#lang br
(require racket/list (for-syntax br/syntax) racket/splicing "bus-properties.rkt")
(provide (all-defined-out))

(module+ test
  (require rackunit))

(define (bitwise-bit-set x bit)
  (if (not (bitwise-bit-set? x bit))
      (bitwise-ior x (expt 2 bit))
      x))

(define (bitwise-bit-unset x bit)
  (if (bitwise-bit-set? x bit)
      (bitwise-and x (bitwise-not (expt 2 bit)))
      x))

(module+ test
  (define x-bitset (string->number "1011" 2)) ; decimal 11
  (check-true (bitwise-bit-set? x-bitset 0))
  (check-true (bitwise-bit-set? x-bitset 1))
  (check-false (bitwise-bit-set? x-bitset 2))
  (check-true (bitwise-bit-set? x-bitset 3))
  (set! x-bitset (bitwise-bit-set x-bitset 2))
  (check-true (bitwise-bit-set? x-bitset 2))
  (set! x-bitset (bitwise-bit-unset x-bitset 2))
  (check-false (bitwise-bit-set? x-bitset 2)))

(define (bus-range start [finish start])
  (range start (add1 finish)))

(define (integer->bitvals int width)
  (reverse (for/list ([i (in-range width)])
                     (bitwise-bit-field int i (add1 i)))))

(define max-bus-width 16)
(define default-bus-width 1)


(define (check-bit-against-width bus-name bit width)
  (unless (< bit width)
    (raise-argument-error bus-name (format "bit less than bus width ~a" width) bit)))

(define (check-val-against-width bus-name val width)
  (when (and val (> val (sub1 (expt 2 width))))
    (raise-argument-error bus-name
                          (format "~a-bit value (0 to ~a inclusive)" width (sub1 (expt 2 width))) val)))


(define (make-bus-reader reader-name width)
  (define-cases bus-reader-func
    [(_ id-thunk-val) (bus-reader-func id-thunk-val 0 (sub1 width))]
    [(_ id-thunk-val bit) (bus-reader-func id-thunk-val bit bit)]
    [(_ id-thunk-val first-bit last-bit)
     (unless (<= first-bit last-bit)
       (raise-argument-error reader-name (format "last bit greater than or equal to first bit ~a" first-bit) last-bit))
     (check-bit-against-width reader-name first-bit width)
     (check-bit-against-width reader-name last-bit width)
     (bitwise-bit-field id-thunk-val first-bit (add1 last-bit))])
  (procedure-rename bus-reader-func reader-name))


(define (make-bus-writer writer-name width)
  (define-cases bus-writer-func
    [(_ id-thunk-val) (raise-argument-error writer-name "new value" empty)]
    [(_ id-thunk-val new-val-in)
     (define new-val (cond
                       [(boolean? new-val-in)
                        (if new-val-in (sub1 (expt 2 width)) 0)]
                       [(or (input-bus? new-val-in) (output-bus? new-val-in)) (new-val-in)]
                       [else new-val-in]))
     (check-val-against-width writer-name new-val width)
     new-val]
    [(_ id-thunk-val bit new-val) (bus-writer-func id-thunk-val bit bit new-val)]
    [(_ id-thunk-val first-bit last-bit new-val-in)
     (define bit-range-width (add1 (- last-bit first-bit)))
     (define new-val (cond
                       [(boolean? new-val-in)
                        (if new-val-in (sub1 (expt 2 bit-range-width)) 0)]
                       [(or (input-bus? new-val-in) (output-bus? new-val-in)) (new-val-in)]
                       [else new-val-in]))
     (unless (<= first-bit last-bit)
       (raise-argument-error writer-name (format "last bit greater than or equal to first bit ~a" first-bit) last-bit))
     (check-bit-against-width writer-name first-bit width)
     (check-bit-against-width writer-name last-bit width)
     (check-val-against-width writer-name new-val bit-range-width)
     (define last-val
       (for/fold ([val id-thunk-val])
                 ([bit (in-range first-bit (add1 last-bit))]
                  [new-bit-val (in-list (integer->bitvals new-val bit-range-width))])
         ((if (= 1 new-bit-val) bitwise-bit-set bitwise-bit-unset) val bit)))
     last-val])
  bus-writer-func)


#|

base bus:
+ can read all, or bits
+ every read invokes a thunk
|#



(define-macro-cases define-base-bus
  [(_ ID THUNK) #'(define-base-bus ID THUNK default-bus-width)]
  [(_ ID THUNK BUS-WIDTH-IN)
   (with-pattern
    ([ID-THUNK (suffix-id #'ID "-val")]
     [BUS-TYPE (or (syntax-property caller-stx 'impersonate) #'bus)])
    #`(splicing-let ([ID-THUNK THUNK]
                     [bus-width BUS-WIDTH-IN])
        (define ID
          (begin
            (unless (<= bus-width max-bus-width)
              (raise-argument-error 'ID (format "bus width <= max width ~a" max-bus-width) bus-width))
            (impersonate-procedure
             (let ([reader (make-bus-reader 'ID bus-width)])
               (procedure-rename (λ args (apply reader (ID-THUNK) args)) (string->symbol (format "~a:~a-bit" 'ID bus-width))))
             #f BUS-TYPE #t)))
        #,(when (syntax-property caller-stx 'writer)
            (with-pattern
             ([ID-WRITE (suffix-id #'ID "-write")])
             #'(define ID-WRITE
                 (let ([writer (make-bus-writer 'id-write bus-width)])
                   (λ args
                     (define result (apply writer (ID-THUNK) args))
                     (set! ID-THUNK (λ () result)))))))))])


(module+ test
  (define-base-bus bb (λ () #b0110) 4)
  (check-true (bus? bb))
  (check-false (input-bus? bb))
  (check-false (output-bus? bb))
  (check-exn exn:fail? (λ () (define-base-bus bb (λ () #b0110) 17) bb)) ; exceeds 16-bit width
  (check-equal? (bb) #b0110)
  (check-equal? (bb 0) #b0)
  (check-equal? (bb 1) #b1)
  (check-equal? (bb 2) #b1)
  (check-equal? (bb 3) #b0)
  (check-exn exn:fail? (λ () (bb 5))) ; exceeds bus width
  (check-equal? (bb 0 1) #b10)
  (check-equal? (bb 1 2) #b11)
  (check-equal? (bb 2 3) #b01)
  (check-exn exn:fail? (λ () (bb 3 2))) ; inverted bus spec
  (check-exn exn:fail? (λ () (bb 5 10))) ; exceeds bus width
  )


#|
output bus:
+ thunk is a runtime computation
+ cannot write
|#




(define-macro (define-output-bus . ARGS)
  (syntax-property #'(define-base-bus . ARGS) 'impersonate #'output-bus))

(module+ test
  (define-output-bus ob (λ () #b0110) 4)
  (check-false (bus? ob))
  (check-false (input-bus? ob))
  (check-true (output-bus? ob))
  (check-exn exn:fail? (λ () (define-base-bus ob (λ () #b0110) 17) ob)) ; exceeds 16-bit width
  (check-equal? (ob) #b0110)
  (check-equal? (ob 0) #b0)
  (check-equal? (ob 1) #b1)
  (check-equal? (ob 2) #b1)
  (check-equal? (ob 3) #b0)
  (check-exn exn:fail? (λ () (ob 5))) ; exceeds bus width
  (check-equal? (ob 0 1) #b10)
  (check-equal? (ob 1 2) #b11)
  (check-equal? (ob 2 3) #b01)
  (check-exn exn:fail? (λ () (ob 3 2))) ; inverted bus spec
  (check-exn exn:fail? (λ () (ob 5 10))) ; exceeds bus width
  )

#|
input bus:
+ thunk returns a constant
+ identifies itself as input bus
+ can write all, or bits
|#


(define-macro-cases define-input-bus
  [(MACRO-NAME ID)
   #'(MACRO-NAME ID default-bus-width)]
  [(MACRO-NAME ID BUS-WIDTH)
   (syntax-property
    (syntax-property #'(define-base-bus ID (λ () 0) BUS-WIDTH)
                     'impersonate #'input-bus)
                     'writer #t)])

(module+ test
  (define-input-bus ib 4)
  (check-false (bus? ib))
  (check-false (output-bus? ib))
  (check-true (input-bus? ib))
  #;(check-exn exn:fail? (λ () (define-input-bus ib 17) ib)) ; exceeds 16-bit width
  (check-equal? (ib) 0)
  (ib-write 11) ; set whole value
  (check-equal? (ib) 11)
  (check-exn exn:fail? (λ () (ib-write #b11111))) ; overflow
  (ib-write 2 1) ; set bit
  (check-equal? (ib) #b1111)  
  (ib-write 0 #b0) ; set bit
  (ib-write 1 #b0) ; set bit
  (ib-write 2 #b0) ; set bit
  (check-equal? (ib) #b1000)
  (check-exn exn:fail? (λ () (ib-write 5 1 #b0))) ; last index smaller than first
  (check-exn exn:fail? (λ () (ib-write 1 300 #b0))) ; overlarge bit index
  (check-exn exn:fail? (λ () (ib-write 300 500 #b0))) ; overlarge bit index
  (check-exn exn:fail? (λ () (ib-write 1 #b11111))) ; overflow value
  (ib-write 0)
  (ib-write 1 2 #b11) 
  (check-equal? (ib) #b0110)
  (ib-write 3 3 #b1)
  (ib-write 0 0 #b1)
  (check-equal? (ib) #b1111)
  (check-exn exn:fail? (λ () (ib-write 0 300 #b0))) ; overlarge bit index
  (check-exn exn:fail? (λ () (ib-write 1 1 #b11111))) ; overflow value
  (ib-write 0)
  (ib-write 1 2 #t) ; using #t to fill certain bits
  (check-equal? (ib) #b0110)
  (ib-write 2 2 #f) ; using #f to fill certain bits
  (check-equal? (ib) #b0010)
  (ib-write 0)
  (ib-write #t) ; using #t to fill all bits
  (check-equal? (ib) #b1111)
  (ib-write #f) ; using #f to fill all bits
  (check-equal? (ib) #b0000)
  (ib-write 1 #t)
  (check-equal? (ib) 2)
  (ib-write 1 #f)
  (check-equal? (ib) 0)
  (ib-write 2 1)
  (check-equal? (ib) 4)
  (ib-write 2 0)
  (check-equal? (ib) 0)
  (ib-write 1 2 #t)
  (check-equal? (ib) 6)
  (ib-write 2 3 #t)
  (check-equal? (ib) 14)
  (ib-write 0 2 #f)
  (check-equal? (ib) 8)
  (ib-write #b1011)
  (check-equal? (ib) 11)
  (define-input-bus ib2 4)
  (check-exn exn:fail? (λ () (ib2-write 16))) ; overflow value
  (ib2-write #b1100)
  (ib-write ib2) ; using bus as input value
  (check-equal? (ib) (ib2))
  )