use hashbrown::HashMap;
use mlua::{Lua, LuaString, MetaMethod, UserData, UserDataMethods, Value};

pub type ComposerGet = fn(&Lua, &[u8]) -> mlua::Result<Value>;
pub type ComposerSet = fn(&Lua, &[u8], Value) -> mlua::Result<Value>;

pub struct Composer<G, S> {
	get:   G,
	set:   S,
	cache: HashMap<Vec<u8>, Value>,
}

impl<G, S> Composer<G, S>
where
	G: Fn(&Lua, &[u8]) -> mlua::Result<Value> + 'static,
	S: Fn(&Lua, &[u8], Value) -> mlua::Result<Value> + 'static,
{
	pub fn new(get: G, set: S) -> Self { Self { get, set, cache: Default::default() } }
}

impl<G, S> UserData for Composer<G, S>
where
	G: Fn(&Lua, &[u8]) -> mlua::Result<Value> + 'static,
	S: Fn(&Lua, &[u8], Value) -> mlua::Result<Value> + 'static,
{
	fn add_methods<M: UserDataMethods<Self>>(methods: &mut M) {
		methods.add_meta_method_mut(MetaMethod::Index, |lua, me, key: LuaString| {
			let key = key.as_bytes();
			if let Some(v) = me.cache.get(key.as_ref()) {
				return Ok(v.clone());
			}

			let value = (me.get)(lua, &key)?;
			me.cache.insert(key.to_owned(), value.clone());

			Ok(value)
		});

		methods.add_meta_method_mut(
			MetaMethod::NewIndex,
			|lua, me, (key, value): (LuaString, Value)| {
				let key = key.as_bytes();
				let value = (me.set)(lua, key.as_ref(), value)?;

				if value.is_nil() {
					me.cache.remove(key.as_ref());
				} else {
					me.cache.insert(key.to_owned(), value);
				}

				Ok(())
			},
		);
	}
}