-- Encoding function

local M = {}

---
-- Converts all UTF-8 character sets to unicode/ASCII characters
-- to generate ISO-8859-1 email bodies etc.
--@param utf8 UTF-8 encoded string
--@return a ASCII/ISO-8859-1 8-bit conform string
-- From http://developer.coronalabs.com/code/utf-8-encode-and-decode

function M.utf8_decode(utf8)

   local unicode = ""
   local mod = math.mod

   local pos = 1
   while pos < string.len(utf8)+1 do

      local v = 1
      local c = string.byte(utf8,pos)
      local n = 0

      if c < 128 then v = c
      elseif c < 192 then v = c
      elseif c < 224 then v = mod(c, 32) n = 2
      elseif c < 240 then v = mod(c, 16) n = 3
      elseif c < 248 then v = mod(c,  8) n = 4
      elseif c < 252 then v = mod(c,  4) n = 5
      elseif c < 254 then v = mod(c,  2) n = 6
      else v = c end

      for i = 2, n do
         pos = pos + 1
         c = string.byte(utf8,pos)
         v = v * 64 + mod(c, 64)
      end

      pos = pos + 1
      if v < 255 then unicode = unicode..string.char(v) end

   end

   return unicode
end

---
-- Converts all unicode characters (>127) into UTF-8 character sets
--@param unicode ASCII or unicoded string
--@return a UTF-8 representation
-- From http://developer.coronalabs.com/code/utf-8-encode-and-decode

function M.utf8_encode(unicode)

   local math = math
   local utf8 = ""

   for i=1,string.len(unicode) do
      local v = string.byte(unicode,i)
      local n, s, b = 1, "", 0
      if v >= 67108864 then n = 6; b = 252
      elseif v >= 2097152 then n = 5; b = 248
      elseif v >= 65536 then n = 4; b = 240
      elseif v >= 2048 then n = 3; b = 224
      elseif v >= 128 then n = 2; b = 192
      end
      for i = 2, n do
         local c = math.mod(v, 64); v = math.floor(v / 64)
         s = string.char(c + 128)..s
      end
      s = string.char(v + b)..s
      utf8 = utf8..s
   end

   return utf8
end


return M