# -*- coding: utf-8 -*-

class Parser

rule
  robotstxt		: opt_blanklines
			  {
			    @sitemaps = []
			  }
			  body
			  {
			    body = val[2]
			    result = RobotsTxt.new(@site, body,
			      :target => @target, :sitemaps => @sitemaps)
			  }

  body			:
			| blocks
			  opt_blanklines

  opt_blanklines	:
			| blanklines

  blanklines		: blankline
			| blanklines
			  blankline

  blankline		: eol

  eol			: EOL
			  {
			    @lineno += 1
			  }

  opt_space		:
			| SPACE

  opt_commentlines	:
			| commentlines

  commentlines		: comment
			| commentlines
			  comment

  comment		: opt_space COMMENT eol
			| 'sitemap' ':' opt_space VALUE eol_opt_comment
			  {
			    @sitemaps << val[3]
			  }

  blocks		: record
			  {
			    result = []
			    result << val[0]
			  }
			| commentblock
			  {
			    result = []
			  }
			| blocks
			  blanklines
			  record
			  {
			    result << val[2]
			  }
			| blocks
			  blanklines
			  rulelines
			  {
			    val[2].each_with_index { |line, i|
			      warn "%s line %d: %s: orphan rule line" %
			        [@site.to_s, @rulelinenos[i], line.token] if $VERBOSE
			    }
			  }
			| blocks
			  blanklines
			  commentblock

  commentblock		: commentlines

  record		: opt_commentlines
			  agentlines
			  opt_rulelines
			  {
			    result = Record.new(val[1], val[2])
			  }

  agentlines		: agentline
			  {
			    result = [val[0]]
			  }
			| agentlines
			  agentline
			  {
			    result << val[1]
			  }
			| agentlines
			  comment

  agentline		: 'user-agent' ':' opt_space VALUE eol_opt_comment
			  {
			    result = AgentLine.new(val[0], val[3])
			  }

  opt_rulelines		:
			| rulelines

  rulelines		: ruleline
			  {
			    result = [result]
			    @rulelinenos = []
			  }
			| rulelines
			  ruleline
			  {
			    result << val[1]
			    @rulelinenos << @lineno
			  }
			| rulelines
			  comment

  ruleline		: allowline
			| disallowline
			| crawldelayline
			| extension

  allowline		: 'allow' ':' opt_space VALUE eol_opt_comment
			  {
			    result = AllowLine.new(val[0], val[3])
			  }

  disallowline		: 'disallow' ':' opt_space VALUE eol_opt_comment
			  {
			    result = DisallowLine.new(val[0], val[3])
			  }

  crawldelayline	: 'crawl-delay' ':' opt_space VALUE eol_opt_comment
			  {
			    result = CrawlDelayLine.new(val[0], val[3])
			  }

  extension		: TOKEN ':' opt_space VALUE eol_opt_comment
			  {
			    result = ExtentionLine.new(val[0], val[3])
			  }

  eol_opt_comment	: eol
			| comment

---- header

require 'strscan'
require 'uri'

class WebRobots
  class Error < StandardError
  end

  class ParseError < Error
  end

  class RobotsTxt
---- inner

      def initialize(target = nil)
        super()
        @target = target
      end

      def parse!(input, site)
        parse(input, site)
      rescue Error => e
        RobotsTxt.new(site, nil, :error => e, :target => @target)
      end

      KNOWN_TOKENS = %w[User-agent Allow Disallow Crawl-delay Sitemap]
      RE_KNOWN_TOKENS = /#{KNOWN_TOKENS.join('|')}/i

      def parse(input, site)
        @q = []
        @errors = []
        @lineno = 1
        @site = site

        string = input.respond_to?(:read) ? input.read : input
        s = StringScanner.new(string)
        value_expected = false

        until s.eos?
          if t = s.scan(/[ \t]*\r?\n/)
            if value_expected
              @q << [:VALUE, '']
            end
            @q << [:EOL, t]
            value_expected = false
          elsif t = s.scan(/[ \t]+/)
            @q << [:SPACE, t]
          elsif t = s.scan(/:/)
            @q << [t, t]
            value_expected = true
          elsif t = s.scan(/#.*/)
            if value_expected
              @q << [:VALUE, '']
            end
            @q << [:COMMENT, t]
          else
            if value_expected
              if t = s.scan(/.*?(?=[ \t]*(?:#|$))/)
                @q << [:VALUE, t]
              else
                parse_error @lineno, "unexpected characters: %s" % s.check(/.*/)
              end
              value_expected = false
            else
              if t = s.scan(RE_KNOWN_TOKENS)
                @q << [t.downcase, t]
              elsif t = s.scan(/[^\x00-\x1f\x7f()<>@,;:\\"\/\[\]?={}]+/)
                @q << [:TOKEN, t]
              else
                parse_error "unexpected characters: %s" % s.check(/.*/)
              end
            end
          end
        end

        @q << [:EOL, ''] if !@q.empty? && @q.last.first != :EOL

        @pos = -1

        do_parse
      rescue Racc::ParseError => e
        raise ParseError, e.message
      end

      def next_token
        @q[@pos += 1]
      end

      def on_error(token_id, value, stack)
        parse_error "unexpected %s: %s" % [token_to_str(token_id), value]
      end

      def parse_error(message)
        message = "%s line %d: %s" % [@site.to_s, @lineno, message]
        if @lax
          @errors << message
        else
          raise Racc::ParseError, message
        end
      end

---- footer
    def initialize(site, records, options = nil)
      @timestamp = Time.now
      @site = site
      @options = options || {}
      @last_checked = nil

      @error = @options[:error]
      @target = @options[:target]
      @sitemaps = @options[:sitemaps] || []

      if records && !records.empty?
        @records, defaults = [], []
        records.each { |record|
          if record.default?
            defaults << record
          elsif !@target || record.match?(@target)
            @records << record
          end
        }
        @records.concat(defaults)
      else
        @records = []
      end
    end

    attr_reader :timestamp, :site, :sitemaps
    attr_accessor :error

    def error!
      raise @error if @error
    end

    def target(user_agent = nil)
      if user_agent
        raise ArgumentError, "this instance is targeted for #{@target}" if @target
        user_agent
      else
        raise ArgumentError, "user_agent is mandatory for an untargeted instance" if !@target
        @target
      end
    end
    private :target

    def find_record(user_agent = nil)
      user_agent = target(user_agent)
      @records.find { |record|
        record.match?(user_agent)
      }
    end
    private :find_record

    def allow?(request_uri, user_agent = nil)
      record = find_record(user_agent) or return true
      allow = record.allow?(request_uri)
      if @last_checked and delay = record.delay
        delay -= Time.now - @last_checked
        sleep delay if delay > 0
      end
      @last_checked = Time.now
      return allow
    end

    def options(user_agent = nil)
      record = find_record(user_agent) or return {}
      record.options
    end

    DISALLOW_ALL = <<-TXT
User-Agent: *
Disallow: /
    TXT

    def self.unfetchable(site, reason, target = nil)
      Parser.new(target).parse(DISALLOW_ALL, site).tap { |robots_txt|
        robots_txt.error = reason
      }
    end

    class Record
      def initialize(agentlines, rulelines)
        @patterns = agentlines.map { |agentline| agentline.pattern }
        @acls = []
        @delay = nil
        @options = {}
        rulelines.each { |ruleline|
          case ruleline
          when AccessControlLine
            @acls << ruleline
          when CrawlDelayLine
            @delay = ruleline.delay
          else
            @options[ruleline.token.downcase] = ruleline.value
          end
        }
        @acls.sort! { |a, b|
          [
            b.value.length, b.is_a?(AllowLine) ? 1 : 0
          ] <=> [
            a.value.length, a.is_a?(AllowLine) ? 1 : 0
          ]
        }
      end

      attr_reader :delay, :options

      def match?(user_agent)
        @patterns.any? { |pattern|
          pattern.match(user_agent)
        }
      end

      def default?
        @patterns.include?(//)
      end

      def allow?(request_uri)
        @acls.each { |acl|
          if acl.match?(request_uri)
            return acl.allow?
          end
        }
        return true
      end
    end

    class Line
      def initialize(token, value)
        @token = token
        @value = value
        compile
      end

      attr_reader :token, :value

      def compile
        self
      end
    end

    class AgentLine < Line
      def compile
        if @value == '*'
          @pattern = //
        else
          @pattern = Regexp.new(Regexp.quote(@value), Regexp::IGNORECASE)
        end
        self
      end

      attr_reader :pattern
    end

    class AccessControlLine < Line
      def compile
        @empty = @value.empty?
        re_src = '\A'
        s = StringScanner.new(@value)
        until s.eos?
          if t = s.scan(/[^%*$]+/)
            re_src << Regexp.quote(t)
          elsif t = s.scan(/%([0-9a-f]{2})/i)
            c = s[1].to_i(16)
            if c == 0x2f
              re_src << '%2[fF]'
            else
              re_src << Regexp.quote('%c' % c)
            end
          elsif t = s.scan(/\*/)
            re_src << '.*'
          elsif t = s.scan(/\$/)
            re_src << '\z'
            break
          else
            re_src << Regexp.quote(s.scan(/./))
          end
        end
        @pattern = Regexp.new(re_src, Regexp::MULTILINE)
        self
      end

      def match?(request_uri)
        return false if @empty
        transformed = request_uri.gsub(/(%2[fF])|%([0-9a-f]{2})/i) { $1 || '%c' % $2.to_i(16) }
        !!@pattern.match(transformed)
      end
    end

    class AllowLine < AccessControlLine
      def allow?
        true
      end
    end

    class DisallowLine < AccessControlLine
      def allow?
        false
      end
    end

    class CrawlDelayLine < Line
      def compile
        case @value
        when /\A((0|[1-9][0-9]*)\.[0-9]+)/
          @delay = @value.to_f
        when /\A(0|[1-9][0-9]*)/
          @delay = @value.to_i
        else
          @delay = nil
        end
        self
      end

      attr_reader :delay
    end

    class ExtentionLine < Line
    end
  end
end