# Ported from http://github.com/maccman/sourcemap
#
# Adopted from ConradIrwin/ruby-source_map
#   https://github.com/ConradIrwin/ruby-source_map/blob/master/lib/source_map/vlq.rb
#
# Resources
#
#   http://en.wikipedia.org/wiki/Variable-length_quantity
#   https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
#   https://github.com/mozilla/source-map/blob/master/lib/source-map/base64-vlq.js
#
module Opal::SourceMap::VLQ
  VLQ_BASE_SHIFT = 5
  VLQ_BASE = 1 << VLQ_BASE_SHIFT
  VLQ_BASE_MASK = VLQ_BASE - 1
  VLQ_CONTINUATION_BIT = VLQ_BASE

  BASE64_DIGITS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'.split('')
  BASE64_VALUES = (0...64).inject({}) { |h, i| h[BASE64_DIGITS[i]] = i; h }

  # Public: Encode a list of numbers into a compact VLQ string.
  #
  # ary - An Array of Integers
  #
  # Returns a VLQ String.
  def self.encode(ary)
    result = []
    ary.each do |n|
      vlq = n < 0 ? ((-n) << 1) + 1 : n << 1
      loop do
        digit  = vlq & VLQ_BASE_MASK
        vlq  >>= VLQ_BASE_SHIFT
        digit |= VLQ_CONTINUATION_BIT if vlq > 0
        result << BASE64_DIGITS[digit]

        break unless vlq > 0
      end
    end
    result.join
  end

  # Public: Decode a VLQ string.
  #
  # str - VLQ encoded String
  #
  # Returns an Array of Integers.
  def self.decode(str)
    result = []
    chars = str.split('')
    while chars.any?
      vlq = 0
      shift = 0
      continuation = true
      while continuation
        char = chars.shift
        raise ArgumentError unless char
        digit = BASE64_VALUES[char]
        continuation = false if (digit & VLQ_CONTINUATION_BIT) == 0
        digit &= VLQ_BASE_MASK
        vlq   += digit << shift
        shift += VLQ_BASE_SHIFT
      end
      result << (vlq & 1 == 1 ? -(vlq >> 1) : vlq >> 1)
    end
    result
  end

  # Public: Encode a mapping array into a compact VLQ string.
  #
  # ary - Two dimensional Array of Integers.
  #
  # Returns a VLQ encoded String seperated by , and ;.
  def self.encode_mappings(ary)
    ary.map { |group|
      group.map { |segment|
        encode(segment)
      }.join(',')
    }.join(';')
  end

  # Public: Decode a VLQ string into mapping numbers.
  #
  # str - VLQ encoded String
  #
  # Returns an two dimensional Array of Integers.
  def self.decode_mappings(str)
    mappings = []

    str.split(';').each_with_index do |group, index|
      mappings[index] = []
      group.split(',').each do |segment|
        mappings[index] << decode(segment)
      end
    end

    mappings
  end
end