library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity encoder is
port ( A : in std_logic; 		-- input A
       B : in std_logic;		-- input B
       res: in std_logic; 		-- reset input
       clk: in std_logic; 		-- clock input
       EN : out std_logic_vector(2 downto 0); -- enable for 7-segment display
       SSEG: out std_logic_vector(7 downto 0) -- 7-segment display
);
end encoder;

architecture arch of encoder is
	signal state: std_logic_vector(3 downto 0);
	constant S0 : std_logic_vector(3 downto 0):= "0000";
	constant S1 : std_logic_vector(3 downto 0):= "0001";
	constant S2 : std_logic_vector(3 downto 0):= "0010";
	constant S3 : std_logic_vector(3 downto 0):= "0011";
	constant S4 : std_logic_vector(3 downto 0):= "0100";
	constant S5 : std_logic_vector(3 downto 0):= "0101";
	constant S10 : std_logic_vector(3 downto 0):= "1001";
	constant S20 : std_logic_vector(3 downto 0):= "1010";
	constant S30 : std_logic_vector(3 downto 0):= "1011";
	constant S40 : std_logic_vector(3 downto 0):= "1100";
	constant S50 : std_logic_vector(3 downto 0):= "1101";	
	signal encoder_clk : std_logic;
	signal encoder_rol : std_logic;
	signal clk_1kHz : std_logic:='0';
	signal bcd_counter : std_logic_vector(3 downto 0):="0000";

BEGIN

process (clk_1kHz, res)
begin
	if res = '0' then
		state <= "0000";
	elsif clk_1kHz'event and clk_1kHz = '1' then
    case state is
      when S0 =>
			encoder_clk <= '0';
			encoder_rol <= '0';
			if A = '1' and B = '0' then
				state <= S1;
			elsif A = '0' and B = '1' then
				state <= S10;
			else state <= S0;
			end if;
		-- path of the state machine for motion detection in the "increase" direction
		when S1 =>
			if A = '1' and B = '1' then
				state <= S2;
			elsif A = '1' and B = '0' then
				state <= S1;
			else state <= S0;
			end if;
		when S2 =>
			if A = '0' and B = '1' then
				state <= S3;
			elsif A = '1' and B = '1' then
				state <= S2;
			else state <= S0;
			end if;
		when S3 =>
			if A = '0' and B = '0' then
				state <= S4;
			elsif A = '0' and B = '1' then
				state <= S3;
			else state <= S0;
			end if;
		when S4 =>
			encoder_rol <= '1';
			state <= S5;
		when S5 =>
			encoder_clk <= '1';
			state <= S0;
		-- path of the state machine for motion detection in the "decrease" direction
		when S10 =>
			if A = '1' and B = '1' then
				state <= S20;
			elsif A = '0' and B = '1' then
				state <= S10;
			else state <= S0;
			end if;
		when S20 =>
			if A = '1' and B = '0' then
				state <= S30;
			elsif A = '1' and B = '1' then
				state <= S20;
			else state <= S0;
			end if;
		when S30 =>
			if A = '0' and B = '0' then
				state <= S40;
			elsif A = '1' and B = '0' then
				state <= S30;
			else state <= S0;
			end if;
		when S40 =>
			encoder_rol <= '0';
			state <= S50;
		when S50 =>
			encoder_clk <= '1';
			state <= S0;
		when others =>
			state <= S0;
		end case;
	end if;
end process;

--clock 1kHz
process(clk)
  variable clock_cnt : integer:=0;
begin
  if rising_edge(clk) then
    if clock_cnt < 6000 then
	  clock_cnt := clock_cnt+1;
	else
	  clock_cnt := 0;
	  clk_1kHz <= not(clk_1kHz);
	end if;
  end if;
end process;

--counter mod 10 with encoder_clk as input
process(encoder_clk)
begin
	if rising_edge(encoder_clk) then
		if(encoder_rol = '1') then
			if(bcd_counter < 10 ) then
				bcd_counter <= bcd_counter + 1;	--encoder knob rotates right
			else
			   bcd_counter <= "0000";
			end if;
		else
			if(bcd_counter > 0 ) then
				bcd_counter <= bcd_counter - 1;	--encoder knob rotates left 
			else
				bcd_counter <= "1001";
			end if;
		end if;
	end if;    
end process;

--bcd to 7-segment display decoder
process(bcd_counter)
begin
	case bcd_counter is
		--------------------abcdefgp
		when "0000"=>SSEG<="00000011";
		when "0001"=>SSEG<="10011111";
		when "0010"=>SSEG<="00100101";
		when "0011"=>SSEG<="00001101";
		when "0100"=>SSEG<="10011001";
		when "0101"=>SSEG<="01001001";
		when "0110"=>SSEG<="01000001";
		when "0111"=>SSEG<="00011111";
		when "1000"=>SSEG<="00000001";
		when "1001"=>SSEG<="00001001";
		when others=>SSEG<="11111111";
	end case;
end process;

EN <= "110";

end arch;