module Scrivito
  #
  # @api public
  #
  class UserDefinition
    def initialize(user_id)
      @user_id = user_id
      @explicit_rules = []
    end

    #
    # Adds an explicit rule that allows the user to _always_ execute an action.
    # A rule consists of an action verb, the subject of the action, and an optional message.
    #
    # @api public
    #
    # @note Usually, the memberships of a workspace decide whether a user is allowed or not to
    #   perform a specific action. This method lets you add an exception to this logic and thus
    #   should be used carefully.
    # @note By default, all users are allowed to create a new workspace.
    # @see https://scrivito.com/user-permissions Defining users and their permissions
    #
    # @param [Symbol] verb the verb of the action (see {Scrivito::User::VERBS}).
    # @param [Symbol] subject the subject of the action. Currently, only +:workspace+ is supported.
    # @param [String] message optional message to be displayed in the UI.
    #
    # @raise [Scrivito::ScrivitoError] if the given verb is invalid
    # @raise [Scrivito::ScrivitoError] if the specified rule conflicts with a
    #   {Scrivito::UserDefinition#can_never} rule.
    #
    # @see Scrivito::User::VERBS
    # @see Scrivito::UserDefinition#can_never
    #
    # @example User can _always_ read from, write to, and publish a workspace, ignoring the memberships:
    #   Scrivito::User.define('alice') do |user|
    #     user.can_always(:read, :workspace)
    #     user.can_always(:write, :workspace)
    #     user.can_always(:publish, :workspace, 'You can always publish a workspace.')
    #   end
    #
    def can_always(verb, subject, message = nil)
      assert_no_conflict(:never, verb, subject)
      @explicit_rules << [:always, verb, subject, message]
    end

    #
    # Adds an explicit rule that forbids the user to execute an action.
    # A rule consists of an action verb, the subject of the action, and an optional message.
    #
    # @api public
    #
    # @note Usually, the memberships of a workspace decide whether a user is allowed or not to
    #   perform a specific action. This method lets you add an exception to this logic and thus
    #   should be used carefully.
    # @note By default, all users are allowed to create a new workspace. Use this method to forbid a
    #   user to create a new workspace.
    #
    # @param [Symbol] verb the verb of the action (see {Scrivito::User::VERBS}).
    # @param [Symbol] subject the subject of the action. Currently, only +:workspace+ is supported.
    # @param [String] message optional message to be displayed in the UI.
    #
    # @raise [Scrivito::ScrivitoError] if the given verb is invalid
    # @raise [Scrivito::ScrivitoError] if the specified rule conflicts with a
    #   {Scrivito::UserDefinition#can_always} rule.
    #
    # @see Scrivito::User::VERBS
    # @see Scrivito::UserDefinition#can_always
    #
    # @example User can _never_ publish a workspace, even if they're a workspace owner:
    #   Scrivito::User.define('alice') do |user|
    #     user.can_never(:publish, :workspace, 'You cannot publish workspaces.')
    #   end
    #
    # @example User cannot create a workspace:
    #   Scrivito::User.define('bob') do |user|
    #     user.can_never(:create, :workspace)
    #   end
    #
    def can_never(verb, subject, message = nil)
      assert_no_conflict(:always, verb, subject)
      @explicit_rules << [:never, verb, subject, message]
    end

    #
    # Enable the user to create workspaces, to read from, write to, publish, delete workspaces,
    # and to invite others to collaborate on any workspace.
    #
    # @api public
    #
    def is_admin!
      @explicit_rules = User::VERBS.map { |verb| [:always, verb, :workspace, nil] }
    end

    #
    # Defines the user description to be displayed in the in-place GUI, e.g. in the workspace menu.
    #
    # @api public
    #
    # @param [String] description_string the description, defaults to the the user id.
    # @param [Proc] description_proc proc to calculate the description, defaults to the the user id.
    #
    # @note The description is calculated "lazyly". The calculated description is cached.
    #
    # @see Scrivito::User.define
    #
    # @example Display the user +alice+ as "alice" in the in-place GUI:
    #   alice = Scrivito::User.define('alice')
    #
    # @example Display the user +bob+ as "Bob Doe" in the in-place GUI:
    #   bob = Scrivito::User.define('bob') do |user|
    #     user.description('Bob Doe')
    #   end
    #
    #   bob = Scrivito::User.define('bob') do |user|
    #     user.description do
    #       'Bob Doe'
    #     end
    #   end
    #
    def description(description_string = nil, &description_proc)
      if description_string
        description { description_string }
      else
        @description_proc = description_proc
      end
    end

    #
    # Defines the proc for fetching users for autocompletion purposes in the in-place GUI.
    # User autocompletion is used in the settings dialog of a workspace.
    # If the proc is not set, {Scrivito::User.find} is used to fetch the suggested users,
    # assuming the input is part of the user id.
    #
    # @api public
    #
    # @note Only the first 20 users returned are displayed in the in-place GUI.
    # @note +suggest_users_proc+ may also be invoked with an empty string.
    #
    # @param [Proc] suggest_users_proc proc for fetching users to be suggested in the in-place GUI
    # @yieldparam [String] input an arbitrary string originating from the user autocompletion input field,
    #   e.g. the first letters of a user name
    # @yieldreturn [Array<Scrivito::User>] users that were found on account of the given input string
    #
    # @example
    #   class MyUserModel
    #     def to_scrivito_user
    #       Scrivito::User.define(id) do |user|
    #         user.suggest_users do |input|
    #           MyUserModel.find_by_prefix(input).map(&:to_scrivito_user)
    #         end
    #       end
    #     end
    #   end
    #
    def suggest_users(&suggest_users_proc)
      @suggest_users_proc = suggest_users_proc
    end

    #
    # Lets you restrict a user's capability to publish a specific CMS object. Each
    # registered callback may refer to one attribute of an object. Multiple
    # callbacks are possible.
    #
    # @api public
    #
    # @note The callback is only executed for {BasicObj Objs} equipped with the attribute
    #   specified using the +:using+ option. It is not executed for a {BasicWidget Widget}
    #   with this attribute.
    #
    # @param [Hash] options
    # @option options [Symbol] :using the attribute you with to refer to in the callback
    # @yield [attribute] the value of the specified attribute
    # @yieldreturn [String, false] either return a message for the user or +false+ if
    #   no restriction applies
    #
    # @example
    #   class MyUserModel
    #     def to_scrivito_user
    #       Scrivito::User.define(id) do |user|
    #         user.restrict_obj_publish(using: :_path) do |path|
    #           if path.start_with?("/en")
    #             false
    #           else
    #             "You are only allowed to edit the English site."
    #           end
    #         end
    #
    #         user.restrict_obj_publish(using: :_obj_class) do |obj_class|
    #           if obj_class == 'BlogPost'
    #             false
    #           else
    #             'You are only allowed to edit Blog Posts.'
    #           end
    #         end
    #       end
    #     end
    #   end
    #
    def restrict_obj_publish(options, &block)
      restriction_set.add(options, &block)
    end

    def user
      User.new(
        id: @user_id,
        explicit_rules: @explicit_rules,
        description_proc: @description_proc,
        suggest_users_proc: @suggest_users_proc,
        restriction_set: restriction_set
      )
    end

    private

    def restriction_set
      @restriction_set ||= RestrictionSet.new
    end

    def assert_no_conflict(type, verb, subject)
      if @explicit_rules.detect { |rule| rule.take(3) == [type, verb, subject] }
        raise ScrivitoError.new("Conflicting rules for verb '#{verb}' and subject '#{subject}'")
      end
    end
  end
end