library ieee;
  use ieee.std_logic_1164.all;
  use ieee.std_logic_arith.all;

entity buzz is
   port ( clk,reset : in std_logic;
          engine    : in std_logic;
          seat      : in std_logic;
          belt      : in std_logic;
          buzzer    : out std_logic );
end buzz;

architecture behavioral of buzz is
type stato is (eoff,idle,seated,belted,buzzing);
signal cs,ns : stato;
signal timeover : std_logic;
signal count,ncount : integer range 0 to 20;
begin

  process(clk,reset)
  begin
    if reset='1' then
       count<=0;
       cs <= idle;
    elsif clk'event and clk='1' then
       count <= ncount;
       cs <= ns;
    end if;
  end process;

  process(ns,engine,seat,belt,timeover)
  begin
     case cs is
     when eoff => if engine='1' then
                        ns <= seated;
                  else 
                        ns <= eoff;
                  end if;  
     when idle => if seat='1' then
                        ns <= seated;
                  elsif engine='0' then
                        ns <= eoff;
                  else 
                        ns <= idle;
                  end if;  
     when seated => 
                  if belt='1' then
                        ns <= belted;
                  elsif seat='0' then
                        ns <= idle;
                  elsif engine='0' then
                        ns <= eoff;
                  elsif timeover='1' then
                        ns <= buzzing;
                  else 
                        ns <= seated;
                  end if;  
      when belted =>
                  if belt='0' then 
                        ns<= seated;
                  elsif seat='0' then
                        ns <= idle;
                  elsif engine='0' then
                        ns <= eoff;
                  else 
                        ns <= belted;
                  end if;  
     
       when buzzing => 
                  if belt='1' then 
                        ns<= belted;
                  elsif seat='0' then
                        ns <= idle;
                  elsif engine='0' then
                        ns <= eoff;
                  else 
                        ns <= buzzing;
                  end if;      
       when others => ns <= idle;    
  end case;
  end process;
  
  Bzz:process(cs)
  begin
    if cs=buzzing then buzzer <= '1';
    else buzzer <= '0';
    end if;
  end process;

  Timer:process(cs,count)
  begin
    if cs=seated then 
           if count=10 then 
              ncount<=0;
              timeover<='1';
           else
              ncount<=count+1;
              timeover<='0';
           end if;
    else 
        ncount<=0;
        timeover <= '0';
    end if;
  end process;
  
end behavioral;