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TodoMVC - Routing

Routing

Routing is required for all implementations. If supported by the framework, use its built-in capabilities. Otherwise, use the Flatiron Director routing library located in the /assets folder. The following routes should be implemented: #/ (all - default), #/active and #/completed (#!/ is also allowed). When the route changes, the todo list should be filtered on a model level and the selected class on the filter links should be toggled. When an item is updated while in a filtered state, it should be updated accordingly. E.g. if the filter is Active and the item is checked, it should be hidden. Make sure the active filter is persisted on reload.

1. view updates

Let's implement proper filter handling in our view functions. (We could do it in the chapter View, however it's better to do it now to refresh you memories - it'll help you to understand routing integration faster.)

fn view(model: &Model) -> Vec<Node<Msg>> {
    ...
            view_main(&model.todos, model.selected_todo.as_ref(), model.filter),
...

fn view_main(todos: &BTreeMap<Ulid, Todo>, selected_todo: Option<&SelectedTodo>, filter: Filter) -> Node<Msg> {
    ...
        view_todo_list(todos, selected_todo, filter),
...

fn view_todo_list(todos: &BTreeMap<Ulid, Todo>, selected_todo: Option<&SelectedTodo>, filter: Filter) -> Node<Msg> {
    let todos = todos.values().filter(|todo| {
        match filter {
            Filter::All => true,
            Filter::Active => not(todo.completed),
            Filter::Completed => todo.completed,
        }
    });
    ul![C!["todo-list"],
        todos.map(|todo| {
...

2. init Url

There is a hard-coded default filter Filter::All in our app. Let's choose the right filter in init function according to the url that is present when the app is starting.

fn init(mut url: Url, _: &mut impl Orders<Msg>) -> Model {
    // TODO: Remove
    log!(url);

    let filter = match url.next_hash_path_part(){
        Some("active") => Filter::Active,
        Some("completed") => Filter::Completed,
        _ => Filter::All,
    };

    // TODO: Remove
    log!(url);

    Model {
        ...
        filter,
        ...
    }
}

Update the code in your app and then go to localhost:8000/#/active and look at the console log. You should see:

Url {
    next_path_part_index: 0,
    next_hash_path_part_index: 0,
    path: [],
    hash_path: [
        "active",
    ],
    hash: Some(
        "/active",
    ),
    search: UrlSearch {
        search: {},
        invalid_components: [],
    },
    invalid_components: [],
}
Url {
    next_path_part_index: 0,
    next_hash_path_part_index: 1,
    path: [],
    hash_path: [
        "active",
    ],
    hash: Some(
        "/active",
    ),
    search: UrlSearch {
        search: {},
        invalid_components: [],
    },
    invalid_components: [],
}

Interesting parts are:

    next_hash_path_part_index: 0, // then changed to 1
    hash_path: [
        "active",
    ],
    hash: Some(
        "/active",
    ),

There are two similar fields - hash_path and hash. One field - hash - would be enough however Seed would need to parse hash too often into Vec and you wouldn't be able to see parsed hash in log! to debug your routing. And we can't use only hash_path because hash is often used for non-routing stuff.

Combination hash_path and next_hash_path_part_index simulates a trivial Iterator - when you call url.next_hash_path_part():

  1. The path part (item in hash_path) at the position next_hash_path_part_index is returned (or None)
  2. next_hash_path_part_index is incremented.

Because of that incrementation, url has to be mutable - fn init(mut url: Url, ...

Seed API design decision: Once your app is big enough and there are many pages and nested paths, your router becomes unreadable and hard to maintain. That's the time when you want to handle each path part in the associated page and pass url into the nested handlers. Then you'll appreciate that url keeps its internal "iterator" states and you don't have to pass multiple iterators and variables through handlers by yourself.

3. remaining_hash_path_parts

Go to localhost:8000/#/active/foo/bar. Active filter is activated. It isn't expected behaviour in the most cases. App should show something like "404 Page Not Found" or at least ignore it to prevent future conflicts when e.g. /active/foo becomes a valid standalone page.

There are two solutions:

  1. Make sure there aren't any other path parts after the first one:

    let filter = match url.next_hash_path_part(){
    Some("active") => {
        if url.next_hash_path_part().is_none() {
            Filter::Active
        } else {
            Filter::All
        }
    }
    ...

  2. Match all path parts at once:

    let filter = match url.remaining_hash_path_parts().as_slice() {
    ["active"] => Filter::Active,
    ["completed"] => Filter::Completed,
    _ => Filter::All,
};

    • remaining_hash_path_parts() increments next_hash_path_part_index in the loop until it points to a non-existent item and returns references to all iterated items. It's similar to collect.

      • Example: remaining_hash_path_parts() returns vec!["active", "foo", "bar"] for url /#/active/foo/bar if you haven't called url.next_hash_path_part() before (i.e. if "iterator" starts from 0).

    • .as_slice() call is basically a leaked implementation detail because Rust can't pattern match on Vec and we can't return a reference to that Vec, too.

    • I recommend to study Rust pattern matching. There are many useful features, see e.g.:

      match url.remaining_hash_path_parts().as_slice() {
    [] => Page::Home,
    ["report", rest @ ..] => {
        match rest {
            ["day"] => Page::ReportDay,
            _ => Page::ReportWeek,
        }
    },
    _ => Page::NotFound,
}

P.S. You can remove both log!(url); now. If you can play more with Url, run the example url.

4. Subscriptions

Let's try to add this one line:

fn init(mut url: Url, orders: &mut impl Orders<Msg>) -> Model {
    orders.subscribe(|_: subs::UrlChanged| log!("url changed!"));

Update your code & refresh the browser tab. Then click the filter buttons and you should see "url changed!" in your console log.

Let's add another line:

orders
    .subscribe(|_: subs::UrlChanged| log!("url changed!"))
    .notify(subs::UrlChanged(url.clone()));

Now you don't have to even click the buttons - there is "url changed!" in the console log just after the app start!

There is no magic - Seed just matches notifications and subscriptions by type. You can write something like:

orders
    .subscribe(|_: i32| log!("a number!"))
    .subscribe(|_: i32| log!("a number!"))
    .notify(123);

and it would work the same. As you can see, you can write multiple subscriptions - that's why the type of sent variables has to implement Clone.

Let's return to UrlChanged. Please change your init code again:

orders.subscribe(|subs::UrlChanged(url)| log!(url));

Rust supports pattern matching also in closure parameters. Another important fact is that this closure behaves like a regular event handler - the output value can be () or Option<Msg> or Msg. We can leverage that fact and write just:

orders.subscribe(Msg::UrlChanged);

The message will be handled by our "old" code in the update function:

fn update(msg: Msg, model: &mut Model, orders: &mut impl Orders<Msg>) {
    match msg {
        Msg::UrlChanged(subs::UrlChanged(url)) => {
            log!("UrlChanged", url);
        }
...

P.S.

  • If you want to play more with subscriptions, run the example subscribe.

  • Keep in mind there is no magic - subscribe, stream, notify, UrlChanged, etc. work the same - Seed or user creates a notification (basically any item) and Seed's or user's subscriptions (closures) handle it.

  • Notify/Subscriptions mechanism in Seed is implemented with the help of any.

5. Handle UrlChanged

Let's write proper Msg::UrlChanged handling. We'll start by copy-pasting the code from init function:

fn update(msg: Msg, model: &mut Model, orders: &mut impl Orders<Msg>) {
    match msg {
        Msg::UrlChanged(subs::UrlChanged(mut url)) => {
            model.filter = match url.remaining_hash_path_parts().as_slice() {
                ["active"] => Filter::Active,
                ["completed"] => Filter::Completed,
                _ => Filter::All,
...

Try to click filter buttons in your browser. Yahoo! Our app should be feature-complete now, everything else is basically refactor...

We want to respect DRY principle and idiomatic Rust so let's implement trait From for Filter and update the code:

fn init(url: Url, orders: &mut impl Orders<Msg>) -> Model {
    orders.subscribe(Msg::UrlChanged);

    Model {
        ...
        filter: Filter::from(url),
        ...
    }
}
...

// ------ Filter ------

#[derive(Copy, Clone, Eq, PartialEq, EnumIter)]
enum Filter {
   All,
   Active,
   Completed,
}

impl From<Url> for Filter {
    fn from(mut url: Url) -> Self {
        match url.remaining_hash_path_parts().as_slice() {
            ["active"] => Self::Active,
            ["completed"] => Self::Completed,
            _ => Self::All,
        }
    }
}

...

fn update(msg: Msg, model: &mut Model, orders: &mut impl Orders<Msg>) {
    match msg {
        Msg::UrlChanged(subs::UrlChanged(url)) => {
            model.filter = Filter::from(url);
        }
...

Tips:

  • Do NOT respect DRY at all costs - it often leads to cumbersome abstractions and tight coupling. And writing abstraction is always much easier than removing it later. See Rule of three.

  • Do NOT try to implement as many standard Rust traits as possible. We decided to implement From for Filter because we are sure it makes perfect sense in our case. If you are not sure, write only Filter::new and implement From only when necessary.

  • Write Filter::from(url) instead of url.into(). The former one is much more expressive. You'll appreciate it once you use a type with many From implementation - especially in places with limited readable context like function calls: foo(url.into()) vs foo(Filter::from(url)).

We'll refactor our filter links in the next chapter.

Our complete
lib.rs
#![allow(clippy::wildcard_imports)]
// TODO: Remove
#![allow(dead_code, unused_variables)]

use seed::{prelude::*, *};

use std::collections::BTreeMap;
use std::mem;
use std::convert::TryFrom;

use serde::{Deserialize, Serialize};
use strum_macros::EnumIter;
use strum::IntoEnumIterator;
use ulid::Ulid;

const ENTER_KEY: &str = "Enter";
const ESCAPE_KEY: &str = "Escape";

const STORAGE_KEY: &str = "todos-seed";

// ------ ------
//     Init
// ------ ------

fn init(url: Url, orders: &mut impl Orders<Msg>) -> Model {
    orders.subscribe(Msg::UrlChanged);

    Model {
        todos: LocalStorage::get(STORAGE_KEY).unwrap_or_default(),
        new_todo_title: String::new(),
        selected_todo: None,
        filter: Filter::from(url),
        base_url: Url::new(),
    }
}

// ------ ------
//     Model
// ------ ------

struct Model {
    todos: BTreeMap<Ulid, Todo>,
    new_todo_title: String,
    selected_todo: Option<SelectedTodo>,
    filter: Filter,
    base_url: Url,
}

#[derive(Deserialize, Serialize)]
struct Todo {
    id: Ulid,
    title: String,
    completed: bool,
}

struct SelectedTodo {
    id: Ulid,
    title: String,
    input_element: ElRef<web_sys::HtmlInputElement>,
}

// ------ Filter ------

#[derive(Copy, Clone, Eq, PartialEq, EnumIter)]
enum Filter {
   All,
   Active,
   Completed,
}

impl From<Url> for Filter {
    fn from(mut url: Url) -> Self {
        match url.remaining_hash_path_parts().as_slice() {
            ["active"] => Self::Active,
            ["completed"] => Self::Completed,
            _ => Self::All,
        }
    }
}

// ------ ------
//    Update
// ------ ------

enum Msg {
    UrlChanged(subs::UrlChanged),
    NewTodoTitleChanged(String),
 
    // ------ Basic Todo operations ------

    CreateTodo,
    ToggleTodo(Ulid),
    RemoveTodo(Ulid),
    
    // ------ Bulk operations ------

    CheckOrUncheckAll,
    ClearCompleted,
    
    // ------ Selection ------
    
    SelectTodo(Option<Ulid>),
    SelectedTodoTitleChanged(String),
    SaveSelectedTodo,
 }

fn update(msg: Msg, model: &mut Model, orders: &mut impl Orders<Msg>) {
    match msg {
        Msg::UrlChanged(subs::UrlChanged(url)) => {
            model.filter = Filter::from(url);
        }
        Msg::NewTodoTitleChanged(title) => {
            model.new_todo_title = title;
        }
     
        // ------ Basic Todo operations ------

        Msg::CreateTodo => {
            let title = model.new_todo_title.trim();
            if not(title.is_empty()) {
                let id = Ulid::new();
                model.todos.insert(id, Todo {
                    id,
                    title: title.to_owned(),
                    completed: false,
                });
                model.new_todo_title.clear();
            }
        }
        Msg::ToggleTodo(id) => {
            if let Some(todo) = model.todos.get_mut(&id) {
                todo.completed = not(todo.completed);
            }
        }
        Msg::RemoveTodo(id) => {
            model.todos.remove(&id);
        }
        
        // ------ Bulk operations ------

        Msg::CheckOrUncheckAll => {
            let all_checked = model.todos.values().all(|todo| todo.completed);
            for todo in model.todos.values_mut() {
                todo.completed = not(all_checked);
            }
        }
        Msg::ClearCompleted => {
            // TODO: Refactor with `BTreeMap::drain_filter` once stable.
            model.todos = mem::take(&mut model.todos)
                .into_iter()
                .filter(|(_, todo)| not(todo.completed))
                .collect();
        }
        
        // ------ Selection ------

        Msg::SelectTodo(Some(id)) => {
            if let Some(todo) = model.todos.get(&id) {
                let input_element = ElRef::new();
                
                model.selected_todo = Some(SelectedTodo {
                    id,
                    title: todo.title.clone(),
                    input_element: input_element.clone(),
                });

                let title_length = u32::try_from(todo.title.len()).expect("title length as u32");
                orders.after_next_render(move |_| {
                    let input_element = input_element.get().expect("input_element");

                    input_element
                        .focus()
                        .expect("focus input_element");

                    input_element
                        .set_selection_range(title_length, title_length)
                        .expect("move cursor to the end of input_element");
                });
            }
        },
        Msg::SelectTodo(None) => {
            model.selected_todo = None;
        },
        Msg::SelectedTodoTitleChanged(title) => {
            if let Some(selected_todo) = &mut model.selected_todo {
                selected_todo.title = title;
            }
        },
        Msg::SaveSelectedTodo => {
            if let Some(selected_todo) = model.selected_todo.take() {
                if let Some(todo) = model.todos.get_mut(&selected_todo.id) {
                    todo.title = selected_todo.title;
                }
            }
        }
    }
    LocalStorage::insert(STORAGE_KEY, &model.todos).expect("save todos to LocalStorage");
}

// ------ ------
//     View
// ------ ------

fn view(model: &Model) -> Vec<Node<Msg>> {
    nodes![
        view_header(&model.new_todo_title),
        IF!(not(model.todos.is_empty()) => vec![
            view_main(&model.todos, model.selected_todo.as_ref(), model.filter), 
            view_footer(&model.todos, model.filter),
        ]),
    ]
}

// ------ header ------

fn view_header(new_todo_title: &str) -> Node<Msg> {
    header![C!["header"],
        h1!["todos"],
        input![C!["new-todo"],
            attrs!{
                At::Placeholder => "What needs to be done?", 
                At::AutoFocus => AtValue::None,
                At::Value => new_todo_title,
            },
            input_ev(Ev::Input, Msg::NewTodoTitleChanged),
            keyboard_ev(Ev::KeyDown, |keyboard_event| {
                IF!(keyboard_event.key() == ENTER_KEY => Msg::CreateTodo)
            }),
        ]
    ]
}

// ------ main ------

fn view_main(todos: &BTreeMap<Ulid, Todo>, selected_todo: Option<&SelectedTodo>, filter: Filter) -> Node<Msg> {
    section![C!["main"],
        view_toggle_all(todos),
        view_todo_list(todos, selected_todo, filter),
    ]
}

fn view_toggle_all(todos: &BTreeMap<Ulid, Todo>) -> Vec<Node<Msg>> {
    let all_completed = todos.values().all(|todo| todo.completed);
    vec![
        input![C!["toggle-all"], 
            attrs!{
                At::Id => "toggle-all", At::Type => "checkbox", At::Checked => all_completed.as_at_value()
            },
            ev(Ev::Change, |_| Msg::CheckOrUncheckAll),
        ],
        label![attrs!{At::For => "toggle-all"}, "Mark all as complete"],
    ]
}

fn view_todo_list(todos: &BTreeMap<Ulid, Todo>, selected_todo: Option<&SelectedTodo>, filter: Filter) -> Node<Msg> {
    let todos = todos.values().filter(|todo| {
        match filter {
            Filter::All => true,
            Filter::Active => not(todo.completed),
            Filter::Completed => todo.completed,
        }
    });
    ul![C!["todo-list"],
        todos.map(|todo| {
            let id = todo.id;
            let is_selected = Some(id) == selected_todo.map(|selected_todo| selected_todo.id);

            li![C![IF!(todo.completed => "completed"), IF!(is_selected => "editing")],
                el_key(&todo.id),
                div![C!["view"],
                    input![C!["toggle"], 
                        attrs!{At::Type => "checkbox", At::Checked => todo.completed.as_at_value()},
                        ev(Ev::Change, move |_| Msg::ToggleTodo(id)),
                    ],
                    label![
                        &todo.title,
                        ev(Ev::DblClick, move |_| Msg::SelectTodo(Some(id))),
                    ],
                    button![C!["destroy"],
                        ev(Ev::Click, move |_| Msg::RemoveTodo(id))
                    ],
                ],
                IF!(is_selected => {
                    let selected_todo = selected_todo.unwrap();
                    input![C!["edit"], 
                        el_ref(&selected_todo.input_element), 
                        attrs!{At::Value => selected_todo.title},
                        input_ev(Ev::Input, Msg::SelectedTodoTitleChanged),
                        keyboard_ev(Ev::KeyDown, |keyboard_event| {
                            Some(match keyboard_event.key().as_str() {
                                ESCAPE_KEY => Msg::SelectTodo(None),
                                ENTER_KEY => Msg::SaveSelectedTodo,
                                _ => return None
                            })
                        }),
                        ev(Ev::Blur, |_| Msg::SaveSelectedTodo),
                    ]
                }),
            ]
        })
    ]
}

// ------ footer ------

fn view_footer(todos: &BTreeMap<Ulid, Todo>, selected_filter: Filter) -> Node<Msg> {
    let completed_count = todos.values().filter(|todo| todo.completed).count();
    let active_count = todos.len() - completed_count;

    footer![C!["footer"],
        span![C!["todo-count"],
            strong![active_count],
            format!(" item{} left", if active_count == 1 { "" } else { "s" }),
        ],
        view_filters(selected_filter),
        IF!(completed_count > 0 =>
            button![C!["clear-completed"],
                "Clear completed",
                ev(Ev::Click, |_| Msg::ClearCompleted),
            ]
        )
    ]
}

fn view_filters(selected_filter: Filter) -> Node<Msg> {
    ul![C!["filters"],
        Filter::iter().map(|filter| {
            let (link, title) = match filter {
                Filter::All => ("#/", "All"),
                Filter::Active => ("#/active", "Active"),
                Filter::Completed => ("#/completed", "Completed"),
            };
            li![
                a![C![IF!(filter == selected_filter => "selected")],
                    attrs!{At::Href => link},
                    title,
                ],
            ]
        })
    ]
}

// ------ ------
//     Start
// ------ ------

#[wasm_bindgen(start)]
pub fn start() {
    console_error_panic_hook::set_once();
    
    let root_element = document()
        .get_elements_by_class_name("todoapp")
        .item(0)
        .expect("element with the class `todoapp`");

    App::start(root_element, init, update, view);
}
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