut self) {
+        match self.state {
+            State::Idle { .. }
+            | State::Finished { .. }
+            | State::Errored { .. } => {
+                self.state = State::Downloading { progress: 0.0 };
+            }
+            _ => {}
+        }
+    }
+
+    pub fn progress(&mut self, new_progress: download::Progress) {
+        match &mut self.state {
+            State::Downloading { progress } => match new_progress {
+                download::Progress::Started => {
+                    *progress = 0.0;
+                }
+                download::Progress::Advanced(percentage) => {
+                    *progress = percentage;
+                }
+                download::Progress::Finished => {
+                    self.state = State::Finished {
+                        button: button::State::new(),
+                    }
+                }
+                download::Progress::Errored => {
+                    self.state = State::Errored {
+                        button: button::State::new(),
+                    };
+                }
+            },
+            _ => {}
+        }
+    }
+
+    pub fn subscription(&self) -> Subscription<Message> {
+        match self.state {
+            State::Downloading { .. } => {
+                download::file(self.id, "https://speed.hetzner.de/100MB.bin?")
                     .map(Message::DownloadProgressed)
             }
             _ => Subscription::none(),
         }
     }
 
-    fn view(&mut self) -> Element<Message> {
-        let current_progress = match self {
-            Example::Idle { .. } => 0.0,
-            Example::Downloading { progress } => *progress,
-            Example::Finished { .. } => 100.0,
-            Example::Errored { .. } => 0.0,
+    pub fn view(&mut self) -> Element<Message> {
+        let current_progress = match &self.state {
+            State::Idle { .. } => 0.0,
+            State::Downloading { progress } => *progress,
+            State::Finished { .. } => 100.0,
+            State::Errored { .. } => 0.0,
         };
 
         let progress_bar = ProgressBar::new(0.0..=100.0, current_progress);
 
-        let control: Element<_> = match self {
-            Example::Idle { button } => {
+        let control: Element<_> = match &mut self.state {
+            State::Idle { button } => {
                 Button::new(button, Text::new("Start the download!"))
-                    .on_press(Message::Download)
+                    .on_press(Message::Download(self.id))
                     .into()
             }
-            Example::Finished { button } => Column::new()
+            State::Finished { button } => Column::new()
                 .spacing(10)
                 .align_items(Align::Center)
                 .push(Text::new("Download finished!"))
                 .push(
                     Button::new(button, Text::new("Start again"))
-                        .on_press(Message::Download),
+                        .on_press(Message::Download(self.id)),
                 )
                 .into(),
-            Example::Downloading { .. } => {
+            State::Downloading { .. } => {
                 Text::new(format!("Downloading... {:.2}%", current_progress))
                     .into()
             }
-            Example::Errored { button } => Column::new()
+            State::Errored { button } => Column::new()
                 .spacing(10)
                 .align_items(Align::Center)
                 .push(Text::new("Something went wrong :("))
                 .push(
                     Button::new(button, Text::new("Try again"))
-                        .on_press(Message::Download),
+                        .on_press(Message::Download(self.id)),
                 )
                 .into(),
         };
 
-        let content = Column::new()
+        Column::new()
             .spacing(10)
             .padding(10)
             .align_items(Align::Center)
             .push(progress_bar)
-            .push(control);
-
-        Container::new(content)
-            .width(Length::Fill)
-            .height(Length::Fill)
-            .center_x()
-            .center_y()
+            .push(control)
             .into()
     }
 }