module Scrivito
  # @api beta
  class UserDefinition < Struct.new(:user_id)
    # Allows user to publish a workspace.
    # @api beta
    PUBLISH_WORKSPACE_ABILITY = 'publish_workspace'

    # Allows user to do everything.
    # @api beta
    ADMINISTRATE_CMS_ABILITY = 'administrate_cms'

    # @api beta
    ABILITY_NAMES = [
      ADMINISTRATE_CMS_ABILITY,
      PUBLISH_WORKSPACE_ABILITY,
    ]

    # Defines a user ability.
    # @api beta
    # @param [String, Symbol] ability_name name of the ability
    # @param [Proc] ability_proc proc to check if the ability can be granted
    # @raise [Scrivito::ScrivitoError] if the given ability name is unknown
    # @raise [Scrivito::ScrivitoError] if no ability proc is given
    # @yieldreturn If the block returns a "truthy" value, then the ability will be granted
    # @yieldreturn If the block returns a "falsy" value, then the ability will be prohibited
    # @see ABILITY_NAMES
    # @see Scrivito::User.define
    # @example
    #   allowed_user = nil
    #
    #   alice = Scrivito::User.define('alice') do |user|
    #     user.can(:publish_workspace) { allowed_user == 'alice' }
    #   end
    #
    #   bob = Scrivito::User.define('bob') do |user|
    #     user.can(:publish_workspace) { allowed_user == 'bob' }
    #   end
    #
    #   # The users `alice` and `bob` will both be not allowed to publish workspace.
    #
    #   allowed_user = 'alice'
    #   # The user `alice` will now be allowed to publish workspace,
    #   # but the user `bob` will still be not allowed.
    #
    #   allowed_user = 'bob'
    #   # The user `bob` will now be allowed to publish workspace,
    #   # but the user `alice` will be not allowed again.
    def can(ability_name, &ability_proc)
      assert_valid_ability(ability_name, ability_proc)
      abilities[ability_name] = ability_proc
    end

    # Defines the user description to be displayed, when the user is shown in the in-place GUI.
    # @api beta
    # @param [Proc] description_proc proc to calculate the description. Defaults to the the user id.
    # @note The description is calculated "lazy".
    # @note The calculated description will be cached.
    # @see Scrivito::User.define
    # @example
    #   alice = Scrivito::User.define('alice') {}
    #   # User `alice` will be displayed as "alice" in the in-place GUI.
    #
    #   bob = Scrivito::User.define('bob') do |user|
    #     user.description { 'Bob Doe' }
    #   end
    #   # User `bob` will be displayed as "Bob Doe" in the in-place GUI.
    def description(&description_proc)
      @description_proc = description_proc
    end

    # Defines the proc for fetching users for the user autocompletion of the in-place GUI.
    # The user autocompletion is for example used in the details dialog of a workspace.
    # @api beta
    # @param [Proc] suggest_users_proc proc for fetching users to be suggested in the in-place GUI
    # @yieldparam [String] input an arbitrary string from the input field of a user autocompletion,
    #   e.g. the first letters of a user name
    # @yieldreturn [Array<Scrivito::User>] users that were found for the given input string
    # @note Only the first 20 of the returnes users will be displayed in the in-place GUI.
    # @note +suggest_users_proc+ may also be invoked with an empty 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 the ability of a user to publish a certain object. Each
    # registered callback can access a certain attribute of an object. Multiple
    # callbacks are possible
    #
    # @api beta
    # @param [Hash] options
    # @option options [Symbol] :uses the attribute you need 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 is needed
    #
    # @note the callback is only called with {BasicObj Objs} that have the attribute
    #   specified by the :uses option and if it is not a {BasicWidget Widget}-attribute
    #
    # @example
    #   class MyUserModel
    #     def to_scrivito_user
    #       Scrivito::User.define(id) do |user|
    #         user.restrict_obj_publish(uses: :_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(uses: :_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, abilities: abilities, 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 abilities
      @abilities ||= Hash.new(-> { false }).with_indifferent_access
    end

    def assert_valid_ability(ability_name, ability_proc)
      unless ABILITY_NAMES.include?(ability_name.to_s)
        raise ScrivitoError.new("'#{ability_name}' is not a valid ability name")
      end

      unless ability_proc
        raise ScrivitoError.new("No proc given for ability '#{ability_name}'")
      end
    end
  end
end