require 'action_dispatch/journey/gtg/transition_table' module ActionDispatch module Journey # :nodoc: module GTG # :nodoc: class Builder # :nodoc: DUMMY = Nodes::Dummy.new attr_reader :root, :ast, :endpoints def initialize(root) @root = root @ast = Nodes::Cat.new root, DUMMY @followpos = nil end def transition_table dtrans = TransitionTable.new marked = {} state_id = Hash.new { |h,k| h[k] = h.length } start = firstpos(root) dstates = [start] until dstates.empty? s = dstates.shift next if marked[s] marked[s] = true # mark s s.group_by { |state| symbol(state) }.each do |sym, ps| u = ps.flat_map { |l| followpos(l) } next if u.empty? if u.uniq == [DUMMY] from = state_id[s] to = state_id[Object.new] dtrans[from, to] = sym dtrans.add_accepting(to) ps.each { |state| dtrans.add_memo(to, state.memo) } else dtrans[state_id[s], state_id[u]] = sym if u.include?(DUMMY) to = state_id[u] accepting = ps.find_all { |l| followpos(l).include?(DUMMY) } accepting.each { |accepting_state| dtrans.add_memo(to, accepting_state.memo) } dtrans.add_accepting(state_id[u]) end end dstates << u end end dtrans end def nullable?(node) case node when Nodes::Group true when Nodes::Star true when Nodes::Or node.children.any? { |c| nullable?(c) } when Nodes::Cat nullable?(node.left) && nullable?(node.right) when Nodes::Terminal !node.left when Nodes::Unary nullable?(node.left) else raise ArgumentError, 'unknown nullable: %s' % node.class.name end end def firstpos(node) case node when Nodes::Star firstpos(node.left) when Nodes::Cat if nullable?(node.left) firstpos(node.left) | firstpos(node.right) else firstpos(node.left) end when Nodes::Or node.children.flat_map { |c| firstpos(c) }.uniq when Nodes::Unary firstpos(node.left) when Nodes::Terminal nullable?(node) ? [] : [node] else raise ArgumentError, 'unknown firstpos: %s' % node.class.name end end def lastpos(node) case node when Nodes::Star firstpos(node.left) when Nodes::Or node.children.flat_map { |c| lastpos(c) }.uniq when Nodes::Cat if nullable?(node.right) lastpos(node.left) | lastpos(node.right) else lastpos(node.right) end when Nodes::Terminal nullable?(node) ? [] : [node] when Nodes::Unary lastpos(node.left) else raise ArgumentError, 'unknown lastpos: %s' % node.class.name end end def followpos(node) followpos_table[node] end private def followpos_table @followpos ||= build_followpos end def build_followpos table = Hash.new { |h, k| h[k] = [] } @ast.each do |n| case n when Nodes::Cat lastpos(n.left).each do |i| table[i] += firstpos(n.right) end when Nodes::Star lastpos(n).each do |i| table[i] += firstpos(n) end end end table end def symbol(edge) case edge when Journey::Nodes::Symbol edge.regexp else edge.left end end end end end end