/* Copyright 2013-2020 Philipp Janda <siffiejoe@gmx.net>
 *
 * You may do anything with this work that copyright law would normally
 * restrict, so long as you retain the above notice(s) and this license
 * in all redistributed copies and derived works.  There is no warranty.
 */

#include <stddef.h>
#include <string.h>
#include <stdio.h>
#include <stdarg.h>
#include <limits.h>
#include <ctype.h>
#include "moon.h"

/* don't compile it again if it's already included via moon.h */
#ifndef MOON_C_
#define MOON_C_

#if LUA_VERSION_NUM < 502
MOON_API int moon_absindex(lua_State *L, int i)
{
  if (i < 0 && i > LUA_REGISTRYINDEX)
    i += lua_gettop(L) + 1;
  return i;
}
#endif

/* struct that is part of some moon objects (those created via
 * `moon_newfield`) and contains a function pointer and a data pointer
 * that can be used to check whether the object is still valid. The
 * check is done automatically in `moon_{check,test}object`, and is
 * primarily needed to safely support tagged unions. */
typedef struct moon_object_vcheck_
{
  int (*check)(void *);
  void *tagp;
  struct moon_object_vcheck_ *next; /* linked list */
} moon_object_vcheck_;

/* For keeping memory consumption as low as possible multiple C
 * values might be stored side-by-side in the same memory block, and
 * we have to figure out the alignment to use for those values. */
typedef union
{
  lua_Number n;
  double d;
  lua_Integer i;
  long l;
  size_t s;
  void *p;
  void (*fp)(void);
} moon_object_alignment_u_;

/* Newer versions of C and C++ have a way to figure out alignment
 * built into the language, and we use those if available. There's
 * also a fallback implementation for older versions. */
#ifndef MOON_ALIGNOF_
#if defined(__cplusplus) && __cplusplus >= 201103L
/* alignof is an operator in newer C++ versions */
#define MOON_ALIGNOF_(_t) alignof(_t)
#elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
/* newer C versions have it in stdalign.h */
#include <stdalign.h>
#define MOON_ALIGNOF_(_t) alignof(_t)
#elif defined(__cplusplus)
/* Same as below, but MSVC++ has problems with that code, so we use a
 * template instead of a type-as-expression. */
template <typename T>
struct moon_alignof_struct_
{
  char _1;
  T _2;
};
#define MOON_ALIGNOF_(_t)                              \
  (offsetof(moon_alignof_struct_<_t>, _2) > sizeof(_t) \
       ? sizeof(_t)                                    \
       : offsetof(moon_alignof_struct_<_t>, _2))
#else
/* Calculate the alignment ourselves. This may give smaller values
 * than using `sizeof( _t )` which is also a portable solution. */
#define MOON_ALIGNOF_(_t) \
  (offsetof(              \
       struct             \
       {                  \
         char _1;         \
         _t _2;           \
       },                 \
       _2) > sizeof(_t)   \
       ? sizeof(_t)       \
       : offsetof(        \
             struct       \
             {            \
               char _1;   \
               _t _2;     \
             },           \
             _2))
#endif
#endif

#define MOON_OBJ_ALIGNMENT_ MOON_ALIGNOF_(moon_object_alignment_u_)
#define MOON_PTR_ALIGNMENT_ MOON_ALIGNOF_(void *)
#define MOON_GCF_ALIGNMENT_ MOON_ALIGNOF_(moon_object_destructor)
#define MOON_VCK_ALIGNMENT_ MOON_ALIGNOF_(moon_object_vcheck_)
#define MOON_ROUNDTO_(_s, _a) ((((_s) + (_a)-1) / (_a)) * (_a))
#define MOON_PTR_(_p, _o) ((void *)(((char *)(_p)) + (_o)))

/* Raise properly formatted argument error messages. */
static int moon_type_error_(lua_State *L, int i, char const *t1,
                            char const *t2)
{
  char const *msg = lua_pushfstring(L, "%s expected, got %s", t1, t2);
  return luaL_argerror(L, i, msg);
}

static int moon_type_error_invalid_(lua_State *L, int i,
                                    char const *tname)
{
  char const *msg = lua_pushfstring(L, "invalid '%s' object", tname);
  return luaL_argerror(L, i, msg);
}

static int moon_type_error_version_(lua_State *L, int i)
{
  char const *msg = lua_pushfstring(L, "not a moon %d.%d object",
                                    MOON_VERSION_MAJOR,
                                    MOON_VERSION_MINOR);
  return luaL_argerror(L, i, msg);
}

static int moon_is_property(char const *name)
{
  return name[0] == '.';
}
static int moon_is_meta(char const *name)
{
  return name[0] == '_' && name[1] == '_';
}
static int moon_is_method(char const *name)
{
  return !moon_is_meta(name) && !moon_is_property(name);
}

/* Default implementation of a __tostring metamethod for moon objects
 * which displays the type name and memory address. */
MOON_LLINKAGE_BEGIN
static int moon_object_default_tostring_(lua_State *L)
{
  void *ptr = lua_touserdata(L, 1);
  char const *name = lua_tostring(L, lua_upvalueindex(1));
  char const *basename = strrchr(name, '.');
  if (basename != NULL)
    name = basename + 1;
  lua_pushfstring(L, "[%s]: %p", name, ptr);
  return 1;
}
MOON_LLINKAGE_END

/* Run the destructor and mark the object as invalid/destroyed. */
static void moon_object_run_destructor_(moon_object_header *h)
{
  if (h->cleanup_offset > 0 && (h->flags & MOON_OBJECT_IS_VALID))
  {
    void *p = MOON_PTR_(h, h->object_offset);
    moon_object_destructor *gc = NULL;
    gc = (moon_object_destructor *)MOON_PTR_(h, h->cleanup_offset);
    if (h->flags & MOON_OBJECT_IS_POINTER)
      p = *((void **)p);
    if (*gc != 0 && p != NULL)
      (*gc)(p);
  }
  h->flags &= ~MOON_OBJECT_IS_VALID;
}

/* Common __gc metamethod for all moon objects. The actual finalizer
 * function is stored in the userdata to support different lifetimes.
 */
MOON_LLINKAGE_BEGIN
static int moon_object_default_gc_(lua_State *L)
{
  moon_object_header *h = (moon_object_header *)lua_touserdata(L, 1);
  moon_object_run_destructor_(h);
  return 0;
}
MOON_LLINKAGE_END

static int moon_index_dispatch_methods_(lua_State *L)
{
  if (lua_type(L, lua_upvalueindex(1)) == LUA_TTABLE)
  {
    lua_pushvalue(L, 2); /* duplicate key */
    lua_rawget(L, lua_upvalueindex(1));
    if (!lua_isnil(L, -1))
      return 1;
    lua_pop(L, 1);
  }
  return 0;
}

static int moon_index_dispatch_properties_(lua_State *L)
{
  if (lua_type(L, lua_upvalueindex(2)) == LUA_TTABLE)
  {
    lua_pushvalue(L, 2); /* duplicate key */
    lua_rawget(L, lua_upvalueindex(2));
    if (!lua_isnil(L, -1))
    {
      lua_pushvalue(L, 1);
      lua_call(L, 1, 1);
      return 1;
    }
    lua_pop(L, 1);
  }
  return 0;
}

static int moon_index_dispatch_function_(lua_State *L)
{
  if (lua_type(L, lua_upvalueindex(3)) == LUA_TFUNCTION)
  {
    lua_pushvalue(L, lua_upvalueindex(3));
    lua_pushvalue(L, 1);
    lua_pushvalue(L, 2);
    lua_call(L, 2, 1);
    return 1;
  }
  return 0;
}

static int moon_newindex_dispatch_properties_(lua_State *L)
{
  if (lua_type(L, lua_upvalueindex(1)) == LUA_TTABLE)
  {
    lua_pushvalue(L, 2); /* duplicate key */
    lua_rawget(L, lua_upvalueindex(1));
    if (lua_isfunction(L, -1))
    {
      lua_pushvalue(L, 1);
      lua_pushvalue(L, 2);
      lua_pushvalue(L, 3);
      lua_call(L, 3, 0);
      return 1;
    }
    lua_pop(L, 1);
  }
  return 0;
}

static int moon_newindex_dispatch_function_(lua_State *L)
{
  if (lua_type(L, lua_upvalueindex(2)) == LUA_TFUNCTION)
  {
    lua_pushvalue(L, lua_upvalueindex(2));
    lua_pushvalue(L, 1);
    lua_pushvalue(L, 2);
    lua_pushvalue(L, 3);
    lua_call(L, 3, 0);
    return 1;
  }
  return 0;
}

/* Check the methods and properties tables for a given key and then
 * (if unsuccessful) call the registered C function for looking up
 * properties. */
MOON_LLINKAGE_BEGIN
static int moon_index_dispatch_(lua_State *L)
{
  if (!moon_index_dispatch_methods_(L) &&
      !moon_index_dispatch_properties_(L) &&
      !moon_index_dispatch_function_(L))
    lua_pushnil(L);
  return 1;
}

static int moon_newindex_dispatch_(lua_State *L)
{
  if (!moon_newindex_dispatch_properties_(L) &&
      !moon_newindex_dispatch_function_(L))
    luaL_error(L, "attempt to set invalid field");
  return 0;
}
MOON_LLINKAGE_END

static lua_CFunction moon_getf_(lua_State *L, char const *name,
                                lua_CFunction def)
{
  lua_CFunction f = 0;
  lua_pushliteral(L, "__moon");
  lua_rawget(L, LUA_REGISTRYINDEX);
  if (lua_type(L, -1) != LUA_TTABLE)
  {
    lua_pop(L, 1);
    lua_newtable(L);
    lua_pushliteral(L, "__moon");
    lua_pushvalue(L, -2);
    lua_rawset(L, LUA_REGISTRYINDEX);
  }
  lua_getfield(L, -1, name);
  f = lua_tocfunction(L, -1);
  lua_pop(L, 1);
  if (!f)
  {
    f = def;
    lua_pushcfunction(L, def);
    lua_setfield(L, -2, name);
  }
  lua_pop(L, 1);
  return f;
}

static void moon_pushreg_(lua_State *L, luaL_Reg const funcs[],
                          int (*predicate)(char const *),
                          int nups, int firstupvalue, int skip)
{
  if (funcs != NULL)
  {
    lua_newtable(L);
    for (; funcs->func; ++funcs)
    {
      if (predicate(funcs->name))
      {
        int i = 0;
        for (i = 0; i < nups; ++i)
          lua_pushvalue(L, firstupvalue + i);
        lua_pushcclosure(L, funcs->func, nups);
        lua_setfield(L, -2, funcs->name + skip);
      }
    }
  }
  else
    lua_pushnil(L);
}

static void moon_pushfunction_(lua_State *L, lua_CFunction func,
                               int nups, int firstupvalue)
{
  if (func != 0)
  {
    int i = 0;
    for (i = 0; i < nups; ++i)
      lua_pushvalue(L, firstupvalue + i);
    lua_pushcclosure(L, func, nups);
  }
  else
    lua_pushnil(L);
}

/* Depending on the availability of a methods table and/or a C
 * function for looking up properties this function creates an __index
 * metamethod (function or table). */
static void moon_makeindex_(lua_State *L, luaL_Reg const methods[],
                            luaL_Reg const properties[],
                            lua_CFunction pindex, int nups)
{
  int firstupvalue = lua_gettop(L) + 1 - nups;
  if (!properties && !pindex)
  { /* methods only (maybe) */
    moon_pushreg_(L, methods, moon_is_method, nups, firstupvalue, 0);
    if (nups > 0)
    {
      lua_replace(L, firstupvalue);
      lua_pop(L, nups - 1);
    }
  }
  else if (!methods && !properties)
  { /* index function only */
    lua_pushcclosure(L, pindex, nups);
  }
  else
  {
    lua_CFunction dispatch = moon_getf_(L, "index", moon_index_dispatch_);
    moon_pushreg_(L, methods, moon_is_method, nups, firstupvalue, 0);
    moon_pushreg_(L, properties, moon_is_property, nups, firstupvalue, 1);
    moon_pushfunction_(L, pindex, nups, firstupvalue);
    lua_pushcclosure(L, dispatch, 3);
    if (nups > 0)
    {
      lua_replace(L, firstupvalue);
      lua_pop(L, nups - 1);
    }
  }
}

static void moon_makenewindex_(lua_State *L, luaL_Reg const properties[],
                               lua_CFunction pnewindex, int nups)
{
  if (!properties && !pnewindex)
  {
    lua_pop(L, nups);
    lua_pushnil(L);
  }
  else if (!properties)
  {
    lua_pushcclosure(L, pnewindex, nups);
  }
  else
  {
    int firstupvalue = lua_gettop(L) + 1 - nups;
    lua_CFunction dispatch = moon_getf_(L, "newindex", moon_newindex_dispatch_);
    moon_pushreg_(L, properties, moon_is_property, nups, firstupvalue, 1);
    moon_pushfunction_(L, pnewindex, nups, firstupvalue);
    lua_pushcclosure(L, dispatch, 2);
    if (nups > 0)
    {
      lua_replace(L, firstupvalue);
      lua_pop(L, nups - 1);
    }
  }
}

/* Type names used by the moon toolkit must not start with a double
 * underscore, because they might be used as keys in the metatable. */
static void moon_check_tname_(lua_State *L, char const *tname)
{
  if (tname == NULL || tname[0] == '_')
    luaL_error(L, "invalid type name: '%s'", tname ? tname : "NULL");
}

MOON_API void moon_defobject(lua_State *L, char const *tname,
                             size_t sz, luaL_Reg const *methods,
                             int nups)
{
  int has_methods = 0;
  int has_properties = 0;
  lua_CFunction index = 0;
  lua_CFunction newindex = 0;
  moon_check_tname_(L, tname);
  luaL_checkstack(L, 2 * nups + 4, "moon_defobject");
  /* we don't use luaL_newmetatable to make sure that we never have a
   * half-constructed metatable in the registry! */
  luaL_getmetatable(L, tname);
  if (!lua_isnil(L, -1))
    luaL_error(L, "type '%s' is already defined", tname);
  lua_pop(L, 1);
  lua_newtable(L);
  lua_pushstring(L, tname);
  lua_pushcclosure(L, moon_object_default_tostring_, 1);
  lua_setfield(L, -2, "__tostring");
  if (methods != NULL)
  {
    luaL_Reg const *l = methods;
    int i = 0;
    for (; l->func != NULL; ++l)
    {
      if (moon_is_meta(l->name))
      {
        int is_index = 0 == strcmp(l->name + 2, "index");
        int is_newindex = 0 == strcmp(l->name + 2, "newindex");
        if (!is_index && !is_newindex)
        {
          for (i = 0; i < nups; ++i)
            lua_pushvalue(L, -nups - 1);
          lua_pushcclosure(L, l->func, nups);
          lua_setfield(L, -2, l->name);
        }
        else if (is_index) /* handle __index later */
          index = l->func;
        else /* handle __newindex later */
          newindex = l->func;
      }
      else if (moon_is_property(l->name))
      {
        has_properties = 1;
      }
      else
        has_methods = 1;
    }
  }
  if (has_methods || has_properties || index)
  {
    int i = 0;
    for (i = 0; i < nups; ++i)
      lua_pushvalue(L, -nups - 1);
    moon_makeindex_(L, has_methods ? methods : NULL,
                    has_properties ? methods : NULL, index, nups);
    lua_setfield(L, -2, "__index");
  }
  if (has_properties || newindex)
  {
    int i = 0;
    for (i = 0; i < nups; ++i)
      lua_pushvalue(L, -nups - 1);
    moon_makenewindex_(L, methods, newindex, nups);
    lua_setfield(L, -2, "__newindex");
  }
  lua_pushboolean(L, 0);
  lua_setfield(L, -2, "__metatable");
  lua_pushstring(L, tname);
  lua_setfield(L, -2, "__name");
  lua_pushcfunction(L, moon_object_default_gc_);
  lua_pushvalue(L, -1);
  lua_setfield(L, -3, "__gc");
  lua_setfield(L, -2, "__close");
  lua_pushinteger(L, MOON_VERSION);
  lua_setfield(L, -2, "__moon_version");
  lua_pushinteger(L, (lua_Integer)sz);
  lua_setfield(L, -2, "__moon_size");
  lua_setfield(L, LUA_REGISTRYINDEX, tname);
  lua_pop(L, nups);
}

/* Verify that the value at the stack top is the metatable for a moon
 * object type. */
static void moon_check_metatable_(lua_State *L, char const *tname)
{
  if (!lua_istable(L, -1))
    luaL_error(L, "no metatable for type '%s' defined", tname);
  lua_getfield(L, -1, "__moon_version");
  if (lua_tointeger(L, -1) != MOON_VERSION)
    luaL_error(L, "'%s' is not a moon %d.%d object type", tname,
               MOON_VERSION_MAJOR, MOON_VERSION_MINOR);
  lua_pop(L, 1);
}

/* Pushes the metatable for the given type onto the Lua stack, and
 * makes sure that the given type is a moon object type. */
static void moon_push_metatable_(lua_State *L, char const *tname)
{
  moon_check_tname_(L, tname);
  luaL_getmetatable(L, tname);
  moon_check_metatable_(L, tname);
}

MOON_API void *moon_newobject(lua_State *L, char const *tname,
                              void (*gc)(void *))
{
  moon_object_header *obj = NULL;
  size_t off1 = 0;
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable : 4116)
#endif
  size_t off2 = MOON_ROUNDTO_(sizeof(moon_object_header),
                              MOON_OBJ_ALIGNMENT_);
  size_t sz = 0;
  luaL_checkstack(L, 2, "moon_newobject");
  moon_push_metatable_(L, tname);
  lua_getfield(L, -1, "__moon_size");
  sz = lua_tointeger(L, -1);
  lua_pop(L, 1);
  if (sz == 0)
    luaL_error(L, "type '%s' is incomplete (size is 0)", tname);
  if (gc != 0)
  {
    off1 = MOON_ROUNDTO_(sizeof(moon_object_header),
                         MOON_GCF_ALIGNMENT_);
    off2 = MOON_ROUNDTO_(off1 + sizeof(moon_object_destructor),
                         MOON_OBJ_ALIGNMENT_);
#ifdef _MSC_VER
#pragma warning(pop)
#endif
  }
  obj = (moon_object_header *)lua_newuserdata(L, sz + off2);
  if (off1 > 0)
  {
    moon_object_destructor *cl = NULL;
    cl = (moon_object_destructor *)MOON_PTR_(obj, off1);
    *cl = gc;
  }
  obj->cleanup_offset = off1;
  obj->object_offset = off2;
  obj->vcheck_offset = 0;
  obj->flags = MOON_OBJECT_IS_VALID;
  lua_insert(L, -2);
  lua_setmetatable(L, -2);
  return MOON_PTR_(obj, off2);
}

MOON_API void **moon_newpointer(lua_State *L, char const *tname,
                                void (*gc)(void *))
{
  moon_object_header *obj = NULL;
  void **p = NULL;
  size_t off1 = 0;
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable : 4116)
#endif
  size_t off2 = MOON_ROUNDTO_(sizeof(moon_object_header),
                              MOON_PTR_ALIGNMENT_);
  luaL_checkstack(L, 2, "moon_newpointer");
  moon_push_metatable_(L, tname);
  if (gc != 0)
  {
    off1 = MOON_ROUNDTO_(sizeof(moon_object_header),
                         MOON_GCF_ALIGNMENT_);
    off2 = MOON_ROUNDTO_(off1 + sizeof(moon_object_destructor),
                         MOON_PTR_ALIGNMENT_);
#ifdef _MSC_VER
#pragma warning(pop)
#endif
  }
  obj = (moon_object_header *)lua_newuserdata(L, sizeof(void *) + off2);
  p = (void **)MOON_PTR_(obj, off2);
  *p = NULL;
  if (off1 > 0)
  {
    moon_object_destructor *cl = NULL;
    cl = (moon_object_destructor *)MOON_PTR_(obj, off1);
    *cl = gc;
  }
  obj->cleanup_offset = off1;
  obj->object_offset = off2;
  obj->vcheck_offset = 0;
  obj->flags = MOON_OBJECT_IS_VALID | MOON_OBJECT_IS_POINTER;
  lua_insert(L, -2);
  lua_setmetatable(L, -2);
  return p;
}

MOON_API void **moon_newfield(lua_State *L, char const *tname,
                              int idx, int (*isvalid)(void *),
                              void *tagp)
{
  moon_object_header *obj = NULL;
  moon_object_vcheck_ *nextcheck = NULL;
  void **p = NULL;
  size_t off1 = 0;
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable : 4116)
#endif
  size_t off2 = MOON_ROUNDTO_(sizeof(moon_object_header),
                              MOON_PTR_ALIGNMENT_);
  luaL_checkstack(L, 3, "moon_newfield");
  if (idx != 0)
  {
    moon_object_header *h = (moon_object_header *)lua_touserdata(L, idx);
    idx = moon_absindex(L, idx);
    if (h != NULL && lua_getmetatable(L, idx))
    {
      lua_getfield(L, -1, "__moon_version");
      if (lua_tointeger(L, -1) == MOON_VERSION)
      {
        if (h->vcheck_offset > 0)
        {
          moon_object_vcheck_ *vc = NULL;
          vc = (moon_object_vcheck_ *)MOON_PTR_(h, h->vcheck_offset);
          if (isvalid == 0)
          { /* inherit vcheck from idx object */
            isvalid = vc->check;
            tagp = vc->tagp;
            nextcheck = vc->next;
          }
          else /* add it to the chain */
            nextcheck = vc;
        }
      }
      lua_pop(L, 2);
    }
  }
  moon_push_metatable_(L, tname);
  if (isvalid != 0)
  {
    off1 = MOON_ROUNDTO_(sizeof(moon_object_header),
                         MOON_VCK_ALIGNMENT_);
    off2 = MOON_ROUNDTO_(off1 + sizeof(moon_object_vcheck_),
                         MOON_PTR_ALIGNMENT_);
#ifdef _MSC_VER
#pragma warning(pop)
#endif
  }
  obj = (moon_object_header *)lua_newuserdata(L, sizeof(void *) + off2);
  p = (void **)MOON_PTR_(obj, off2);
  *p = NULL;
  obj->vcheck_offset = off1;
  obj->object_offset = off2;
  obj->cleanup_offset = 0;
  obj->flags = MOON_OBJECT_IS_VALID | MOON_OBJECT_IS_POINTER;
  if (off1 > 0)
  {
    moon_object_vcheck_ *vc = NULL;
    vc = (moon_object_vcheck_ *)MOON_PTR_(obj, off1);
    vc->check = isvalid;
    vc->tagp = tagp;
    vc->next = nextcheck;
  }
  lua_insert(L, -2);
  lua_setmetatable(L, -2);
  if (idx != 0)
  {
    lua_newtable(L);
    lua_pushvalue(L, idx);
    lua_rawseti(L, -2, 1);
#if LUA_VERSION_NUM < 502
    lua_setfenv(L, -2);
#else
    lua_setuservalue(L, -2);
#endif
  }
  return p;
}

MOON_API int moon_getmethods(lua_State *L, char const *tname)
{
  int t = 0;
  luaL_checkstack(L, 2, "moon_getmethods");
  moon_push_metatable_(L, tname);
  lua_getfield(L, -1, "__index");
  lua_replace(L, -2);
  t = lua_type(L, -1);
  if (t == LUA_TTABLE)
    return t;
  else if (t == LUA_TFUNCTION)
  {
    lua_CFunction dispatch = moon_getf_(L, "index",
                                        moon_index_dispatch_);
    if (lua_tocfunction(L, -1) == dispatch &&
        lua_getupvalue(L, -1, 1) != NULL)
    {
      lua_replace(L, -2);
      if (lua_type(L, -1) == LUA_TTABLE)
        return LUA_TTABLE;
    }
  }
  lua_pop(L, 1);
  return LUA_TNIL;
}

MOON_API void moon_killobject(lua_State *L, int idx)
{
  moon_object_header *h = (moon_object_header *)lua_touserdata(L, idx);
  luaL_checkstack(L, 2, "moon_killobject");
  if (h == NULL || !lua_getmetatable(L, idx))
    moon_type_error_version_(L, idx);
  lua_getfield(L, -1, "__moon_version");
  if (lua_tointeger(L, -1) != MOON_VERSION)
    moon_type_error_version_(L, idx);
  lua_pop(L, 2);
  moon_object_run_destructor_(h);
}

MOON_API void moon_defcast(lua_State *L, char const *tname1,
                           char const *tname2,
                           moon_object_cast cast)
{
  luaL_checkstack(L, 2, "moon_defcast");
  moon_push_metatable_(L, tname1);
  moon_check_tname_(L, tname2);
  lua_pushcfunction(L, (lua_CFunction)(void (*)(void))cast);
  lua_setfield(L, -2, tname2);
  lua_pop(L, 1);
}

/* Validates a chain of vcheck objects. The chain won't be long, so
 * a recursive approach should be fine! */
static int moon_validate_vcheck_(moon_object_vcheck_ const *vc)
{
  if (vc->next != NULL)
    return moon_validate_vcheck_(vc->next) &&
           (vc->check == 0 || vc->check(vc->tagp));
  else
    return vc->check == 0 || vc->check(vc->tagp);
}

MOON_API void *moon_checkobject(lua_State *L, int idx,
                                char const *tname)
{
  moon_object_header *h = (moon_object_header *)lua_touserdata(L, idx);
  void *p = NULL;
  int res = 0;
  moon_object_cast cast = 0;
  moon_check_tname_(L, tname);
  luaL_checkstack(L, 3, "moon_checkobject");
  idx = moon_absindex(L, idx);
  if (h == NULL)
    moon_type_error_(L, idx, tname, luaL_typename(L, idx));
  if (lua_islightuserdata(L, idx))
    moon_type_error_(L, idx, tname, "lightuserdata");
  if (!lua_getmetatable(L, idx))
    moon_type_error_(L, idx, tname, "userdata");
  lua_getfield(L, -1, "__moon_version");
  if (lua_tointeger(L, -1) != MOON_VERSION)
  {
    lua_pop(L, 2);
    moon_type_error_version_(L, idx);
  }
  lua_pop(L, 1);
  luaL_getmetatable(L, tname);
  res = lua_rawequal(L, -1, -2);
  lua_pop(L, 1);
  if (!res)
  {
    lua_getfield(L, -1, tname);
    cast = (moon_object_cast)(void (*)(void))lua_tocfunction(L, -1);
    lua_pop(L, 1);
    if (cast == 0)
    {
      char const *name = NULL;
      lua_getfield(L, -1, "__name");
      name = lua_tostring(L, -1);
      moon_type_error_(L, idx, tname, name ? name : "userdata");
    }
  }
  lua_pop(L, 1);
  if (!(h->flags & MOON_OBJECT_IS_VALID))
    moon_type_error_invalid_(L, idx, tname);
  if (h->vcheck_offset > 0)
  {
    moon_object_vcheck_ *vc = NULL;
    vc = (moon_object_vcheck_ *)MOON_PTR_(h, h->vcheck_offset);
    if (!moon_validate_vcheck_(vc))
      moon_type_error_invalid_(L, idx, tname);
  }
  p = MOON_PTR_(h, h->object_offset);
  if (h->flags & MOON_OBJECT_IS_POINTER)
    p = *((void **)p);
  if (p == NULL)
    moon_type_error_invalid_(L, idx, tname);
  if (cast != 0)
  {
    p = cast(p);
    if (p == NULL)
      moon_type_error_invalid_(L, idx, tname);
  }
  return p;
}

MOON_API void *moon_testobject(lua_State *L, int idx,
                               char const *tname)
{
  moon_object_header *h = (moon_object_header *)lua_touserdata(L, idx);
  void *p = NULL;
  int res = 0;
  moon_object_cast cast = 0;
  moon_check_tname_(L, tname);
  luaL_checkstack(L, 2, "moon_testobject");
  if (h == NULL || !lua_getmetatable(L, idx))
    return NULL;
  lua_getfield(L, -1, "__moon_version");
  if (lua_tointeger(L, -1) != MOON_VERSION)
  {
    lua_pop(L, 2);
    return NULL;
  }
  lua_pop(L, 1);
  luaL_getmetatable(L, tname);
  res = lua_rawequal(L, -1, -2);
  lua_pop(L, 1);
  if (!res)
  {
    lua_getfield(L, -1, tname);
    cast = (moon_object_cast)(void (*)(void))lua_tocfunction(L, -1);
    lua_pop(L, 2);
    if (cast == 0)
      return NULL;
  }
  else
    lua_pop(L, 1);
  if (!(h->flags & MOON_OBJECT_IS_VALID))
    return NULL;
  if (h->vcheck_offset > 0)
  {
    moon_object_vcheck_ *vc = NULL;
    vc = (moon_object_vcheck_ *)MOON_PTR_(h, h->vcheck_offset);
    if (!moon_validate_vcheck_(vc))
      return NULL;
  }
  p = MOON_PTR_(h, h->object_offset);
  if (h->flags & MOON_OBJECT_IS_POINTER)
    p = *((void **)p);
  if (cast != 0)
    p = cast(p);
  return p;
}

static void *moon_cast_id_(void *p)
{
  return p;
}

static void moon_copy_table_(lua_State *L, int src, int dst)
{
  src = moon_absindex(L, src);
  dst = moon_absindex(L, dst);
  lua_pushnil(L);
  while (lua_next(L, src))
  {
    lua_pushvalue(L, -2); /* duplicate key */
    lua_pushvalue(L, -2); /* duplicate value */
    lua_rawset(L, dst);
    lua_pop(L, 1); /* pop value */
  }
}

MOON_LLINKAGE_BEGIN
MOON_API int moon_derive(lua_State *L)
{
  char const *newtype = luaL_checkstring(L, 1);
  char const *oldtype = luaL_checkstring(L, 2);
  int t = 0;
  lua_settop(L, 2);
  moon_check_tname_(L, newtype);
  lua_pushvalue(L, 1);
  lua_rawget(L, LUA_REGISTRYINDEX);
  luaL_argcheck(L, lua_isnil(L, -1), 1,
                "attempt to redefine type");
  lua_pop(L, 1);
  lua_pushvalue(L, 2);
  lua_rawget(L, LUA_REGISTRYINDEX); /* 3: old metatable */
  moon_check_metatable_(L, oldtype);
  /* clone metatable */
  lua_newtable(L); /* 4: new metatable */
  moon_copy_table_(L, 3, 4);
  /* replace __tostring */
  lua_pushvalue(L, 1);
  lua_pushcclosure(L, moon_object_default_tostring_, 1);
  lua_setfield(L, 4, "__tostring");
  /* add cast to old type */
  lua_pushvalue(L, 2);
  lua_pushcfunction(L, moon_getf_(L, "cast",
                                  (lua_CFunction)(void (*)(void))moon_cast_id_));
  lua_rawset(L, 4);
  /* replace __index metamethod */
  lua_pushliteral(L, "__index");
  lua_rawget(L, 4); /* 5: __index metamethod */
  t = lua_type(L, 5);
  lua_newtable(L);               /* 6: new methods table */
  lua_pushliteral(L, "__index"); /* 7: string "__index" */
  if (t == LUA_TTABLE)
  {
    moon_copy_table_(L, 5, 6);
    lua_pushvalue(L, 6); /* 8: new methods table */
  }
  else if (t == LUA_TFUNCTION)
  {
    lua_CFunction dispatch = moon_getf_(L, "index",
                                        moon_index_dispatch_);
    if (lua_tocfunction(L, 5) == dispatch)
    {
      lua_getupvalue(L, 5, 1); /* 8: old methods table */
      if (lua_istable(L, -1))
        moon_copy_table_(L, -1, 6);
      lua_pop(L, 1);
      lua_pushvalue(L, 6);              /* 8: new methods table */
      lua_getupvalue(L, 5, 2);          /* 9: properties */
      lua_getupvalue(L, 5, 3);          /* 10: index func */
      lua_pushcclosure(L, dispatch, 3); /* 8: dispatcher */
    }
    else
    {
      lua_pushvalue(L, 6);              /* 8: new methods table */
      lua_pushnil(L);                   /* 9: no properties */
      lua_pushvalue(L, 5);              /* 10: index func */
      lua_pushcclosure(L, dispatch, 3); /* 8: dispatcher */
    }
  }
  else
    lua_pushvalue(L, 6); /* 8: new methods table */
  lua_rawset(L, 4);
  /* register new type */
  lua_pushvalue(L, 1);
  lua_pushvalue(L, 4);
  lua_rawset(L, LUA_REGISTRYINDEX);
  return 1;
}
MOON_LLINKAGE_END

MOON_LLINKAGE_BEGIN
MOON_API int moon_downcast(lua_State *L)
{
  void *h = lua_touserdata(L, 1);
  char const *tname = luaL_checkstring(L, 2);
  moon_object_cast cast = 0, id_cast = 0;
  lua_settop(L, 2);
  luaL_argcheck(L, h != NULL && lua_getmetatable(L, 1), 1,
                "object expected"); /* 3: metatable */
  luaL_argcheck(L, lua_istable(L, -1), 1, "object expected");
  lua_getfield(L, -1, "__moon_version");
  luaL_argcheck(L, lua_tointeger(L, -1) == MOON_VERSION, 1,
                "object expected");
  lua_pop(L, 1);
  moon_check_tname_(L, tname);
  lua_getfield(L, -1, "__name"); /* 4: __name */
  lua_pushvalue(L, 2);
  lua_rawget(L, LUA_REGISTRYINDEX); /* 5: metatable */
  moon_check_metatable_(L, tname);
  lua_pushvalue(L, 4);
  lua_rawget(L, 5); /* 6: cast function */
  cast = (moon_object_cast)(void (*)(void))lua_tocfunction(L, -1);
  id_cast = (moon_object_cast)(void (*)(void))moon_getf_(L, "cast", (lua_CFunction)(void (*)(void))moon_cast_id_);
  luaL_argcheck(L, cast == id_cast, 1, "invalid downcast");
  lua_pop(L, 1);
  lua_setmetatable(L, 1);
  lua_settop(L, 1);
  return 1;
}
MOON_LLINKAGE_END

MOON_API lua_Integer moon_checkint(lua_State *L, int idx,
                                   lua_Integer low,
                                   lua_Integer high)
{
  lua_Integer v = luaL_checkinteger(L, idx);
  int valid = (high < low) ? (low <= v || v <= high)
                           : (low <= v && v <= high);
  if (!valid)
  {
    char const *msg = NULL;
#if LUA_VERSION_NUM >= 503
    msg = lua_pushfstring(L, "value out of range [%I,%I]", low, high);
#else
    if (low >= INT_MIN && low <= INT_MAX &&
        high >= INT_MIN && high <= INT_MAX)
      msg = lua_pushfstring(L, "value out of range [%d,%d]",
                            (int)low, (int)high);
    else
      msg = lua_pushfstring(L, "value out of range [%f,%f]",
                            (lua_Number)low, (lua_Number)high);
#endif
    luaL_argerror(L, idx, msg);
  }
  return v;
}

MOON_API lua_Integer moon_optint(lua_State *L, int idx,
                                 lua_Integer low, lua_Integer high,
                                 lua_Integer def)
{
  if (!lua_isnoneornil(L, idx))
    def = moon_checkint(L, idx, low, high);
  return def;
}

MOON_API int *moon_atexit(lua_State *L, lua_CFunction func)
{
  int *flag = NULL;
  luaL_checkstack(L, 3, "moon_atexit");
  flag = (int *)lua_newuserdata(L, sizeof(int));
  *flag = 0;
  /* setmetatable( flag, { __gc = func } ) */
  lua_newtable(L);
  lua_pushcfunction(L, func);
  lua_setfield(L, -2, "__gc");
  lua_setmetatable(L, -2);
  /* registry[ flag ] = flag */
  lua_pushvalue(L, -1);
  lua_pushvalue(L, -2);
  lua_settable(L, LUA_REGISTRYINDEX);
  return flag;
}

MOON_API void moon_setuvfield(lua_State *L, int i, char const *key)
{
  luaL_checkstack(L, 2, "moon_setuvfield");
#if LUA_VERSION_NUM < 502
  lua_getfenv(L, i);
#else
  lua_getuservalue(L, i);
#endif
  if (!lua_istable(L, -1))
    luaL_error(L, "attempt to add to non-table uservalue");
  lua_pushvalue(L, -2);
  lua_setfield(L, -2, key);
  lua_pop(L, 2);
}

MOON_API int moon_getuvfield(lua_State *L, int i, char const *key)
{
  luaL_checkstack(L, 2, "moon_getuvfield");
#if LUA_VERSION_NUM < 502
  lua_getfenv(L, i);
#else
  lua_getuservalue(L, i);
#endif
  if (lua_istable(L, -1))
  {
    int t = 0;
    lua_getfield(L, -1, key);
    lua_replace(L, -2);
    t = lua_type(L, -1);
    if (t != LUA_TNIL)
      return t;
  }
  lua_pop(L, 1);
  return LUA_TNIL;
}

MOON_API void moon_getcache(lua_State *L, int index)
{
  static char xyz = 0; /* used as a unique key */
  luaL_checkstack(L, 3, "moon_getcache");
  index = moon_absindex(L, index);
  lua_pushlightuserdata(L, &xyz);
  lua_rawget(L, index);
  if (!lua_istable(L, -1))
  {
    lua_pop(L, 1);
    lua_createtable(L, 0, 1);
    lua_pushliteral(L, "__mode");
    lua_pushliteral(L, "v");
    lua_rawset(L, -3);
    lua_pushvalue(L, -1);
    lua_setmetatable(L, -2);
    lua_pushlightuserdata(L, &xyz);
    lua_pushvalue(L, -2);
    lua_rawset(L, index);
  }
}

static int moon_check_type_(lua_State *L, int idx, char const *spec)
{
  int t = lua_type(L, idx);
  while (*spec != '\0')
  {
    switch (*spec)
    {
    case 'n':
      if (t == LUA_TNIL)
        return 1;
      break;
    case 'b':
      if (t == LUA_TBOOLEAN)
        return 1;
      break;
    case 'l':
      if (t == LUA_TLIGHTUSERDATA)
        return 1;
      break;
    case 'i':
      if (t == LUA_TNUMBER
#if LUA_VERSION_NUM >= 503
          && lua_isinteger(L, idx)
#endif
      )
        return 1;
      break;
    case 'd':
      if (t == LUA_TNUMBER)
        return 1;
      break;
    case 's':
      if (t == LUA_TSTRING)
        return 1;
      break;
    case 't':
      if (t == LUA_TTABLE)
        return 1;
      break;
    case 'f':
      if (t == LUA_TFUNCTION)
        return 1;
      break;
    case 'u':
      if (t == LUA_TUSERDATA)
        return 1;
      break;
    case 'c':
      if (t == LUA_TTHREAD)
        return 1;
      break;
    case 'a':
      if (t != LUA_TNIL)
        return 1;
      break;
    }
    ++spec;
  }
  return 0;
}

static char const *moon_type2spec_(int t)
{
  switch (t)
  {
  case LUA_TNONE:
  case LUA_TNIL:
    return "n";
  case LUA_TBOOLEAN:
    return "b";
  case LUA_TLIGHTUSERDATA:
    return "l";
  case LUA_TNUMBER:
    return "d";
  case LUA_TSTRING:
    return "s";
  case LUA_TTABLE:
    return "t";
  case LUA_TFUNCTION:
    return "f";
  case LUA_TUSERDATA:
    return "u";
  case LUA_TTHREAD:
    return "c";
  default:
    return "?";
  }
}

#define MOON_SEP_ \
  "######################################################################"

MOON_API void moon_stack_assert_(lua_State *L, char const *file,
                                 int line, char const *func, ...)
{
  int top = lua_gettop(L);
  int nargs = 0;
  int skip = 0;
  int have_error = 0;
  int i = 0;
  char const *arg;
  va_list ap;
  va_start(ap, func);
  while ((arg = va_arg(ap, char const *)) != NULL)
    ++nargs;
  va_end(ap);
  if (nargs > top)
  {
    fputs(MOON_SEP_ "\n", stderr);
    fprintf(stderr, "Lua stack assertion failed:"
                    " less stack slots (%d) than expected (%d)!\n",
            top, nargs);
    have_error = 1;
    skip = nargs - top;
  }
  va_start(ap, func);
  for (i = 0; i < skip; ++i)
    arg = va_arg(ap, char const *);
  for (i = top + skip - nargs + 1; i <= top; ++i)
  {
    arg = va_arg(ap, char const *);
    if (!moon_check_type_(L, i, arg))
    {
      if (!have_error)
        fputs(MOON_SEP_ "\n", stderr);
      fprintf(stderr, "Lua stack assertion failed:"
                      " '%s' at slot %d (expected %s'%s')!\n",
              moon_type2spec_(lua_type(L, i)), i,
              (arg[0] != '\0' && arg[1] == 0) ? "" : "one of ",
              arg);
      have_error = 1;
    }
  }
  va_end(ap);
  if (have_error)
  {
    moon_stack_(L, file, line, func);
    luaL_error(L, "Lua stack assertion failed!");
  }
}

MOON_API void moon_stack_(lua_State *L, char const *file, int line,
                          char const *func)
{
  int n = lua_gettop(L);
  int i = 0;
  fputs(MOON_SEP_ "\n", stderr);
  fprintf(stderr, "Lua stack in function '%s' at '%s:%d':\n",
          func != NULL ? func : "(unknown)", file, line);
  for (i = 1; i <= n; ++i)
  {
    fprintf(stderr, "%02d: %s ", i, luaL_typename(L, i));
    switch (lua_type(L, i))
    {
    case LUA_TNONE:
      fputs("(none)\n", stderr);
      break;
    case LUA_TNIL:
      fputs("(nil)\n", stderr);
      break;
    case LUA_TBOOLEAN:
      fprintf(stderr, "(%s)\n", lua_toboolean(L, i) ? "true" : "false");
      break;
    case LUA_TNUMBER:
#if LUA_VERSION_NUM >= 503
      if (lua_isinteger(L, i))
        fprintf(stderr, "(" LUA_INTEGER_FMT ")\n",
                lua_tointeger(L, i));
      else
#endif
        fprintf(stderr, "(" LUA_NUMBER_FMT ")\n",
                lua_tonumber(L, i));
      break;
    case LUA_TSTRING:
    {
      char const *str = lua_tostring(L, i);
      char const *ellipsis = "";
#if LUA_VERSION_NUM < 502
      unsigned len = (unsigned)lua_objlen(L, i);
#else
      unsigned len = (unsigned)lua_rawlen(L, i);
#endif
      unsigned i = 0;
      fprintf(stderr, "(len: %u, str: \"", len);
      if (len > 15)
      {
        len = 15;
        ellipsis = "...";
      }
      for (i = 0; i < len; ++i)
      {
        if (isprint((unsigned char)str[i]))
          putc((unsigned char)str[i], stderr);
        else
          fprintf(stderr, "\\x%02X", (unsigned)str[i]);
      }
      fputs(ellipsis, stderr);
      fputs("\")\n", stderr);
      break;
    }
    case LUA_TLIGHTUSERDATA:
      fprintf(stderr, "(%p)\n", lua_touserdata(L, i));
      break;
    case LUA_TUSERDATA:
      if (luaL_getmetafield(L, i, "__name"))
      {
        char const *name = lua_tostring(L, -1);
        fprintf(stderr, "(type: \"%s\", size: %u, ptr: %p)\n",
                name != NULL ? name : "(NULL)",
#if LUA_VERSION_NUM < 502
                (unsigned)lua_objlen(L, i),
#else
                (unsigned)lua_rawlen(L, i),
#endif
                lua_touserdata(L, i));
        lua_pop(L, 1);
      }
      else
      {
        fprintf(stderr, "(size: %u, ptr: %p)\n",
#if LUA_VERSION_NUM < 502
                (unsigned)lua_objlen(L, i),
#else
                (unsigned)lua_rawlen(L, i),
#endif
                lua_touserdata(L, i));
      }
      break;
    default: /* thread, table, function */
      fprintf(stderr, "(%p)\n", lua_topointer(L, i));
      break;
    }
  }
  fputs(MOON_SEP_ "\n", stderr);
}

#undef MOON_SEP_

/* clean up internally used macros */
#undef MOON_ALIGNOF_
#undef MOON_OBJ_ALIGNMENT_
#undef MOON_PTR_ALIGNMENT_
#undef MOON_GCF_ALIGNMENT_
#undef MOON_VCK_ALIGNMENT_
#undef MOON_ROUNDTO_
#undef MOON_PTR_

#endif /* MOON_C_ */