defmodule Iteraptor do
  @moduledoc """
  `Iteraptor` makes complicated nested structures (currently `map`s, `list`s
    and `Keyword`s) iteration easier.

  ## Usage

  #### Iterating, Mapping, Reducing

  * [`Iteraptor.each/3`](https://hexdocs.pm/iteraptor/Iteraptor.html#each/3)
    to iterate a deeply nested map/list/keyword;
  * [`Iteraptor.map/3`](https://hexdocs.pm/iteraptor/Iteraptor.html#map/3)
    to map a deeply nested map/list/keyword;
  * [`Iteraptor.reduce/4`](https://hexdocs.pm/iteraptor/Iteraptor.html#reduce/4)
    to reduce a deeply nested map/list/keyword;
  * [`Iteraptor.map_reduce/4`](https://hexdocs.pm/iteraptor/Iteraptor.html#map_reduce/4)
    to map and reduce a deeply nested map/list/keyword;

  #### Flattening

  * [`Iteraptor.to_flatmap/2`](https://hexdocs.pm/iteraptor/Iteraptor.html#to_flatmap/2)
    to flatten a deeply nested map/list/keyword into
    flatten map with concatenated keys;
  * [`Iteraptor.from_flatmap/3`](https://hexdocs.pm/iteraptor/Iteraptor.html#from_flatmap/3)
    to “unveil”/“unflatten” the previously flattened map into nested structure;

  """

  import Iteraptor.Utils

  @doc """
  Build a flatmap out of nested structure, concatenating the names of keys.

      %{a: %{b: %{c: 42, d: [nil, 42]}, e: [:f, 42]}} |> Iteraptor.to_flatmap
      %{"a.b.c": 42, "a.b.d.0": nil, "a.b.d.1": 42, "a.e.0": :f, "a.e.1": 42}

  Lists are handled gracefully, index is used as a key in resulting map.

  ## Parameters

  - `input`: nested map/list/keyword/struct to be flattened,  
  - `opts`: the additional options to be passed through:  
    — `delimiter` (_default:_ `"."`,) might be passed explicitly or
    configured with `:iteraptor, :delimiter` application setting.

  ## Examples

      iex> [:a, 42] |> Iteraptor.to_flatmap
      %{0 => :a, 1 => 42}

      iex> %{a: 42} |> Iteraptor.to_flatmap
      %{a: 42}

      iex> %{a: 42, b: 42} |> Iteraptor.to_flatmap
      %{a: 42, b: 42}

      iex> %{a: %{b: 42}, d: 42} |> Iteraptor.to_flatmap
      %{"a.b" => 42, d: 42}

      iex> %{a: [:b, 42], d: 42} |> Iteraptor.to_flatmap
      %{"a.0" => :b, "a.1" => 42, d: 42}

      iex> %{a: %{b: [:c, 42]}, d: 42} |> Iteraptor.to_flatmap
      %{"a.b.0" => :c, "a.b.1" => 42, d: 42}

      iex> %{a: %{b: 42}} |> Iteraptor.to_flatmap
      %{"a.b" => 42}

      iex> %{a: %{b: %{c: 42}}} |> Iteraptor.to_flatmap
      %{"a.b.c" => 42}

      iex> %{a: %{b: %{c: 42}}, d: 42} |> Iteraptor.to_flatmap
      %{"a.b.c" => 42, d: 42}

      iex> [a: [b: [c: 42]], d: 42] |> Iteraptor.to_flatmap
      %{"a.b.c" => 42, d: 42}

      iex> [a: [[:b], 42], d: 42] |> Iteraptor.to_flatmap
      %{"a.0.0" => :b, "a.1" => 42, d: 42}

      iex> %{a: %{b: %{c: 42, d: [nil, 42]}, e: [:f, 42]}} |> Iteraptor.to_flatmap
      %{"a.b.c" => 42, "a.b.d.0" => nil, "a.b.d.1" => 42, "a.e.0" => :f, "a.e.1" => 42}

      iex> %{a: %{b: %{c: 42, d: [nil, 42]}, e: [:f, 42]}}
      ...> |> Iteraptor.to_flatmap(delimiter: "_")
      %{"a_b_c" => 42, "a_b_d_0" => nil, "a_b_d_1" => 42, "a_e_0" => :f, "a_e_1" => 42}
  """

  @spec to_flatmap(Map.t() | List.t() | Keyword.t() | Access.t(), List.t()) :: Map.t()

  def to_flatmap(input, opts \\ []) when is_map(input) or is_list(input) do
    reducer = fn {k, v}, acc ->
      key =
        case k do
          [key] -> key
          _ -> Enum.join(k, delimiter(opts))
        end

      # FIXME maybe keyword would be better?
      Map.put(acc, key, v)
    end

    with {_, flattened} <- reduce(input, %{}, reducer, opts), do: flattened
  end

  @doc """
  Build a nested structure out of a flatmap given, decomposing the names of keys
  and handling lists carefully.

      %{"a.b.c": 42, "a.b.d.0": nil, "a.b.d.1": 42, "a.e.0": :f, "a.e.1": 42}
      |> Iteraptor.from_flatmap
      #⇒ %{a: %{b: %{c: 42, d: [nil, 42]}, e: [:f, 42]}}

  ## Parameters

  - `input`: flat map to be “expanded” to nested maps/lists,  
  - `transformer`: the transformer function to be called on all the elements,  
  - `opts`: additional options to be passed through.

  ## Examples

      iex> %{"a.b.c": 42} |> Iteraptor.from_flatmap
      %{a: %{b: %{c: 42}}}

      iex> %{"a.b.c": 42, "a.b.d": 42} |> Iteraptor.from_flatmap
      %{a: %{b: %{c: 42, d: 42}}}

      iex> %{"a.b.c": 42, "a.b.d": 42, "a.e": 42} |> Iteraptor.from_flatmap
      %{a: %{b: %{c: 42, d: 42}, e: 42}}

      iex> %{"0": 42, "1": 42} |> Iteraptor.from_flatmap
      [42, 42]

      iex> %{"1": :a1, "0": :a0, "2": :a2, "3": :a3, "4": :a4, "5": :a5,
      ...>   "6": :a6, "7": :a7, "8": :a8, "9": :a9, "10": :a10, "11": :a11}
      ...> |> Iteraptor.from_flatmap
      [:a0, :a1, :a2, :a3, :a4, :a5, :a6, :a7, :a8, :a9, :a10, :a11]

      iex> %{"0.a": 42, "0.b": 42} |> Iteraptor.from_flatmap
      [%{a: 42, b: 42}]

      iex> %{"a.0.0" => :b, "a.1" => 42, d: 42} |> Iteraptor.from_flatmap
      %{a: [[:b], 42], d: 42}

      iex> %{"a.b.c": 42, "a.b.d.0": nil, "a.b.d.1": 42, "a.e.0": :f, "a.e.1": 42}
      ...> |> Iteraptor.from_flatmap
      %{a: %{b: %{c: 42, d: [nil, 42]}, e: [:f, 42]}}

      iex> %{"0.a": 42, "0.b": 42} |> Iteraptor.from_flatmap(&IO.inspect/1)
      {[0, :a], 42}
      {[0, :b], 42}
      [%{a: 42, b: 42}]
  """
  @spec from_flatmap(Map.t() | List.t() | Keyword.t() | Access.t(), Function.t(), List.t()) ::
          Map.t() | List.t() | Keyword.t()

  def from_flatmap(input, transformer \\ nil, opts \\ []) when is_map(input) do
    reducer = fn {k, v}, acc ->
      key =
        case k |> Enum.join(delimiter(opts)) |> String.split(delimiter(opts)) do
          [k] -> [smart_convert(k)]
          list -> Enum.map(list, &smart_convert/1)
        end

      value =
        if is_nil(transformer) do
          v
        else
          case transformer.({key, v}) do
            {^key, any} -> any
            any -> any
          end
        end

      deep_put_in(acc, {key, value}, opts)
    end

    input
    |> reduce(%{}, reducer, opts)
    |> squeeze()
  end

  @doc """
  Iterates the given nested structure, calling the callback provided on each
    value. The key returned is an array of all the parent keys (and/or indices
    in a case of an array.)

  The return value is `self`.

  ## Parameters

  - `input`: nested map/list/keyword to be walked through.
  - `fun`: callback to be called on each **`{key, value}`** pair, where `key`
    is an array or deeply nested keys;
  e.g. on `%{a: {b: 42}}` will be called once, with tuple `{[:a, :b], 42}`;
  - `opts`: the options to be passed to the iteration
    - `yield`: `[:all | :maps | :keywords |` what to yield; _default:_ `nil`
    for yielding _values only_.

  ## Examples

      iex> %{a: %{b: %{c: 42}}} |> Iteraptor.each(&IO.inspect/1)
      {[:a, :b, :c], 42}
      %{a: %{b: %{c: 42}}}

      iex> %{a: %{b: %{c: 42}}} |> Iteraptor.each(&IO.inspect/1, yield: :all)
      {[:a], %{b: %{c: 42}}}
      {[:a, :b], %{c: 42}}
      {[:a, :b, :c], 42}
      %{a: %{b: %{c: 42}}}
  """

  @spec each(Map.t() | Keyword.t() | List.t() | Access.t(), Function.t(), List.t()) ::
          Map.t() | Keyword.t() | List.t() | Access.t()

  def each(input, fun, opts \\ []) do
    map(input, fun, opts)
    input
  end

  @doc """
  Maps the given nested structure, calling the callback provided on each value.
    The key returned is a concatenated names of all the parent keys
  (and/or indices in a case of an array.)

  The return value is the result of subsequent calls to the transformer given.

  ## Parameters

  - `input`: nested map/list/keyword to be mapped.
  - `fun`: callback to be called on each **`{key, value}`** pair, where `key`
    is an array or deeply nested keys;
  e.g. on `%{a: {b: 42}}` will be called once, with tuple `{[:a, :b], 42}`;
  - `opts`: the options to be passed to the iteration
    - `yield`: `[:all | :maps | :keywords |` what to yield; _default:_ `nil`
    for yielding _values only_.

  ## Examples

      iex> %{a: %{b: %{c: 42}}} |> Iteraptor.map(fn {_, v} -> v * 2 end)
      %{a: %{b: %{c: 84}}}

      iex> %{a: %{b: %{c: 42}}} |> Iteraptor.map(fn {k, _} -> Enum.join(k) end)
      %{a: %{b: %{c: "abc"}}}

      iex> %{a: %{b: %{c: 42}}}
      ...> |> Iteraptor.map(fn
      ...>      {[_], _} = self -> self
      ...>      {[_, _], _} -> "YAY"
      ...>    end, yield: :all)
      %{a: %{b: "YAY"}}
  """

  @spec map(Map.t() | Keyword.t() | List.t() | Access.t(), Function.t(), List.t()) ::
          Map.t() | Keyword.t() | List.t() | Access.t()

  def map(input, fun, opts \\ []) do
    unless is_function(fun, 1), do: raise("Function or arity fun/1 is required")
    {result, _} = traverse(input, fun, opts, {[], nil})
    result
  end

  @doc """
  Iteration with reducing. The function of arity `2`, called back on each
    iteration with `{k, v}` pair _and_ an accumulator is accepted.

  The return value is the result of the last call to the passed reducer function.

  ## Parameters

  - `input`: nested map/list/keyword to be mapped.
  - `fun`: callback to be called on each **`{key, value}, acc`** pair,
    where `key` is an array or deeply nested keys, `value` is the value and
    `acc` is the accumulator;
  - `opts`: the options to be passed to the iteration
    - `yield`: `[:all | :maps | :keywords |` what to yield; _default:_ `nil`
    for yielding _values only_.

  ## Examples

      iex> %{a: %{b: %{c: 42}}}
      ...> |> Iteraptor.reduce([], fn {k, _}, acc ->
      ...>      [Enum.join(k, "_") | acc]
      ...>    end, yield: :all)
      ...> |> :lists.reverse()
      ["a", "a_b", "a_b_c"]
  """

  @spec reduce(Map.t() | Keyword.t() | List.t() | Access.t(), Access.t(), Function.t(), List.t()) ::
          Map.t() | Keyword.t() | List.t() | Access.t()

  def reduce(input, acc \\ %{}, fun, opts \\ []) do
    unless is_function(fun, 2), do: raise("Function or arity fun/2 is required")
    fun_wrapper = fn kv, acc -> {kv, fun.(kv, acc)} end
    {_, result} = traverse(input, fun_wrapper, opts, {[], acc})
    result
  end

  @doc """
  Iteration with mapping and reducing. The function of arity `2`, called back on each
    iteration with `{k, v}` pair _and_ an accumulator is accepted.

  The return value is the tuple, consisting of mapped input _and_ the
    accumulator from the last call to the passed map-reducer.

  ## Parameters

  - `input`: nested map/list/keyword to be mapped.
  - `fun`: callback to be called on each **`{key, value}, acc`** pair,
    where `key` is an array or deeply nested keys, `value` is the value and
    `acc` is the accumulator;
  - `opts`: the options to be passed to the iteration
    - `yield`: `[:all | :maps | :keywords |` what to yield; _default:_ `nil`
    for yielding _values only_.

  ## Examples

      iex> %{a: %{b: %{c: 42}}}
      ...> |> Iteraptor.map_reduce([], fn
      ...>      {k, %{} = v}, acc -> {{k, v}, [Enum.join(k, ".") | acc]}
      ...>      {k, v}, acc -> {{k, v * 2}, [Enum.join(k, ".") <> "=" | acc]}
      ...>    end, yield: :all)
      {%{a: %{b: %{c: 84}}}, ["a.b.c=", "a.b", "a"]}
  """

  @spec map_reduce(
          Map.t() | Keyword.t() | List.t() | Access.t(),
          Access.t(),
          Function.t(),
          List.t()
        ) :: {Map.t() | Keyword.t() | List.t() | Access.t(), any()}

  def map_reduce(input, acc \\ %{}, fun, opts \\ []) do
    unless is_function(fun, 2), do: raise("Function or arity fun/2 is required")
    traverse(input, fun, opts, {[], acc})
  end

  ##############################################################################

  defp traverse_callback(fun, {value, acc}) do
    case fun do
      f when is_function(fun, 1) -> {f.(value), nil}
      f when is_function(fun, 2) -> f.(value, acc)
    end
  end

  defp traverse(input, fun, opts, key_acc)

  defp traverse(input, fun, opts, {key, acc}) when is_list(input) or is_map(input) do
    {_type, into} = type(input)

    {value, acc} =
      input
      |> Enum.with_index()
      |> Enum.map_reduce(acc, fn {kv, idx}, acc ->
        {k, v} =
          case kv do
            {k, v} -> {k, v}
            v -> {idx, v}
          end

        deep = key ++ [k]

        {value, acc} =
          case {opts[:yield], is_map(v), is_list(v)} do
            {_, false, false} -> traverse_callback(fun, {{deep, v}, acc})
            {:all, _, _} -> traverse_callback(fun, {{deep, v}, acc})
            {:lists, _, true} -> traverse_callback(fun, {{deep, v}, acc})
            {:maps, true, _} -> traverse_callback(fun, {{deep, v}, acc})
            _ -> {{deep, v}, acc}
          end

        case value do
          ^v ->
            {value, acc} = traverse(v, fun, opts, {deep, acc})
            {{k, value}, acc}

          {^deep, v} ->
            {value, acc} = traverse(v, fun, opts, {deep, acc})
            {{k, value}, acc}

          {^k, v} ->
            {value, acc} = traverse(v, fun, opts, {deep, acc})
            {{k, value}, acc}

          {k, v} ->
            {value, acc} = traverse(v, fun, opts, {deep, acc})
            {{k, value}, acc}

          v ->
            {value, acc} = traverse(v, fun, opts, {deep, acc})
            {{k, value}, acc}
        end
      end)

    {value |> Enum.into(into) |> squeeze(), acc}
  end

  defp traverse(input, _fun, _opts, {_key, acc}), do: {input, acc}

  # defp process(input, :struct, {acc, key, fun}, opts) do
  #   struct_name = input.__struct__ |> inspect |> String.replace(".", struct_joiner(opts))
  #   input
  #     |> Map.keys
  #     |> Enum.reject(& &1 == :__struct__)
  #     |> Enum.map(fn e ->
  #          {"#{struct_name}%#{e}", get_in(input, [Access.key!(e)])}
  #        end)
  #     |> Enum.into(into(opts))
  #     |> process(Map, {acc, key, fun}, opts)
  # end

  ##############################################################################

  ##############################################################################

  # defp is_struct(input) when is_map(input) do
  #   input |> Enum.reduce(nil, fn {k, _}, acc ->
  #     case k |> to_string |> String.split(~r{#{@struct_joiner}(?=[^#{@struct_joiner}]*$)}) do
  #       [^acc, _] -> acc
  #       [struct_name, _] -> if acc == nil, do: struct_name, else: false
  #       _ -> false
  #     end
  #   end)
  # end
  # defp is_struct(_), do: false
end