defmodule Microwaveprop.Accounts.User do
  @moduledoc false
  use Ecto.Schema

  import Ecto.Changeset

  alias Microwaveprop.Radio.Maidenhead

  @admin_email "graham@mcintire.me"

  @primary_key {:id, :binary_id, autogenerate: true}
  @foreign_key_type :binary_id
  schema "users" do
    field :callsign, :string
    field :name, :string
    field :email, :string
    field :password, :string, virtual: true, redact: true
    field :hashed_password, :string, redact: true
    field :confirmed_at, :utc_datetime
    field :is_admin, :boolean, default: false
    field :authenticated_at, :utc_datetime, virtual: true

    field :home_grid, :string
    field :home_lat, :float
    field :home_lon, :float
    field :home_elevation_m, :integer

    has_many :contacts, Microwaveprop.Radio.Contact
    has_many :beacons, Microwaveprop.Propagation.Beacon

    timestamps(type: :utc_datetime)
  end

  @type t :: %__MODULE__{}

  @doc """
  Returns the email address that is automatically granted admin
  privileges on registration.
  """
  @spec admin_email() :: String.t()
  def admin_email, do: @admin_email

  @doc """
  A user changeset for registering a new user.

  Requires callsign, name, email, and password with confirmation.
  Sets `confirmed_at` so the account is usable immediately after
  password-based registration (there is no magic link confirmation flow).

  ## Options

    * `:hash_password` - Hashes the password so it can be stored securely.
      Defaults to `true`. Set to `false` for form validations in LiveView.
    * `:validate_unique` - Set to false to skip uniqueness validation.
      Defaults to `true`.
  """
  @spec registration_changeset(t() | Ecto.Changeset.t(), map(), keyword()) :: Ecto.Changeset.t()
  def registration_changeset(user, attrs, opts \\ []) do
    user
    |> cast(attrs, [:callsign, :name, :email, :password])
    |> validate_callsign(opts)
    |> validate_name()
    |> validate_email(opts)
    |> validate_confirmation(:password, message: "does not match password")
    |> validate_password(opts)
    |> maybe_grant_admin()
  end

  defp maybe_grant_admin(changeset) do
    case get_field(changeset, :email) do
      nil -> changeset
      email -> if String.downcase(email) == @admin_email, do: put_change(changeset, :is_admin, true), else: changeset
    end
  end

  @doc """
  Admin-only changeset for editing another user's profile fields
  and admin flag. Does not touch the password.
  """
  @spec admin_changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
  def admin_changeset(user, attrs) do
    user
    |> cast(attrs, [:callsign, :name, :email, :is_admin])
    |> update_change(:callsign, fn cs -> cs && cs |> String.trim() |> String.upcase() end)
    |> validate_required([:callsign, :name, :email])
    |> validate_format(:callsign, ~r/^[A-Z0-9]{3,10}$/, message: "must be 3-10 letters and digits")
    |> validate_length(:name, min: 1, max: 100)
    |> validate_format(:email, ~r/^[^@,;\s]+@[^@,;\s]+$/, message: "must have the @ sign and no spaces")
    |> validate_length(:email, max: 160)
    |> unsafe_validate_unique(:callsign, Microwaveprop.Repo)
    |> unique_constraint(:callsign)
    |> unsafe_validate_unique(:email, Microwaveprop.Repo)
    |> unique_constraint(:email)
  end

  defp validate_callsign(changeset, opts) do
    changeset =
      changeset
      |> update_change(:callsign, &String.upcase(&1 || ""))
      |> validate_required([:callsign])
      |> validate_format(:callsign, ~r/^[A-Z0-9]{3,10}$/, message: "must be 3-10 letters and digits")

    if Keyword.get(opts, :validate_unique, true) do
      changeset
      |> unsafe_validate_unique(:callsign, Microwaveprop.Repo)
      |> unique_constraint(:callsign)
    else
      changeset
    end
  end

  defp validate_name(changeset) do
    changeset
    |> validate_required([:name])
    |> validate_length(:name, min: 1, max: 100)
  end

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

  It requires the email to change otherwise an error is added.

  ## Options

    * `:validate_unique` - Set to false if you don't want to validate the
      uniqueness of the email, useful when displaying live validations.
      Defaults to `true`.
  """
  @spec email_changeset(t() | Ecto.Changeset.t(), map(), keyword()) :: Ecto.Changeset.t()
  def email_changeset(user, attrs, opts \\ []) do
    user
    |> cast(attrs, [:email])
    |> validate_email(opts)
    |> validate_email_changed()
  end

  defp validate_email(changeset, opts) do
    changeset =
      changeset
      |> validate_required([:email])
      |> validate_format(:email, ~r/^[^@,;\s]+@[^@,;\s]+$/, message: "must have the @ sign and no spaces")
      |> validate_length(:email, max: 160)

    if Keyword.get(opts, :validate_unique, true) do
      changeset
      |> unsafe_validate_unique(:email, Microwaveprop.Repo)
      |> unique_constraint(:email)
    else
      changeset
    end
  end

  defp validate_email_changed(changeset) do
    if get_field(changeset, :email) && get_change(changeset, :email) == nil do
      add_error(changeset, :email, "did not change")
    else
      changeset
    end
  end

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

  It is important to validate the length of the password, as long passwords may
  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`.
  """
  @spec password_changeset(t() | Ecto.Changeset.t(), map(), keyword()) :: Ecto.Changeset.t()
  def password_changeset(user, attrs, opts \\ []) do
    user
    |> cast(attrs, [:password])
    |> validate_confirmation(:password, message: "does not match password")
    |> validate_password(opts)
  end

  defp validate_password(changeset, opts) do
    changeset
    |> validate_required([:password])
    |> validate_length(:password, min: 8, 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
      # If using Bcrypt, then further validate it is at most 72 bytes long
      |> validate_length(:password, max: 72, count: :bytes)
      # 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, Bcrypt.hash_pwd_salt(password))
      |> delete_change(:password)
    else
      changeset
    end
  end

  @doc """
  Confirms the account by setting `confirmed_at`.
  """
  @spec confirm_changeset(t() | Ecto.Changeset.t()) :: Ecto.Changeset.t()
  def confirm_changeset(user) do
    now = DateTime.utc_now(:second)
    change(user, confirmed_at: now)
  end

  @doc """
  Changeset for the rover-page "home QTH" fields.

  Accepts either a Maidenhead grid or an explicit lat/lon. When only the
  grid is given, lat/lon are derived from its centre; when only lat/lon
  are given, a 10-character grid is computed from the coordinate pair so
  callers always end up with both fields populated. An empty `home_grid`
  paired with explicit nil lat/lon clears all home fields (used by the
  "clear home" affordance on /rover).
  """
  @spec change_home_qth(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
  def change_home_qth(user, attrs) do
    user
    |> cast(attrs, [:home_grid, :home_lat, :home_lon, :home_elevation_m])
    |> normalize_home_grid()
    |> validate_home_grid_format()
    |> derive_home_latlon_from_grid()
    |> derive_home_grid_from_latlon()
    |> validate_home_latlon_range()
    |> require_home_qth_pair()
  end

  defp normalize_home_grid(changeset) do
    case get_change(changeset, :home_grid) do
      nil ->
        changeset

      "" ->
        put_change(changeset, :home_grid, nil)

      grid when is_binary(grid) ->
        put_change(changeset, :home_grid, normalize_grid(grid))
    end
  end

  defp normalize_grid(grid) do
    trimmed = String.trim(grid)

    case String.length(trimmed) do
      4 -> String.upcase(trimmed)
      6 -> String.upcase(String.slice(trimmed, 0, 4)) <> String.downcase(String.slice(trimmed, 4, 2))
      _ -> trimmed
    end
  end

  defp validate_home_grid_format(changeset) do
    case get_field(changeset, :home_grid) do
      nil ->
        changeset

      grid ->
        if Maidenhead.valid?(grid),
          do: changeset,
          else: add_error(changeset, :home_grid, "must be a 4 or 6 character Maidenhead locator")
    end
  end

  defp derive_home_latlon_from_grid(changeset) do
    cond do
      not changeset.valid? ->
        changeset

      get_change(changeset, :home_lat) || get_change(changeset, :home_lon) ->
        changeset

      grid = get_change(changeset, :home_grid) ->
        case Maidenhead.to_latlon(grid) do
          {:ok, {lat, lon}} ->
            changeset
            |> put_change(:home_lat, lat)
            |> put_change(:home_lon, lon)

          :error ->
            changeset
        end

      true ->
        changeset
    end
  end

  # If lat/lon were provided without a grid, encode a 10-char Maidenhead
  # grid from the coordinates so the UI always has a human-readable label
  # to render and downstream callers can rely on `home_grid` being set
  # whenever the QTH is set. Skipped on invalid changesets (lat/lon range
  # check has not run yet) and when both fields aren't numeric.
  defp derive_home_grid_from_latlon(changeset) do
    lat = get_field(changeset, :home_lat)
    lon = get_field(changeset, :home_lon)

    cond do
      not changeset.valid? ->
        changeset

      not (is_number(lat) and is_number(lon)) ->
        changeset

      get_field(changeset, :home_grid) not in [nil, ""] ->
        changeset

      true ->
        put_change(changeset, :home_grid, Maidenhead.from_latlon(lat * 1.0, lon * 1.0, 10))
    end
  end

  defp validate_home_latlon_range(changeset) do
    changeset
    |> validate_number(:home_lat, greater_than_or_equal_to: -90.0, less_than_or_equal_to: 90.0)
    |> validate_number(:home_lon, greater_than_or_equal_to: -180.0, less_than_or_equal_to: 180.0)
  end

  defp require_home_qth_pair(changeset) do
    if home_qth_satisfied?(changeset),
      do: changeset,
      else: add_error(changeset, :home_grid, "must provide a grid or lat/lon")
  end

  defp home_qth_satisfied?(changeset) do
    grid = get_field(changeset, :home_grid)
    lat = get_field(changeset, :home_lat)
    lon = get_field(changeset, :home_lon)

    cond do
      is_binary(grid) and grid != "" -> true
      is_number(lat) and is_number(lon) -> true
      is_nil(grid) and is_nil(lat) and is_nil(lon) -> any_home_change?(changeset)
      true -> false
    end
  end

  defp any_home_change?(changeset) do
    Enum.any?([:home_grid, :home_lat, :home_lon], &Map.has_key?(changeset.changes, &1))
  end

  @doc """
  Verifies the password.

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

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