# frozen_string_literal: true
module Temple
  module Filters
    # Compile [:multi, [:static, 'foo'], [:dynamic, 'bar']] to [:dynamic, '"foo#{bar}"']
    class DynamicMerger < Filter
      def on_multi(*exps)
        exps = exps.dup
        result = [:multi]
        buffer = []

        until exps.empty?
          type, arg = exps.first
          if type == :dynamic && arg.count("\n") == 0
            buffer << exps.shift
          elsif type == :static && exps.size > (count = arg.count("\n")) &&
                exps[1, count].all? { |e| e == [:newline] }
            (1 + count).times { buffer << exps.shift }
          elsif type == :newline && exps.size > (count = count_newline(exps)) &&
                exps[count].first == :static && count == exps[count].last.count("\n")
            (count + 1).times { buffer << exps.shift }
          else
            result.concat(merge_dynamic(buffer))
            buffer = []
            result << compile(exps.shift)
          end
        end
        result.concat(merge_dynamic(buffer))

        result.size == 2 ? result[1] : result
      end

      private

      def merge_dynamic(exps)
        # Merge exps only when they have both :static and :dynamic
        unless exps.any? { |type,| type == :static } && exps.any? { |type,| type == :dynamic }
          return exps
        end

        strlit_body = String.new
        exps.each do |type, arg|
          case type
          when :static
            strlit_body << arg.dump.sub!(/\A"/, '').sub!(/"\z/, '').gsub('\n', "\n")
          when :dynamic
            strlit_body << "\#{#{arg}}"
          when :newline
            # newline is added by `gsub('\n', "\n")`
          else
            raise "unexpected type #{type.inspect} is given to #merge_dynamic"
          end
        end
        [[:dynamic, "%Q\0#{strlit_body}\0"]]
      end

      def count_newline(exps)
        count = 0
        exps.each do |exp|
          if exp == [:newline]
            count += 1
          else
            return count
          end
        end
        return count
      end
    end
  end
end