defmodule MishkaDeveloperTools.Helper.Crypto do
  @moduledoc """
  In reality, this module serves as a support for other libraries in addition
  to Erlang's built-in functions for encryption, hashing, and other topics that are associated
  with the language.

  It should be brought to your attention that certain functions necessitate the addition of their
  dependencies to the primary project. Consequently, prior to making use of these functionalities,
  establish the appropriate dependence within the project in accordance with your requirements.

  These functions are custom or wrappers, Copy from:

  - https://hexdocs.pm/plug_crypto/2.0.0/Plug.Crypto.html
  - https://hexdocs.pm/phoenix/Phoenix.Token.html
  - https://github.com/dashbitco/nimble_totp/blob/master/lib/nimble_totp.ex
  - https://dashbit.co/blog/introducing-nimble-totp
  - https://hex.pm/packages/bcrypt_elixir
  - https://hex.pm/packages/pbkdf2_elixir
  - https://password-hashing.net/
  - https://hex.pm/packages/argon2_elixir
  - https://github.com/malach-it/boruta_auth
  - https://github.com/joken-elixir/joken
  - https://hexdocs.pm/phoenix/mix_phx_gen_auth.html
  - https://hexdocs.pm/phoenix/Mix.Tasks.Phx.Gen.Secret.html
  """
  alias Postgrex.Extensions.JSON
  @type based32_url :: <<_::64, _::_*8>>

  @hash_algs %{
    "RS256" => %{"type" => :asymmetric, "hash_algorithm" => :sha256, "binary_size" => 16},
    "RS384" => %{"type" => :asymmetric, "hash_algorithm" => :sha384, "binary_size" => 24},
    "RS512" => %{"type" => :asymmetric, "hash_algorithm" => :sha512, "binary_size" => 32},
    "HS256" => %{"type" => :symmetric, "hash_algorithm" => :sha256, "binary_size" => 16},
    "HS384" => %{"type" => :symmetric, "hash_algorithm" => :sha384, "binary_size" => 24},
    "HS512" => %{"type" => :symmetric, "hash_algorithm" => :sha512, "binary_size" => 32}
  }

  @hash_algs_keys Map.keys(@hash_algs)

  @doc """
  Generate a binary composed of random bytes.

  The number of bytes is defined by the `size` argument. Default is `20` per the
  [HOTP RFC](https://tools.ietf.org/html/rfc4226#section-4).

  **based on: https://github.com/dashbitco/nimble_totp/blob/master/lib/nimble_totp.ex**

  ## Examples
  ```elixir
  alias MishkaDeveloperTools.Helper.Crypto

  Crypto.secret()
  #=> <<178, 117, 46, 7, 172, 202, 108, 127, 186, 180, ...>>
  ```
  """
  @spec secret(integer()) :: any()
  def secret(size \\ 20) do
    :crypto.strong_rand_bytes(size)
  end

  if Code.ensure_loaded?(NimbleTOTP) do
    @doc """
      Generates an OTP authentication URL with a given secret, issuer, and label.

    #### Parameters:

    - **secret (binary)**: The secret key used to generate the OTP,
    it should be `:crypto.strong_rand_bytes/1`.
    - **issuer (String)**: The name of the issuer.
    This helps to identify which service the OTP is associated with.
    - **label (String)**: A label used to identify the specific account or user.

    #### Returns:

    It returns a map containing:

    - `:secret` (string) - It should be `:crypto.strong_rand_bytes/1` output which is
    converted to `base32`.
    - `:url` (String) - The complete OTP authentication URL.

    #### Example:
    ```elixir
    secret = :crypto.strong_rand_bytes(20)
    create_otp_link(secret, "Mishka", "user_test")
    ```

    > #### Use cases information {: .info}
    >
    > You are able to generate a QR code from the URL that you have made and then provide
    > it to the user. The majority of devices are able to scan it and utilize it as a
    > two-factor authentication one-time password with ease.

    - **More info: https://dashbit.co/blog/introducing-nimble-totp**
    """
    @spec create_otp_link(binary(), String.t(), String.t()) :: %{
            secret: String.t(),
            url: based32_url()
          }
    def create_otp_link(secret, issuer, label) do
      user_url = NimbleTOTP.otpauth_uri("#{issuer}:#{label}", secret, issuer: issuer)
      base32_secret = URI.decode_query(URI.parse(user_url).query)["secret"]
      %{secret: base32_secret, url: user_url}
    end

    @doc """
    Generates an OTP authentication URL with a given issuer, and label.

    #### Parameters:

    - **issuer (String)**: The name of the issuer.
    This helps to identify which service the OTP is associated with.
    - **label (String)**: A label used to identify the specific account or user.

    #### Returns:

    It returns a map containing:

    - `:secret` (string) - It should be `:crypto.strong_rand_bytes/1` output which is
    converted to `base32`.
    - `:url` (String) - The complete OTP authentication URL.

    #### Example:
    ```elixir
    create_otp_link_and_secret("Mishka", "user_test")
    ```

    > #### Use cases information {: .info}
    >
    > You are able to generate a QR code from the URL that you have made and then provide
    > it to the user. The majority of devices are able to scan it and utilize it as a
    > two-factor authentication one-time password with ease.

    - **More info: https://dashbit.co/blog/introducing-nimble-totp**
    """
    @spec create_otp_link_and_secret(String.t(), String.t()) :: %{
            secret: String.t(),
            url: based32_url()
          }
    def create_otp_link_and_secret(issuer, label) do
      secret = NimbleTOTP.secret()
      user_url = NimbleTOTP.otpauth_uri("#{issuer}:#{label}", secret, issuer: issuer)
      base32_secret = URI.decode_query(URI.parse(user_url).query)["secret"]
      %{secret: base32_secret, url: user_url}
    end

    @doc """
    For information See `create_otp_link/3`
    """
    @spec create_otp(binary(), String.t(), String.t()) :: %{
            secret: String.t(),
            url: based32_url()
          }
    def create_otp(secret, issuer, label), do: create_otp_link(secret, issuer, label)

    @doc """
    For information See `create_otp_link_and_secret/2`
    """
    @spec create_otp(binary(), String.t()) :: %{secret: String.t(), url: <<_::64, _::_*8>>}
    def create_otp(issuer, label), do: create_otp_link_and_secret(issuer, label)

    @doc """
    Checks if a provided OTP is valid for the given secret.

    #### Parameters:

    - **secret (binary)**: The secret key used to generate the OTP,
    it should be `:crypto.strong_rand_bytes/1`.
    - `otp` (String): The OTP to verify, for example `"581234"`.

    #### Example:
    ```elixir
    valid_otp?(secret, "581234")

    # Or, you might put the time when the token was used for the last time to
    # prohibit the user from using it again.

    last_used = System.os_time(:second)
    valid_otp?(secret, "581234", last_used)
    ```

    > #### Use cases information {: .tip}
    >
    > One thing to keep in mind is that you ought to have already kept the
    > secret of each user in a location such as a database.
    """
    @spec valid_otp?(binary(), String.t()) :: boolean()
    def valid_otp?(secret, otp) do
      NimbleTOTP.valid?(secret, otp)
    end

    @doc """
    Checks if a provided OTP is valid for the given secret which is based32.

    #### Parameters:

    - **secret (binary)**: The secret key used to generate the OTP,
    it should be `:crypto.strong_rand_bytes/1`.
    - `otp` (String): The OTP to verify, for example `"581234"`.

    #### Example:
    ```elixir
    valid_otp?(secret, "581234", :base32)

    # Or, you might put the time when the token was used for the last time to
    # prohibit the user from using it again.

    last_used = System.os_time(:second)
    valid_otp?(secret, "581234", last_used, :base32)
    ```

    > #### Use cases information {: .tip}
    >
    > One thing to keep in mind is that you ought to have already kept the
    > secret of each user in a location such as a database.
    """
    @spec valid_otp?(binary(), String.t(), :base32 | NimbleTOTP.time()) :: boolean()
    def valid_otp?(secret, otp, :base32), do: base32_valid_otp?(secret, otp)

    def valid_otp?(secret, otp, last_used) do
      NimbleTOTP.valid?(secret, otp, since: last_used)
    end

    @doc """
    For information See `valid_otp?/3` and `valid_otp?/2`
    """
    @spec valid_otp?(binary(), String.t(), NimbleTOTP.time(), :base32) :: boolean()
    def valid_otp?(secret, otp, last_used, :base32), do: base32_valid_otp?(secret, otp, last_used)

    @doc """
    For information See `valid_otp?/3` and `valid_otp?/2`
    """
    @spec base32_valid_otp?(binary(), String.t()) :: boolean()
    def base32_valid_otp?(secret, otp) do
      Base.decode32!(secret)
      |> NimbleTOTP.valid?(otp)
    end

    @doc """
    For information See `valid_otp?/3` and `valid_otp?/2`
    """
    @spec base32_valid_otp?(binary(), String.t(), NimbleTOTP.time()) :: boolean()
    def base32_valid_otp?(secret, otp, last_used) do
      Base.decode32!(secret)
      |> NimbleTOTP.valid?(otp, since: last_used)
    end
  end

  if Code.ensure_loaded?(Bcrypt) or Code.ensure_loaded?(Pbkdf2) or Code.ensure_loaded?(Argon2) do
    @doc """
    ### Bcrypt

    - `bcrypt_elixir`: https://hex.pm/packages/bcrypt_elixir
    - `LICENSE`: https://github.com/riverrun/comeonin/blob/master/LICENSE

    > #### Use cases information {: .warning}
    >
    > Make sure you have a `C compiler` installed. See the Comeonin wiki for details.
    > Wiki link: https://github.com/riverrun/comeonin/wiki/Requirements

    Bcrypt is a key derivation function for passwords designed by Niels
    Provos and David Mazières. Bcrypt is an adaptive function, which means
    that it can be configured to remain slow and resistant to brute-force
    attacks even as computational power increases.

    Bcrypt has no known vulnerabilities and has been widely tested for over 15 years.
    However, as it has a low memory use, it is susceptible to GPU cracking attacks.

    ---

    You are required to make use of this function in order to generate an irreversible (hashed)
    duplicate of the user's password when you are storing your password.

    Additionally, you should save it in the database together with other unique features
    of your unique program.

    ### Exmple:

    ```elixir
    create_hash_password("USER_HARD_PASSWORD", :bcrypt)
    ```

    ---

    ### Pbkdf2

    - `pbkdf2` - pbkdf2_elixir https://hex.pm/packages/pbkdf2_elixir
    - `LICENSE`: https://github.com/riverrun/pbkdf2_elixir/blob/master/LICENSE.md

    Pbkdf2 is a password-based key derivation function that uses a password, a variable-length
    salt and an iteration count and applies a pseudorandom function to these to produce a key.

    Pbkdf2 has no known vulnerabilities and has been widely tested for over 15 years.
    However, like Bcrypt, as it has a low memory use, it is susceptible to GPU cracking attacks.

    The original implementation of Pbkdf2 used SHA-1 as the pseudorandom function,
    but this version uses HMAC-SHA-512, the default, or HMAC-SHA-256.

    ### Exmple:

    ```elixir
    create_hash_password("USER_HARD_PASSWORD", :pbkdf2)
    ```

    ---

    ### Argon2

    Argon2 is the winner of the Password Hashing Competition (PHC).

    - https://password-hashing.net/
    - `argon2`: argon2_elixir https://hex.pm/packages/argon2_elixir (recommended)
    - https://github.com/riverrun/argon2_elixir/blob/master/LICENSE.md

    Argon2 is a memory-hard password hashing function which can be used to hash passwords for credential
    storage, key derivation, or other applications.

    Being memory-hard means that it is not only computationally expensive, but it also uses a
    lot of memory (which can be configured). This means that it is much more difficult
    to attack Argon2 hashes using GPUs or dedicated hardware.

    > #### Use cases information {: .warning}
    >
    > Make sure you have a `C compiler` installed. See the Comeonin wiki for details.
    > Wiki link: https://github.com/riverrun/comeonin/wiki/Requirements

    #### Configuration
    The following four parameters can be set in the config file (these can all be overridden using keyword options):

    - t_cost - time cost
    > the amount of computation, given in number of iterations
    >
    > 3 is the default

    - m_cost - memory usage

    > 16 is the default - this will produce a memory usage of 64 MiB (2 ^ 16 KiB)
    >
    > parallelism - number of parallel threads
    >
    > 4 is the default

    - argon2_type - argon2 variant to use

    > 0 (Argon2d), 1 (Argon2i) or 2 (Argon2id)
    >
    > 2 is the default (Argon2id)

    ---

    For verifing you can use like this:

    ```elixir
    verify_password(hash, "USER_HARD_PASSWORD", :bcrypt)

    verify_password(hash, "USER_HARD_PASSWORD", :pbkdf2)

    verify_password(hash, "USER_HARD_PASSWORD", :argon2)
    ```
    """
  end

  if Code.ensure_loaded?(Bcrypt) do
    @spec create_hash_password(String.t(), :argon2 | :bcrypt | :pbkdf2) :: String.t()
    def create_hash_password(password, :bcrypt) do
      Bcrypt.hash_pwd_salt(password)
    end
  end

  if Code.ensure_loaded?(Pbkdf2) do
    def create_hash_password(password, :pbkdf2) do
      Pbkdf2.hash_pwd_salt(password, digest: :sha512)
    end
  end

  if Code.ensure_loaded?(Argon2) do
    def create_hash_password(password, :argon2) do
      Argon2.hash_pwd_salt(password, digest: :sha512)
    end
  end

  if Code.ensure_loaded?(Bcrypt) do
    @doc """
    For information See `create_hash_password/2`.
    """
    @spec verify_password(binary(), String.t(), :argon2 | :bcrypt | :bcrypt_2b | :pbkdf2) ::
            boolean()
    def verify_password(hash, password, :bcrypt) do
      Bcrypt.verify_pass(password, hash)
    end

    def verify_password(hash, password, :bcrypt_2b) do
      String.replace_prefix(hash, "$2y$", "$2b$")
      |> then(&Bcrypt.verify_pass(password, &1))
    end
  end

  if Code.ensure_loaded?(Pbkdf2) do
    def verify_password(hash, password, :pbkdf2) do
      Pbkdf2.verify_pass(password, hash)
    end
  end

  if Code.ensure_loaded?(Argon2) do
    def verify_password(hash, password, :argon2) do
      Argon2.verify_pass(password, hash)
    end
  end

  if Code.ensure_loaded?(Bcrypt) do
    @spec no_user_verify_password(String.t(), :argon2 | :bcrypt | :pbkdf2) :: false
    def no_user_verify_password(password, :bcrypt) do
      Bcrypt.no_user_verify(password: password)
    end
  end

  if Code.ensure_loaded?(Pbkdf2) do
    def no_user_verify_password(password, :pbkdf2) do
      Pbkdf2.no_user_verify(password: password)
    end
  end

  if Code.ensure_loaded?(Argon2) do
    def no_user_verify_password(password, :argon2) do
      Argon2.no_user_verify(password: password)
    end
  end

  @doc """
  This is a straightforward data hashing function that does not differentiate between
  **`symmetric`** and **`asymmetric`** functions according to their characteristics. Take, for instance,
  the use of **`checksums`** or codes associated with `nonce`, `c_hash`, `at_hash`,
  `short-lived Access Token`, and other similar concepts.

  > #### Security issue {: .warning}
  >
  > It is not recommended to use this function for hashing passwords or JWTs.

  ##### I inspired the initial code from this path:

  - https://github.com/malach-it/boruta_auth/blob/master/lib/boruta/oauth/schemas/client.ex#L173

  ### Example:
  ```elixir
  simple_hash("Your text", "RS512")
  simple_hash("Your text", "RS512", 32)

  # OR
  simple_hash()
  simple_hash(32)
  ```

  > This function in all types of input and output is as follows

  ```elixir
  {URL Encode64, Binary}
  ```
  """
  @spec simple_hash(String.t(), String.t()) :: {binary(), binary()}
  def simple_hash(text, alg, truncated \\ nil) when alg in @hash_algs_keys do
    hashed =
      :crypto.hash(@hash_algs[alg]["hash_algorithm"], text)
      |> binary_part(0, truncated || @hash_algs[alg]["binary_size"])

    {Base.url_encode64(hashed, padding: false), hashed}
  end

  @doc """
  For information See `simple_hash/2` and `simple_hash/3`.
  """
  @spec simple_hash() :: {binary(), binary()}
  def simple_hash(rand_size \\ 32) do
    token = :crypto.strong_rand_bytes(rand_size)
    hashed = :crypto.hash(:sha256, token)

    {Base.url_encode64(token, padding: false), hashed}
  end

  if Code.ensure_loaded?(JSON) and Code.ensure_loaded?(Joken) do
    defmodule Token do
      use Joken.Config
    end

    @doc """
    For your convenience, this function will generate a signature for you, allowing you to sign
    the data that you desire. It is necessary to create a signature before you can create a `JWT`.
    Pay a visit to the `Joken` library if you have certain requirements that you need to fulfill.

    ### Example:
    ```elixir
    create_signer("HS384", "YOUR SECURE KEY")
    create_signer("RS512", %{"pem" => pem_file})
    // OR
    create_typed_signer("HS384", "YOUR SECURE KEY")
    create_typed_signer("RS512", %{"pem" => pem_file})
    ```

    For more information about `pem`:
    - https://hexdocs.pm/joken/signers.html#pem-privacy-enhanced-mail


    If you want to create `signer` with pem like RSA as an asymmetric, see `create_typed_signer/2`
    or `create_typed_signer/3`

    See this issue:
    - https://github.com/joken-elixir/joken/issues/420
    """
    @spec create_signer(String.t(), binary() | map()) :: Joken.Signer.t()
    def create_signer(alg, key) when alg in @hash_algs_keys do
      Joken.Signer.create(alg, key)
    end

    @doc """
    For information See `create_signer/2`.
    """
    @spec create_typed_signer(String.t(), binary(), binary() | nil) :: Joken.Signer.t()
    def create_typed_signer(alg, key, pem \\ nil) when alg in @hash_algs_keys do
      case @hash_algs[alg]["type"] do
        :asymmetric when not is_nil(pem) -> Joken.Signer.create(alg, %{"pem" => pem})
        _ -> create_signer(alg, key)
      end
    end

    @doc """
    It is possible to use a signature that you have already made in order to sign a
    piece of data by utilizing this function. Take note that signing guarantees
    that no changes will be made to the data, and that all of your information will
    be entirely transparent.

    ### Example:
    ```elixir
    signer = create_typed_signer("HS384", "YOUR SECURE KEY")
    generate_and_sign(extra_claims, signer)
    ```

    > If you do not send the signer, it will attempt to retrieve it from the config of
    > your `Joken` module.
    >
    > Generates claims with the given token configuration and merges them with the given extra claims.
    """
    @spec generate_and_sign(map(), Joken.Signer.t() | nil) ::
            {:error, atom() | keyword()} | {:ok, binary(), %{optional(binary()) => any()}}
    def generate_and_sign(extra_claims, signer \\ nil) do
      if !is_nil(signer),
        do: Token.generate_and_sign(extra_claims, signer),
        else: Token.generate_and_sign(extra_claims)
    end

    @doc """
    For information See `generate_and_sign/2` or `generate_and_sign/1`.
    """
    @spec generate_and_sign!(map(), Joken.Signer.t() | nil) :: binary()
    def generate_and_sign!(extra_claims, signer \\ nil) do
      if !is_nil(signer),
        do: Token.generate_and_sign!(extra_claims, signer),
        else: Token.generate_and_sign!(extra_claims)
    end

    @doc """
    It is like `generate_and_sign/2` or `generate_and_sign/1`, but it did not generate claims.
    """
    @spec encode_and_sign(map(), Joken.Signer.t() | nil) ::
            {:error, atom() | keyword()} | {:ok, binary(), %{optional(binary()) => any()}}
    def encode_and_sign(extra_claims, signer \\ nil) do
      if !is_nil(signer),
        do: Token.encode_and_sign(extra_claims, signer),
        else: Token.encode_and_sign(extra_claims)
    end

    @doc """
    Verifies a bearer_token using the given signer and executes hooks if any are given.

    > If you do not send the signer, it will attempt to retrieve it from the config of
    > your `Joken` module.

    ### Example:
    ```elixir
    signer = create_typed_signer("HS384", "YOUR SECURE KEY")
    verify_and_validate(token, signer)
    ```
    """
    @spec verify_and_validate(binary(), Joken.Signer.t() | nil) ::
            {:error, atom() | keyword()} | {:ok, %{optional(binary()) => any()}}
    def verify_and_validate(token, signer \\ nil) do
      if !is_nil(signer),
        do: Token.verify_and_validate(token, signer),
        else: Token.verify_and_validate(token)
    end

    @doc """
    For information See `verify_and_validate/2` or `verify_and_validate/1`.
    """
    @spec verify_and_validate!(binary(), Joken.Signer.t() | nil) :: %{optional(binary()) => any()}
    def verify_and_validate!(token, signer \\ nil) do
      if !is_nil(signer),
        do: Token.verify_and_validate!(token, signer),
        else: Token.verify_and_validate!(token)
    end
  end

  if Code.ensure_loaded?(Plug) do
    @doc """
    Encodes, encrypts, and signs data into a token you can send to
    clients. Its usage is identical to that of `sign/4`, but the data
    is extracted using `decrypt/4`, rather than `verify/4`.

      - Copy from: https://github.com/phoenixframework/phoenix/blob/v1.7.12/lib/phoenix/token.ex

    ## Options

    * `:key_iterations` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to 1000
    * `:key_length` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to 32
    * `:key_digest` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to `:sha256`
    * `:signed_at` - set the timestamp of the token in seconds.
      Defaults to `System.system_time(:second)`
    * `:max_age` - the default maximum age of the token. Defaults to
      86400 seconds (1 day) and it may be overridden on `decrypt/4`.
    """
    def encrypt(key_base, secret, data, opts \\ []) when is_binary(secret) do
      key_base
      |> Plug.Crypto.encrypt(secret, data, opts)
    end

    @doc """
    Decrypts the original data from the token and verifies its integrity.
    Its usage is identical to `verify/4` but for encrypted tokens.

    - Copy from: https://github.com/phoenixframework/phoenix/blob/v1.7.12/lib/phoenix/token.ex

    ## Options

    * `:key_iterations` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to 1000
    * `:key_length` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to 32
    * `:key_digest` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to `:sha256`
    * `:max_age` - verifies the token only if it has been generated
      "max age" ago in seconds. Defaults to the max age signed in the
      token by `encrypt/4`.
    """
    def decrypt(key_base, secret, token, opts \\ []) when is_binary(secret) do
      key_base
      |> Plug.Crypto.decrypt(secret, token, opts)
    end

    @doc """
    Decodes the original data from the token and verifies its integrity.

    ## Examples

    In this scenario we will create a token, sign it, then provide it to a client
    application.

    ```elixir
    iex> user_id    = 99
    iex> secret     = "kjoy3o1zeidquwy1398juxzldjlksahdk3"
    iex> namespace  = "user auth"
    iex> token      = sign(secret, namespace, user_id)
    ```

    The mechanism for passing the token to the client is typically through a
    cookie, a JSON response body, or HTTP header. For now, assume the client has
    received a token it can use to validate requests for protected resources.

    When the server receives a request, it can use `verify/4` to determine if it
    should provide the requested resources to the client:

    ```elixir
    iex> verify(secret, namespace, token, max_age: 86400)
    {:ok, 99}
    ```

    In this example, we know the client sent a valid token because `verify/4`
    returned a tuple of type `{:ok, user_id}`. The server can now proceed with
    the request.

    However, if the client had sent an expired token, an invalid token, or `nil`,
    `verify/4` would have returned an error instead:

    ```elixir
    iex> verify(secret, namespace, expired, max_age: 86400)
    {:error, :expired}

    iex> verify(secret, namespace, invalid, max_age: 86400)
    {:error, :invalid}

    iex> verify(secret, namespace, nil, max_age: 86400)
    {:error, :missing}
    ```

    ## Options

    * `:key_iterations` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to 1000
    * `:key_length` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to 32
    * `:key_digest` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to `:sha256`
    * `:max_age` - verifies the token only if it has been generated
      "max age" ago in seconds. Defaults to the max age signed in the
      token by `sign/4`.
    """
    def verify(key_base, salt, token, opts \\ []) when is_binary(salt) do
      key_base
      |> Plug.Crypto.verify(salt, token, opts)
    end

    @doc """
    Encodes and signs data into a token you can send to clients.

    ## Options

    * `:key_iterations` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to 1000
    * `:key_length` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to 32
    * `:key_digest` - option passed to `Plug.Crypto.KeyGenerator`
      when generating the encryption and signing keys. Defaults to `:sha256`
    * `:signed_at` - set the timestamp of the token in seconds.
      Defaults to `System.system_time(:second)`
    * `:max_age` - the default maximum age of the token. Defaults to
      86400 seconds (1 day) and it may be overridden on `verify/4`.

    ### Example:
    ```elixir
    key_base = random_key_base()
    sign(key_base, "user-secret", {:elixir, :terms})
    ```
    """
    def sign(key_base, salt, data, opts \\ []) when is_binary(salt) do
      key_base
      |> Plug.Crypto.sign(salt, data, opts)
    end
  end

  @doc false
  def random_key_base(length \\ 64) when length > 31 do
    :crypto.strong_rand_bytes(length)
    |> Base.encode64(padding: false)
    |> binary_part(0, length)
  end
end