-- lua-basex
-- version 0.1.1
-- un.def, 2016

local basex, alphabets, basex_meta, basex_instance_meta

local math_floor = math.floor
local table_insert = table.insert
local table_concat = table.concat
local string_char = string.char

alphabets = {
  BASE16LOWER = '0123456789abcdef',
  BASE16UPPER = '0123456789ABCDEF',
  BASE58BITCOIN = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz',
  BASE58FLICKR = '123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ',
  BASE58RIPPLE = 'rpshnaf39wBUDNEGHJKLM4PQRST7VWXYZ2bcdeCg65jkm8oFqi1tuvAxyz',
}

basex = {
  _VERSION = 'lua-basex 0.1.0',
  _URL = 'https://github.com/un-def/lua-basex',
  _DESCRIPTION = 'Base encoding/decoding of any given alphabet ' ..
                 'using bitcoin style leading zero compression',
  _LICENSE = [[
    Copyright (c) 2016, un.def
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:

     * Redistributions of source code must retain the above copyright notice,
       this list of conditions and the following disclaimer.
     * Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
    WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
    DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY
    DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
    (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
    SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
    OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
    DAMAGE.
  ]],
  alphabets = alphabets,
}


basex_meta = {
  __call = function(_, alphabet)
    local alphabet_map = {}
    local base = #alphabet
    local leader = alphabet:sub(1, 1)
    for i = 1, base do
      alphabet_map[alphabet:sub(i, i)] = i - 1
    end
    local basex_instance = {
      alphabet = alphabet,
      base = base,
      leader = leader,
      alphabet_map = alphabet_map,
    }
    return setmetatable(basex_instance, basex_instance_meta)
  end,

  __index = function(cls, key)
    local alphabet = cls.alphabets[key:upper()]
    if not alphabet then return nil end
    local basex_instance = cls(alphabet)
    cls[key] = basex_instance
    return basex_instance
  end
}


basex_instance_meta = {
  __index = {
    encode = function(self, source)
      if #source == 0 then return '' end

      local digits = {0}

      for i = 1, #source do
        local carry = source:byte(i, i)
        for j = 1, #digits do
          carry = carry + digits[j] * 256
          digits[j] = carry % self.base
          carry = math_floor(carry / self.base)
        end
        while carry > 0 do
           table_insert(digits, carry % self.base)
           carry = math_floor(carry / self.base)
        end
      end

      for k = 1, #source-1 do
        if source:byte(k, k) ~= 0 then break end
        table_insert(digits, 0)
      end

      local ii = 1
      local jj = #digits
      local tmp
      while true do
        tmp = self.alphabet:sub(digits[ii]+1, digits[ii]+1)
        digits[ii] = self.alphabet:sub(digits[jj]+1, digits[jj]+1)
        digits[jj] = tmp
        ii = ii + 1
        jj = jj - 1
        if ii > jj then break end
      end

      return table_concat(digits)
    end,

    decode = function(self, str)
      if #str == 0 then return '' end

      local bytes = {0}

      local value, carry
      for i = 1, #str do
        value = self.alphabet_map[str:sub(i, i)]
        if value == nil then error('Non-base' .. self.base .. ' character') end
        carry = value
        for j = 1, #bytes do
          carry = carry + bytes[j] * self.base
          bytes[j] = carry % 256
          carry = math_floor(carry / 256)
        end
        while carry > 0 do
          table_insert(bytes, carry % 256)
          carry = math_floor(carry / 256)
        end
      end

      for k = 1, #str-1 do
        if str:sub(k, k) ~= self.leader then break end
        table_insert(bytes, 0)
      end

      local decoded = ''
      for i = #bytes, 1, -1 do
        decoded = decoded .. string_char(bytes[i])
      end

      return decoded
    end
  }
}


return setmetatable(basex, basex_meta)
