AndyObtiva/glimmer

# Copyright (c) 2007-2024 Andy Maleh
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

require 'forwardable'
require 'facets/string/camelcase'

require 'glimmer/dsl/expression_handler'

module Glimmer
  module DSL
    # Glimmer DSL Engine
    #
    # Follows Interpreter, Chain of Responsibility, and Singleton Design Patterns
    #
    # When DSL engine interprets an expression, it attempts to handle
    # with ordered expression array specified via `.expressions=` method.
    class Engine
      MESSAGE_NO_DSLS = "Glimmer has no DSLs configured. Add glimmer-dsl-swt gem or visit https://github.com/AndyObtiva/glimmer#multi-dsl-support for more details.\n"
      STATIC_EXPRESSION_METHOD_FACTORY = lambda do |keyword|
        lambda do |*args, &block|
          if Glimmer::DSL::Engine.no_dsls?
            Glimmer::Config.logger.error {Glimmer::DSL::Engine::MESSAGE_NO_DSLS}
          else
            retrieved_static_expression = Glimmer::DSL::Engine.static_expressions[keyword][Glimmer::DSL::Engine.dsl]
            # TODO consider replacing Glimmer::DSL::Engine.static_expressions[keyword].keys - Glimmer::DSL::Engine.disabled_dsls with Glimmer::DSL::Engine.enabled_static_expression_dsls(keyword)
            static_expression_dsl = (Glimmer::DSL::Engine.static_expressions[keyword].keys - Glimmer::DSL::Engine.disabled_dsls).first
            interpretation = nil
            if retrieved_static_expression.nil? && Glimmer::DSL::Engine.dsl && (static_expression_dsl.nil? || !Glimmer::DSL::Engine.static_expressions[keyword][static_expression_dsl].is_a?(TopLevelExpression))
              begin
                interpretation = Glimmer::DSL::Engine.interpret(keyword, *args, &block)
              rescue => e
                raise e if static_expression_dsl.nil? || !Glimmer::DSL::Engine.static_expressions[keyword][static_expression_dsl].is_a?(TopLevelExpression)
              end
            end
            if interpretation
              interpretation
            else
              raise Glimmer::Error, "Unsupported keyword: #{keyword}" unless static_expression_dsl || retrieved_static_expression
              Glimmer::DSL::Engine.dsl_stack.push(static_expression_dsl || Glimmer::DSL::Engine.dsl)
              Glimmer::Config.logger.info {"Assuming DSL: #{Glimmer::DSL::Engine.dsl_stack.last}"}
              static_expression = Glimmer::DSL::Engine.static_expressions[keyword][Glimmer::DSL::Engine.dsl]
              static_expression_can_interpret = nil
              if static_expression.nil? || !(static_expression_can_interpret = static_expression.can_interpret?(Glimmer::DSL::Engine.parent, keyword, *args, &block))
                begin
                  Glimmer::DSL::Engine.interpret(keyword, *args, &block)
                rescue => e
                  raise Error, "Invalid use of Glimmer keyword #{keyword} with args #{args} under parent #{Glimmer::DSL::Engine.parent.inspect} with DSL #{Glimmer::DSL::Engine.dsl.inspect} and static expression #{static_expression.inspect} having can_interpret? as #{static_expression_can_interpret.inspect} and no dynamic expressions to be able to handle either!"
                end
              else
                Glimmer::Config.logger.info {"#{static_expression.class.name} will handle expression keyword #{keyword}"}
                Glimmer::DSL::Engine.interpret_expression(static_expression, keyword, *args, &block)
              end
            end
          end
        end
      end
      
      class << self
        extend Forwardable
        
        def_delegator :dsl_stack, :last, :dsl

        def dsls
          static_expressions.values.map(&:keys).flatten.uniq
        end

        def disable_dsl(dsl_name)
          dsl_name = dsl_name.to_sym
          disabled_dsls << dsl_name
        end

        def enable_dsl(dsl_name)
          dsl_name = dsl_name.to_sym
          disabled_dsls.delete(dsl_name)
        end

        def disabled_dsls
          @disabled_dsls ||= Concurrent::Array.new
        end

        def enabled_dsls=(dsl_names)
          dsls.each {|dsl_name| disable_dsl(dsl_name)}
          dsl_names.each {|dsl_name| enable_dsl(dsl_name)}
        end
    
        # Resets Glimmer's engine activity and configuration. Useful in rspec before or after blocks in tests.
        def reset
          parent_stacks.values.each do |a_parent_stack|
            a_parent_stack.clear
          end
          dsl_stack.clear
          disabled_dsls.clear
        end
        
        def no_dsls?
          static_expressions.empty? && dynamic_expression_chains_of_responsibility.empty?
        end

        # Dynamic expression chains of responsibility indexed by dsl
        def dynamic_expression_chains_of_responsibility
          @dynamic_expression_chains_of_responsibility ||= Concurrent::Hash.new
        end

        # Static expressions indexed by keyword and dsl
        def static_expressions
          @static_expressions ||= Concurrent::Hash.new
        end

        # Sets dynamic expression chains of responsibility. Useful for internal testing
        attr_writer :dynamic_expression_chains_of_responsibility

        # Sets static expressions. Useful for internal testing
        attr_writer :static_expressions

        # Sets an ordered array of DSL expressions to support
        #
        # Every expression has an underscored name corresponding to an upper
        # camelcase AbstractExpression subclass name in glimmer/dsl
        #
        # They are used in order following the Chain of Responsibility Design
        # Pattern when interpretting a DSL expression
        def add_dynamic_expressions(dsl_namespace, *expression_names)
          expression_names = expression_names.flatten
          dsl = dsl_namespace.name.split("::").last.downcase.to_sym
          dynamic_expression_chains_of_responsibility[dsl] = expression_names.reverse.map do |expression_name|
            expression_class(dsl_namespace, expression_name).new
          end.reduce(nil) do |last_expresion_handler, expression|
            Glimmer::Config.logger.info {"Adding dynamic expression: #{expression.class.name}"}
            expression_handler = ExpressionHandler.new(expression)
            expression_handler.next = last_expresion_handler if last_expresion_handler
            expression_handler
          end
        end

        def add_downcased_static_expression(static_expression)
          Glimmer::Config.logger.info {"Adding static expression: #{static_expression.class.name}"}
          keyword = static_expression.class.keyword
          static_expressions[keyword] ||= Concurrent::Hash.new
          static_expression_dsl = static_expression.class.dsl
          static_expressions[keyword][static_expression_dsl] = static_expression
          Glimmer.send(:define_method, keyword, &STATIC_EXPRESSION_METHOD_FACTORY.call(keyword))
        end
        alias add_static_expression add_downcased_static_expression
        
        def remove_downcased_static_expression(static_expression)
          if !static_expression.class.downcased?
            keyword = static_expression.class.keyword
            static_expressions[keyword].delete(static_expression_dsl) if static_expressions[keyword]
            static_expressions.delete(keyword) if static_expressions[keyword].empty?
            Glimmer.send(:undef_method, keyword) if (Glimmer.method(keyword) rescue nil)
          end
        end
        
        def add_upcased_static_expression(static_expression)
          if static_expression.class.upcased?
            Glimmer::Config.logger.info {"Adding upcased static expression: #{static_expression.class.name}"}
            keyword = static_expression.class.keyword
            static_expression_dsl = static_expression.class.dsl
            static_expressions[keyword.upcase] ||= Concurrent::Hash.new
            static_expressions[keyword.upcase][static_expression_dsl] = static_expression
            Glimmer.send(:define_method, keyword.upcase, &STATIC_EXPRESSION_METHOD_FACTORY.call(keyword.upcase))
          end
        end
        
        def add_capitalized_static_expression(static_expression)
          if static_expression.class.capitalized?
            Glimmer::Config.logger.info {"Adding capitalized static expression: #{static_expression.class.name}"}
            keyword = static_expression.class.keyword
            static_expression_dsl = static_expression.class.dsl
            static_expressions[keyword.capitalize] ||= Concurrent::Hash.new
            static_expressions[keyword.capitalize][static_expression_dsl] = static_expression
            Glimmer.send(:define_method, keyword.capitalize, &STATIC_EXPRESSION_METHOD_FACTORY.call(keyword.capitalize))
          end
        end

        def expression_class(dsl_namespace, expression_name)
          dsl_namespace.const_get(expression_class_name(expression_name).to_sym)
        end

        def expression_class_name(expression_name)
          "#{expression_name}_expression".camelcase(:upper)
        end

        # Interprets Glimmer dynamic DSL expression consisting of keyword, args, and block (e.g. shell(:no_resize) { ... })
        def interpret(keyword, *args, &block)
          return puts(MESSAGE_NO_DSLS) if no_dsls? # TODO consider switching to an error log statement
          keyword = keyword.to_s
          dynamic_expression_dsl = (dynamic_expression_chains_of_responsibility.keys - disabled_dsls).first if dsl.nil?
          # TODO consider pushing this code into interpret_expresion to provide hooks that work around it regardless of static vs dynamic
          dsl_stack.push(dynamic_expression_dsl || dsl)
          Glimmer::Config.logger.info {"Assuming DSL: #{dsl_stack.last}"}
          expression = dynamic_expression_chains_of_responsibility[dsl].handle(parent, keyword, *args, &block)
          interpret_expression(expression, keyword, *args, &block)
        end
        
        def interpret_expression(expression, keyword, *args, &block)
          new_parent = nil
          expression.around(parent, keyword, args, block) do
            new_parent = expression.interpret(parent, keyword, *args, &block).tap do |new_parent|
              add_content(new_parent, expression, keyword, *args, &block)
              dsl_stack.pop
            end
          end
          new_parent
        end

        # Adds content block to parent UI object
        #
        # This allows evaluating parent UI object properties and children
        #
        # For example, a shell widget would get properties set and children added
        def add_content(new_parent, expression, keyword, *args, &block)
          if block_given? && expression.is_a?(ParentExpression)
            dsl_stack.push(expression.class.dsl)
            parent_stack.push(new_parent)
            begin
              expression.add_content(new_parent, keyword, *args, &block)
            ensure
              parent_stack.pop
              dsl_stack.pop
            end
          end
        end

        # Current parent while evaluating Glimmer DSL (nil if just started or done evaluatiing)
        #
        # Parents are maintained in a stack while evaluating Glimmer DSL
        # to ensure properly ordered interpretation of DSL syntax
        def_delegator :parent_stack, :last, :parent

        def parent_stack
          parent_stacks[dsl] ||= Concurrent::Array.new
        end

        def parent_stacks
          @parent_stacks ||= Concurrent::Hash.new
        end

        # Enables multiple DSLs to play well with each other when mixing together
        def dsl_stack
          @dsl_stack ||= Concurrent::Array.new
        end
      end
    end
  end
end