defmodule Mv.Accounts.User do
  @moduledoc """
  The ressource for keeping user-specific data related to the login process. It is used by AshAuthentication to handle the Authentication strategies like SSO.
  """
  use Ash.Resource,
    domain: Mv.Accounts,
    data_layer: AshPostgres.DataLayer,
    extensions: [AshAuthentication]

  # authorizers: [Ash.Policy.Authorizer]

  postgres do
    table "users"
    repo Mv.Repo

    references do
      # When a member is deleted, set the user's member_id to NULL
      # This allows users to continue existing even if their linked member is removed
      reference :member, on_delete: :nilify
    end
  end

  @doc """
  AshAuthentication specific: Defines the strategies we want to use for authentication.
  Currently password and SSO with Rauthy as OIDC provider
  """
  authentication do
    session_identifier Application.compile_env!(:mv, :session_identifier)

    tokens do
      enabled? true
      token_resource Mv.Accounts.Token

      require_token_presence_for_authentication? Application.compile_env!(
                                                   :mv,
                                                   :require_token_presence_for_authentication
                                                 )

      store_all_tokens? true

      # signing_algorithm "EdDSA" -> https://git.local-it.org/local-it/mitgliederverwaltung/issues/87

      signing_secret fn _, _ ->
        {:ok, Application.get_env(:mv, :token_signing_secret)}
      end
    end

    strategies do
      oidc :rauthy do
        client_id Mv.Secrets
        base_url Mv.Secrets
        redirect_uri Mv.Secrets
        client_secret Mv.Secrets
        auth_method :client_secret_jwt
        code_verifier true

        # id_token_signed_response_alg "EdDSA" #-> https://git.local-it.org/local-it/mitgliederverwaltung/issues/87
      end

      password :password do
        identity_field :email
        hash_provider AshAuthentication.BcryptProvider
        confirmation_required? false
      end
    end
  end

  actions do
    # Default actions for framework/tooling integration:
    # - :read   -> Standard read used across the app and by admin tooling.
    # - :destroy-> Standard delete used by admin tooling and maintenance tasks.
    # 
    # NOTE: :create is INTENTIONALLY excluded from defaults!
    #       Using a default :create would bypass email-synchronization logic.
    #       Always use one of these explicit create actions instead:
    #       - :create_user (for manual user creation with optional member link)
    #       - :register_with_password (for password-based registration)
    #       - :register_with_rauthy (for OIDC-based registration)
    defaults [:read, :destroy]

    # Primary generic update action:
    # - Selected by AshAdmin's generated "Edit" UI and generic AshPhoenix
    #   helpers that assume a default update action.
    # - Intended for simple attribute updates (e.g., :email) and scenarios
    #   that do NOT need to manage the :member relationship.
    # - For linking/unlinking a member (and the related validations), prefer
    #   the specialized :update_user action below.
    update :update do
      primary? true

      # Required because custom validation functions (email validation, member relationship validation)
      # cannot be executed atomically. These validations need to query the database and perform
      # complex checks that are not supported in atomic operations.
      require_atomic? false

      # Sync email changes to linked member (User → Member)
      # Only runs when email is being changed
      change Mv.EmailSync.Changes.SyncUserEmailToMember do
        where [changing(:email)]
      end
    end

    create :create_user do
      description "Creates a new user with optional member relationship. The member relationship is managed through the :member argument."
      # Only accept email directly - member_id is NOT in accept list
      # This prevents direct foreign key manipulation, forcing use of manage_relationship
      accept [:email]
      # Allow member to be passed as argument for relationship management
      argument :member, :map, allow_nil?: true
      upsert? true

      # Manage the member relationship during user creation
      change manage_relationship(:member, :member,
               # Look up existing member and relate to it
               on_lookup: :relate,
               # Error if member doesn't exist in database
               on_no_match: :error,
               # If member already linked to this user, ignore (shouldn't happen in create)
               on_match: :ignore,
               # If no member provided, that's fine (optional relationship)
               on_missing: :ignore
             )

      # Sync user email to member when linking (User → Member)
      change Mv.EmailSync.Changes.SyncUserEmailToMember
    end

    update :update_user do
      description "Updates a user and manages the optional member relationship. To change an existing member link, first remove it (set member to nil), then add the new one."
      # Only accept email directly - member_id is NOT in accept list
      # This prevents direct foreign key manipulation, forcing use of manage_relationship
      accept [:email]
      # Allow member to be passed as argument for relationship management
      argument :member, :map, allow_nil?: true

      # Required because custom validation functions (email validation, member relationship validation)
      # cannot be executed atomically. These validations need to query the database and perform
      # complex checks that are not supported in atomic operations.
      require_atomic? false

      # Manage the member relationship during user update
      change manage_relationship(:member, :member,
               # Look up existing member and relate to it
               on_lookup: :relate,
               # Error if member doesn't exist in database
               on_no_match: :error,
               # If same member provided, that's fine (allows updates with same member)
               on_match: :ignore,
               # If no member provided, remove existing relationship (allows member removal)
               on_missing: :unrelate
             )

      # Sync email changes and handle linking (User → Member)
      # Runs when email OR member relationship changes
      change Mv.EmailSync.Changes.SyncUserEmailToMember do
        where any([changing(:email), changing(:member)])
      end
    end

    # Admin action for direct password changes in admin panel
    # Uses the official Ash Authentication HashPasswordChange with correct context
    update :admin_set_password do
      accept [:email]
      argument :password, :string, allow_nil?: false, sensitive?: true
      require_atomic? false

      # Set the strategy context that HashPasswordChange expects
      change set_context(%{strategy_name: :password})

      # Use the official Ash Authentication password change
      change AshAuthentication.Strategy.Password.HashPasswordChange
    end

    read :get_by_subject do
      description "Get a user by the subject claim in a JWT"
      argument :subject, :string, allow_nil?: false
      get? true
      prepare AshAuthentication.Preparations.FilterBySubject
    end

    read :sign_in_with_rauthy do
      argument :user_info, :map, allow_nil?: false
      argument :oauth_tokens, :map, allow_nil?: false
      prepare AshAuthentication.Strategy.OAuth2.SignInPreparation

      filter expr(email == get_path(^arg(:user_info), [:preferred_username]))
    end

    create :register_with_rauthy do
      argument :user_info, :map, allow_nil?: false
      argument :oauth_tokens, :map, allow_nil?: false
      upsert? true
      upsert_identity :unique_oidc_id

      validate &__MODULE__.validate_oidc_id_present/2

      change AshAuthentication.GenerateTokenChange

      change fn changeset, _ctx ->
        user_info = Ash.Changeset.get_argument(changeset, :user_info)

        changeset
        |> Ash.Changeset.change_attribute(:email, user_info["preferred_username"])
        |> Ash.Changeset.change_attribute(:oidc_id, user_info["sub"] || user_info["id"])
      end

      # Sync user email to member when linking (User → Member)
      change Mv.EmailSync.Changes.SyncUserEmailToMember
    end
  end

  # Global validations - applied to all relevant actions
  validations do
    # Password strength policy: minimum 8 characters for all password-related actions
    validate string_length(:password, min: 8),
      where: [action_is([:register_with_password, :admin_set_password])],
      message: "must have length of at least 8"

    # Email uniqueness check for all actions that change the email attribute
    # Validates that user email is not already used by another (unlinked) member
    validate Mv.Accounts.User.Validations.EmailNotUsedByOtherMember

    # Email validation with EctoCommons.EmailValidator (same as Member)
    # This ensures consistency between User and Member email validation
    validate fn changeset, _ ->
      # Get email from attribute (Ash.CiString) and convert to string
      email = Ash.Changeset.get_attribute(changeset, :email)
      email_string = if email, do: to_string(email), else: nil

      # Only validate if email is present
      if email_string do
        changeset2 =
          {%{}, %{email: :string}}
          |> Ecto.Changeset.cast(%{email: email_string}, [:email])
          |> EctoCommons.EmailValidator.validate_email(:email, checks: [:html_input, :pow])

        if changeset2.valid? do
          :ok
        else
          {:error, field: :email, message: "is not a valid email"}
        end
      else
        :ok
      end
    end

    # Prevent overwriting existing member relationship
    # This validation ensures race condition safety by requiring explicit two-step process:
    # 1. Remove existing member (set member to nil)
    # 2. Add new member
    # This prevents accidental overwrites when multiple admins work simultaneously
    validate fn changeset, _context ->
      member_arg = Ash.Changeset.get_argument(changeset, :member)
      current_member_id = changeset.data.member_id

      # Only trigger if:
      # - member argument is provided AND has an ID
      # - user currently has a member
      # - the new member ID is different from current member ID
      if member_arg && member_arg[:id] && current_member_id &&
           member_arg[:id] != current_member_id do
        {:error,
         field: :member, message: "User already has a member. Remove existing member first."}
      else
        :ok
      end
    end
  end

  def validate_oidc_id_present(changeset, _context) do
    user_info = Ash.Changeset.get_argument(changeset, :user_info) || %{}

    if is_binary(user_info["sub"]) or is_binary(user_info["id"]) do
      :ok
    else
      {:error, [user_info: "OIDC user_info must contain a non-empty 'sub' or 'id' field"]}
    end
  end

  attributes do
    uuid_primary_key :id

    # IMPORTANT: Email Synchronization
    # When user and member are linked, emails are automatically synced bidirectionally.
    # User.email is the source of truth - when a link is established, member.email
    # is overridden to match user.email. Subsequent changes to either email will
    # sync to the other resource.
    # See: Mv.EmailSync.Changes.SyncUserEmailToMember
    #      Mv.EmailSync.Changes.SyncMemberEmailToUser
    attribute :email, :ci_string do
      allow_nil? false
      public? true
      # Same constraints as Member email for consistency
      constraints min_length: 5, max_length: 254
    end

    attribute :hashed_password, :string, sensitive?: true, allow_nil?: true
    attribute :oidc_id, :string, allow_nil?: true
  end

  relationships do
    # 1:1 relationship - User can optionally belong to one Member
    # This automatically creates a `member_id` attribute in the User table
    # The relationship is optional (allow_nil? true by default)
    belongs_to :member, Mv.Membership.Member
  end

  identities do
    identity :unique_email, [:email]
    identity :unique_oidc_id, [:oidc_id]
    identity :unique_member, [:member_id]
  end

  # You can customize this if you wish, but this is a safe default that
  # only allows user data to be interacted with via AshAuthentication.
  # policies do
  #   bypass AshAuthentication.Checks.AshAuthenticationInteraction do
  #     authorize_if(always())
  #   end

  #   policy always() do
  #     forbid_if(always())
  #   end
  # end
end