#! /usr/bin/env ruby

# Build a grammar whose LALR(1) parser has a given number of states.
# Useful to test edge cases (e.g., 256 and 257 states, etc.).

class Linear
  def initialize(states)
    @states = states - 4
    @cols = Math.sqrt(@states).to_i
    @lines = @states / @cols
    @rest = @states % @cols

    @n = @lines * (@cols - 1) + (@rest == 0 ? 1 : @rest == 1 ? 2 : @rest)
  end

  def nterms
    last = @lines + ([0, 1].include?(@rest) ? 0 : 1)
    (0...last).map { |i| "t#{i}" }.join(' ')
  end

  def rules
    res = (0...@lines).map { |i| "t#{i}:#{' N' * (@cols - 1)}" }.join("\n")
    case @rest
    when 0
      res += ' N'
    when 1
      res += ' N N'
    else
      res += "\nt#{@lines}:#{" N" * @rest}"
    end
    res
  end

  def to_s
    puts <<~EOF
      // states: #{@states}
      // cols: #{@cols}
      // lines: #{@lines}
      // rest: #{@rest}
      // n: #{@n}

      %code {
        #include <stdio.h>
        #include <stdlib.h>

        static int yylex (void);
        static void yyerror (const char *msg);
       }

      %debug
      %define api.value.type union
      %define parse.lac full
      %define parse.error verbose
      %printer { fprintf (yyo, "%ld", $$); } <long>
      %token <long> N

      %%

      exp: #{nterms}

      #{rules}

      %%

      static
      int yylex (void)
      {
        static long count = 0;
        if (count++ < #{@n})
          {
            yylval.N = count;
            return N;
          }
        else
          return 0;
      }

      static
      void yyerror (const char *msg)
      {
        fprintf (stderr, "%s\\n", msg);
      }

      int
      main (void)
      {
        yydebug = !!getenv ("YYDEBUG");
        return yyparse ();
      }
      EOF
  end
end

puts Linear.new(ARGV[0].to_i).to_s