package main

/*
#cgo LDFLAGS: -llua
#include <stdlib.h>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
*/
import "C"
import (
	"errors"
	"unsafe"
	"log"
)

type LuaRef C.longlong
type Lua struct {
	l *C.lua_State
}

func (l *Lua) Start() {
	l.l = C.luaL_newstate()
	C.luaL_openlibs(l.l)
}

func (l *Lua) Close() {
	C.lua_close(l.l)
	C.free(unsafe.Pointer(l.l))
}

func (l *Lua) Require(file string) (LuaRef, error) {
	if !l.LoadFile(file) {
		errMsg := l.ToString(-1)
		l.Pop(1)
		return 0, errors.New("could not open the file:\n" + errMsg)
	}
	if !l.PCall(0, C.LUA_MULTRET) {
		errMsg := l.ToString(-1)
		l.Pop(1)
		return 0, errors.New("could not execute the file:\n" + errMsg)
	}
	if !l.IsTable(-1) {
		return 0, errors.New("module did not return a table")
	}
	return l.PopToRef(), nil
}


func (l *Lua) PCall(nargs int, nresults int) bool {
	res := C.lua_pcallk(l.l, C.int(nargs), C.int(nresults), 0, 0, nil)
	return res == C.LUA_OK
}

func (l *Lua) LoadFile(file string) bool {
	cfile := C.CString(file)
	defer C.free(unsafe.Pointer(cfile))
	res := C.luaL_loadfilex(l.l, cfile, nil)
	return res == C.LUA_OK
}

func (l *Lua) StackLen() int {
	return int(C.lua_gettop(l.l))
}

func (l *Lua) ToString(index int) string {
	return C.GoString(C.lua_tolstring(l.l, C.int(index), nil))
}

func (l *Lua) ToInt(index int) int {
	return int(C.lua_tonumberx(l.l, C.int(index), nil))
}

func (l *Lua) PopToRef() LuaRef {
	return LuaRef(C.luaL_ref(l.l, C.LUA_REGISTRYINDEX))
}

func (l *Lua) Pop(n int) {
	C.lua_settop(l.l, C.int(-n - 1))
}

func (l *Lua) PushNil() {
	C.lua_pushnil(l.l)
}

func (l *Lua) PushString(str string) {
	cstr := C.CString(str)
	defer C.free(unsafe.Pointer(cstr))
	C.lua_pushstring(l.l, cstr)
}

func (l *Lua) PushTable(table map[string]string) {
	C.lua_createtable(l.l, 0, C.int(len(table)))
	for k, v := range table {
		l.PushString(v)
		C.lua_setfield(l.l, -2, C.CString(k))
	}
}

func (l *Lua) PushFromRef(ref LuaRef) {
	C.lua_rawgeti(l.l, C.LUA_REGISTRYINDEX, C.longlong(ref));
}

func (l *Lua) IsString(index int) bool {
	return C.lua_isstring(l.l, C.int(index)) == 1
}

func (l *Lua) IsNumber(index int) bool {
	return C.lua_isnumber(l.l, C.int(index)) == 1
}

func (l *Lua) IsFunction(index int) bool {
	return C.lua_type(l.l, C.int(index)) == C.LUA_TFUNCTION
}

func (l *Lua) IsTable(index int) bool {
	return C.lua_type(l.l, C.int(index)) == C.LUA_TTABLE
}

func (l *Lua) Next() bool {
	return C.lua_next(l.l, -2) != 0
}

func (l *Lua) LoadString(code string) error {
	cstr := C.CString(code)
	defer C.free(unsafe.Pointer(cstr))
	if C.luaL_loadstring(l.l, cstr) != C.LUA_OK {
		errMsg := l.ToString(-1)
		l.Pop(1)
		return errors.New(errMsg)
	}
	if !l.PCall(0, 0) {
		errMsg := l.ToString(-1)
		l.Pop(1)
		return errors.New(errMsg)
	}
	l.Pop(l.StackLen())
	return nil
}

func (l *Lua) PushTableItem(key string) {
	ckey := C.CString(key)
	defer C.free(unsafe.Pointer(ckey))
	C.lua_pushstring(l.l, ckey);
	C.lua_gettable(l.l, -2);
}

func (l *Lua) RestoreStackFunc() func () {
	before := l.StackLen()
	return func () {
		after := l.StackLen()
		diff := after - before
		if diff == 0 {
			return
		} else if diff < 0 {
			log.Fatalf(
				"too many stack pops: len before: %d, after: %d\n",
				before,
				after,
			)
		}
		C.lua_settop(l.l, C.int(before))
	}
}