require 'kpeg/position'

module KPeg
  class CompiledParser

    # Must be outside the STANDALONE block because a standalone
    # parser always injects it's own version of this method.
    def setup_foreign_grammar
    end

    # Leave these markers in! They allow us to generate standalone
    # code automatically!

    # INITIALIZE START

    # This is distinct from setup_parser so that a standalone parser
    # can redefine #initialize and still have access to the proper
    # parser setup code.
    def initialize(str, debug=false)
      setup_parser(str, debug)
    end

    # INITIALIZE END

    # STANDALONE START

    # Prepares for parsing +str+.  If you define a custom initialize you must
    # call this method before #parse
    def setup_parser(str, debug=false)
      set_string str, 0
      @memoizations = Hash.new { |h,k| h[k] = {} }
      @result = nil
      @failed_rule = nil
      @failing_rule_offset = -1

      setup_foreign_grammar
    end

    attr_reader :string
    attr_reader :failing_rule_offset
    attr_accessor :result, :pos

    include Position

    def get_text(start)
      @string[start..@pos-1]
    end

    # Sets the string and current parsing position for the parser.
    def set_string string, pos
      @string = string
      @string_size = string ? string.size : 0
      @pos = pos
    end

    def show_pos
      width = 10
      if @pos < width
        "#{@pos} (\"#{@string[0,@pos]}\" @ \"#{@string[@pos,width]}\")"
      else
        "#{@pos} (\"... #{@string[@pos - width, width]}\" @ \"#{@string[@pos,width]}\")"
      end
    end

    def failure_info
      l = current_line @failing_rule_offset
      c = current_column @failing_rule_offset

      if @failed_rule.kind_of? Symbol
        info = self.class::Rules[@failed_rule]
        "line #{l}, column #{c}: failed rule '#{info.name}' = '#{info.rendered}'"
      else
        "line #{l}, column #{c}: failed rule '#{@failed_rule}'"
      end
    end

    def failure_caret
      l = current_line @failing_rule_offset
      c = current_column @failing_rule_offset

      line = lines[l-1]
      "#{line}\n#{' ' * (c - 1)}^"
    end

    def failure_character
      l = current_line @failing_rule_offset
      c = current_column @failing_rule_offset
      lines[l-1][c-1, 1]
    end

    def failure_oneline
      l = current_line @failing_rule_offset
      c = current_column @failing_rule_offset

      char = lines[l-1][c-1, 1]

      if @failed_rule.kind_of? Symbol
        info = self.class::Rules[@failed_rule]
        "@#{l}:#{c} failed rule '#{info.name}', got '#{char}'"
      else
        "@#{l}:#{c} failed rule '#{@failed_rule}', got '#{char}'"
      end
    end

    class ParseError < RuntimeError
    end

    def raise_error
      raise ParseError, failure_oneline
    end

    def show_error(io=STDOUT)
      error_pos = @failing_rule_offset
      line_no = current_line(error_pos)
      col_no = current_column(error_pos)

      io.puts "On line #{line_no}, column #{col_no}:"

      if @failed_rule.kind_of? Symbol
        info = self.class::Rules[@failed_rule]
        io.puts "Failed to match '#{info.rendered}' (rule '#{info.name}')"
      else
        io.puts "Failed to match rule '#{@failed_rule}'"
      end

      io.puts "Got: #{string[error_pos,1].inspect}"
      line = lines[line_no-1]
      io.puts "=> #{line}"
      io.print(" " * (col_no + 3))
      io.puts "^"
    end

    def set_failed_rule(name)
      if @pos > @failing_rule_offset
        @failed_rule = name
        @failing_rule_offset = @pos
      end
    end

    attr_reader :failed_rule

    def match_string(str)
      len = str.size
      if @string[pos,len] == str
        @pos += len
        return str
      end

      return nil
    end

    def scan(reg)
      if m = reg.match(@string, @pos)
        @pos = m.end(0)
        return true
      end

      return nil
    end

    if "".respond_to? :ord
      def get_byte
        if @pos >= @string_size
          return nil
        end

        s = @string[@pos].ord
        @pos += 1
        s
      end
    else
      def get_byte
        if @pos >= @string_size
          return nil
        end

        s = @string[@pos]
        @pos += 1
        s
      end
    end

    def parse(rule=nil)
      # We invoke the rules indirectly via apply
      # instead of by just calling them as methods because
      # if the rules use left recursion, apply needs to
      # manage that.

      if !rule
        apply(:_root)
      else
        method = rule.gsub("-","_hyphen_")
        apply :"_#{method}"
      end
    end

    class MemoEntry
      def initialize(ans, pos)
        @ans = ans
        @pos = pos
        @result = nil
        @set = false
        @left_rec = false
      end

      attr_reader :ans, :pos, :result, :set
      attr_accessor :left_rec

      def move!(ans, pos, result)
        @ans = ans
        @pos = pos
        @result = result
        @set = true
        @left_rec = false
      end
    end

    def external_invoke(other, rule, *args)
      old_pos = @pos
      old_string = @string

      set_string other.string, other.pos

      begin
        if val = __send__(rule, *args)
          other.pos = @pos
          other.result = @result
        else
          other.set_failed_rule "#{self.class}##{rule}"
        end
        val
      ensure
        set_string old_string, old_pos
      end
    end

    def apply_with_args(rule, *args)
      memo_key = [rule, args]
      if m = @memoizations[memo_key][@pos]
        @pos = m.pos
        if !m.set
          m.left_rec = true
          return nil
        end

        @result = m.result

        return m.ans
      else
        m = MemoEntry.new(nil, @pos)
        @memoizations[memo_key][@pos] = m
        start_pos = @pos

        ans = __send__ rule, *args

        lr = m.left_rec

        m.move! ans, @pos, @result

        # Don't bother trying to grow the left recursion
        # if it's failing straight away (thus there is no seed)
        if ans and lr
          return grow_lr(rule, args, start_pos, m)
        else
          return ans
        end
      end
    end

    def apply(rule)
      if m = @memoizations[rule][@pos]
        @pos = m.pos
        if !m.set
          m.left_rec = true
          return nil
        end

        @result = m.result

        return m.ans
      else
        m = MemoEntry.new(nil, @pos)
        @memoizations[rule][@pos] = m
        start_pos = @pos

        ans = __send__ rule

        lr = m.left_rec

        m.move! ans, @pos, @result

        # Don't bother trying to grow the left recursion
        # if it's failing straight away (thus there is no seed)
        if ans and lr
          return grow_lr(rule, nil, start_pos, m)
        else
          return ans
        end
      end
    end

    def grow_lr(rule, args, start_pos, m)
      while true
        @pos = start_pos
        @result = m.result

        if args
          ans = __send__ rule, *args
        else
          ans = __send__ rule
        end
        return nil unless ans

        break if @pos <= m.pos

        m.move! ans, @pos, @result
      end

      @result = m.result
      @pos = m.pos
      return m.ans
    end

    class RuleInfo
      def initialize(name, rendered)
        @name = name
        @rendered = rendered
      end

      attr_reader :name, :rendered
    end

    def self.rule_info(name, rendered)
      RuleInfo.new(name, rendered)
    end

    # STANDALONE END

  end
end
