--
 -- lua
 -- 判断utf8字符byte长度
 -- 0xxxxxxx - 1 byte
 -- 110yxxxx - 192, 2 byte
 -- 1110yyyy - 225, 3 byte
 -- 11110zzz - 240, 4 byte
 local function chsize(char)
     if not char then
         print("not char")
         return 0
     elseif char > 240 then
         return 4
     elseif char > 225 then
         return 3
     elseif char > 192 then
         return 2
     else
         return 1
     end
 end
 
 -- 计算utf8字符串字符数, 各种字符都按一个字符计算
 -- 例如utf8len("1你好") => 3
 function utf8len(str)
     local len = 0
     local currentIndex = 1
     while currentIndex <= #str do
         local char = string.byte(str, currentIndex)
         currentIndex = currentIndex + chsize(char)
         len = len +1
     end
     return len
 end
 
 -- 截取utf8 字符串
 -- str:            要截取的字符串
 -- startChar:    开始字符下标,从1开始
 -- numChars:    要截取的字符长度
 function utf8sub(str, startChar, numChars)
     local startIndex = 1
     while startChar > 1 do
         local char = string.byte(str, startIndex)
         startIndex = startIndex + chsize(char)
         startChar = startChar - 1
     end
 
     local currentIndex = startIndex
 
     while numChars > 0 and currentIndex <= #str do
         local char = string.byte(str, currentIndex)
         currentIndex = currentIndex + chsize(char)
         numChars = numChars -1
     end
     return str:sub(startIndex, currentIndex - 1)
 end
 
 -- 自测
 function test()
     -- test utf8len
     assert(utf8len("你好1世界哈哈") == 7)
     assert(utf8len("你好世界1哈哈 ") == 8)
     assert(utf8len(" 你好世 界1哈哈") == 9)
     assert(utf8len("12345678") == 8)
     assert(utf8len("øpø你好pix") == 8)
 
     -- test utf8sub
     assert(utf8sub("你好1世界哈哈",2,5) == "好1世界哈")
     assert(utf8sub("1你好1世界哈哈",2,5) == "你好1世界")
     assert(utf8sub(" 你好1世界 哈哈",2,6) == "你好1世界 ")
     assert(utf8sub("你好世界1哈哈",1,5) == "你好世界1")
     assert(utf8sub("12345678",3,5) == "34567")
     assert(utf8sub("øpø你好pix",2,5) == "pø你好p")
 
     print("all test succ")
 end
 
 test()