module MDUrl
  module Decode

    @@decodeCache = {};

    DEFTAULT_CHARS   = ';/?:@&=+$,#'
    COMPONENT_CHARS  = ''


    #------------------------------------------------------------------------------
    def self.getDecodeCache(exclude)
      cache = @@decodeCache[exclude]
      return cache if (cache)

      cache = @@decodeCache[exclude] = []

      (0...128).each do |i|
        ch = i.chr
        cache.push(ch)
      end

      (0...exclude.length).each do |i|
        ch = exclude[i].ord
        cache[ch] = '%' + ('0' + ch.to_s(16).upcase).slice(-2, 2)
      end

      return cache
    end


    # Decode percent-encoded string.
    #------------------------------------------------------------------------------
    def self.decode(string, exclude = nil)
      if !exclude.is_a? String
        exclude = DEFTAULT_CHARS
      end

      cache = getDecodeCache(exclude)

      return string.gsub(/(%[a-f0-9]{2})+/i) do |seq|
        result = ''

        i = 0
        l = seq.length
        while i < l
          b1 = seq.slice((i + 1)...(i + 3)).to_i(16)

          if (b1 < 0x80)
            result += cache[b1]
            i += 3
            next
          end

          if ((b1 & 0xE0) == 0xC0 && (i + 3 < l))
            # 110xxxxx 10xxxxxx
            b2 = seq.slice((i + 4)...(i + 6)).to_i(16)

            if ((b2 & 0xC0) == 0x80)
              char = ((b1 << 6) & 0x7C0) | (b2 & 0x3F)

              if (char < 0x80)
                result += "\ufffd\ufffd"
              else
                result += char.chr(Encoding::UTF_8)
              end

              i += 6
              next
            end
          end

          if ((b1 & 0xF0) == 0xE0 && (i + 6 < l))
            # 1110xxxx 10xxxxxx 10xxxxxx
            b2 = seq.slice((i + 4)...(i + 6)).to_i(16)
            b3 = seq.slice((i + 7)...(i + 9)).to_i(16)

            if ((b2 & 0xC0) == 0x80 && (b3 & 0xC0) == 0x80)
              char = ((b1 << 12) & 0xF000) | ((b2 << 6) & 0xFC0) | (b3 & 0x3F)

              if (char < 0x800 || (char >= 0xD800 && char <= 0xDFFF))
                result += "\ufffd\ufffd\ufffd"
              else
                result += char.chr(Encoding::UTF_8)
              end

              i += 9
              next
            end
          end

          if ((b1 & 0xF8) == 0xF0 && (i + 9 < l))
            # 111110xx 10xxxxxx 10xxxxxx 10xxxxxx
            b2 = seq.slice((i + 4)...(i + 6)).to_i(16)
            b3 = seq.slice((i + 7)...(i + 9)).to_i(16)
            b4 = seq.slice((i + 10)...(i + 12)).to_i(16)

            if ((b2 & 0xC0) == 0x80 && (b3 & 0xC0) == 0x80 && (b4 & 0xC0) == 0x80)
              char = ((b1 << 18) & 0x1C0000) | ((b2 << 12) & 0x3F000) | ((b3 << 6) & 0xFC0) | (b4 & 0x3F)

              if (char < 0x10000 || char > 0x10FFFF)
                result += "\ufffd\ufffd\ufffd\ufffd"
              else
                # TODO don't know how to handle surrogate pairs properly.
                char   -= 0x10000
                result += [0xD800 + (char >> 10), 0xDC00 + (char & 0x3FF)].map{|c| c.chr(Encoding::UTF_8)}.join

                # high = ((char - 0x10000) / 0x400).floor + 0xD800
                # low  = ((char - 0x10000) % 0x400) + 0xDC00
                # result += '\u' + [high, low].map { |x| x.to_s(16) }.join('\u').downcase
              end

              i += 12
              next
            end
          end

          result += "\ufffd"
          i += 3
        end

        result
      end
    end

  end
end

# https://gist.github.com/kreeger/4480326
# class Fixnum
#   def to_surrogate_pair
#     if self >= 0x10000 && self <= 0x10FFFF
#       high = ((self - 0x10000) / 0x400).floor + 0xD800
#       low = ((self - 0x10000) % 0x400) + 0xDC00
#     end
#     '\U' + [high, low].map { |x| x.to_s(16) }.join('\U').upcase
#   end
#
# end
#
# class String
#   def to_hex
#     self.gsub('\U000', '0x').to_i(16)
#   end
# end
#