#![allow(non_camel_case_types, non_snake_case)]
use bitflags::bitflags;
use bstr::{BStr, BString, ByteSlice};
use luaffi::future::lua_pollable;
use std::{
    alloc::{Layout, alloc, dealloc, realloc},
    ffi::{CString, NulError},
    fmt,
    ops::{Deref, DerefMut},
    os::raw::{c_char, c_int, c_void},
    process,
    ptr::{self, NonNull},
    rc::Rc,
    slice,
    str::Utf8Error,
};
use thiserror::Error;

include!(env!("LJ_BINDINGS"));

// constants not exposed by lua.h
pub const LUA_TPROTO: c_int = LUA_TTHREAD + 1;
pub const LUA_TCDATA: c_int = LUA_TTHREAD + 2;

// macros not translated by bindgen
pub unsafe fn lua_upvalueindex(i: c_int) -> c_int {
    LUA_GLOBALSINDEX - i
}

pub unsafe fn lua_pop(L: *mut lua_State, n: c_int) {
    unsafe { lua_settop(L, -n - 1) }
}

pub unsafe fn lua_newtable(L: *mut lua_State) {
    unsafe { lua_createtable(L, 0, 0) }
}

pub unsafe fn lua_register(L: *mut lua_State, n: *const c_char, f: lua_CFunction) {
    unsafe { (lua_pushcfunction(L, f), lua_setglobal(L, n)) };
}

pub unsafe fn lua_pushcfunction(L: *mut lua_State, f: lua_CFunction) {
    unsafe { lua_pushcclosure(L, f, 0) }
}

pub unsafe fn lua_strlen(L: *mut lua_State, i: c_int) -> usize {
    unsafe { lua_objlen(L, i) }
}

pub unsafe fn lua_isfunction(L: *mut lua_State, n: c_int) -> c_int {
    unsafe { (lua_type(L, n) == LUA_TFUNCTION) as c_int }
}

pub unsafe fn lua_istable(L: *mut lua_State, n: c_int) -> c_int {
    unsafe { (lua_type(L, n) == LUA_TTABLE) as c_int }
}

pub unsafe fn lua_islightuserdata(L: *mut lua_State, n: c_int) -> c_int {
    unsafe { (lua_type(L, n) == LUA_TLIGHTUSERDATA) as c_int }
}

pub unsafe fn lua_isnil(L: *mut lua_State, n: c_int) -> c_int {
    unsafe { (lua_type(L, n) == LUA_TNIL) as c_int }
}

pub unsafe fn lua_isboolean(L: *mut lua_State, n: c_int) -> c_int {
    unsafe { (lua_type(L, n) == LUA_TBOOLEAN) as c_int }
}

pub unsafe fn lua_isthread(L: *mut lua_State, n: c_int) -> c_int {
    unsafe { (lua_type(L, n) == LUA_TTHREAD) as c_int }
}

pub unsafe fn lua_isnone(L: *mut lua_State, n: c_int) -> c_int {
    unsafe { (lua_type(L, n) == LUA_TNONE) as c_int }
}

pub unsafe fn lua_isnoneornil(L: *mut lua_State, n: c_int) -> c_int {
    unsafe { (lua_type(L, n) <= LUA_TNIL) as c_int }
}

pub unsafe fn lua_pushliteral(L: *mut lua_State, s: impl AsRef<[u8]>) {
    unsafe { lua_pushlstring(L, s.as_ref().as_ptr().cast(), s.as_ref().len()) }
}

pub unsafe fn lua_setglobal(L: *mut lua_State, s: *const c_char) {
    unsafe { lua_setfield(L, LUA_GLOBALSINDEX, s) }
}

pub unsafe fn lua_getglobal(L: *mut lua_State, s: *const c_char) {
    unsafe { lua_getfield(L, LUA_GLOBALSINDEX, s) }
}

pub unsafe fn lua_tostring(L: *mut lua_State, i: c_int) -> *const c_char {
    unsafe { lua_tolstring(L, i, ptr::null_mut()) }
}

pub unsafe fn lua_open() -> *mut lua_State {
    unsafe { luaL_newstate() }
}

pub unsafe fn lua_getregistry(L: *mut lua_State) {
    unsafe { lua_pushvalue(L, LUA_REGISTRYINDEX) }
}

pub unsafe fn lua_getgccount(L: *mut lua_State) -> c_int {
    unsafe { lua_gc(L, LUA_GCCOUNT, 0) }
}

#[derive(Debug, Error)]
pub enum Error {
    #[error("out of memory")]
    OutOfMemory,
    #[error("{msg}")]
    Syntax { chunk: BString, msg: BString },
    #[error("bad chunk name: {0}")]
    BadChunkName(NulError),
    #[error("{msg}")]
    Call { msg: BString },
    #[error("{msg}")]
    Resume { msg: BString, trace: BString },
    #[error("{0} expected, got {1}")]
    InvalidType(&'static str, &'static str),
    #[error("{0}")]
    InvalidUtf8(#[from] Utf8Error),
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
pub enum Type {
    #[default]
    Nil,
    Boolean,
    Lightuserdata,
    Number,
    String,
    Table,
    Function,
    Userdata,
    Thread,
    Cdata,
}

impl Type {
    pub fn from_code(code: c_int) -> Option<Self> {
        Some(match code {
            LUA_TNIL => Self::Nil,
            LUA_TBOOLEAN => Self::Boolean,
            LUA_TLIGHTUSERDATA => Self::Lightuserdata,
            LUA_TNUMBER => Self::Number,
            LUA_TSTRING => Self::String,
            LUA_TTABLE => Self::Table,
            LUA_TFUNCTION => Self::Function,
            LUA_TUSERDATA => Self::Userdata,
            LUA_TTHREAD => Self::Thread,
            LUA_TCDATA => Self::Cdata,
            _ => return None,
        })
    }

    pub fn name(&self) -> &'static str {
        match self {
            Self::Nil => "nil",
            Self::Boolean => "boolean",
            Self::Lightuserdata => "lightuserdata",
            Self::Number => "number",
            Self::String => "string",
            Self::Table => "table",
            Self::Function => "function",
            Self::Userdata => "userdata",
            Self::Thread => "thread",
            Self::Cdata => "cdata",
        }
    }
}

impl fmt::Display for Type {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.name())
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
pub enum Status {
    #[default]
    Normal,
    Dead,
    Suspended,
}

impl Status {
    pub fn from_code(code: c_int) -> Option<Self> {
        Some(match code {
            LUA_OK => Self::Normal,
            LUA_YIELD => Self::Suspended,
            LUA_ERRRUN | LUA_ERRSYNTAX | LUA_ERRMEM | LUA_ERRERR => Self::Dead,
            _ => return None,
        })
    }

    pub fn name(&self) -> &'static str {
        match self {
            Status::Normal => "normal",
            Status::Dead => "dead",
            Status::Suspended => "suspended",
        }
    }
}

impl fmt::Display for Status {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.name())
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum ResumeStatus {
    #[default]
    Ok,
    Suspended,
}

impl ResumeStatus {
    pub fn name(&self) -> &'static str {
        match self {
            ResumeStatus::Ok => "ok",
            ResumeStatus::Suspended => "suspended",
        }
    }
}

impl fmt::Display for ResumeStatus {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.name())
    }
}

bitflags! {
    pub struct LoadMode: usize {
        const AUTO   = 0b_00_11;
        const TEXT   = 0b_00_01;
        const BINARY = 0b_00_10;
        const GC64   = 0b_01_10;
        const GC32   = 0b_10_10;
    }
}

impl Default for LoadMode {
    fn default() -> Self {
        Self::AUTO
    }
}

impl LoadMode {
    fn mode_str(&self) -> CString {
        let mut s = String::new();

        if self.contains(Self::TEXT) {
            s.push_str("t");
        }

        if self.contains(Self::BINARY) {
            s.push_str("b");
            if self.contains(Self::GC64) {
                s.push_str("X");
            } else if self.contains(Self::GC32) {
                s.push_str("W");
            }
        }

        CString::new(s).unwrap()
    }
}

bitflags! {
    pub struct DumpMode: usize {
        const DEFAULT       = 0b_00_1_0;
        const STRIP         = 0b_00_0_1;
        const DETERMINISTIC = 0b_00_1_0;
        const GC64          = 0b_01_0_0;
        const GC32          = 0b_10_0_0;
    }
}

impl Default for DumpMode {
    fn default() -> Self {
        Self::DEFAULT
    }
}

impl DumpMode {
    fn mode_str(&self) -> CString {
        let mut s = String::new();

        if self.contains(Self::STRIP) {
            s.push_str("s");
        }

        if self.contains(Self::DETERMINISTIC) {
            s.push_str("d");
        }

        if self.contains(Self::GC64) {
            s.push_str("X");
        } else if self.contains(Self::GC32) {
            s.push_str("W");
        }

        CString::new(s).unwrap()
    }
}

#[derive(Debug)]
struct GlobalState {
    ptr: NonNull<lua_State>,
}

impl GlobalState {
    pub fn new() -> Result<Self, Error> {
        unsafe {
            let ptr = NonNull::new(lua_newstate(Some(Self::alloc_cb), ptr::null_mut()))
                .ok_or(Error::OutOfMemory)?;

            lua_atpanic(ptr.as_ptr(), Some(Self::panic_cb));
            Ok(Self { ptr })
        }
    }

    unsafe extern "C" fn alloc_cb(
        _ud: *mut c_void,
        ptr: *mut c_void,
        osize: usize,
        nsize: usize,
    ) -> *mut c_void {
        // https://github.com/tikv/jemallocator/blob/main/jemallocator/src/lib.rs
        #[cfg(any(target_arch = "arm", target_arch = "mips", target_arch = "powerpc"))]
        const ALIGNOF_MAX_ALIGN_T: usize = 8;
        #[cfg(any(
            target_arch = "x86",
            target_arch = "x86_64",
            target_arch = "aarch64",
            target_arch = "powerpc64",
            target_arch = "loongarch64",
            target_arch = "mips64",
            target_arch = "riscv64",
            target_arch = "s390x",
            target_arch = "sparc64"
        ))]
        const ALIGNOF_MAX_ALIGN_T: usize = 16;

        let old_layout = Layout::from_size_align(osize, ALIGNOF_MAX_ALIGN_T)
            .expect("alloc error: requested osize is too large");
        let new_layout = Layout::from_size_align(nsize, ALIGNOF_MAX_ALIGN_T)
            .expect("alloc error: requested nsize is too large");

        if nsize != 0 {
            if osize != 0 {
                unsafe { realloc(ptr.cast(), old_layout, nsize).cast() }
            } else {
                unsafe { alloc(new_layout).cast() }
            }
        } else {
            if osize != 0 {
                unsafe { dealloc(ptr.cast(), old_layout) }
            }
            ptr::null_mut()
        }
    }

    unsafe extern "C" fn panic_cb(L: *mut lua_State) -> c_int {
        // we cannot recover from uncaught lua exceptions; abort instead
        let stack = unsafe { Stack::new_unchecked(L) };
        let msg = stack.string(-1).unwrap_or(b"unknown lua panic".into());
        eprintln!("lua panicked: {msg}");
        process::abort()
    }

    pub fn as_ptr(&self) -> *mut lua_State {
        self.ptr.as_ptr()
    }
}

impl Drop for GlobalState {
    fn drop(&mut self) {
        unsafe { lua_close(self.as_ptr()) }
    }
}

#[derive(Debug)]
pub struct State {
    stack: Stack,
    ref_key: c_int,
    global: Rc<GlobalState>,
}

impl State {
    pub fn new() -> Result<Self, Error> {
        let global = Rc::new(GlobalState::new()?);
        let mut state = Self {
            stack: unsafe { Stack::new_unchecked(global.as_ptr()) },
            ref_key: LUA_NOREF,
            global,
        };

        state.push_function(Some(Self::open_cb));
        state.call(0, 0)?;
        Ok(state)
    }

    unsafe extern "C" fn open_cb(L: *mut lua_State) -> c_int {
        unsafe { luaL_openlibs(L) }
        0
    }

    pub fn new_thread(&self) -> Self {
        // SAFETY: lua_newthread never returns null, but may panic on oom
        self.ensure(1);
        Self {
            stack: unsafe { Stack::new_unchecked(lua_newthread(self.as_ptr())) },
            ref_key: unsafe { luaL_ref(self.as_ptr(), LUA_REGISTRYINDEX) },
            global: Rc::clone(&self.global),
        }
    }
}

impl Deref for State {
    type Target = Stack;

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

impl DerefMut for State {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.stack
    }
}

impl Drop for State {
    fn drop(&mut self) {
        unsafe { luaL_unref(self.global.as_ptr(), LUA_REGISTRYINDEX, self.ref_key) }
    }
}

pub struct Stack {
    ptr: NonNull<lua_State>,
}

impl Stack {
    unsafe fn new_unchecked(ptr: *mut lua_State) -> Self {
        let ptr = unsafe { NonNull::new_unchecked(ptr) };
        Self { ptr }
    }

    pub fn as_ptr(&self) -> *mut lua_State {
        self.ptr.as_ptr()
    }

    pub fn top(&self) -> c_int {
        unsafe { lua_gettop(self.as_ptr()) }
    }

    pub fn set_top(&mut self, idx: c_int) {
        assert!(0 <= idx, "cannot resize to {idx}");
        // lua_settop throws on oom when growing, so we call ensure first
        let top = self.top();
        (top < idx).then(|| self.ensure(idx - top));
        unsafe { lua_settop(self.as_ptr(), idx) }
    }

    pub fn ensure(&self, n: c_int) {
        // lua_checkstack throws on oom in puc lua 5.1, but it is fine in luajit
        unsafe { assert!(lua_checkstack(self.as_ptr(), n) != 0, "stack out of memory") }
    }

    pub fn pop(&mut self, n: c_int) {
        assert!(0 <= n && n <= self.top(), "cannot pop {n}: {self:?}");
        unsafe { lua_pop(self.as_ptr(), n) }
    }

    pub fn pop_replace(&mut self, idx: c_int) {
        assert!(1 <= self.top(), "cannot pop 1: {self:?}");
        unsafe { lua_replace(self.as_ptr(), self.index(idx).index()) }
    }

    pub fn status(&self) -> Status {
        Status::from_code(unsafe { lua_status(self.as_ptr()) }).unwrap()
    }

    pub fn iter<'s>(&'s self) -> StackIter<'s> {
        StackIter::new(self)
    }

    pub fn guard<'s>(&'s mut self) -> StackGuard<'s> {
        StackGuard::new(self)
    }

    pub fn index<'s>(&'s self, idx: c_int) -> Value<'s> {
        self.try_index(idx)
            .unwrap_or_else(|| panic!("invalid index {idx}: {self:?}"))
    }

    pub fn try_index<'s>(&'s self, idx: c_int) -> Option<Value<'s>> {
        self.absindex(idx)
            .map(|idx| unsafe { Value::new_unchecked(self, idx) })
    }

    fn absindex(&self, idx: c_int) -> Option<c_int> {
        if LUA_REGISTRYINDEX < idx && idx <= 0 {
            // SAFETY: must check any relative index that gets passed to index2adr in lj_api.c
            // luajit doesn't check out-of-bounds access for relative indices with assertions disabled
            let top = self.top();
            let idx = top + idx + 1;
            (0 < idx && idx <= top).then_some(idx)
        } else {
            unsafe { lua_type(self.as_ptr(), idx) != LUA_TNONE }.then_some(idx)
        }
    }

    pub fn type_of(&self, idx: c_int) -> Type {
        self.index(idx).type_of()
    }

    pub fn parse<'s, T: Parse<'s>>(&'s self, idx: c_int) -> Result<T, Error> {
        self.index(idx).parse()
    }

    pub fn boolean(&self, idx: c_int) -> bool {
        self.index(idx).boolean()
    }

    pub fn lightuserdata<T>(&self, idx: c_int) -> *mut T {
        self.index(idx).lightuserdata()
    }

    pub fn number(&self, idx: c_int) -> Option<lua_Number> {
        self.index(idx).number()
    }

    pub fn integer(&self, idx: c_int) -> Option<lua_Integer> {
        self.index(idx).integer()
    }

    pub fn string(&self, idx: c_int) -> Option<&BStr> {
        self.index(idx).string()
    }

    pub fn function(&self, idx: c_int) -> lua_CFunction {
        self.index(idx).function()
    }

    pub fn cdata<T>(&self, idx: c_int) -> *const T {
        self.index(idx).cdata()
    }

    pub fn pointer(&self, idx: c_int) -> *const c_void {
        self.index(idx).pointer()
    }

    pub fn push<T: Push>(&mut self, value: T) {
        value.push(self)
    }

    pub fn push_table(&mut self) {
        self.ensure(1);
        unsafe { lua_newtable(self.as_ptr()) }
    }

    pub fn push_function(&mut self, f: lua_CFunction) {
        assert!(f.is_some(), "function must not be null");
        self.ensure(1);
        unsafe { lua_pushcfunction(self.as_ptr(), f) }
    }

    pub fn push_thread(&mut self) -> bool {
        self.ensure(1);
        unsafe { lua_pushthread(self.as_ptr()) != 0 }
    }

    pub fn push_index(&mut self, idx: c_int) {
        self.ensure(1);
        unsafe { lua_pushvalue(self.as_ptr(), self.index(idx).index()) }
    }

    pub fn get(&mut self, idx: c_int) {
        assert!(1 <= self.top(), "expected 1 value: {self:?}");
        unsafe { lua_rawget(self.as_ptr(), self.index(idx).index()) }
    }

    pub fn geti(&mut self, idx: c_int, n: c_int) {
        self.ensure(1);
        unsafe { lua_rawgeti(self.as_ptr(), self.index(idx).index(), n) }
    }

    pub fn set(&mut self, idx: c_int) {
        assert!(2 <= self.top(), "expected 2 values: {self:?}");
        unsafe { lua_rawset(self.as_ptr(), self.index(idx).index()) }
    }

    pub fn seti(&mut self, idx: c_int, n: c_int) {
        assert!(1 <= self.top(), "expected 1 value: {self:?}");
        unsafe { lua_rawseti(self.as_ptr(), self.index(idx).index(), n) }
    }

    pub fn load(
        &mut self,
        name: Option<impl AsRef<[u8]>>,
        chunk: impl AsRef<[u8]>,
        mode: LoadMode,
    ) -> Result<(), Error> {
        let mode = mode.mode_str();
        let name = name
            .map(|s| CString::new(s.as_ref()))
            .transpose()
            .map_err(Error::BadChunkName)?
            .unwrap_or(c"?".into());

        type State<'s> = Option<&'s [u8]>;
        let mut state: State = Some(chunk.as_ref());

        unsafe extern "C" fn reader_cb(
            _L: *mut lua_State,
            state: *mut c_void,
            size: *mut usize,
        ) -> *const c_char {
            unsafe {
                if let Some(chunk) = (*(state as *mut State)).take() {
                    *size = chunk.len();
                    chunk.as_ptr().cast()
                } else {
                    *size = 0;
                    ptr::null()
                }
            }
        }

        self.ensure(1);

        match unsafe {
            lua_loadx(
                self.as_ptr(),
                Some(reader_cb),
                &raw mut state as *mut c_void,
                name.as_ptr(),
                mode.as_ptr(),
            )
        } {
            LUA_OK => Ok(()),
            LUA_ERRMEM => {
                self.pop(1);
                Err(Error::OutOfMemory)
            }
            LUA_ERRSYNTAX => {
                let chunk = name.into_bytes().into();
                let msg = self.string(-1).unwrap_or(b"unknown error".into()).into();
                self.pop(1);
                Err(Error::Syntax { chunk, msg })
            }
            _ => unreachable!(),
        }
    }

    pub fn dump(&mut self, idx: c_int, mode: DumpMode) -> Result<BString, Error> {
        let value = self.index(idx);
        let idx = match value.type_of() {
            Type::Function => value.index(),
            _ => panic!("expected function at index {}: {self:?}", value.index()),
        };

        let mut s = self.guard();
        s.push("string");
        s.get(LUA_GLOBALSINDEX);
        s.push("dump");
        s.get(-2); // local dump = string.dump
        s.push_index(idx);
        s.push(mode.mode_str().as_bytes());
        s.call(2, 1)?;
        s.index(-1).parse() // return dump(idx, mode)
    }

    pub fn call(&mut self, narg: c_int, nret: c_int) -> Result<c_int, Error> {
        assert!(0 <= narg && (0 <= nret || nret == LUA_MULTRET));

        let top = self.top();
        let need = narg + 1; // need the function on the stack
        assert!(need <= top, "expected {need} values: {self:?}");
        assert!(
            self.status() == Status::Normal,
            "thread {:p} called in wrong state",
            self.as_ptr()
        );

        let base = top - need;
        match unsafe { lua_pcall(self.as_ptr(), narg, nret, 0) } {
            LUA_OK => {
                let n = self.top() - base;
                assert!(
                    n == nret || nret == LUA_MULTRET,
                    "expected {nret} values, got {n}: {self:?}"
                );
                Ok(n)
            }
            LUA_ERRMEM => {
                self.pop(1);
                Err(Error::OutOfMemory)
            }
            LUA_ERRRUN | LUA_ERRERR => {
                let msg = self.string(-1).unwrap_or(b"unknown error".into()).into();
                self.pop(1);
                Err(Error::Call { msg })
            }
            _ => unreachable!(),
        }
    }

    pub async fn call_async(&mut self, mut narg: c_int) -> Result<(), Error> {
        loop {
            match self.resume(narg)? {
                ResumeStatus::Ok => return Ok(()),
                ResumeStatus::Suspended => {
                    self.set_top(1);
                    let value = self.index(1);
                    let ptr = value.cdata::<lua_pollable>().cast_mut();
                    if ptr.is_null() {
                        return Err(Error::InvalidType("cdata", value.type_of().name()));
                    } else {
                        unsafe { (&mut *ptr).await }
                        narg = 1;
                    }
                }
            }
        }
    }

    pub fn resume(&mut self, narg: c_int) -> Result<ResumeStatus, Error> {
        assert!(0 <= narg);
        let need = match self.status() {
            Status::Suspended => narg,
            _ => narg + 1, // need the function on the stack
        };
        assert!(need <= self.top(), "expected {need} values: {self:?}");

        match unsafe { lua_resume(self.as_ptr(), narg) } {
            LUA_OK => Ok(ResumeStatus::Ok),
            LUA_YIELD => Ok(ResumeStatus::Suspended),
            LUA_ERRMEM => {
                self.pop(1);
                Err(Error::OutOfMemory)
            }
            LUA_ERRRUN | LUA_ERRERR => {
                unsafe { luaL_traceback(self.as_ptr(), self.as_ptr(), ptr::null(), 0) }

                let msg = self.string(-2).unwrap_or(b"unknown error".into()).into();
                let trace = self
                    .string(-1)
                    .map(|s| s.strip_prefix(b"stack traceback:\n").unwrap_or(s).as_bstr())
                    .filter(|s| !s.is_empty())
                    .unwrap_or(b"<no stack trace>".into())
                    .into();

                self.pop(2);
                Err(Error::Resume { msg, trace })
            }
            _ => unreachable!(),
        }
    }
}

impl fmt::Debug for Stack {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        struct PointerValue(&'static str, *const c_void);
        impl<'s> fmt::Debug for PointerValue {
            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                write!(f, "{} {:p}", self.0, self.1)
            }
        }

        struct Values<'s>(&'s Stack);
        impl<'s> fmt::Debug for Values<'s> {
            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                let mut list = f.debug_list();
                for value in self.0.iter() {
                    match value.type_of() {
                        Type::Nil => list.entry(&"nil"),
                        Type::Boolean => list.entry(&value.boolean()),
                        Type::Number => list.entry(&value.number()),
                        Type::String => list.entry(&value.string().unwrap()),
                        ty => list.entry(&PointerValue(ty.name(), value.pointer())),
                    };
                }
                list.finish()
            }
        }

        f.debug_struct("Stack")
            .field("ptr", &self.ptr)
            .field("values", &Values(self))
            .finish()
    }
}

#[derive(Debug)]
pub struct StackGuard<'s> {
    stack: &'s mut Stack,
    idx: c_int,
}

impl<'s> StackGuard<'s> {
    pub fn new(stack: &'s mut Stack) -> Self {
        let idx = stack.top();
        Self { stack, idx }
    }
}

impl<'s> Deref for StackGuard<'s> {
    type Target = Stack;

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

impl<'s> DerefMut for StackGuard<'s> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        self.stack
    }
}

impl<'s> Drop for StackGuard<'s> {
    fn drop(&mut self) {
        self.stack.set_top(self.idx);
    }
}

#[derive(Debug)]
pub struct StackIter<'s> {
    stack: &'s Stack,
    idx: c_int,
    top: c_int,
}

impl<'s> StackIter<'s> {
    pub fn new(stack: &'s Stack) -> Self {
        let top = stack.top();
        Self { stack, idx: 0, top }
    }
}

impl<'s> Iterator for StackIter<'s> {
    type Item = Value<'s>;

    fn next(&mut self) -> Option<Self::Item> {
        (self.idx < self.top).then(|| {
            self.idx += 1;
            unsafe { Value::new_unchecked(self.stack, self.idx) }
        })
    }
}

pub struct Value<'s> {
    stack: &'s Stack,
    idx: c_int,
}

impl<'s> Value<'s> {
    unsafe fn new_unchecked(stack: &'s Stack, idx: c_int) -> Self {
        Self { stack, idx }
    }

    pub fn index(&self) -> c_int {
        self.idx
    }

    pub fn type_of(&self) -> Type {
        Type::from_code(unsafe { lua_type(self.stack.as_ptr(), self.idx) }).unwrap_or(Type::Nil)
    }

    pub fn parse<T: Parse<'s>>(&self) -> Result<T, Error> {
        T::parse(self)
    }

    pub fn boolean(&self) -> bool {
        self.parse().unwrap_or(false)
    }

    pub fn lightuserdata<T>(&self) -> *mut T {
        self.parse().unwrap_or(ptr::null_mut())
    }

    pub fn number(&self) -> Option<lua_Number> {
        self.parse().ok()
    }

    pub fn integer(&self) -> Option<lua_Integer> {
        self.parse().ok()
    }

    pub fn string(&self) -> Option<&'s BStr> {
        self.parse().ok()
    }

    pub fn function(&self) -> lua_CFunction {
        unsafe { lua_tocfunction(self.stack.as_ptr(), self.idx) }
    }

    pub fn cdata<T>(&self) -> *const T {
        (self.type_of() == Type::Cdata)
            .then(|| self.pointer().cast())
            .unwrap_or(ptr::null_mut())
    }

    pub fn pointer(&self) -> *const c_void {
        unsafe { lua_topointer(self.stack.as_ptr(), self.idx).cast() }
    }
}

pub trait Push {
    fn push(&self, stack: &mut Stack);
}

impl<T: Push> Push for &T {
    fn push(&self, stack: &mut Stack) {
        T::push(self, stack)
    }
}

impl<T: Push> Push for &mut T {
    fn push(&self, stack: &mut Stack) {
        T::push(self, stack)
    }
}

impl<T: Push> Push for Option<T> {
    fn push(&self, stack: &mut Stack) {
        match self {
            Some(value) => value.push(stack),
            None => ().push(stack),
        }
    }
}

impl Push for () {
    fn push(&self, stack: &mut Stack) {
        stack.ensure(1);
        unsafe { lua_pushnil(stack.as_ptr()) }
    }
}

impl Push for bool {
    fn push(&self, stack: &mut Stack) {
        stack.ensure(1);
        unsafe { lua_pushboolean(stack.as_ptr(), *self as c_int) }
    }
}

macro_rules! impl_push_ptr {
    ($type:ty) => {
        impl<T> Push for $type {
            fn push(&self, stack: &mut Stack) {
                stack.ensure(1);
                unsafe { lua_pushlightuserdata(stack.as_ptr(), *self as *mut c_void) }
            }
        }
    };
}

impl_push_ptr!(*const T);
impl_push_ptr!(*mut T);

macro_rules! impl_push_num {
    ($type:ty) => {
        impl Push for $type {
            fn push(&self, stack: &mut Stack) {
                stack.ensure(1);
                unsafe { lua_pushnumber(stack.as_ptr(), *self as lua_Number) }
            }
        }
    };
}

impl_push_num!(f32);
impl_push_num!(f64);

macro_rules! impl_push_int {
    ($type:ty) => {
        impl Push for $type {
            fn push(&self, stack: &mut Stack) {
                stack.ensure(1);
                unsafe { lua_pushinteger(stack.as_ptr(), *self as lua_Integer) }
            }
        }
    };
}

impl_push_int!(u8);
impl_push_int!(u16);
impl_push_int!(u32);
impl_push_int!(u64);
impl_push_int!(usize);
impl_push_int!(i8);
impl_push_int!(i16);
impl_push_int!(i32);
impl_push_int!(i64);
impl_push_int!(isize);

macro_rules! impl_push_str {
    ($type:ty) => {
        impl Push for $type {
            fn push(&self, stack: &mut Stack) {
                stack.ensure(1);
                unsafe { lua_pushliteral(stack.as_ptr(), self) }
            }
        }
    };
}

impl_push_str!(&[u8]);
impl_push_str!(Vec<u8>);
impl_push_str!(&BStr);
impl_push_str!(BString);
impl_push_str!(&str);
impl_push_str!(String);

pub trait Parse<'s>: Sized {
    fn parse(value: &Value<'s>) -> Result<Self, Error>;
}

impl Parse<'_> for () {
    fn parse(value: &Value) -> Result<Self, Error> {
        match value.type_of() {
            Type::Nil => Ok(()),
            ty => Err(Error::InvalidType("nil", ty.name())),
        }
    }
}

impl Parse<'_> for bool {
    fn parse(value: &Value) -> Result<Self, Error> {
        Ok(unsafe { lua_toboolean(value.stack.as_ptr(), value.idx) != 0 })
    }
}

macro_rules! impl_parse_ptr {
    ($type:ty) => {
        impl<T> Parse<'_> for $type {
            fn parse(value: &Value) -> Result<Self, Error> {
                let ptr = unsafe { lua_touserdata(value.stack.as_ptr(), value.idx) };
                if !ptr.is_null() {
                    Ok(ptr as $type)
                } else {
                    Err(Error::InvalidType("lightuserdata", value.type_of().name()))
                }
            }
        }
    };
}

impl_parse_ptr!(*mut T);
impl_parse_ptr!(*const T);

macro_rules! impl_parse_num {
    ($type:ty) => {
        impl Parse<'_> for $type {
            fn parse(value: &Value) -> Result<Self, Error> {
                let mut isnum = 0;
                let n = unsafe { lua_tonumberx(value.stack.as_ptr(), value.idx, &raw mut isnum) };
                if isnum != 0 {
                    Ok(n as $type)
                } else {
                    Err(Error::InvalidType("number", value.type_of().name()))
                }
            }
        }
    };
}

impl_parse_num!(f32);
impl_parse_num!(f64);

macro_rules! impl_parse_int {
    ($type:ty) => {
        impl Parse<'_> for $type {
            fn parse(value: &Value) -> Result<Self, Error> {
                let mut isnum = 0;
                let n = unsafe { lua_tointegerx(value.stack.as_ptr(), value.idx, &raw mut isnum) };
                if isnum != 0 {
                    Ok(n as $type)
                } else {
                    Err(Error::InvalidType("number", value.type_of().name()))
                }
            }
        }
    };
}

impl_parse_int!(u8);
impl_parse_int!(u16);
impl_parse_int!(u32);
impl_parse_int!(u64);
impl_parse_int!(usize);
impl_parse_int!(i8);
impl_parse_int!(i16);
impl_parse_int!(i32);
impl_parse_int!(i64);
impl_parse_int!(isize);

macro_rules! impl_parse_str {
    ($type:ty) => {
        impl<'s> Parse<'s> for $type {
            fn parse(value: &Value<'s>) -> Result<Self, Error> {
                let mut len = 0;
                let ptr = unsafe { lua_tolstring(value.stack.as_ptr(), value.idx, &mut len) };
                if !ptr.is_null() {
                    Ok(unsafe { slice::from_raw_parts(ptr.cast(), len).into() })
                } else {
                    Err(Error::InvalidType("string", value.type_of().name()))
                }
            }
        }
    };
}

macro_rules! impl_parse_str_utf8 {
    ($type:ty) => {
        impl<'s> Parse<'s> for $type {
            fn parse(value: &Value<'s>) -> Result<Self, Error> {
                Ok(std::str::from_utf8(Parse::parse(value)?)?.into())
            }
        }
    };
}

impl_parse_str!(&'s [u8]);
impl_parse_str!(&'s BStr);
impl_parse_str!(Vec<u8>);
impl_parse_str!(BString);
impl_parse_str_utf8!(&'s str);
impl_parse_str_utf8!(String);