package DelayLine;

import List::*;

interface DelayLine#(type value);
   method Action _write (value v);
   method value _read();
   method Bool ready();
endinterface

module mkDelayLine(Integer delay_cycles, DelayLine#(a) ifc)
   provisos (Bits#(a, a_sz));

   DelayLine#(a) ret = ?;

   if (delay_cycles == 0) begin
      RWire#(a) w <- mkRWire();
      ret = (interface DelayLine;
                method Action _write(a value);
                   w.wset(value);
                endmethod
                method a _read() if (w.wget matches tagged Valid .val);
                   return val;
                endmethod
                method Bool ready();
                   return isValid(w.wget);
                endmethod
             endinterface);
   end
   else begin
      RWire#(a) inputVal <- mkRWire;
      List#(Reg#(Maybe#(a))) delay = tagged Nil;
      for (Integer i = 0; i < delay_cycles; i = i+1) begin
         let r <- mkReg(tagged Invalid);
         delay = cons(r, delay);
      end

      (* no_implicit_conditions, fire_when_enabled *)
      rule pump_line;
         delay[0] <= inputVal.wget();
         for (Integer i = 0; i < delay_cycles-1; i = i+1)
            delay[i+1] <= delay[i];
      endrule

      ret = (interface DelayLine;
                method Action _write(a value);
                   inputVal.wset(value);
                endmethod
                method a _read() if (delay[delay_cycles-1] matches tagged Valid .val);
                   return val;
                endmethod
                method Bool ready();
                   return isValid(delay[delay_cycles-1]);
                endmethod
             endinterface);
   end
   return ret;
endmodule

endpackage