use mlua::{chunk, Lua, MetaMethod, Result, UserData};

#[derive(Default)]
struct Rectangle {
    length: u32,
    width: u32,
}

impl UserData for Rectangle {
    fn add_fields<F: mlua::UserDataFields<Self>>(fields: &mut F) {
        fields.add_field_method_get("length", |_, this| Ok(this.length));
        fields.add_field_method_set("length", |_, this, val| {
            this.length = val;
            Ok(())
        });
        fields.add_field_method_get("width", |_, this| Ok(this.width));
        fields.add_field_method_set("width", |_, this, val| {
            this.width = val;
            Ok(())
        });
    }

    fn add_methods<M: mlua::UserDataMethods<Self>>(methods: &mut M) {
        methods.add_method("area", |_, this, ()| Ok(this.length * this.width));
        methods.add_method("diagonal", |_, this, ()| {
            Ok((this.length.pow(2) as f64 + this.width.pow(2) as f64).sqrt())
        });

        // Constructor
        methods.add_meta_function(MetaMethod::Call, |_, ()| Ok(Rectangle::default()));
    }
}

fn main() -> Result<()> {
    let lua = Lua::new();
    let rectangle = Rectangle::default();
    lua.load(chunk! {
        local rect = $rectangle()
        rect.width = 10
        rect.length = 5
        assert(rect:area() == 50)
        assert(rect:diagonal() - 11.1803 < 0.0001)
    })
    .exec()
}