access.ex

defmodule Access do
  @moduledoc """
  Key-based access to data structures.

  The `Access` module defines a behaviour for dynamically accessing
  keys of any type in a data structure via the `data[key]` syntax.

  `Access` supports keyword lists (`Keyword`) and maps (`Map`) out
  of the box. Keywords supports only atoms keys, keys for maps can
  be of any type. Both return `nil` if the key does not exist:

      iex> keywords = [a: 1, b: 2]
      iex> keywords[:a]
      1
      iex> keywords[:c]
      nil

      iex> map = %{a: 1, b: 2}
      iex> map[:a]
      1

      iex> star_ratings = %{1.0 => "★", 1.5 => "★☆", 2.0 => "★★"}
      iex> star_ratings[1.5]
      "★☆"

  This syntax is very convenient as it can be nested arbitrarily:

      iex> keywords = [a: 1, b: 2]
      iex> keywords[:c][:unknown]
      nil

  This works because accessing anything on a `nil` value, returns
  `nil` itself:

      iex> nil[:a]
      nil

  The access syntax can also be used with the `Kernel.put_in/2`,
  `Kernel.update_in/2` and `Kernel.get_and_update_in/2` macros
  to allow values to be set in nested data structures:

      iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
      iex> put_in(users["john"][:age], 28)
      %{"john" => %{age: 28}, "meg" => %{age: 23}}

  ## Maps and structs

  While the access syntax is allowed in maps via `map[key]`,
  if your map is made of predefined atom keys, you should prefer
  to access those atom keys with `map.key` instead of `map[key]`,
  as `map.key` will raise if the key is missing (which is not
  supposed to happen if the keys are predefined).

  Similarly, since structs are maps and structs have predefined
  keys, they only allow the `struct.key` syntax and they do not
  allow the `struct[key]` access syntax. `Access.key/1` can also
  be used to construct dynamic access to structs and maps.

  In a nutshell, when using `put_in/2` and friends:

      put_in(struct_or_map.key, :value)
      put_in(keyword_or_map[:key], :value)

  When using `put_in/3` and friends:

      put_in(struct_or_map, [Access.key!(:key)], :value)
      put_in(keyword_or_map, [:key], :value)

  This covers the dual nature of maps in Elixir, as they can be
  either for structured data or as a key-value store. See the `Map`
  module for more information.

  ## Nested data structures

  Both key-based access syntaxes can be used with the nested update
  functions and macros in `Kernel`, such as `Kernel.get_in/2`,
  `Kernel.put_in/3`, `Kernel.update_in/3`, `Kernel.pop_in/2`, and
  `Kernel.get_and_update_in/3`.

  For example, to update a map inside another map:

      iex> users = %{"john" => %{age: 27}, "meg" => %{age: 23}}
      iex> put_in(users["john"].age, 28)
      %{"john" => %{age: 28}, "meg" => %{age: 23}}

  This module provides convenience functions for traversing other
  structures, like tuples and lists. These functions can be used
  in all the `Access`-related functions and macros in `Kernel`.

  For instance, given a user map with the `:name` and `:languages`
  keys, here is how to deeply traverse the map and convert all
  language names to uppercase:

      iex> languages = [
      ...>   %{name: "elixir", type: :functional},
      ...>   %{name: "c", type: :procedural}
      ...> ]
      iex> user = %{name: "john", languages: languages}
      iex> update_in(user, [:languages, Access.all(), :name], &String.upcase/1)
      %{
        name: "john",
        languages: [
          %{name: "ELIXIR", type: :functional},
          %{name: "C", type: :procedural}
        ]
      }

  See the functions `key/1`, `key!/1`, `elem/1`, and `all/0` for
  some of the available accessors.
  """

  @type container :: keyword | struct | map
  @type nil_container :: nil
  @type t :: container | nil_container | any
  @type key :: any
  @type value :: any

  @type get_fun(data) ::
          (:get, data, (term -> term) -> new_data :: container)

  @type get_and_update_fun(data, current_value) ::
          (:get_and_update, data, (term -> term) ->
             {current_value, new_data :: container} | :pop)

  @type access_fun(data, current_value) ::
          get_fun(data) | get_and_update_fun(data, current_value)

  @doc """
  Invoked in order to access the value stored under `key` in the given term `term`.

  This function should return `{:ok, value}` where `value` is the value under
  `key` if the key exists in the term, or `:error` if the key does not exist in
  the term.

  Many of the functions defined in the `Access` module internally call this
  function. This function is also used when the square-brackets access syntax
  (`structure[key]`) is used: the `fetch/2` callback implemented by the module
  that defines the `structure` struct is invoked and if it returns `{:ok,
  value}` then `value` is returned, or if it returns `:error` then `nil` is
  returned.

  See the `Map.fetch/2` and `Keyword.fetch/2` implementations for examples of
  how to implement this callback.
  """
  @callback fetch(term :: t, key) :: {:ok, value} | :error

  @doc """
  Invoked in order to access the value under `key` and update it at the same time.

  The implementation of this callback should invoke `fun` with the value under
  `key` in the passed structure `data`, or with `nil` if `key` is not present in it.
  This function must return either `{current_value, new_value}` or `:pop`.

  If the passed function returns `{current_value, new_value}`,
  the return value of this callback should be `{current_value, new_data}`, where:

    * `current_value` is the retrieved value (which can be operated on before being returned)

    * `new_value` is the new value to be stored under `key`

    * `new_data` is `data` after updating the value of `key` with `new_value`.

  If the passed function returns `:pop`, the return value of this callback
  must be `{value, new_data}` where `value` is the value under `key`
  (or `nil` if not present) and `new_data` is `data` without `key`.

  See the implementations of `Map.get_and_update/3` or `Keyword.get_and_update/3`
  for more examples.
  """
  @callback get_and_update(data, key, (value | nil -> {current_value, new_value :: value} | :pop)) ::
              {current_value, new_data :: data}
            when current_value: value, data: container

  @doc """
  Invoked to "pop" the value under `key` out of the given data structure.

  When `key` exists in the given structure `data`, the implementation should
  return a `{value, new_data}` tuple where `value` is the value that was under
  `key` and `new_data` is `term` without `key`.

  When `key` is not present in the given structure, a tuple `{value, data}`
  should be returned, where `value` is implementation-defined.

  See the implementations for `Map.pop/3` or `Keyword.pop/3` for more examples.
  """
  @callback pop(data, key) :: {value, data} when data: container

  defmacrop raise_undefined_behaviour(exception, module, top) do
    quote do
      exception =
        case __STACKTRACE__ do
          [unquote(top) | _] ->
            reason =
              """
              #{inspect(unquote(module))} does not implement the Access behaviour

              You can use the "struct.field" syntax to access struct fields. \
              You can also use Access.key!/1 to access struct fields dynamically \
              inside get_in/put_in/update_in\
              """

            %{unquote(exception) | reason: reason}

          _ ->
            unquote(exception)
        end

      reraise exception, __STACKTRACE__
    end
  end

  @doc """
  Fetches the value for the given key in a container (a map, keyword
  list, or struct that implements the `Access` behaviour).

  Returns `{:ok, value}` where `value` is the value under `key` if there is such
  a key, or `:error` if `key` is not found.

  ## Examples

      iex> Access.fetch(%{name: "meg", age: 26}, :name)
      {:ok, "meg"}

      iex> Access.fetch([ordered: true, on_timeout: :exit], :timeout)
      :error

  """
  @spec fetch(container, term) :: {:ok, term} | :error
  @spec fetch(nil_container, any) :: :error
  def fetch(container, key)

  def fetch(%module{} = container, key) do
    module.fetch(container, key)
  rescue
    exception in UndefinedFunctionError ->
      raise_undefined_behaviour(exception, module, {^module, :fetch, [^container, ^key], _})
  end

  def fetch(map, key) when is_map(map) do
    case map do
      %{^key => value} -> {:ok, value}
      _ -> :error
    end
  end

  def fetch(list, key) when is_list(list) and is_atom(key) do
    case :lists.keyfind(key, 1, list) do
      {_, value} -> {:ok, value}
      false -> :error
    end
  end

  def fetch(list, key) when is_list(list) do
    raise ArgumentError,
          "the Access calls for keywords expect the key to be an atom, got: " <> inspect(key)
  end

  def fetch(nil, _key) do
    :error
  end

  @doc """
  Same as `fetch/2` but returns the value directly,
  or raises a `KeyError` exception if `key` is not found.

  ## Examples

      iex> Access.fetch!(%{name: "meg", age: 26}, :name)
      "meg"

  """
  @doc since: "1.10.0"
  @spec fetch!(container, term) :: term
  def fetch!(container, key) do
    case fetch(container, key) do
      {:ok, value} -> value
      :error -> raise(KeyError, key: key, term: container)
    end
  end

  @doc """
  Gets the value for the given key in a container (a map, keyword
  list, or struct that implements the `Access` behaviour).

  Returns the value under `key` if there is such a key, or `default` if `key` is
  not found.

  ## Examples

      iex> Access.get(%{name: "john"}, :name, "default name")
      "john"
      iex> Access.get(%{name: "john"}, :age, 25)
      25

      iex> Access.get([ordered: true], :timeout)
      nil

  """
  @spec get(container, term, term) :: term
  @spec get(nil_container, any, default) :: default when default: var
  def get(container, key, default \\ nil)

  # Reimplementing the same logic as Access.fetch/2 here is done for performance, since
  # this is called a lot and calling fetch/2 means introducing some overhead (like
  # building the "{:ok, _}" tuple and deconstructing it back right away).

  def get(%module{} = container, key, default) do
    try do
      module.fetch(container, key)
    rescue
      exception in UndefinedFunctionError ->
        raise_undefined_behaviour(exception, module, {^module, :fetch, [^container, ^key], _})
    else
      {:ok, value} -> value
      :error -> default
    end
  end

  def get(map, key, default) when is_map(map) do
    case map do
      %{^key => value} -> value
      _ -> default
    end
  end

  def get(list, key, default) when is_list(list) and is_atom(key) do
    case :lists.keyfind(key, 1, list) do
      {_, value} -> value
      false -> default
    end
  end

  def get(list, key, _default) when is_list(list) and is_integer(key) do
    raise ArgumentError, """
    the Access module does not support accessing lists by index, got: #{inspect(key)}

    Accessing a list by index is typically discouraged in Elixir, \
    instead we prefer to use the Enum module to manipulate lists \
    as a whole. If you really must access a list element by index, \
    you can Enum.at/1 or the functions in the List module\
    """
  end

  def get(list, key, _default) when is_list(list) do
    raise ArgumentError, """
    the Access module supports only keyword lists (with atom keys), got: #{inspect(key)}

    If you want to search lists of tuples, use List.keyfind/3\
    """
  end

  def get(nil, _key, default) do
    default
  end

  @doc """
  Gets and updates the given key in a `container` (a map, a keyword list,
  a struct that implements the `Access` behaviour).

  The `fun` argument receives the value of `key` (or `nil` if `key` is not
  present in `container`) and must return a two-element tuple `{current_value, new_value}`:
  the "get" value `current_value` (the retrieved value, which can be operated on before
  being returned) and the new value to be stored under `key` (`new_value`).
  `fun` may also return `:pop`, which means the current value
  should be removed from the container and returned.

  The returned value is a two-element tuple with the "get" value returned by
  `fun` and a new container with the updated value under `key`.

  ## Examples

      iex> Access.get_and_update([a: 1], :a, fn current_value ->
      ...>   {current_value, current_value + 1}
      ...> end)
      {1, [a: 2]}

  """
  @spec get_and_update(data, key, (value | nil -> {current_value, new_value :: value} | :pop)) ::
          {current_value, new_data :: data}
        when current_value: var, data: container
  def get_and_update(container, key, fun)

  def get_and_update(%module{} = container, key, fun) do
    module.get_and_update(container, key, fun)
  rescue
    exception in UndefinedFunctionError ->
      raise_undefined_behaviour(
        exception,
        module,
        {^module, :get_and_update, [^container, ^key, ^fun], _}
      )
  end

  def get_and_update(map, key, fun) when is_map(map) do
    Map.get_and_update(map, key, fun)
  end

  def get_and_update(list, key, fun) when is_list(list) and is_atom(key) do
    Keyword.get_and_update(list, key, fun)
  end

  def get_and_update(list, key, _fun) when is_list(list) and is_integer(key) do
    raise ArgumentError, """
    the Access module does not support accessing lists by index, got: #{inspect(key)}

    Accessing a list by index is typically discouraged in Elixir, \
    instead we prefer to use the Enum module to manipulate lists \
    as a whole. If you really must mostify a list element by index, \
    you can Access.at/1 or the functions in the List module\
    """
  end

  def get_and_update(list, key, _fun) when is_list(list) do
    raise ArgumentError,
          "the Access module supports only keyword lists (with atom keys), got: " <> inspect(key)
  end

  def get_and_update(nil, key, _fun) do
    raise ArgumentError, "could not put/update key #{inspect(key)} on a nil value"
  end

  @doc """
  Removes the entry with a given key from a container (a map, keyword
  list, or struct that implements the `Access` behaviour).

  Returns a tuple containing the value associated with the key and the
  updated container. `nil` is returned for the value if the key isn't
  in the container.

  ## Examples

  With a map:

      iex> Access.pop(%{name: "Elixir", creator: "Valim"}, :name)
      {"Elixir", %{creator: "Valim"}}

  A keyword list:

      iex> Access.pop([name: "Elixir", creator: "Valim"], :name)
      {"Elixir", [creator: "Valim"]}

  An unknown key:

      iex> Access.pop(%{name: "Elixir", creator: "Valim"}, :year)
      {nil, %{creator: "Valim", name: "Elixir"}}

  """
  @spec pop(data, key) :: {value, data} when data: container
  def pop(%module{} = container, key) do
    module.pop(container, key)
  rescue
    exception in UndefinedFunctionError ->
      raise_undefined_behaviour(exception, module, {^module, :pop, [^container, ^key], _})
  end

  def pop(map, key) when is_map(map) do
    Map.pop(map, key)
  end

  def pop(list, key) when is_list(list) do
    Keyword.pop(list, key)
  end

  def pop(nil, key) do
    raise ArgumentError, "could not pop key #{inspect(key)} on a nil value"
  end

  ## Accessors

  @doc """
  Returns a function that accesses the given key in a map/struct.

  The returned function is typically passed as an accessor to `Kernel.get_in/2`,
  `Kernel.get_and_update_in/3`, and friends.

  The returned function uses the default value if the key does not exist.
  This can be used to specify defaults and safely traverse missing keys:

      iex> get_in(%{}, [Access.key(:user, %{}), Access.key(:name, "meg")])
      "meg"

  Such is also useful when using update functions, allowing us to introduce
  values as we traverse the data structure for updates:

      iex> put_in(%{}, [Access.key(:user, %{}), Access.key(:name)], "Mary")
      %{user: %{name: "Mary"}}

  ## Examples

      iex> map = %{user: %{name: "john"}}
      iex> get_in(map, [Access.key(:unknown, %{}), Access.key(:name, "john")])
      "john"
      iex> get_and_update_in(map, [Access.key(:user), Access.key(:name)], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {"john", %{user: %{name: "JOHN"}}}
      iex> pop_in(map, [Access.key(:user), Access.key(:name)])
      {"john", %{user: %{}}}

  An error is raised if the accessed structure is not a map or a struct:

      iex> get_in([], [Access.key(:foo)])
      ** (BadMapError) expected a map, got: []

  """
  @spec key(key, term) :: access_fun(data :: struct | map, current_value :: term)
  def key(key, default \\ nil) do
    fn
      :get, data, next ->
        next.(Map.get(data, key, default))

      :get_and_update, data, next ->
        value = Map.get(data, key, default)

        case next.(value) do
          {get, update} -> {get, Map.put(data, key, update)}
          :pop -> {value, Map.delete(data, key)}
        end
    end
  end

  @doc """
  Returns a function that accesses the given key in a map/struct.

  The returned function is typically passed as an accessor to `Kernel.get_in/2`,
  `Kernel.get_and_update_in/3`, and friends.

  Similar to `key/2`, but the returned function raises if the key does not exist.

  ## Examples

      iex> map = %{user: %{name: "john"}}
      iex> get_in(map, [Access.key!(:user), Access.key!(:name)])
      "john"
      iex> get_and_update_in(map, [Access.key!(:user), Access.key!(:name)], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {"john", %{user: %{name: "JOHN"}}}
      iex> pop_in(map, [Access.key!(:user), Access.key!(:name)])
      {"john", %{user: %{}}}
      iex> get_in(map, [Access.key!(:user), Access.key!(:unknown)])
      ** (KeyError) key :unknown not found in: %{name: \"john\"}

  The examples above could be partially written as:

      iex> map = %{user: %{name: "john"}}
      iex> map.user.name
      "john"
      iex> get_and_update_in(map.user.name, fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {"john", %{user: %{name: "JOHN"}}}

  However, it is not possible to remove fields using the dot notation,
  as it is implified those fields must also be present. In any case,
  `Access.key!/1` is useful when the key is not known in advance
  and must be accessed dynamically.

  An error is raised if the accessed structure is not a map/struct:

      iex> get_in([], [Access.key!(:foo)])
      ** (RuntimeError) Access.key!/1 expected a map/struct, got: []

  """
  @spec key!(key) :: access_fun(data :: struct | map, current_value :: term)
  def key!(key) do
    fn
      :get, %{} = data, next ->
        next.(Map.fetch!(data, key))

      :get_and_update, %{} = data, next ->
        value = Map.fetch!(data, key)

        case next.(value) do
          {get, update} -> {get, Map.put(data, key, update)}
          :pop -> {value, Map.delete(data, key)}
        end

      _op, data, _next ->
        raise "Access.key!/1 expected a map/struct, got: #{inspect(data)}"
    end
  end

  @doc ~S"""
  Returns a function that accesses the element at the given index in a tuple.

  The returned function is typically passed as an accessor to `Kernel.get_in/2`,
  `Kernel.get_and_update_in/3`, and friends.

  The returned function raises if `index` is out of bounds.

  Note that popping elements out of tuples is not possible and raises an
  error.

  ## Examples

      iex> map = %{user: {"john", 27}}
      iex> get_in(map, [:user, Access.elem(0)])
      "john"
      iex> get_and_update_in(map, [:user, Access.elem(0)], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {"john", %{user: {"JOHN", 27}}}
      iex> pop_in(map, [:user, Access.elem(0)])
      ** (RuntimeError) cannot pop data from a tuple

  An error is raised if the accessed structure is not a tuple:

      iex> get_in(%{}, [Access.elem(0)])
      ** (RuntimeError) Access.elem/1 expected a tuple, got: %{}

  """
  @spec elem(non_neg_integer) :: access_fun(data :: tuple, current_value :: term)
  def elem(index) when is_integer(index) and index >= 0 do
    pos = index + 1

    fn
      :get, data, next when is_tuple(data) ->
        next.(:erlang.element(pos, data))

      :get_and_update, data, next when is_tuple(data) ->
        value = :erlang.element(pos, data)

        case next.(value) do
          {get, update} -> {get, :erlang.setelement(pos, data, update)}
          :pop -> raise "cannot pop data from a tuple"
        end

      _op, data, _next ->
        raise "Access.elem/1 expected a tuple, got: #{inspect(data)}"
    end
  end

  @doc ~S"""
  Returns a function that accesses all the elements in a list.

  The returned function is typically passed as an accessor to `Kernel.get_in/2`,
  `Kernel.get_and_update_in/3`, and friends.

  ## Examples

      iex> list = [%{name: "john"}, %{name: "mary"}]
      iex> get_in(list, [Access.all(), :name])
      ["john", "mary"]
      iex> get_and_update_in(list, [Access.all(), :name], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {["john", "mary"], [%{name: "JOHN"}, %{name: "MARY"}]}
      iex> pop_in(list, [Access.all(), :name])
      {["john", "mary"], [%{}, %{}]}

  Here is an example that traverses the list dropping even
  numbers and multiplying odd numbers by 2:

      iex> require Integer
      iex> get_and_update_in([1, 2, 3, 4, 5], [Access.all()], fn num ->
      ...>   if Integer.is_even(num), do: :pop, else: {num, num * 2}
      ...> end)
      {[1, 2, 3, 4, 5], [2, 6, 10]}

  An error is raised if the accessed structure is not a list:

      iex> get_in(%{}, [Access.all()])
      ** (RuntimeError) Access.all/0 expected a list, got: %{}

  """
  @spec all() :: access_fun(data :: list, current_value :: list)
  def all() do
    &all/3
  end

  defp all(:get, data, next) when is_list(data) do
    Enum.map(data, next)
  end

  defp all(:get_and_update, data, next) when is_list(data) do
    all(data, next, _gets = [], _updates = [])
  end

  defp all(_op, data, _next) do
    raise "Access.all/0 expected a list, got: #{inspect(data)}"
  end

  defp all([head | rest], next, gets, updates) do
    case next.(head) do
      {get, update} -> all(rest, next, [get | gets], [update | updates])
      :pop -> all(rest, next, [head | gets], updates)
    end
  end

  defp all([], _next, gets, updates) do
    {:lists.reverse(gets), :lists.reverse(updates)}
  end

  @doc ~S"""
  Returns a function that accesses the element at `index` (zero based) of a list.

  Keep in mind that index lookups in lists take linear time: the larger the list,
  the longer it will take to access its index. Therefore index-based operations
  are generally avoided in favor of other functions in the `Enum` module.

  The returned function is typically passed as an accessor to `Kernel.get_in/2`,
  `Kernel.get_and_update_in/3`, and friends.

  ## Examples

      iex> list = [%{name: "john"}, %{name: "mary"}]
      iex> get_in(list, [Access.at(1), :name])
      "mary"
      iex> get_in(list, [Access.at(-1), :name])
      "mary"
      iex> get_and_update_in(list, [Access.at(0), :name], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {"john", [%{name: "JOHN"}, %{name: "mary"}]}
      iex> get_and_update_in(list, [Access.at(-1), :name], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {"mary", [%{name: "john"}, %{name: "MARY"}]}

  `at/1` can also be used to pop elements out of a list or
  a key inside of a list:

      iex> list = [%{name: "john"}, %{name: "mary"}]
      iex> pop_in(list, [Access.at(0)])
      {%{name: "john"}, [%{name: "mary"}]}
      iex> pop_in(list, [Access.at(0), :name])
      {"john", [%{}, %{name: "mary"}]}

  When the index is out of bounds, `nil` is returned and the update function is never called:

      iex> list = [%{name: "john"}, %{name: "mary"}]
      iex> get_in(list, [Access.at(10), :name])
      nil
      iex> get_and_update_in(list, [Access.at(10), :name], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {nil, [%{name: "john"}, %{name: "mary"}]}

  An error is raised if the accessed structure is not a list:

      iex> get_in(%{}, [Access.at(1)])
      ** (RuntimeError) Access.at/1 expected a list, got: %{}

  """
  @spec at(integer) :: access_fun(data :: list, current_value :: term)
  def at(index) when is_integer(index) do
    fn op, data, next -> at(op, data, index, next) end
  end

  defp at(:get, data, index, next) when is_list(data) do
    data |> Enum.at(index) |> next.()
  end

  defp at(:get_and_update, data, index, next) when is_list(data) do
    get_and_update_at(data, index, next, [], fn -> nil end)
  end

  defp at(_op, data, _index, _next) do
    raise "Access.at/1 expected a list, got: #{inspect(data)}"
  end

  defp get_and_update_at([head | rest], 0, next, updates, _default_fun) do
    case next.(head) do
      {get, update} -> {get, :lists.reverse([update | updates], rest)}
      :pop -> {head, :lists.reverse(updates, rest)}
    end
  end

  defp get_and_update_at([_ | _] = list, index, next, updates, default_fun) when index < 0 do
    list_length = length(list)

    if list_length + index >= 0 do
      get_and_update_at(list, list_length + index, next, updates, default_fun)
    else
      {default_fun.(), list}
    end
  end

  defp get_and_update_at([head | rest], index, next, updates, default_fun) when index > 0 do
    get_and_update_at(rest, index - 1, next, [head | updates], default_fun)
  end

  defp get_and_update_at([], _index, _next, updates, default_fun) do
    {default_fun.(), :lists.reverse(updates)}
  end

  @doc ~S"""
  Same as `at/1` except that it raises `Enum.OutOfBoundsError`
  if the given index is out of bounds.

  ## Examples

      iex> get_in([:a, :b, :c], [Access.at!(2)])
      :c
      iex> get_in([:a, :b, :c], [Access.at!(3)])
      ** (Enum.OutOfBoundsError) out of bounds error

  """
  @doc since: "1.11.0"
  @spec at!(integer) :: access_fun(data :: list, current_value :: term)
  def at!(index) when is_integer(index) do
    fn op, data, next -> at!(op, data, index, next) end
  end

  defp at!(:get, data, index, next) when is_list(data) do
    case Enum.fetch(data, index) do
      {:ok, value} -> next.(value)
      :error -> raise Enum.OutOfBoundsError
    end
  end

  defp at!(:get_and_update, data, index, next) when is_list(data) do
    get_and_update_at(data, index, next, [], fn -> raise Enum.OutOfBoundsError end)
  end

  defp at!(_op, data, _index, _next) do
    raise "Access.at!/1 expected a list, got: #{inspect(data)}"
  end

  @doc ~S"""
  Returns a function that accesses all elements of a list that match the provided predicate.

  The returned function is typically passed as an accessor to `Kernel.get_in/2`,
  `Kernel.get_and_update_in/3`, and friends.

  ## Examples

      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}]
      iex> get_in(list, [Access.filter(&(&1.salary > 20)), :name])
      ["francine"]
      iex> get_and_update_in(list, [Access.filter(&(&1.salary <= 20)), :name], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {["john"], [%{name: "JOHN", salary: 10}, %{name: "francine", salary: 30}]}

  `filter/1` can also be used to pop elements out of a list or
  a key inside of a list:

      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}]
      iex> pop_in(list, [Access.filter(&(&1.salary >= 20))])
      {[%{name: "francine", salary: 30}], [%{name: "john", salary: 10}]}
      iex> pop_in(list, [Access.filter(&(&1.salary >= 20)), :name])
      {["francine"], [%{name: "john", salary: 10}, %{salary: 30}]}

  When no match is found, an empty list is returned and the update function is never called

      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}]
      iex> get_in(list, [Access.filter(&(&1.salary >= 50)), :name])
      []
      iex> get_and_update_in(list, [Access.filter(&(&1.salary >= 50)), :name], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {[], [%{name: "john", salary: 10}, %{name: "francine", salary: 30}]}

  An error is raised if the predicate is not a function or is of the incorrect arity:

      iex> get_in([], [Access.filter(5)])
      ** (FunctionClauseError) no function clause matching in Access.filter/1

  An error is raised if the accessed structure is not a list:

      iex> get_in(%{}, [Access.filter(fn a -> a == 10 end)])
      ** (RuntimeError) Access.filter/1 expected a list, got: %{}

  """
  @doc since: "1.6.0"
  @spec filter((term -> boolean)) :: access_fun(data :: list, current_value :: list)
  def filter(func) when is_function(func) do
    fn op, data, next -> filter(op, data, func, next) end
  end

  defp filter(:get, data, func, next) when is_list(data) do
    data |> Enum.filter(func) |> Enum.map(next)
  end

  defp filter(:get_and_update, data, func, next) when is_list(data) do
    get_and_update_filter(data, func, next, [], [])
  end

  defp filter(_op, data, _func, _next) do
    raise "Access.filter/1 expected a list, got: #{inspect(data)}"
  end

  defp get_and_update_filter([head | rest], func, next, updates, gets) do
    if func.(head) do
      case next.(head) do
        {get, update} ->
          get_and_update_filter(rest, func, next, [update | updates], [get | gets])

        :pop ->
          get_and_update_filter(rest, func, next, updates, [head | gets])
      end
    else
      get_and_update_filter(rest, func, next, [head | updates], gets)
    end
  end

  defp get_and_update_filter([], _func, _next, updates, gets) do
    {:lists.reverse(gets), :lists.reverse(updates)}
  end

  @doc ~S"""
  Returns a function that accesses all items of a list that are within the provided range.

  The range will be normalized following the same rules from `Enum.slice/2`.

  The returned function is typically passed as an accessor to `Kernel.get_in/2`,
  `Kernel.get_and_update_in/3`, and friends.

  ## Examples

      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}, %{name: "vitor", salary: 25}]
      iex> get_in(list, [Access.slice(1..2), :name])
      ["francine", "vitor"]
      iex> get_and_update_in(list, [Access.slice(1..3//2), :name], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {["francine"], [%{name: "john", salary: 10}, %{name: "FRANCINE", salary: 30}, %{name: "vitor", salary: 25}]}

  `slice/1` can also be used to pop elements out of a list or
  a key inside of a list:

      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}, %{name: "vitor", salary: 25}]
      iex> pop_in(list, [Access.slice(-2..-1)])
      {[%{name: "francine", salary: 30}, %{name: "vitor", salary: 25}], [%{name: "john", salary: 10}]}
      iex> pop_in(list, [Access.slice(-2..-1), :name])
      {["francine", "vitor"], [%{name: "john", salary: 10}, %{salary: 30}, %{salary: 25}]}

  When no match is found, an empty list is returned and the update function is never called

      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}, %{name: "vitor", salary: 25}]
      iex> get_in(list, [Access.slice(5..10//2), :name])
      []
      iex> get_and_update_in(list, [Access.slice(5..10//2), :name], fn prev ->
      ...>   {prev, String.upcase(prev)}
      ...> end)
      {[], [%{name: "john", salary: 10}, %{name: "francine", salary: 30}, %{name: "vitor", salary: 25}]}

  An error is raised if the accessed structure is not a list:

      iex> get_in(%{}, [Access.slice(2..10//3)])
      ** (ArgumentError) Access.slice/1 expected a list, got: %{}

  An error is raised if the step of the range is negative:

      iex> get_in([], [Access.slice(2..10//-1)])
      ** (ArgumentError) Access.slice/1 does not accept ranges with negative steps, got: 2..10//-1

  """
  @doc since: "1.14"
  @spec slice(Range.t()) :: access_fun(data :: list, current_value :: list)
  def slice(%Range{} = range) do
    if range.step > 0 do
      fn op, data, next -> slice(op, data, range, next) end
    else
      raise ArgumentError,
            "Access.slice/1 does not accept ranges with negative steps, got: #{inspect(range)}"
    end
  end

  defp slice(:get, data, %Range{} = range, next) when is_list(data) do
    data
    |> Enum.slice(range)
    |> Enum.map(next)
  end

  defp slice(:get_and_update, data, range, next) when is_list(data) do
    range = normalize_range(range, data)

    if range.first > range.last do
      {[], data}
    else
      get_and_update_slice(data, range, next, [], [], 0)
    end
  end

  defp slice(_op, data, _range, _next) do
    raise ArgumentError, "Access.slice/1 expected a list, got: #{inspect(data)}"
  end

  defp normalize_range(%Range{first: first, last: last, step: step}, list)
       when first < 0 or last < 0 do
    count = length(list)
    first = if first >= 0, do: first, else: Kernel.max(first + count, 0)
    last = if last >= 0, do: last, else: last + count
    Range.new(first, last, step)
  end

  defp normalize_range(range, _list), do: range

  defp get_and_update_slice([head | rest], range, next, updates, gets, index) do
    if index in range do
      case next.(head) do
        :pop ->
          get_and_update_slice(rest, range, next, updates, [head | gets], index + 1)

        {get, update} ->
          get_and_update_slice(
            rest,
            range,
            next,
            [update | updates],
            [get | gets],
            index + 1
          )
      end
    else
      get_and_update_slice(rest, range, next, [head | updates], gets, index + 1)
    end
  end

  defp get_and_update_slice([], _range, _next, updates, gets, _index) do
    {:lists.reverse(gets), :lists.reverse(updates)}
  end
end