module EBNF
  module LL1
    autoload :Lexer,    "ebnf/ll1/lexer"
    autoload :Parser,   "ebnf/ll1/parser"
    autoload :Scanner,  "ebnf/ll1/scanner"

    # Branch table, represented as a recursive hash.
    # The table is indexed by rule symbol, which in-turn references a hash of terminals (which are the first terminals of the production), which in turn reference the sequence of rules that follow, given that terminal as input
    #
    # @return [Hash{Symbol => Hash{String, Symbol => Array<Symbol>}}]
    attr_reader :branch

    # First table
    #
    # @return [Hash{Symbol => Array<String, Symbol>}]
    attr_reader :first

    # Follow table
    #
    # @return [Hash{Symbol => Array<String, Symbol>}]
    attr_reader :follow

    # EBNF Cleanup table
    #
    # The list of terminals used in the grammar.
    #
    # @return [Hash{Symbol => Symbol}]
    attr_reader :cleanup

    # Terminal table
    #
    # The list of terminals used in the grammar.
    #
    # @return [Array<String, Symbol>]
    attr_reader :terminals

    # Pass expression
    #
    # A Terminal symbol used for skipping whitespace and comments
    #
    # @return [Symbol, String]
    attr_reader :pass

    # Start symbol
    #
    # The rule which starts the grammar
    #
    # @return [Symbol]
    attr_reader :start

    ##
    # Create first/follow for each rule using techniques defined for LL(1) parsers.
    #
    # @return [EBNF] self
    # @see http://en.wikipedia.org/wiki/LL_parser#Constructing_an_LL.281.29_parsing_table
    # @param [Array<Symbol>] starts
    #   Set of symbols which are start rules
    def first_follow(*starts)
      # Add _eof to follow all start rules
      @starts = starts
      if @start = starts.first
        starts.each do |start|
          start_rule = find_rule(start)
          raise "No rule found for start symbol #{start}" unless start_rule
          start_rule.add_follow([:_eof])
          start_rule.start = true
        end
      end

      # Comprehnsion rule, create shorter versions of all non-terminal sequences. This is necessary as the FF rules reference w', which is a comprehension.
      comprehensions = []
      ittr = 0
      depth do
        begin
          comprehensions = []
          ast.select {|r| r.rule? && r.seq? && r.comp.nil? && r.expr.length > 2}.each do |rule|
            new_expr = rule.expr[2..-1].unshift(:seq)
            if new_rule = ast.detect {|r| r.expr == new_expr}
              # Link to existing comprehension used for another rules
              debug("FF.c") {"(#{ittr}) link comprehension rule for #{rule.sym} => #{new_rule.sym}[#{new_expr.inspect}]"}
            else
              new_rule = rule.build(new_expr)
              debug("FF.c") {"(#{ittr}) add comprehension rule for #{rule.sym} => #{new_rule.sym}[#{new_expr.inspect}]"}
              comprehensions << new_rule
            end
            rule.comp = new_rule
          end

          @ast += comprehensions
          progress("FF.c") {"(#{ittr}) comprehensions #{comprehensions.length}"}
          ittr += 1
        end while !comprehensions.empty?

        ittr = 0
        begin
          firsts, follows = 0, 0
          # add Fi(wi) to Fi(Ai) for every rule Ai → wi
          #
          # For sequences, this is the first rule in the sequence.
          # For alts, this is every rule in the sequence
          each(:rule) do |ai|
            # Fi(a w' ) = { a } for every terminal a
            ai.terminals(ast).each do |t|
              debug("Fi.2.1") {"(#{ittr}) add terminal #{t} to #{ai.sym}"}
              firsts += ai.add_first([t])
            end

            ai.non_terminals(ast).select(&:first).each do |a|
              if !a.first_includes_eps?
                # Fi(A w' ) = Fi(A) for every nonterminal A with ε not in Fi(A)
                debug("Fi.2.2") {"(#{ittr}) add first from #{a.sym} to #{ai.sym}: #{a.first.inspect}"}
                firsts += ai.add_first(a.first)
              else
                # Fi(A w' ) = Fi(A) \ { ε } ∪ Fi(w' ) for every nonterminal A with ε in Fi(A)
                if ai.seq?
                  # w' is either comprehnsion of ai, or empty, if there is no comprehension
                  comp = ai.comp || find_rule(:_empty)

                  fi = a.first - [:_eps] + (comp.first || [])
                  debug("Fi.2.3a") {"(#{ittr}) add first #{fi.inspect} from #{a.sym} and #{comp.sym} to #{ai.sym}"}
                  firsts += ai.add_first(fi)
                else
                  # ai is an alt, so there are no comprehensions of non-terminals, add Fi(A) including ε
                  debug("Fi.2.3b") {"(#{ittr}) add first #{a.first} from #{a.sym} to #{ai.sym}"}
                  firsts += ai.add_first(a.first)
                end
              end
            end
          end

          # # Fi(ε) = { ε }
          # Add _eps as a first of _empty
          find_rule(:_empty).add_first([:_eps])

          # Add follows
          # if there is a rule of the form Aj → wAiw' , then
          # First do this for the case when Ai is the first rule
          each(:rule) do |aj|
            comp = aj.comp || find_rule(:_empty)
            aj.non_terminals(ast).reject {|r| r.sym == :_empty}.each do |ai|
              # if the terminal a is in Fi(w' ), then add a to Fo(Ai)
              # Basically, this says that the firsts of a comprehension of a rule are the follows of the first non-terminal in the rule.
              if comp.first
                debug("Fo.2.1") {"(#{ittr}) add follow #{comp.first.inspect} from #{comp.sym} to #{ai.sym}"}
                follows += ai.add_follow(comp.first)
              end

              # If there is no comprehension of this rule (meaning, it is a sequence of one non-terminal), then the follows of the non-terminal include the follows of the rule. This handles rules with multiple sequences because it will have a comprehension that includes the last element in the sequence
              if !aj.comp && aj.follow
                debug("Fo.2.1a") {"(#{ittr}) add follow #{aj.follow.inspect} from #{aj.sym} to #{ai.sym}"}
                follows += ai.add_follow(aj.follow)
              end

              # if ε is in Fi(w' ), then add Fo(Aj) to Fo(Ai)
              if comp.first_includes_eps? && aj.follow
                debug("Fo.2.2") {"(#{ittr}) add follow #{aj.follow.inspect} from #{aj.sym} to #{ai.sym}"}
                follows += ai.add_follow(aj.follow)
              end
            end

            # Since the rules are of the form wAiw', and we've handled the case which is just Aiw', this leaves those cases that have rules prior to Ai. This basically says that the follows of a rule are added to the follows of the comprehension of the rule
            if aj.comp && aj.follow
              debug("Fo.2.3") {"(#{ittr}) add follow #{aj.follow.inspect} from #{aj.sym} to #{aj.comp.sym}"}
              follows += aj.comp.add_follow(aj.follow)
            end
          end

          progress("first_follow") {"(#{ittr}) firsts #{firsts}, follows #{follows}"}
          ittr += 1
        end while (firsts + follows) > 0
      end
    end

    ##
    # Generate parser tables, {#branch}, {#first}, {#follow}, and {#terminals}
    def build_tables
      progress("build_tables") {
        "Terminals: #{ast.count {|r| r.terminal?}} " +
        "Non-Terminals: #{ast.count {|r| r.rule?}}"
      }

      @first = ast.
        select(&:first).
        inject({}) {|memo, r|
          memo.merge(r.sym => r.first)
        }
      @follow = ast.
        select(&:follow).
        inject({}) {|memo, r|
          memo.merge(r.sym => r.follow)
        }

      @cleanup = ast.
        select(&:cleanup).
        inject({}) {|memo, r| memo.merge(r.sym => r.cleanup)}

      @terminals = ast.map {|r| Array(r.first) + Array(r.follow)}.flatten.uniq
      @terminals = (@terminals - [:_eps, :_eof]).sort_by{|t| t.to_s.sub(/^_/, '')}
      # FIXME: assumes that this is a (seq :PASS), or similar
      if pass = ast.detect {|r| r.pass?}
        @pass = pass.expr.last
      end

      # If a generated terminal is found, this indicates an error, as this version does not automatically generate regular expressions for automatic terminals
      @terminals.
        select {|t| t.to_s.start_with?("_")}.
        reject {|t| t.to_s.start_with?("_pass_")}.  # Concession to backwards compatibility
        each do |term|

        error("build_tables",
              "terminal #{term} is automatically generated; " +
              "regular expressions are not yet generated and parsing " +
              "is not supported")
      end

      @branch = {}
      @already = []
      @agenda = []
      @starts.each do |start|
        do_production(start)
        while !@agenda.empty?
          x = @agenda.shift
          do_production(x)
        end
      end

      if !@errors.empty?
        progress("###### FAILED with #{errors.length} errors.")
        @errors.each {|s| progress("  #{s}")}
        raise "Table creation failed with errors"
      else
        progress("Ok for predictive parsing")
      end 
    end

    # Generate an output table in Ruby format
    # @param [IO, StringIO] io
    # @param [String] name of the table constant
    # @param [String] table
    #   to output, one of {#branch}, {#first}, {#follow}, {#cleanup} or {#terminals}
    # @param [Integer] indent = 0
    def outputTable(io, name, table, indent = 0)
      ind0 = '  ' * indent
      ind1 = ind0 + '  '
      ind2 = ind1 + '  '

      if table.is_a?(Hash)
        io.puts "#{ind0}#{name} = {"
        table.keys.sort_by{|t| t.to_s.sub(/^_/, '')}.each do |prod|
          case table[prod]
          when Symbol, String
            io.puts "#{ind1}#{prod.inspect} => #{table[prod].inspect},"
          when Array
            list = table[prod].map(&:inspect).join(",\n#{ind2}")
            io.puts "#{ind1}#{prod.inspect} => [\n#{ind2}#{list}],"
          when Hash
            io.puts "#{ind1}#{prod.inspect} => {"
            table[prod].keys.sort_by{|t| t.to_s.sub(/^_/, '')}.each do |term|
              list = table[prod][term].map(&:inspect).join(", ")
              io.puts "#{ind2}#{term.inspect} => [#{list}],"
            end
            io.puts "#{ind1}},"
          else
            "Unknown table entry type: #{table[prod].class}"
          end
        end
        io.puts "#{ind0}}.freeze\n"
      else
        io.puts "#{ind0}#{name} = [\n#{ind1}" +
          table.sort_by{|t| t.to_s.sub(/^_/, '')}.map(&:inspect).join(",\n#{ind1}") +
          "\n#{ind0}].freeze\n"
      end
    end

    private
    def do_production(lhs)
      rule = find_rule(lhs)
      if rule.nil? || !rule.rule? || rule.sym == :_empty
        progress("prod") {"Skip: #{lhs.inspect}"}
        return
      end
      @already << lhs

      branchDict = {}

      progress("prod") {"Production #{lhs.inspect}"}

      if rule.expr.first == :matches
        debug("prod") {"Rule is regexp: #{rule}"}

        error("No record of what token #{lhs} can start with") unless rule.first
        return
      end

      if rule.alt?
        # A First/Follow conflict appears when _eps is in the first
        # of one rule and there is a token in the first and
        # follow of the same rule
        if rule.first.include?(:_eps) && !(overlap = ((rule.first & (rule.follow || [])) - [:eps])).empty?
          error("First/Follow Conflict: #{overlap.first.inspect} is both first and follow of #{rule.sym}")
        end

        # Add entries for each alternative, based on the alternative's first/seq
        rule.expr[1..-1].each do |prod|
          prod_rule = find_rule(prod)
          debug("  Alt", prod)

          @agenda << prod unless @already.include?(prod) || @agenda.include?(prod)
          if prod == :_empty
            debug("    empty")
            # Skip empty, rules added bellow for follows
          elsif prod_rule.nil? || prod_rule.first.nil?
            debug("    no first =>", prod)
            branchDict[prod] = [prod]
          else
            prod_rule.first.reject{|f| f == :_eps}.each do |f|
              # A First/First conflict appears when there are two rules having
              # the same first, so the parser can't know which one to choose.
              if branchDict.has_key?(f)
                error("First/First Conflict: #{f.inspect} is the condition for both #{prod_rule.sym} and #{branchDict[f].first}")
              end

              debug("   alt") {"[#{f}] => #{prod}"}
              branchDict[f] = [prod]
            end
          end
        end
      else
        error("prod") {"Expected lhs to be alt or seq, was: #{rule}"} unless rule.seq?
        debug("  Seq", rule)
        # Entries for each first element referencing the sequence
        (rule.first || []).each do |f|
          if [:_eps, :_eof].include?(f)
            # Skip eps/eof, rules added below for follows
          else
            debug("   seq") {"[#{f}] => #{rule.expr[1..-1].inspect}"}
            branchDict[f] = rule.expr[1..-1]
          end
        end
      
        # Add each production to the agenda
        rule.expr[1..-1].each do |prod|
          @agenda << prod unless @already.include?(prod) || @agenda.include?(prod)
        end
      end

      # Add follow rules, if first includes eps
      if rule.first_includes_eps?
        (rule.follow || []).reject {|f| f == :_eof}.each do |f|
          debug("  Follow") {f.inspect}
          branchDict[f] ||= []
        end
      end

      @branch[lhs] = branchDict
    end
  end
end