module ActionDispatch
  module Journey # :nodoc:
    module Path # :nodoc:
      class Pattern # :nodoc:
        attr_reader :spec, :requirements, :anchored

        def self.from_string(string)
          build(string, {}, "/.?", true)
        end

        def self.build(path, requirements, separators, anchored)
          parser = Journey::Parser.new
          ast = parser.parse path
          new ast, requirements, separators, anchored
        end

        def initialize(ast, requirements, separators, anchored)
          @spec         = ast
          @requirements = requirements
          @separators   = separators
          @anchored     = anchored

          @names          = nil
          @optional_names = nil
          @required_names = nil
          @re             = nil
          @offsets        = nil
        end

        def build_formatter
          Visitors::FormatBuilder.new.accept(spec)
        end

        def eager_load!
          required_names
          offsets
          to_regexp
          nil
        end

        def ast
          @spec.find_all(&:symbol?).each do |node|
            re = @requirements[node.to_sym]
            node.regexp = re if re
          end

          @spec.find_all(&:star?).each do |node|
            node = node.left
            node.regexp = @requirements[node.to_sym] || /(.+)/
          end

          @spec
        end

        def names
          @names ||= spec.find_all(&:symbol?).map(&:name)
        end

        def required_names
          @required_names ||= names - optional_names
        end

        def optional_names
          @optional_names ||= spec.find_all(&:group?).flat_map { |group|
            group.find_all(&:symbol?)
          }.map(&:name).uniq
        end

        class AnchoredRegexp < Journey::Visitors::Visitor # :nodoc:
          def initialize(separator, matchers)
            @separator = separator
            @matchers  = matchers
            @separator_re = "([^#{separator}]+)"
            super()
          end

          def accept(node)
            %r{\A#{visit node}\Z}
          end

          def visit_CAT(node)
            [visit(node.left), visit(node.right)].join
          end

          def visit_SYMBOL(node)
            node = node.to_sym

            return @separator_re unless @matchers.key?(node)

            re = @matchers[node]
            "(#{re})"
          end

          def visit_GROUP(node)
            "(?:#{visit node.left})?"
          end

          def visit_LITERAL(node)
            Regexp.escape(node.left)
          end
          alias :visit_DOT :visit_LITERAL

          def visit_SLASH(node)
            node.left
          end

          def visit_STAR(node)
            re = @matchers[node.left.to_sym] || ".+"
            "(#{re})"
          end

          def visit_OR(node)
            children = node.children.map { |n| visit n }
            "(?:#{children.join(?|)})"
          end
        end

        class UnanchoredRegexp < AnchoredRegexp # :nodoc:
          def accept(node)
            %r{\A#{visit node}}
          end
        end

        class MatchData # :nodoc:
          attr_reader :names

          def initialize(names, offsets, match)
            @names   = names
            @offsets = offsets
            @match   = match
          end

          def captures
            Array.new(length - 1) { |i| self[i + 1] }
          end

          def [](x)
            idx = @offsets[x - 1] + x
            @match[idx]
          end

          def length
            @offsets.length
          end

          def post_match
            @match.post_match
          end

          def to_s
            @match.to_s
          end
        end

        def match(other)
          return unless match = to_regexp.match(other)
          MatchData.new(names, offsets, match)
        end
        alias :=~ :match

        def source
          to_regexp.source
        end

        def to_regexp
          @re ||= regexp_visitor.new(@separators, @requirements).accept spec
        end

        private

          def regexp_visitor
            @anchored ? AnchoredRegexp : UnanchoredRegexp
          end

          def offsets
            return @offsets if @offsets

            @offsets = [0]

            spec.find_all(&:symbol?).each do |node|
              node = node.to_sym

              if @requirements.key?(node)
                re = /#{@requirements[node]}|/
                @offsets.push((re.match("").length - 1) + @offsets.last)
              else
                @offsets << @offsets.last
              end
            end

            @offsets
          end
      end
    end
  end
end