//-------------------------------------------------------------------
//Stoplight inclass problem - skeleton 
//-------------------------------------------------------------------

module stoplight (
  input reset_n,            //reset async active low
  input clk,                //input clock
  output northsouth_red,    //stoplight output    
  output northsouth_yellow, //stoplight output    
  output northsouth_green,  //stoplight output    
  output eastwest_red,      //stoplight output    
  output eastwest_yellow,   //stoplight output   
  output eastwest_green     //stoplight output    
  );

//enumerated values for stoplight_sm
  enum reg [1:0] {a             = 2'b00,
                  ??????????????????????
                  ??????????????????????
                  ??????????????????????
                  stoplightxx   = 'x} ??_ps, ??_ns;

reg [3:0] timer; //count time for light intervals
reg timer_reset;

//-------------------------------------------------------------------------------
// stoplight_sm
//-------------------------------------------------------------------------------
  always_ff @(????????????????????????????)
    if (!reset_n) stoplight_ps <=????????        //if reset_n asserted, go to state a 
    else          stoplight_ps <=????????        //else, go to next state

  always_comb begin
    stoplight_ns = stoplightxx;   //default assignments
    timer_reset  = 1'b0;           
    unique case (stoplight_ps)
     a :
      if (timer == 10) begin stoplight_ns = b; timer_reset = 1'b1; end
      else                   stoplight_ns = a;
     b :
      ????????????????????????????????????????????????????????????????
      ????????????????????????????????????????????????????????????????
     c :
      ????????????????????????????????????????????????????????????????
      ????????????????????????????????????????????????????????????????
     d : 
      ????????????????????????????????????????????????????????????????
     ????????????????????????????????????????????????????????????????
    endcase
  end//always_comb 
   
assign eastwest_red      = ((stoplight_ps == a) || (stoplight_ps == b))  ? 1'b1 : 1'b0;
assign eastwest_yellow   =  ???????????????????????????????????????????????????????????
assign eastwest_green    =  ???????????????????????????????????????????????????????????
assign northsouth_red    =  ???????????????????????????????????????????????????????????
assign northsouth_yellow =  ???????????????????????????????????????????????????????????
assign northsouth_green  =  ???????????????????????????????????????????????????????????

//-------------------------------------------------------------------------------
//timer for stoplight_sm is below 
//-------------------------------------------------------------------------------
  always_ff @(?????????????????????????????
    if (!reset_n) timer         ??????????  //if reset_n asserted, clear counter 
    else if (timer_reset) timer ??????????  //reset when told to
    else timer                  ??????????  //else increment

endmodule