defmodule Elixush.Util do
  import Elixush.Globals.Agent

  @doc "If thing is a literal, return its type -- otherwise return false."
  def recognize_literal(thing) do
    # HACK: anonymous functions used to emulate loop/recur from clojure
    loop = fn(f, m) ->
      if m |> Map.to_list |> List.first |> is_nil do
        nil
      else
        {type, pred} = hd(Map.to_list(m))
        if pred.(thing) do
          type
        else
          f.(f, Map.new(tl(Map.to_list(m))))
        end
      end
    end
    loop.(loop, get_globals(:literals))
  end

  @doc "really make-list-if-not-seq, but close enough for here"
  def ensure_list(thing) do
    if is_list(thing) do
      thing
    else
      # REVIEW: Is just Enum.to_list sufficient here?
      Enum.to_list(thing)
    end
  end

  @doc "Prints the provided thing and returns it."
  def print_return(thing) do
    IO.puts(Macro.to_string(thing))
    thing
  end

  @doc "Returns a version of n that obeys limit parameters."
  @spec keep_number_reasonable(number) :: number
  def keep_number_reasonable(n) do
    max_number_magnitude = get_globals(:max_number_magnitude)
    cond do
      is_integer(n) ->
        cond do
          n > max_number_magnitude -> max_number_magnitude
          n < -max_number_magnitude -> -max_number_magnitude
          true -> n
        end
      true ->
        cond do
          n > max_number_magnitude -> max_number_magnitude * 1.0
          n < -max_number_magnitude -> -max_number_magnitude * 1.0
          n < -max_number_magnitude and n > max_number_magnitude -> 0.0
          true -> n
        end
    end
  end

  @doc "If a number, rounds float f to n decimal places."
  def round_to_n_decimal_places(f, n) do
    if !is_number(f) do
      f
    else
      factor = :math.pow(10, n)
      round(f * factor) / factor
    end
  end

  @doc "Returns the number of paren pairs in tree"
  @spec count_parens(Enum.t) :: integer
  def count_parens(tree) do
    # HACK: anonymous functions used to emulate loop/recur from clojure
    loop = fn(f, remaining, total) ->
      cond do
        not is_list(remaining) -> total
        Enum.empty?(remaining) -> total + 1
        not is_list(hd(remaining)) -> f.(f, tl(remaining), total)
        true -> f.(f, remaining, total + 1)
      end
    end
    loop.(loop, tree, 0)
  end

  @doc """
  Returns the number of points in tree, where each atom and each pair of parentheses
  counts as a point.
  """
  @spec count_points(Enum.t) :: integer
  def count_points(tree) do
    # HACK: anonymous functions used to emulate loop/recur from clojure
    loop = fn(f, remaining, total) ->
      cond do
        not is_list(remaining) -> total + 1
        Enum.empty?(remaining) -> total + 1
        not is_list(hd(remaining)) -> f.(f, tl(remaining), total + 1)
        true -> f.(f, remaining, total + 1)
      end
    end
    loop.(loop, tree, 0)
  end

  @doc "Like walk, but only for lists."
  def walklist(inner, outer, form) do
    if is_list(form) do
      outer.(Enum.map(form, inner))
    else
      outer.(form)
    end
  end

  @doc "Like postwalk, but only for lists"
  # REVIEW: check that this works correctly
  def postwalklist(f, form) do
    walklist(&(postwalklist(f, &1)), f, form)
  end

  # TODO: insert-code-at-point, remove-code-at-point

  @doc "computes the next row using the prev-row current-element and the other seq"
  def compute_next_row(prev_row, current_element, other_seq, pred) do
    Enum.reduce(List.zip([prev_row, Enum.fetch(prev_row, 1), other_seq]), (hd(prev_row) + 1),
    fn(row, [diagonal, above, other_element]) ->
      update_val = if pred.(other_element, current_element) do
        # if the elements are deemed equivalent according to the predicate
        # pred, then no change has taken place to the string, so we are
        # going to set it the same value as diagonal (which is the previous edit-distance)
        diagonal
      else
        # in the case where the elements are not considered equivalent, then we are going
        # to figure out if its a substitution (then there is a change of 1 from the previous
        # edit distance) thus the value is diagonal + 1 or if its a deletion, then the value
        # is present in the columns, but not in the rows, the edit distance is the edit-distance
        # of last of row + 1 (since we will be using vectors, peek is more efficient)
        # or it could be a case of insertion, then the value is above+1, and we chose
        # the minimum of the three
        Enum.min([diagonal, above, hd(row)]) + 1
      end
      List.insert_at(row, 0, update_val)
    end)
  end

  @doc """
  Levenshtein Distance - http://en.wikipedia.org/wiki/Levenshtein_distance
    In information theory and computer science, the Levenshtein distance is a
    metric for measuring the amount of difference between two sequences. This
    is a functional implementation of the levenshtein edit
    distance with as little mutability as possible.
    Still maintains the O(n*m) guarantee.
  """
  def levenshtein_distance(a, b, p) do
    cond do
      List.empty? a -> length b
      List.empty? b -> length a
      true -> Enum.reduce()
      fn(prev_row, current_element) ->
        compute_next_row(prev_row, current_element, b, p)
      end
      Range.new(0, length(b) + 1)
    end
  end
end