defmodule Exun.Fun do
  @moduledoc """
  Function management.
  @base and  @compound are the definitions of external functions.
  """

  @doc """
  base is a map that holds functions names and a tupla
   For example:
  ```
  "ln(F)" => {&:math.log/1, "F'x/F", "x*ln(F)-$(x/F),x"}
  ```
  - ln(F) : means function name is 'ln' and can receive Functions as argument
  - &:math.log/1 : Is the Elixir numeric function for ln
  - F'x/F : is the symbolic derivative of ln, deriv(F,x)/F
  - x*ln(F)-$(x/F),x : is the symbolic integral for ln

  For now the definitions are
  ```
      "ln(F)" => {&:math.log/1, "F'x/F", "x*ln(F)-$(x/F),x", "exp"},
      "exp(F)" => {&:math.exp/1, "F'x*exp(F)", nil, "ln"},
      "sin(F)" => {&:math.sin/1, "F'x*cos(F)", nil, "asin"},
      "cos(F)" => {&:math.cos/1, "-F'x*sin(F)", nil, "acos"},
      "tan(F)" => {&:math.tan/1, "F'x/cos(F)^2", nil, "atan"},
      "acos(F)" => {&:math.acos/1, "-F'x/(1-F^2)^0.5", nil, "cos"},
      "asin(F)" => {&:math.asin/1, "F'x/(1-F^2)^0.5", nil, "sin"},
      "atan(F)" => {&:math.atan/1, "F'x/(1+F^2)", nil, "tan"},
      "sinh(F)" => {&:math.sinh/1, "F'x*cosh(F)", nil, "asinh"},
      "cosh(F)" => {&:math.cosh/1, "F'x*sinh(F)", nil, "acosh"},
      "tanh(F)" => {&:math.tanh/1, "F'x/cosh(F)^2", nil, "atanh"},
      "asinh(F)" => {&:math.asinh/1, "F'x/(F^2+1)^0.5", nil, "sinh"},
      "acosh(F)" => {&:math.acosh/1, "F'x/(F^2-1)^0.5", nil, "cosh"},
      "atanh(F)" => {&:math.atanh/1, "F'x/(1-F^2)", nil, "tanh"}
  ```
  """
  # name => Numeric implementation, Derivate, Integrate
  def base,
    do: %{
      "ln(F)" => {&:math.log/1, "F'x/F", "x*ln(F)-$(x/F),x", "exp"},
      "exp(F)" => {&:math.exp/1, "F'x*exp(F)", nil, "ln"},
      "sin(F)" => {&:math.sin/1, "F'x*cos(F)", nil, "asin"},
      "cos(F)" => {&:math.cos/1, "-F'x*sin(F)", nil, "acos"},
      "tan(F)" => {&:math.tan/1, "F'x/cos(F)^2", nil, "atan"},
      "acos(F)" => {&:math.acos/1, "-F'x/(1-F^2)^0.5", nil, "cos"},
      "asin(F)" => {&:math.asin/1, "F'x/(1-F^2)^0.5", nil, "sin"},
      "atan(F)" => {&:math.atan/1, "F'x/(1+F^2)", nil, "tan"},
      "sinh(F)" => {&:math.sinh/1, "F'x*cosh(F)", nil, "asinh"},
      "cosh(F)" => {&:math.cosh/1, "F'x*sinh(F)", nil, "acosh"},
      "tanh(F)" => {&:math.tanh/1, "F'x/cosh(F)^2", nil, "atanh"},
      "asinh(F)" => {&:math.asinh/1, "F'x/(F^2+1)^0.5", nil, "sinh"},
      "acosh(F)" => {&:math.acosh/1, "F'x/((F-1)^0.5*(F+1)^0.5)", nil, "cosh"},
      "atanh(F)" => {&:math.atanh/1, "F'x/(1-F^2)", nil, "tanh"}
    }

  @doc """
  Compounds is a map that holds synthetic definitions. Function
  revert_compounds is able to look in an ast and identify this list,
  substituting the values.
  For now, the definitions are:
  ```
  "sqrt(F)" => "F^0.5",
  "tan(F)" => "sin(F)/cos(F)"
  ```
  """
  def compounds,
    do: %{
      "sqrt(F)" => "F^0.5",
      "tan(F)" => "sin(F)/cos(F)",
      "tanh(F)" => "sinh(F)/cosh(F)"
    }

  @doc """
  Finds and exec a function call. Search in base and compounds, if cannot find any
  returns a symbolic fcall.
  """
  def fcall(name, args) do
    # IO.inspect({name, args}, label: "fcall")
    aau = allargs_numbers(args)

    cond do
      (bfunc = base()[name <> "(F)"]) != nil ->
        cond do
          aau -> {:numb, elem(bfunc, 0).(args |> List.first() |> elem(1)), 1}
          true -> {:fcall, name, args}
        end

      (cfunc = compounds()[name <> "(F)"]) != nil ->
        ast = Exun.new(cfunc).ast
        mapdef = %{{:vari, "F"} => args |> List.first(), {:vari, "x"} => {:vari, "x"}}
        Exun.replace(ast, mapdef)

      true ->
        {:fcall, name, args}
    end
  end

  defp allargs_numbers(args) do
    Enum.reduce(args, true, fn el, ac ->
      ac and elem(el, 0) == :numb
    end)
  end

  @doc """
  Looks in compounds for a match of ast and return it.
  Thw first wins.
  """
  def revert_compounds(ast) do
    matches =
      Enum.map(compounds(), fn {k, v} ->
        # Compile value
        vast = Exun.new(v).ast
        # Match, get the first match
        res = Exun.Pattern.match_ast(vast, ast, [], false)
        {k, res |> List.first()}
      end) |> Enum.reject(fn {_, v} -> v == nil end)

    match =
      matches
      |> Enum.reject(fn {_, {:ok,map}} ->
        # Have to be same fcall names
        Enum.reduce(map, true, fn {key, value}, res ->
          case {key, value} do
            {{:fcall, n1, _}, {:fcall, n2, _}} ->
              res and n1 != n2

            _ ->
              res
          end
        end)
      end)
      |> List.first()

    if match != nil do
      {tk, {:ok, map}} = match
      atk = Exun.new(tk, %{}).ast
      Exun.replace(atk, map)
    else
      nil
    end
  end

  @doc """
  returns true if ast is a polynomial element on v
  """
  def is_poly(ast, v) do
    case ast do
      {:numb, _, _} -> true
      {:unit, _, _} -> true
      {:vari, _} -> true
      {:fcall, _, args} -> not Enum.any?(args, &contains(&1, v))
      {:minus, a} -> is_poly(a, v)
      {:deriv, f, _} -> not contains(f, v)
      {:integ, f, _} -> not contains(f, v)
      {{:m, :suma}, list} -> Enum.all?(list, &is_poly(&1, v))
      {{:m, :mult}, list} -> Enum.all?(list, &is_poly(&1, v))
      {:elev, _, b} -> not contains(b, v)
    end
  end

  @doc """
  returns true if ast contains variable vc
  """
  def contains(ast, vc) do
    case ast do
      {:numb, _, _} -> false
      {:unit, _, _} -> false
      v = {:vari, _} -> v == vc
      {:fcall, _, args} -> Enum.any?(args, &contains(&1, vc))
      {:minus, a} -> contains(a, vc)
      {:deriv, f, _} -> contains(f, vc)
      {:integ, f, _} -> contains(f, vc)
      {{:m, :suma}, list} -> Enum.any?(list, &contains(&1, vc))
      {{:m, :mult}, list} -> Enum.any?(list, &contains(&1, vc))
      {:elev, a, b} -> contains(a, vc) or contains(b, vc)
    end
  end

  def finv(name) do
    case base()["#{name}(F)"] do
      {_, _, _, r} -> r
      other -> other
    end
  end
end