elua/src/main.rs

use std::{sync::Arc, ffi::CStr};

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::*;

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

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

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

    lua.execute(r#"
        --[[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]]--

        print("x is " .. X.x)

        cool_num = 50

        function say_number(num)
            print("I'm lua and I said " .. num)
        end

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

        function multiply_ret(a, b)
            return a * b
        end
    "#).unwrap();

    let num = globals.get::<_, i32>("cool_num")?;
    assert_eq!(num, 50);
    println!("Got number as 50!");

    let num = globals.get::<_, Function>("say_number")?;
    num.exec::<_, ()>(50)?;

    let num = globals.get::<_, Function>("multiply_print")?;
    num.exec::<_, ()>((10, 5))?;

    let num = globals.get::<_, Function>("multiply_ret")?;
    let num: i32 = num.exec::<_, i32>((10, 5))?;
    assert_eq!(num, 50);
    println!("Did math in lua and got 50!");

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

        unsafe {
            state.ensure_stack(1)?;
            lua::lua_rawgeti(s, lua::LUA_REGISTRYINDEX, *self.0 as i64);
        }

        Ok(())
    }
}

#[derive(Debug, thiserror::Error)]
pub enum Error {
    #[error("Lua runtime error: {0}")]
    /// An error returned from lua
    Runtime(String),
    #[error("Ran out of memory when attempting to use `lua_checkstack`")]
    /// Ran into a not enough memory error when trying to grow the lua stack.
    Oom,
    #[error("Ran into a nill value on the stack")]
    Nil,
    #[error("Unexpected type, expected {0} but got {1}")]
    UnexpectedType(String, 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())
    }
}

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

pub trait PushToLuaStack {
    unsafe fn push_to_lua_stack(&self, state: &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_push_to_lua_stack_number {
    ($ty: ident) => {
        impl PushToLuaStack for $ty {
            unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
                state.ensure_stack(1)?;
                lua::lua_pushnumber(state.state_ptr(), *self as f64);
                Ok(())
            }
        }
    };
}

impl<'a> FromLuaStack<'a> for i32 {
    unsafe fn from_lua_stack(state: &'a State) -> Result<Self> {
        let s = state.state_ptr();

        if lua::lua_isnumber(s, -1) == 1 {
            let v = lua::lua_tonumber(s, -1) as i32;
            lua::lua_pop(s, -1);
            Ok(v)
        } else {
            let lua_ty = lua_type(s, -1);
            let typec = CStr::from_ptr(lua_typename(s, lua_ty));
            let type_str = typec.to_str()
                .expect("Type has invalid bytes!");

            Err(Error::unexpected_type("Number", type_str))
        }
    }
}

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

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

impl_push_to_lua_stack_number!(f32);
impl_push_to_lua_stack_number!(f64);

impl PushToLuaStack 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 PushToLuaStack 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(())
    }
}