multi.rs

use std::collections::{vec_deque, VecDeque};
use std::iter::FromIterator;
use std::mem;
use std::ops::{Deref, DerefMut};
use std::os::raw::c_int;
use std::result::Result as StdResult;

use crate::error::Result;
use crate::state::{Lua, RawLua};
use crate::traits::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti};
use crate::util::check_stack;
use crate::value::{Nil, Value};

/// Result is convertible to [`MultiValue`] following the common Lua idiom of returning the result
/// on success, or in the case of an error, returning `nil` and an error message.
impl<T: IntoLua, E: IntoLua> IntoLuaMulti for StdResult<T, E> {
    #[inline]
    fn into_lua_multi(self, lua: &Lua) -> Result<MultiValue> {
        match self {
            Ok(val) => (val,).into_lua_multi(lua),
            Err(err) => (Nil, err).into_lua_multi(lua),
        }
    }

    #[inline]
    unsafe fn push_into_stack_multi(self, lua: &RawLua) -> Result<c_int> {
        match self {
            Ok(val) => (val,).push_into_stack_multi(lua),
            Err(err) => (Nil, err).push_into_stack_multi(lua),
        }
    }
}

impl<E: IntoLua> IntoLuaMulti for StdResult<(), E> {
    #[inline]
    fn into_lua_multi(self, lua: &Lua) -> Result<MultiValue> {
        match self {
            Ok(_) => const { Ok(MultiValue::new()) },
            Err(err) => (Nil, err).into_lua_multi(lua),
        }
    }

    #[inline]
    unsafe fn push_into_stack_multi(self, lua: &RawLua) -> Result<c_int> {
        match self {
            Ok(_) => Ok(0),
            Err(err) => (Nil, err).push_into_stack_multi(lua),
        }
    }
}

impl<T: IntoLua> IntoLuaMulti for T {
    #[inline]
    fn into_lua_multi(self, lua: &Lua) -> Result<MultiValue> {
        let mut v = MultiValue::with_capacity(1);
        v.push_back(self.into_lua(lua)?);
        Ok(v)
    }

    #[inline]
    unsafe fn push_into_stack_multi(self, lua: &RawLua) -> Result<c_int> {
        self.push_into_stack(lua)?;
        Ok(1)
    }
}

impl<T: FromLua> FromLuaMulti for T {
    #[inline]
    fn from_lua_multi(mut values: MultiValue, lua: &Lua) -> Result<Self> {
        T::from_lua(values.pop_front().unwrap_or(Nil), lua)
    }

    #[inline]
    fn from_lua_args(mut args: MultiValue, i: usize, to: Option<&str>, lua: &Lua) -> Result<Self> {
        T::from_lua_arg(args.pop_front().unwrap_or(Nil), i, to, lua)
    }

    #[inline]
    unsafe fn from_stack_multi(nvals: c_int, lua: &RawLua) -> Result<Self> {
        if nvals == 0 {
            return T::from_lua(Nil, lua.lua());
        }
        T::from_stack(-nvals, lua)
    }

    #[inline]
    unsafe fn from_stack_args(nargs: c_int, i: usize, to: Option<&str>, lua: &RawLua) -> Result<Self> {
        if nargs == 0 {
            return T::from_lua_arg(Nil, i, to, lua.lua());
        }
        T::from_stack_arg(-nargs, i, to, lua)
    }
}

/// Multiple Lua values used for both argument passing and also for multiple return values.
#[derive(Default, Debug, Clone)]
pub struct MultiValue(VecDeque<Value>);

impl Deref for MultiValue {
    type Target = VecDeque<Value>;

    #[inline]
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl DerefMut for MultiValue {
    #[inline]
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl MultiValue {
    /// Creates an empty `MultiValue` containing no values.
    #[inline]
    pub const fn new() -> MultiValue {
        MultiValue(VecDeque::new())
    }

    /// Creates an empty `MultiValue` container with space for at least `capacity` elements.
    pub fn with_capacity(capacity: usize) -> MultiValue {
        MultiValue(VecDeque::with_capacity(capacity))
    }

    /// Creates a `MultiValue` container from vector of values.
    ///
    /// This methods needs *O*(*n*) data movement if the circular buffer doesn't happen to be at the
    /// beginning of the allocation.
    #[inline]
    pub fn from_vec(vec: Vec<Value>) -> MultiValue {
        vec.into()
    }

    /// Consumes the `MultiValue` and returns a vector of values.
    ///
    /// This methods works in *O*(1) time and does not allocate any additional memory.
    #[inline]
    pub fn into_vec(self) -> Vec<Value> {
        self.into()
    }

    #[inline]
    pub(crate) fn from_lua_iter<T: IntoLua>(lua: &Lua, iter: impl IntoIterator<Item = T>) -> Result<Self> {
        let iter = iter.into_iter();
        let mut multi_value = MultiValue::with_capacity(iter.size_hint().0);
        for value in iter {
            multi_value.push_back(value.into_lua(lua)?);
        }
        Ok(multi_value)
    }
}

impl From<Vec<Value>> for MultiValue {
    #[inline]
    fn from(value: Vec<Value>) -> Self {
        MultiValue(value.into())
    }
}

impl From<MultiValue> for Vec<Value> {
    #[inline]
    fn from(value: MultiValue) -> Self {
        value.0.into()
    }
}

impl FromIterator<Value> for MultiValue {
    #[inline]
    fn from_iter<I: IntoIterator<Item = Value>>(iter: I) -> Self {
        let mut multi_value = MultiValue::new();
        multi_value.extend(iter);
        multi_value
    }
}

impl IntoIterator for MultiValue {
    type Item = Value;
    type IntoIter = vec_deque::IntoIter<Value>;

    #[inline]
    fn into_iter(mut self) -> Self::IntoIter {
        let deque = mem::take(&mut self.0);
        mem::forget(self);
        deque.into_iter()
    }
}

impl<'a> IntoIterator for &'a MultiValue {
    type Item = &'a Value;
    type IntoIter = vec_deque::Iter<'a, Value>;

    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        self.0.iter()
    }
}

impl IntoLuaMulti for MultiValue {
    #[inline]
    fn into_lua_multi(self, _: &Lua) -> Result<MultiValue> {
        Ok(self)
    }
}

impl FromLuaMulti for MultiValue {
    #[inline]
    fn from_lua_multi(values: MultiValue, _: &Lua) -> Result<Self> {
        Ok(values)
    }
}

/// Wraps a variable number of `T`s.
///
/// Can be used to work with variadic functions more easily. Using this type as the last argument of
/// a Rust callback will accept any number of arguments from Lua and convert them to the type `T`
/// using [`FromLua`]. `Variadic<T>` can also be returned from a callback, returning a variable
/// number of values to Lua.
///
/// The [`MultiValue`] type is equivalent to `Variadic<Value>`.
///
/// # Examples
///
/// ```
/// # use mlua::{Lua, Result, Variadic};
/// # fn main() -> Result<()> {
/// # let lua = Lua::new();
/// let add = lua.create_function(|_, vals: Variadic<f64>| -> Result<f64> {
///     Ok(vals.iter().sum())
/// })?;
/// lua.globals().set("add", add)?;
/// assert_eq!(lua.load("add(3, 2, 5)").eval::<f32>()?, 10.0);
/// # Ok(())
/// # }
/// ```
#[derive(Default, Debug, Clone)]
pub struct Variadic<T>(Vec<T>);

impl<T> Variadic<T> {
    /// Creates an empty `Variadic` wrapper containing no values.
    pub const fn new() -> Variadic<T> {
        Variadic(Vec::new())
    }

    /// Creates an empty `Variadic` container with space for at least `capacity` elements.
    pub fn with_capacity(capacity: usize) -> Variadic<T> {
        Variadic(Vec::with_capacity(capacity))
    }
}

impl<T> Deref for Variadic<T> {
    type Target = Vec<T>;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl<T> DerefMut for Variadic<T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl<T> From<Vec<T>> for Variadic<T> {
    #[inline]
    fn from(vec: Vec<T>) -> Self {
        Variadic(vec)
    }
}

impl<T> From<Variadic<T>> for Vec<T> {
    #[inline]
    fn from(value: Variadic<T>) -> Self {
        value.0
    }
}

impl<T> FromIterator<T> for Variadic<T> {
    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
        Variadic(Vec::from_iter(iter))
    }
}

impl<T> IntoIterator for Variadic<T> {
    type Item = T;
    type IntoIter = <Vec<T> as IntoIterator>::IntoIter;

    fn into_iter(self) -> Self::IntoIter {
        self.0.into_iter()
    }
}

impl<T: IntoLua> IntoLuaMulti for Variadic<T> {
    #[inline]
    fn into_lua_multi(self, lua: &Lua) -> Result<MultiValue> {
        MultiValue::from_lua_iter(lua, self)
    }
}

impl<T: FromLua> FromLuaMulti for Variadic<T> {
    #[inline]
    fn from_lua_multi(mut values: MultiValue, lua: &Lua) -> Result<Self> {
        values
            .drain(..)
            .map(|val| T::from_lua(val, lua))
            .collect::<Result<Vec<T>>>()
            .map(Variadic)
    }
}

macro_rules! impl_tuple {
    () => (
        impl IntoLuaMulti for () {
            #[inline]
            fn into_lua_multi(self, _: &Lua) -> Result<MultiValue> {
                const { Ok(MultiValue::new()) }
            }

            #[inline]
            unsafe fn push_into_stack_multi(self, _lua: &RawLua) -> Result<c_int> {
                Ok(0)
            }
        }

        impl FromLuaMulti for () {
            #[inline]
            fn from_lua_multi(_values: MultiValue, _lua: &Lua) -> Result<Self> {
                Ok(())
            }

            #[inline]
            unsafe fn from_stack_multi(_nvals: c_int, _lua: &RawLua) -> Result<Self> {
                Ok(())
            }
        }
    );

    ($last:ident $($name:ident)*) => (
        impl<$($name,)* $last> IntoLuaMulti for ($($name,)* $last,)
            where $($name: IntoLua,)*
                  $last: IntoLuaMulti
        {
            #[allow(unused_mut, non_snake_case)]
            #[inline]
            fn into_lua_multi(self, lua: &Lua) -> Result<MultiValue> {
                let ($($name,)* $last,) = self;

                let mut results = $last.into_lua_multi(lua)?;
                push_reverse!(results, $($name.into_lua(lua)?,)*);
                Ok(results)
            }

            #[allow(non_snake_case)]
            #[inline]
            unsafe fn push_into_stack_multi(self, lua: &RawLua) -> Result<c_int> {
                let ($($name,)* $last,) = self;
                let mut nresults = 0;
                $(
                    _ = $name;
                    nresults += 1;
                )*
                check_stack(lua.state(), nresults + 1)?;
                $(
                    $name.push_into_stack(lua)?;
                )*
                nresults += $last.push_into_stack_multi(lua)?;
                Ok(nresults)
            }
        }

        impl<$($name,)* $last> FromLuaMulti for ($($name,)* $last,)
            where $($name: FromLua,)*
                  $last: FromLuaMulti
        {
            #[allow(unused_mut, non_snake_case)]
            #[inline]
            fn from_lua_multi(mut values: MultiValue, lua: &Lua) -> Result<Self> {
                $(let $name = FromLua::from_lua(values.pop_front().unwrap_or(Nil), lua)?;)*
                let $last = FromLuaMulti::from_lua_multi(values, lua)?;
                Ok(($($name,)* $last,))
            }

            #[allow(unused_mut, non_snake_case)]
            #[inline]
            fn from_lua_args(mut args: MultiValue, mut i: usize, to: Option<&str>, lua: &Lua) -> Result<Self> {
                $(
                    let $name = FromLua::from_lua_arg(args.pop_front().unwrap_or(Nil), i, to, lua)?;
                    i += 1;
                )*
                let $last = FromLuaMulti::from_lua_args(args, i, to, lua)?;
                Ok(($($name,)* $last,))
            }

            #[allow(unused_mut, non_snake_case)]
            #[inline]
            unsafe fn from_stack_multi(mut nvals: c_int, lua: &RawLua) -> Result<Self> {
                $(
                    let $name = if nvals > 0 {
                        nvals -= 1;
                        FromLua::from_stack(-(nvals + 1), lua)
                    } else {
                        FromLua::from_lua(Nil, lua.lua())
                    }?;
                )*
                let $last = FromLuaMulti::from_stack_multi(nvals, lua)?;
                Ok(($($name,)* $last,))
            }

            #[allow(unused_mut, non_snake_case)]
            #[inline]
            unsafe fn from_stack_args(mut nargs: c_int, mut i: usize, to: Option<&str>, lua: &RawLua) -> Result<Self> {
                $(
                    let $name = if nargs > 0 {
                        nargs -= 1;
                        FromLua::from_stack_arg(-(nargs + 1), i, to, lua)
                    } else {
                        FromLua::from_lua_arg(Nil, i, to, lua.lua())
                    }?;
                    i += 1;
                )*
                let $last = FromLuaMulti::from_stack_args(nargs, i, to, lua)?;
                Ok(($($name,)* $last,))
            }
        }
    );
}

macro_rules! push_reverse {
    ($multi_value:expr, $first:expr, $($rest:expr,)*) => (
        push_reverse!($multi_value, $($rest,)*);
        $multi_value.push_front($first);
    );

    ($multi_value:expr, $first:expr) => (
        $multi_value.push_front($first);
    );

    ($multi_value:expr,) => ();
}

impl_tuple!();
impl_tuple!(A);
impl_tuple!(A B);
impl_tuple!(A B C);
impl_tuple!(A B C D);
impl_tuple!(A B C D E);
impl_tuple!(A B C D E F);
impl_tuple!(A B C D E F G);
impl_tuple!(A B C D E F G H);
impl_tuple!(A B C D E F G H I);
impl_tuple!(A B C D E F G H I J);
impl_tuple!(A B C D E F G H I J K);
impl_tuple!(A B C D E F G H I J K L);
impl_tuple!(A B C D E F G H I J K L M);
impl_tuple!(A B C D E F G H I J K L M N);
impl_tuple!(A B C D E F G H I J K L M N O);
impl_tuple!(A B C D E F G H I J K L M N O P);

#[cfg(test)]
mod assertions {
    use super::*;

    #[cfg(not(feature = "send"))]
    static_assertions::assert_not_impl_any!(MultiValue: Send);
    #[cfg(feature = "send")]
    static_assertions::assert_impl_all!(MultiValue: Send, Sync);
}