require 'set'

module CodeRay
  module Scanners
    class RuleBasedScanner < Scanner
      
      Pattern = Struct.new :pattern
      Groups = Struct.new :token_kinds
      Kind = Struct.new :token_kind
      Push = Struct.new :state, :group
      Pop = Struct.new :group
      PushState = Struct.new :state
      PopState = Class.new
      Check = Struct.new :condition
      CheckIf = Class.new Check
      CheckUnless = Class.new Check
      ValueSetter = Struct.new :targets, :value
      Increment = Struct.new :targets, :operation, :value
      Continue = Class.new
      
      class << self
        attr_accessor :states
        
        def state *names, &block
          @code ||= ""
          
          @code << "when #{names.map(&:inspect).join(', ')}\n"
          
          @first = true
          instance_eval(&block)
          @code << "  else\n"
          @code << "    puts \"no match for \#{state.inspect} => skip char\"\n" if $DEBUG
          @code << "    encoder.text_token getch, :error\n"
          @code << "  end\n"
          @code << "  \n"
        end
        
        def on? pattern
          pattern_expression = pattern.inspect
          @code << "  #{'els' unless @first}if check(#{pattern_expression})\n"
          
          @first = true
          yield
          @code << "  end\n"
          
          @first = false
        end
        
        def on *pattern_and_actions
          if index = pattern_and_actions.find_index { |item| !(item.is_a?(Check) || item.is_a?(Regexp) || item.is_a?(Pattern)) }
            conditions = pattern_and_actions[0..index - 1] or raise 'I need conditions or a pattern!'
            actions    = pattern_and_actions[index..-1]    or raise 'I need actions!'
          else
            raise "invalid rule structure: #{pattern_and_actions.map(&:class)}"
          end
          
          condition_expressions = []
          if conditions
            for condition in conditions
              case condition
              when CheckIf
                case condition.condition
                when Proc
                  condition_expressions << "#{make_callback(condition.condition)}"
                when Symbol
                  condition_expressions << "#{condition.condition}"
                else
                  raise "I don't know how to evaluate this check_if condition: %p" % [condition.condition]
                end
              when CheckUnless
                case condition.condition
                when Proc
                  condition_expressions << "!#{make_callback(condition.condition)}"
                when Symbol
                  condition_expressions << "!#{condition.condition}"
                else
                  raise "I don't know how to evaluate this check_unless condition: %p" % [condition.condition]
                end
              when Pattern
                case condition.pattern
                when Proc
                  condition_expressions << "match = scan(#{make_callback(condition.pattern)})"
                else
                  raise "I don't know how to evaluate this pattern: %p" % [condition.pattern]
                end
              when Regexp
                condition_expressions << "match = scan(#{condition.inspect})"
              else
                raise "I don't know how to evaluate this pattern/condition: %p" % [condition]
              end
            end
          end
          
          @code << "  #{'els' unless @first}if #{condition_expressions.join(' && ')}\n"
          
          for action in actions
            case action
            when String
              raise
              @code << "    p 'evaluate #{action.inspect}'\n" if $DEBUG
              @code << "    #{action}\n"
              
            when Symbol
              @code << "    p 'text_token %p %p' % [match, #{action.inspect}]\n" if $DEBUG
              @code << "    encoder.text_token match, #{action.inspect}\n"
            when Kind
              case action.token_kind
              when Proc
                @code << "    encoder.text_token match, kind = #{make_callback(action.token_kind)}\n"
              else
                raise "I don't know how to evaluate this kind: %p" % [action.token_kind]
              end
            when Groups
              @code << "    p 'text_tokens %p in groups %p' % [match, #{action.token_kinds.inspect}]\n" if $DEBUG
              action.token_kinds.each_with_index do |kind, i|
                @code << "    encoder.text_token self[#{i + 1}], #{kind.inspect} if self[#{i + 1}]\n"
              end
            
            when Push, PushState
              case action.state
              when String
                raise
                @code << "    p 'push %p' % [#{action.state}]\n" if $DEBUG
                @code << "    state = #{action.state}\n"
                @code << "    states << state\n"
              when Symbol
                @code << "    p 'push %p' % [#{action.state.inspect}]\n" if $DEBUG
                @code << "    state = #{action.state.inspect}\n"
                @code << "    states << state\n"
              when Proc
                @code << "    if new_state = #{make_callback(action.state)}\n"
                @code << "      state = new_state\n"
                @code << "      states << new_state\n"
                @code << "    end\n"
              else
                raise "I don't know how to evaluate this push state: %p" % [action.state]
              end
              if action.is_a? Push
                if action.state == action.group
                  @code << "    encoder.begin_group state\n"
                else
                  case action.state
                  when Symbol
                    @code << "    p 'begin group %p' % [#{action.group.inspect}]\n" if $DEBUG
                    @code << "    encoder.begin_group #{action.group.inspect}\n"
                  when Proc
                    @code << "    encoder.begin_group #{make_callback(action.group)}\n"
                  else
                    raise "I don't know how to evaluate this push state: %p" % [action.state]
                  end
                end
              end
            when Pop, PopState
              @code << "    p 'pop %p' % [states.last]\n" if $DEBUG
              if action.is_a? Pop
                if action.group
                  case action.group
                  when Symbol
                    @code << "    encoder.end_group #{action.group.inspect}\n"
                  else
                    raise "I don't know how to evaluate this pop group: %p" % [action.group]
                  end
                  @code << "    states.pop\n"
                else
                  @code << "    encoder.end_group states.pop\n"
                end
              else
                @code << "    states.pop\n"
              end
              @code << "    state = states.last\n"
            
            when ValueSetter
              case action.value
              when Proc
                @code << "    #{action.targets.join(' = ')} = #{make_callback(action.value)}\n"
              when Symbol
                @code << "    #{action.targets.join(' = ')} = #{action.value}\n"
              else
                @code << "    #{action.targets.join(' = ')} = #{action.value.inspect}\n"
              end
            
            when Increment
              case action.value
              when Proc
                @code << "    #{action.targets.join(' = ')} #{action.operation}= #{make_callback(action.value)}\n"
              when Symbol
                @code << "    #{action.targets.join(' = ')} #{action.operation}= #{action.value}\n"
              else
                @code << "    #{action.targets.join(' = ')} #{action.operation}= #{action.value.inspect}\n"
              end
            
            when Proc
              @code << "    #{make_callback(action)}\n"
              
            when Continue
              @code << "    next\n"
              
            else
              raise "I don't know how to evaluate this action: %p" % [action]
            end
          end
          
          @first = false
        end
        
        def groups *token_kinds
          Groups.new token_kinds
        end
        
        def pattern pattern = nil, &block
          Pattern.new pattern || block
        end
        
        def kind token_kind = nil, &block
          Kind.new token_kind || block
        end
        
        def push state = nil, group = state, &block
          raise 'push requires a state or a block; got nothing' unless state || block
          Push.new state || block, group || block
        end
        
        def pop group = nil
          Pop.new group
        end
        
        def push_state state = nil, &block
          raise 'push_state requires a state or a block; got nothing' unless state || block
          PushState.new state || block
        end
        
        def pop_state
          PopState.new
        end
        
        def check_if value = nil, &callback
          CheckIf.new value || callback
        end
        
        def check_unless value = nil, &callback
          CheckUnless.new value || callback
        end
        
        def flag_on *flags
          flags.each { |name| variables << name }
          ValueSetter.new Array(flags), true
        end
        
        def flag_off *flags
          flags.each { |name| variables << name }
          ValueSetter.new Array(flags), false
        end
        
        def set flag, value = nil, &callback
          variables << flag
          ValueSetter.new [flag], value || callback || true
        end
        
        def unset *flags
          flags.each { |name| variables << name }
          ValueSetter.new Array(flags), nil
        end
        
        def increment *counters
          counters.each { |name| variables << name }
          Increment.new Array(counters), :+, 1
        end
        
        def decrement *counters
          counters.each { |name| variables << name }
          Increment.new Array(counters), :-, 1
        end
        
        def continue
          Continue.new
        end
        
        def define_scan_tokens!
          if ENV['PUTS']
            puts CodeRay.scan(scan_tokens_code, :ruby).terminal
            puts "callbacks: #{callbacks.size}"
          end
          
          class_eval scan_tokens_code
        end
        
        protected
        
        def callbacks
          @callbacks ||= {}
        end
        
        def variables
          @variables ||= Set.new
        end
        
        def additional_variables
          variables - %i(encoder options state states match kind)
        end
        
        def make_callback block
          base_name = "__callback_line_#{block.source_location.last}"
          callback_name = base_name
          counter = 'a'
          while callbacks.key?(callback_name)
            callback_name = "#{base_name}_#{counter}"
            counter.succ!
          end
          
          callbacks[callback_name] = define_method(callback_name, &block)
          
          parameters = block.parameters
          
          if parameters.empty?
            callback_name
          else
            parameter_names = parameters.map(&:last)
            parameter_names.each { |name| variables << name }
            "#{callback_name}(#{parameter_names.join(', ')})"
          end
        end
        
        def scan_tokens_code
          <<-"RUBY"
    def scan_tokens encoder, options
      state = options[:state] || @state
      
#{ restore_local_variables_code.chomp.gsub(/^/, '  ' * 3) }
      
      states = [state]
      
      until eos?
        case state
#{ @code.chomp.gsub(/^/, '  ' * 4) }
        else
          raise_inspect 'Unknown state: %p' % [state], encoder
        end
      end
      
      if options[:keep_state]
        @state = state
      end
      
#{ close_groups_code.chomp.gsub(/^/, '  ' * 3) }
      
      encoder
    end
          RUBY
        end
        
        def restore_local_variables_code
          additional_variables.sort.map { |name| "#{name} = @#{name}" }.join("\n")
        end
        
        def close_groups_code
          "close_groups(encoder, states)"
        end
      end
      
      def scan_tokens tokens, options
        self.class.define_scan_tokens!

        scan_tokens tokens, options
      end
      
      def setup
        @state = :initial
      end
      
      def close_groups encoder, states
        # TODO
      end
      
    end
  end
end