//go:build puc

package main

/*
#cgo LDFLAGS: -llua
#include <stdlib.h>
#include <stdint.h>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>

extern int luna_run_go_func(uintptr_t);

static inline int luna_run(lua_State *l) {
	return luna_run_go_func(lua_tonumber(l, lua_upvalueindex(1)));
}

static inline void luna_push_function(lua_State *l, uintptr_t f) {
	lua_pushinteger(l, f);
	lua_pushcclosure(l, luna_run, 1);
}
*/
import "C"
import (
	"errors"
	"runtime/cgo"
	"unsafe"
)

type LuaRef C.int

// Lua is a wrapper around C Lua state with several conveniences.
type Lua struct {
	l *C.lua_State
	running **Lua
	yield func()
	resume func() bool
	deferred func()
}

//export luna_run_go_func
// luna_run_go_func calls a Go function from C/Lua.
func luna_run_go_func(f C.uintptr_t) C.int {
	fn := cgo.Handle(f).Value().(func() int)
	return C.int(fn())
}

// Start opens the Lua context with all built-in libraries.
func (l *Lua) Start() error {
	if l.l != nil {
		return errors.New("already started")
	}
	l.l = C.luaL_newstate()
	l.running = &l
	l.yield = nil
	l.resume = nil
	C.luaL_openlibs(l.l)

	// Put traceback function at the start of the stack so it's always
	// possible to refer to it via stack index 1.
	l.PushGoFunction(TracebackHandler)
	return nil
}

// Close closes the Lua context.
func (l *Lua) Close() {
	C.lua_close(l.l)
	l.l = nil
}

// PCall calls a function with the stack index (-nargs-1) expecting nresults
// number of results.
func (l *Lua) PCall(nargs int, nresults int, errfunc int) error {
	*l.running = l
	res := C.lua_pcallk(
		l.l, C.int(nargs), C.int(nresults), C.int(errfunc), 0, nil,
	)
	if res != C.LUA_OK {
		errMsg := l.ToString(-1)
		l.Pop(1)
		l.deferred = nil
		return errors.New(errMsg)
	}
	if l.deferred != nil {
		l.deferred()
		l.deferred = nil
	}
	return nil
}

// LoadFile loads the file code in the current Lua context.
func (l *Lua) LoadFile(file string) error {
	cstr := C.CString(file)
	defer C.free(unsafe.Pointer(cstr))
	res := C.luaL_loadfilex(l.l, cstr, nil)
	if res != C.LUA_OK {
		errMsg := l.ToString(-1)
		l.Pop(1)
		return errors.New(errMsg)
	}
	return nil
}

// StackLen returns the length of the Lua stack.
func (l *Lua) StackLen() int {
	return int(C.lua_gettop(l.l))
}

// ToString converts a stack value with stack index into a string.
func (l *Lua) ToString(index int) string {
	return C.GoString(C.lua_tolstring(l.l, C.int(index), nil))
}

// ToInt converts a stack value with stack index -1 into a number.
func (l *Lua) ToInt(index int) int {
	return int(C.lua_tonumberx(l.l, C.int(index), nil))
}

// ToBoolean converts a stack value with stack index -1 into a boolean.
func (l *Lua) ToBoolean(index int) bool {
	return int(C.lua_toboolean(l.l, C.int(index))) == 1
}

// PopToRef pops the item (stack offset -1) from the stack and then stores it
// in the registry.
func (l *Lua) PopToRef() LuaRef {
	return LuaRef(C.luaL_ref(l.l, C.LUA_REGISTRYINDEX))
}

// Pop pops N items from the Lua stack.
func (l *Lua) Pop(n int) {
	C.lua_settop(l.l, C.int(-n - 1))
}

// SetTop sets head of the stack at top.
func (l *Lua) SetTop(top int) {
	C.lua_settop(l.l, C.int(top))
}

// PushNil pushes tnil onto the Lua stack.
func (l *Lua) PushNil() {
	C.lua_pushnil(l.l)
}

// PushBoolean pushes a boolean onto the Lua stack.
func (l *Lua) PushBoolean(b bool) {
	// For some reason this is needed here to not mess up threads.
	*l.running = l
	if b {
		C.lua_pushboolean(l.l, 1)
	} else {
		C.lua_pushboolean(l.l, 0)
	}
}

// PushNumber pushes a number onto the Lua stack.
func (l *Lua) PushNumber(num int) {
	C.lua_pushnumber(l.l, C.double(num))
}

// PushFloatNumber pushes a float number onto the Lua stack.
func (l *Lua) PushFloatNumber(num float64) {
	C.lua_pushnumber(l.l, C.double(num))
}

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

// PushGoFunction pushes a Go function onto the Lua stack so it's possible to
// call it from Lua. You may need to delete returned handle with .Delete()
// method later.
func (l *Lua) PushGoFunction(f func (l *Lua) int) cgo.Handle {
	h := cgo.NewHandle(func () int {
		return f(*l.running)
	})
	C.luna_push_function(l.l, C.uintptr_t(h))
	return h
}

// CreateTable pushes a new Lua table onto the stack.
func (l *Lua) CreateTable(len int) {
	C.lua_createtable(l.l, 0, C.int(len))
}

// SetTableItem adds a value (stack offset -1) to a table (offset -2) under
// the specified key.
func (l *Lua) SetTableItem(key string) {
	cstr := C.CString(key)
	defer C.free(unsafe.Pointer(cstr))
	C.lua_setfield(l.l, -2, C.CString(key))
}

// GetTableItem gets a value from the table (offset -1) under the specified key
// and puts it onto the stack.
func (l *Lua) GetTableItem(key string) {
	cstr := C.CString(key)
	defer C.free(unsafe.Pointer(cstr))
	C.lua_getfield(l.l, -1, C.CString(key))
}

// RawGetI pushes onto the stack value from table from tableOffset at index i.
func (l *Lua) RawGetI(tableOffset, i int) {
	C.lua_rawgeti(l.l, C.int(tableOffset), C.longlong(i))
}

// PushArray recursively pushes an array of Go values onto the stack.
func (l *Lua) PushArray(array []any) error {
	l.CreateTable(len(array))
	for k, v := range array {
		l.PushNumber(k + 1)
		err := l.PushAny(v)
		if err != nil {
			return err
		}
		C.lua_settable(l.l, C.int(-3))
	}
	return nil
}

// PushFromRef pushes a value from registry ref onto the stack.
func (l *Lua) PushFromRef(ref LuaRef) {
	C.lua_rawgeti(l.l, C.LUA_REGISTRYINDEX, C.longlong(ref));
}

// Unref removes the ref from the registry.
func (l *Lua) Unref(ref LuaRef) {
	C.luaL_unref(l.l, C.LUA_REGISTRYINDEX, C.int(ref))
}

// Type returns type of the value sitting at n index on the stack.
func (l *Lua) Type(n int) int {
	return int(C.lua_type(l.l, C.int(n)))
}

// IsNil checks if the stack contains nil under the given index.
func (l *Lua) IsNil(index int) bool {
	return C.lua_type(l.l, C.int(index)) == C.LUA_TNIL
}

// IsString checks if the stack contains a string under the given index.
func (l *Lua) IsString(index int) bool {
	return C.lua_isstring(l.l, C.int(index)) == 1
}

// IsNumber checks if the stack contains a number (both int and float) under
// the given index.
func (l *Lua) IsNumber(index int) bool {
	return C.lua_isnumber(l.l, C.int(index)) == 1
}

// IsBoolean checks if the stack contains a boolean under the given index.
func (l *Lua) IsBoolean(index int) bool {
	return C.lua_type(l.l, C.int(index)) == C.LUA_TBOOLEAN
}

// IsFunction checks if the stack contains a function under the given index.
func (l *Lua) IsFunction(index int) bool {
	return C.lua_type(l.l, C.int(index)) == C.LUA_TFUNCTION
}

// IsTable checks if the stack contains a table under the given index.
func (l *Lua) IsTable(index int) bool {
	return C.lua_type(l.l, C.int(index)) == C.LUA_TTABLE
}

// Next advances a table iterator at the stack index -2.
// IsTable checks if the stack contains a table under the given index.
func (l *Lua) Next() bool {
	return C.lua_next(l.l, -2) != 0
}

// LoadAndCall loads and calls the code in the current Lua context. Whatever
// the code returns is stored in the stack. To drop the results use l.Pop.
func (l *Lua) LoadAndCall(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)
	}
	return l.PCall(0, C.LUA_MULTRET, 1)
}

// SetGlobal sets a global value at the -1 stack index with the name.
func (l *Lua) SetGlobal(name string) {
	cstr := C.CString(name)
	defer C.free(unsafe.Pointer(cstr))
	C.lua_setglobal(l.l, cstr)
}

// GetGlobal gets a global value under the name.
func (l *Lua) GetGlobal(name string) {
	cstr := C.CString(name)
	defer C.free(unsafe.Pointer(cstr))
	C.lua_getglobal(l.l, cstr)
}

func (l *Lua) NewThread(yield func(), resume func() bool) *Lua {
	newl := &Lua{
		l: C.lua_newthread(l.l),
		running: l.running,
		resume: resume,
		yield: yield,
	}
	newl.PushGoFunction(TracebackHandler)
	return newl
}

// TracebackHandler handles stack trace formatting on errors.
func TracebackHandler(l *Lua) int {
	msg := l.ToString(-1)
	l.GetGlobal("debug")
	l.GetTableItem("traceback")
	l.PushString(msg)
	C.lua_callk(l.l, 1, 1, 0, nil)
	return 1
}