package main

import (
    "fmt"
    "unsafe"
    lua "github.com/aarzilli/golua/lua"
)

type Book struct {
    Id int64
    Title string
}

func BookCreate(L *lua.State) int {
    title := L.ToString(1)
    book := (*Book)(L.NewUserdata(uintptr(unsafe.Sizeof(Book{}))))

    L.LGetMetaTable("Book")
    L.SetMetaTable(-2)

    book.Id = 1;
    book.Title = title;

    return 1
}

func BookToString(L *lua.State) int {
    book := (*Book)(L.ToUserdata(1))
    L.PushString(fmt.Sprintf("Book(Id=%d, Title=\"%s\")", book.Id, book.Title))

    return 1
}

const test = `
    local book = Book.Create('Le Petit Prince')
    print(book)
    print(book:__tostring())
    print(Book.__tostring(book))
`

func main() {
    L := lua.NewState()
    defer L.Close()
    L.OpenLibs()

    L.NewMetaTable("Book")
    L.PushString("__index")
    L.PushValue(-2)
    L.SetTable(-3)
    L.SetMetaMethod("Create", BookCreate)
    L.SetMetaMethod("__tostring", BookToString)
    L.SetGlobal("Book")

    err := L.DoString(test)
    if err != nil {
        fmt.Println("Error: ", err)
    }
}