lord/anchors

use crate::singlethread::*;
let mut engine = Engine::new();

// create a couple `Var`s
let (my_name, my_name_updater) = {
    let var = Var::new("Bob".to_string());
    (var.watch(), var)
};
let (my_unread, my_unread_updater) = {
    let var = Var::new(999usize);
    (var.watch(), var)
};

// `my_name` is a `Var`, our first type of `Anchor`. we can pull an `Anchor`'s value out with our `engine`:
assert_eq!(&engine.get(&my_name), "Bob");
assert_eq!(engine.get(&my_unread), 999);

// we can create a new `Anchor` from another one using `map`. The function won't actually run until absolutely necessary.
// also feel free to clone an `Anchor` — the clones will all refer to the same inner state
let my_greeting = my_name.clone().map(|name| {
    println!("calculating name!");
    format!("Hello, {}!", name)
});
assert_eq!(engine.get(&my_greeting), "Hello, Bob!"); // prints "calculating name!"

// we can update a `Var` with its updater. values are cached unless one of its dependencies changes
assert_eq!(engine.get(&my_greeting), "Hello, Bob!"); // doesn't print anything
my_name_updater.set("Robo".to_string());
assert_eq!(engine.get(&my_greeting), "Hello, Robo!"); // prints "calculating name!"

// a `map` can take values from multiple `Anchor`s. just use tuples:
let header = (&my_greeting, &my_unread)
    .map(|greeting, unread| format!("{} You have {} new messages.", greeting, unread));
assert_eq!(
    engine.get(&header),
    "Hello, Robo! You have 999 new messages."
);

// just like a future, you can dynamically decide which `Anchor` to use with `then`:
let (insulting_name, _) = {
    let var = Var::new("Lazybum".to_string());
    (var.watch(), var)
};
let dynamic_name = my_unread.then(move |unread| {
    // only use the user's real name if the have less than 100 messages in their inbox
    if *unread < 100 {
        my_name.clone()
    } else {
        insulting_name.clone()
    }
});
assert_eq!(engine.get(&dynamic_name), "Lazybum");
my_unread_updater.set(50);
assert_eq!(engine.get(&dynamic_name), "Robo");

engine.mark_observed(&dynamic_name);