fn main() {
    println!("Hello, world!");
    use Template::*;

    enum Action {
        Increment,
        Decrement,
    }

    let mut foo: Widget<i32, _, _, Action> = Widget {
        model: 0,
        update: |x, a| match a {
            Action::Increment => x + 1,
            Action::Decrement => x - 1,
        },
        template: |x| {
            let children = if x > 0 {
                text("Greater than Zero".to_string())
            } else {
                text(x.to_string())
            };

            div{
                children: vec![children],
                on_click: Action::Increment,
            }
        },
        inbox: Vec::new(),
    };
    println!("{}", foo.render().to_string());
    foo.tick(Action::Increment);
    println!("{}", foo.render().to_string());
    foo.tick(Action::Increment);
    println!("{}", foo.render().to_string());
    foo.tick(Action::Decrement);
    println!("{}", foo.render().to_string());
    foo.tick(Action::Decrement);
    println!("{}", foo.render().to_string());
}

struct Widget<S, U, T, A>
    where S: Sized + Copy + Clone,
          A: Sized,
          U: Fn(S, A) -> S,
          T: FnMut(S) -> Template<A>
{
    model: S,
    update: U,
    template: T,
    inbox: Vec<A>,
}

impl<S, U, T, A> Widget<S, U, T, A>
    where S: Sized + Copy + Clone,
          U: Fn(S, A) -> S,
          T: FnMut(S) -> Template<A>,
          A: Sized,
{
    fn render(&mut self) -> Template<A> {
        (self.template)(self.model)
    }

    fn tick(&mut self, action: A) -> () {
        let value: S = (self.update)(self.model, action);
        self.model = value;
    }
}

enum Template<A>
    where A: Sized
{
    div {
        on_click: A,
        children: Vec<Template<A>>,
    },
    h1 {
        on_click: A,
        children: Vec<Template<A>>,
    },
    h2 {
        on_click: A,
        children: Vec<Template<A>>
    },
    text(String),
}

impl<A> Template<A> where A: Sized {
    fn to_string(&self) -> String {
        match self {
            &Template::div{ref children,..} => {
                let mut buffer = String::new();
                buffer.push_str("<div>");
                for child in children.iter() {
                    buffer.push_str(&child.to_string());
                }
                buffer.push_str("</div>");
                buffer
            }
            &Template::h1{ref children,..} => {
                                let mut buffer = String::new();
                buffer.push_str("<h1>");
                for child in children.iter() {
                    buffer.push_str(&child.to_string());
                }
                buffer.push_str("</h1>");
                buffer
            },
            &Template::h2{ref children, ..} => {
                                let mut buffer = String::new();
                buffer.push_str("<h2>");
                for child in children.iter() {
                    buffer.push_str(&child.to_string());
                }
                buffer.push_str("</h2>");
                buffer
            },
            &Template::text(ref value) => value.to_string(),
        }
    }
}