sloanelybutsurely.com/lib/core/accounts/user.ex

defmodule Core.Accounts.User do
  @moduledoc false
  import Ecto.Changeset

  @doc """
  A user changeset for registration.

  It is important to validate the length of both username and password.
  Otherwise databases may truncate the username without warnings, which
  could lead to unpredictable or insecure behaviour. Long passwords may
  also be very expensive to hash for certain algorithms.

  ## Options

    * `:hash_password` - Hashes the password so it can be stored securely
      in the database and ensures the password field is cleared to prevent
      leaks in the logs. If password hashing is not needed and clearing the
      password field is not desired (like when using this changeset for
      validations on a LiveView form), this option can be set to `false`.
      Defaults to `true`.

    * `:validate_username` - Validates the uniqueness of the username, in case
      you don't want to validate the uniqueness of the username (like when
      using this changeset for validations on a LiveView form before
      submitting the form), this option can be set to `false`.
      Defaults to `true`.
  """
  def registration_changeset(user, attrs, opts \\ []) do
    user
    |> cast(attrs, [:username, :password])
    |> validate_username(opts)
    |> validate_password(opts)
  end

  defp validate_username(changeset, opts) do
    changeset
    |> validate_required([:username])
    |> validate_length(:username, max: 160)
    |> maybe_validate_unique_username(opts)
  end

  defp validate_password(changeset, opts) do
    changeset
    |> validate_required([:password])
    |> validate_length(:password, min: 12, max: 72)
    # Examples of additional password validation:
    # |> validate_format(:password, ~r/[a-z]/, message: "at least one lower case character")
    # |> validate_format(:password, ~r/[A-Z]/, message: "at least one upper case character")
    # |> validate_format(:password, ~r/[!?@#$%^&*_0-9]/, message: "at least one digit or punctuation character")
    |> maybe_hash_password(opts)
  end

  defp maybe_hash_password(changeset, opts) do
    hash_password? = Keyword.get(opts, :hash_password, true)
    password = get_change(changeset, :password)

    if hash_password? && password && changeset.valid? do
      changeset
      # Hashing could be done with `Ecto.Changeset.prepare_changes/2`, but that
      # would keep the database transaction open longer and hurt performance.
      |> put_change(:hashed_password, Argon2.hash_pwd_salt(password))
      |> delete_change(:password)
    else
      changeset
    end
  end

  defp maybe_validate_unique_username(changeset, opts) do
    if Keyword.get(opts, :validate_username, true) do
      changeset
      |> unsafe_validate_unique(:username, Core.Repo)
      |> unique_constraint(:username)
    else
      changeset
    end
  end

  @doc """
  A user changeset for changing the username.

  It requires the username to change otherwise an error is added.
  """
  def username_changeset(user, attrs, opts \\ []) do
    user
    |> cast(attrs, [:username])
    |> validate_username(opts)
    |> case do
      %{changes: %{username: _}} = changeset -> changeset
      %{} = changeset -> add_error(changeset, :username, "did not change")
    end
  end

  @doc """
  A user changeset for changing the password.

  ## Options

    * `:hash_password` - Hashes the password so it can be stored securely
      in the database and ensures the password field is cleared to prevent
      leaks in the logs. If password hashing is not needed and clearing the
      password field is not desired (like when using this changeset for
      validations on a LiveView form), this option can be set to `false`.
      Defaults to `true`.
  """
  def password_changeset(user, attrs, opts \\ []) do
    user
    |> cast(attrs, [:password])
    |> validate_confirmation(:password, message: "does not match password")
    |> validate_password(opts)
  end

  @doc """
  Verifies the password.

  If there is no user or the user doesn't have a password, we call
  `Argon2.no_user_verify/0` to avoid timing attacks.
  """
  def valid_password?(%Schema.User{hashed_password: hashed_password}, password)
      when is_binary(hashed_password) and byte_size(password) > 0 do
    Argon2.verify_pass(password, hashed_password)
  end

  def valid_password?(_, _) do
    Argon2.no_user_verify()
    false
  end

  @doc """
  Validates the current password otherwise adds an error to the changeset.
  """
  def validate_current_password(changeset, password) do
    changeset = cast(changeset, %{current_password: password}, [:current_password])

    if valid_password?(changeset.data, password) do
      changeset
    else
      add_error(changeset, :current_password, "is not valid")
    end
  end

  defmodule Query do
    @moduledoc false
    import Ecto.Query

    def base do
      from _ in Schema.User, as: :users
    end

    def has_users_query(query \\ base()) do
      query
      |> limit(1)
      |> select([users: _], true)
    end
  end
end