;;;
;;; An implementation of the Memory Array Redcode Simulator (MARS)
;;;

(import (chicken io)
        (chicken string)
        (chicken random)
        matchable)

;;; Constants
;;

(define core-size 20)
(define max-steps 10000)


;;; Instructions
;;

(define ((make-instr opcode modifier A-mode A-num B-mode B-num name) . args)
  (match args
    (('copy n) (make-instr opcode modifier A-mode A-num B-mode B-num n))
    (('opcode) opcode)
    (('modifier) modifier)
    (('A-mode) A-mode)
    (('A-num) A-num)
    (('B-mode) B-mode)
    (('B-num) B-num)
    (('name) name)
    (('print) (print opcode
                     (if (null? modifier) "" (conc "." modifier))
                     " " (mode-string A-mode) A-num
                     ", " (mode-string B-mode) B-num
                     (if (null? name) "" (conc " ; " name))))
    (('set-opcode! x n) (set! opcode x) (set! name n))
    (('set-modifier! x n) (set! modifier x) (set! name n))
    (('set-A-mode! x n) (set! A-mode x) (set! name n))
    (('set-A-num! x n) (set! A-num x) (set! name n))
    (('set-B-mode! x n) (set! B-mode x) (set! name n))
    (('set-B-num! x n) (set! B-num x) (set! name n))))

(define (mode-string mode)
   (case mode
     ((immediate) "#")
     ((direct) "")
     ((indirect-A "*"))
     ((indirect-B "@"))
     ((pre-indirect-A "{"))
     ((pre-indirect-B "<"))
     ((post-indirect-A "}"))
     ((post-indirect-B ">"))))

(define initial-instruction
  (make-instr 'DAT '() 'immediate 0 'immediate 0 '()))


;;; Memory setup and addressing
;;

(define core (make-vector core-size '()))

(define (initialize-core)
  (let loop ((i 0))
    (unless (>= i core-size)
      (vector-set! core i (initial-instruction 'copy '()))
      (loop (+ i 1)))))

(define (core-dump)
  (let loop ((i 0))
    (unless (>= i core-size)
      ((vector-ref core i) 'print)
      (loop (+ i 1)))))

(define (addr+ . args)
  (foldl (lambda (a b)
           (modulo (+ a b core-size) core-size))
         0 args))

;;; Programmes
;;

(define (make-prog name instrs offset)
  (list name instrs offset))

(define (prog-name prog) (list-ref prog 0))
(define (prog-instrs prog) (list-ref prog 1))
(define (prog-offset prog) (list-ref prog 2))

(define (install-prog prog addr)
  (let loop ((ptr addr)
             (instrs (prog-instrs prog)))
    (unless (null? instrs)
      (vector-set! core ptr ((car instrs) 'copy (prog-name prog)))
      (loop (addr+ ptr 1) (cdr instrs))))
  (make-player (prog-name prog)
               (addr+ addr (prog-offset prog))))

(define (can-install-prog? prog-len addr)
  (let loop ((ptr addr)
             (remaining prog-len))
    (if (= remaining 0)
        #t
        (if (null? ((vector-ref core ptr) 'name))
            (loop (addr+ ptr 1)
                  (- remaining 1))
            #f))))

(define (install-progs progs)
  (let loop ((players '())
             (progs-left progs))
    (if (null? progs-left)
        players
        (let ((addr (pseudo-random-integer core-size))
              (prog (car progs-left)))
          (if (can-install-prog? (length (prog-instrs prog)) addr)
              (loop (cons (install-prog prog addr) players)
                    (cdr progs-left))
              (loop players progs-left))))))

(define (make-player name ptr)
  (list name ptr))

(define (player-set-ptrs! player ptrs)
  (set-cdr! prog-queue ptrs))


;;; Executive function
;;

(define (run players step)
  (cond
   ((> step max-steps) players)      ;Tie between remaining players
   ((<= (length players) 1) players) ;There's only one player left who thus wins
   (else
    (let ((player (car players))
          (other-players (cdr players))
          (ptrs (player-ptrs player)))
      (let ((new-ptrs (execute-instr (car ptrs))))
        (if (null? new-ptrs)
            (run other-players (+ step 1))
            (begin
              (player-set-ptrs! (append (cdr ptrs) new-ptrs))
              (run (append other-players (list player)) (+ step 1)))))))))

(define (execute-instr ptr)
  (let* ((instr (vector-ref core ptr))
         (A-pointer (eval-operand (instr-A-mode instr) (instr-A-num) ptr))
         (B-pointer (eval-operand (instr-B-mode instr) (instr-B-num) ptr))
         (modifier (instr-modifier instr)))
    (case (instr-opcode instr)
      ((DAT) '()) ;Game over, man, game over!
      ((MOV))
      ((ADD))
      ((SUB))
      ((MUL))
      ((DIV))
      ((MOD))
      ((JMP))
      ((JMN))
      ((DJN))
      ((SEQ CMP))
      ((SNE))
      ((SLT))
      ((SPL))
      ((NOP))
      (else
       (error "Unrecognised opcode" (instr-opcode instr))))))

(define (eval-operand mode num ptr)
  (addr+ ptr
         (case mode
           ((immediate) 0)
           ((direct) num)
           ((indirect-A) (addr+ num (instr-A-num (vector-ref core (addr+ ptr num)))))
           ((indirect-B) (addr+ num (instr-B-num (vector-ref core (addr+ ptr num)))))
           ((pre-indirect-A)
            (let ((aux-instr (vector-ref core (addr+ ptr num))))
              (instr-set-A-num! aux-instr (addr+ -1 (instr-A-num aux-instr)))
              (addr+ num (instr-A-num aux-instr))))
           ((pre-indirect-B)
            (let ((aux-instr (vector-ref core (addr+ ptr num))))
              (instr-set-B-num! aux-instr (addr+ -1 (instr-B-num aux-instr)))
              (addr+ num (instr-B-num aux-instr))))
           ((post-indirect-A)
            (let* ((aux-instr (vector-ref core (addr+ ptr num)))
                   (old-A-num (instr-A-num aux-instr)))
              (instr-set-A-num! aux-instr (addr+ 1 (instr-A-num aux-instr)))
              (addr+ num old-A-num)))
           ((post-indirect-B)
            (let* ((aux-instr (vector-ref core (addr+ ptr num)))
                   (old-B-num (instr-B-num aux-instr)))
              (instr-set-B-num! aux-instr (addr+ 1 (instr-B-num aux-instr)))
              (addr+ num old-B-num)))
           (else
            (error "Unrecognized mode" mode)))))