elua/src/main.rs

use std::{any::type_name, ffi::CStr, marker::PhantomData, mem, ptr, str::Utf8Error, sync::Arc};

use lua::{lua_typename, lua_type};
use mlua_sys as lua;

pub mod state;
use state::*;

pub mod table;
use table::*;

pub mod function;
use function::*;

pub mod value;
use value::*;

pub mod guard;
use guard::*;

pub mod userdata;
use userdata::*;

pub mod util;
use util::*;

fn main() -> Result<()> {
    let lua = State::new();
    lua.expose_libraries(&[StdLibrary::Debug, StdLibrary::Package]);

    let globals = lua.globals()?;

    let a = |_lua: &State, (num,): (i32,)| -> Result<i32> {
        println!("Rust got number from lua: {}", num);
        Ok(999)
    };
    
    let f = lua.create_function(a)?;
    globals.set("native_test", f)?;
    
    let ud = lua.create_userdata("Vec2", Vec2 { x: 0.0, y: 0.0})?;
    globals.set("Vec2", ud)?;

    let tbl = lua.create_table()?;
    tbl.set("x", 10)?;

    //let globals = lua.globals()?;
    globals.set("X", tbl)?;

    lua.execute(r#"
        require "util"

        --[[function dump_table(tbl)
            for k, v in pairs(tbl) do
                if type(v) == "table" then
                    dump_table(v)
                elseif type(v) == "function" then

                else
                    print(k .. "=" .. tostring(v))
                end
                
            end
        end

        for k, v in pairs(_G) do
            --print("Found global named " .. k)

            if k == "X" then
                --dump_table(v)
            end
        end]]--

        function multiply_print(a, b)
            print(a .. " * " .. b .. " = " .. a*b)
        end

        function multiply_ret(a, b)
            return a * b
        end

        function say_number(a)
            print("Lua says " .. a)
        end

        cool_num = 50

        local res = native_test(50)
        print("Lua got " .. res .. " back from rust!")

        print("Vec2: " .. dump_table(Vec2))
        print("Meta Vec2: " .. dump_table(getmetatable(Vec2)))
        --local vec2 = Vec2.new(50, 50)
        print("Vec2 is (" .. Vec2.x .. ", " .. Vec2.y .. ")")
    "#).unwrap();

    unsafe {
        assert_eq!(lua::lua_gettop(lua.state_ptr()), 0); // ensure that nothing is left on the stack
    }

    Ok(())
}

#[derive(Clone)]
pub struct LuaRef(Arc<i32>);

impl From<i32> for LuaRef {
    fn from(value: i32) -> Self {
        Self(Arc::new(value))
    }
}

impl LuaRef {
    /// Creates a reference to what is at the top of the stack.
    pub unsafe fn from_stack(state: &State) -> Result<Self> {
        let s = state.state_ptr();

        let r = lua::luaL_ref(s, lua::LUA_REGISTRYINDEX);
        if r == lua::LUA_REFNIL {
            Err(Error::Nil)
        } else {
            Ok(LuaRef::from(r))
        }
    }
}

impl<'a> PushToLuaStack<'a> for LuaRef {
    unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
        let s = state.state_ptr();

        unsafe {
            state.ensure_stack(1)?;
            let top = lua::lua_gettop(s);
            let ty = lua::lua_rawgeti(s, lua::LUA_REGISTRYINDEX, *self.0 as i64);
            let new_top = lua::lua_gettop(s);

            if ty == lua::LUA_TNIL || ty == lua::LUA_TNONE || top == new_top {
                return Err(Error::Nil);
            }
        }

        Ok(())
    }
}

#[derive(Debug, thiserror::Error)]
pub enum Error {
    /// An error returned from lua
    #[error("Lua runtime error: {0}")]
    Runtime(String),
    /// Ran into a not enough memory error when trying to grow the lua stack.
    #[error("Ran out of memory when attempting to use `lua_checkstack`")]
    Oom,
    #[error("Ran into a nill value on the stack")]
    Nil,
    #[error("Unexpected type, expected {0} but got {1}")]
    UnexpectedType(String, String),
    #[error("Bad argument provided to {func:?}! Argument #{arg_index} (name: {arg_name:?}), cause: {error}")]
    BadArgument {
        func: Option<String>,
        arg_index: i32,
        arg_name: Option<String>,
        /// the error that describes what was wrong for this argument
        error: Arc<Error>
    },
    #[error("There is already a registry entry with the key {0}")]
    RegistryConflict(String)
}

impl Error {
    pub fn runtime(msg: &str) -> Self {
        Self::Runtime(msg.to_string())
    }

    pub fn unexpected_type(expected: &str, got: &str) -> Self {
        Self::UnexpectedType(expected.to_string(), got.to_string())
    }

    /// Throw the error in lua.
    /// 
    /// This method never returns
    pub unsafe fn throw_lua(self, lua: *mut lua::lua_State) -> ! {
        let msg = format!("{}", self);
        let msg_c = msg.as_ptr() as *const i8;
        lua::luaL_error(lua, msg_c);
        unreachable!();
    }
}

/// A result for use with lua functions
type Result<T> = core::result::Result<T, Error>;

pub trait PushToLuaStack<'a> {
    unsafe fn push_to_lua_stack(&self, state: &'a State) -> Result<()>;
}

pub trait FromLuaStack<'a>: Sized {
    unsafe fn from_lua_stack(state: &'a State) -> Result<Self>;
}

/// Implements PushToLuaStack for a number
macro_rules! impl_as_lua_number {
    ($ty: ident) => {
        impl<'a> AsLua<'a> for $ty {
            fn as_lua(&self, _lua: &'a State) -> crate::Result<Value<'a>> {
                Ok(Value::Number(*self as f64))
            }
        }

        impl FromLua for $ty {
            fn from_lua(_lua: &State, val: Value) -> crate::Result<Self> {
                match val {
                    Value::Number(v) => Ok(v as $ty),
                    _ => {
                        Err(Error::UnexpectedType("Number".to_string(), val.type_name().to_string()))
                    },
                }
            }
        }

        impl<'a> PushToLuaStack<'a> for $ty {
            unsafe fn push_to_lua_stack(&self, state: &'a State) -> crate::Result<()> {
                let v = self.as_lua(state)?;
                v.push_to_lua_stack(state)
            }
        }
        
    };
}

impl_as_lua_number!(i8);
impl_as_lua_number!(i16);
impl_as_lua_number!(i32);
impl_as_lua_number!(i64);

impl_as_lua_number!(u8);
impl_as_lua_number!(u16);
impl_as_lua_number!(u32);
impl_as_lua_number!(u64);

impl_as_lua_number!(f32);
impl_as_lua_number!(f64);

impl<'a> PushToLuaStack<'a> for String {
    unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
        state.ensure_stack(1)?;

        let s = format!("{}\0", self);
        let cstr = s.as_ptr() as *const i8;
        lua::lua_pushstring(state.state_ptr(), cstr);

        Ok(())
    }
}

impl<'a> FromLuaStack<'a> for String {
    unsafe fn from_lua_stack(state: &'a State) -> Result<Self> {
        let s = state.state_ptr();

        let cstr = lua::lua_tostring(s, -1);
        lua::lua_pop(s, 1);

        let cstr = CStr::from_ptr(cstr);
        Ok(cstr.to_str().unwrap().to_string())
    }
}

impl<'a> PushToLuaStack<'a> for &str {
    unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
        state.ensure_stack(1)?;

        let s = format!("{}\0", self);
        let cstr = s.as_ptr() as *const i8;
        lua::lua_pushstring(state.state_ptr(), cstr);
        
        Ok(())
    }
}

pub struct Vec2 {
    x: f32,
    y: f32,
}

impl Userdata for Vec2 {
    fn build<'a>(builder: &mut UserdataBuilder<'a, Vec2>) -> crate::Result<()> {
        builder.name("Vec2")
            .field_getter("x", |_, this| Ok(this.x))
            .field_getter("y", |_, this| Ok(this.y));

        Ok(())
    }
}

pub struct UserdataProxy<T: Userdata>(PhantomData<T>);

impl<T: Userdata> UserdataProxy<T> {
    pub fn new() -> Self {
        Self(PhantomData)
    }
}

impl<'a, T: Userdata> AsLua<'a> for UserdataProxy<T> {
    fn as_lua(&self, lua: &'a State) -> crate::Result<Value<'a>> {
        todo!()
    }
}

impl<T: Userdata> Userdata for UserdataProxy<T> {
    fn build<'a>(builder: &mut UserdataBuilder<'a, Self>) -> crate::Result<()> {

        let mut other = UserdataBuilder::<T>::new();
        T::build(&mut other)?;

        builder.name(&other.name.unwrap());

        for (lbl, getters) in other.field_getters.into_iter() {
            let wrap = |state: &State, data: &Self| {
                Ok(())
            };
            builder.field_getter(&lbl, wrap);
        }

        Ok(())
    }
}