Case incentive String comparison for ASCII strings

case_insensitive_string

defmodule InsensitiveString do
  @moduledoc """
  Case insensitive string functions for
  ASCII string

  """

  @doc """
  Compare two ascii strings in a case insensitive
  manner

  ## Example

      iex> InsensitiveString.cmp "aaa", "bbb"
      :lt

      iex> InsensitiveString.cmp "aaa", "BBB"
      :lt

  """
  def cmp("", "") do
    :eq
  end

  def cmp(<< h1 :: 3, c1 :: 5, rest1 :: binary>>, << h2 :: 3, c2 :: 5, rest2 :: binary>>)
      when c1 < 128 and c2 < 128 and c1 == c2 and h1 in [2,3] and h2 in [2,3] do
    cmp(rest1, rest2)
  end

  def cmp(<< h1 :: 3, c1 :: 5, _rest1 :: binary>>, << h2 :: 3, c2 :: 5, _rest2 :: binary>>)
      when c1 < 128 and c2 < 128 and c1 > c2 and h1 in [2,3] and h2 in [2,3] do
    :gt
  end

  def cmp(<< h1 :: 3, c1 :: 5, _rest1 :: binary>>, << h2 :: 3, c2 :: 5, _rest2 :: binary>>)
      when c1 < 128 and c2 < 128 and c1 < c2 and h1 in [2,3] and h2 in [2,3] do
    :lt
  end

  def cmp(<< c1 :: 8, rest1 :: binary>>, << c2 :: 8, rest2 :: binary>>)
      when c1 < 128 and c2 < 128 and c1 == c2 do
    cmp(rest1, rest2)
  end

  def cmp(<< c1 :: 8, _rest1 :: binary>>, << c2 :: 8, _rest2 :: binary>>)
      when c1 < 128 and c2 < 128 and c1 > c2 do
    :gt
  end

  def cmp(<< c1 :: 8, _rest1 :: binary>>, << c2 :: 8, _rest2 :: binary>>)
      when c1 < 128 and c2 < 128 and c1 < c2 do
    :lt
  end

  def cmp2(a, b) do
    raise ArgumentError, "String #{inspect a} or #{inspect b} is not ASCII"
  end
end