defmodule NucleotideCount do
  @nucleotides [?A, ?C, ?G, ?T]

  @doc """
  Counts individual nucleotides in a NucleotideCount strand.

  ## Examples

  iex> NucleotideCount.count('AATAA', ?A)
  4

  iex> NucleotideCount.count('AATAA', ?T)
  1
  """
  @spec count([char], char) :: non_neg_integer
  def count(strand, nucleotide) do
    length(Enum.filter(strand, (fn x -> x == nucleotide end)))
  end

  @doc """
  Returns a summary of counts by nucleotide.

  ## Examples

  iex> NucleotideCount.histogram('AATAA')
  %{?A => 4, ?T => 1, ?C => 0, ?G => 0}
  """
  @spec histogram([char]) :: map
  def histogram(strand) do
    temp = Enum.map(@nucleotides, (fn x -> %{x => count(strand, x)} end))
    Enum.reduce(temp, Map.new(), (fn (x, acc) -> Map.merge(x, acc) end))
  end
end