#lang racket

(require (for-syntax syntax/parse))

;-----------------------
; Memory Data Structure
;-----------------------
; Methods for accessing a 16 bit addressing memory
; including support for banking (planned) and
; access controls for ROM (planned)
;-----------------------

; Needs:
;  Banking
;  Routes based on memory location
;  Banking based on memory
; Registers:
;  Fast access
;  Hash?
;  

(struct memory
   (registers state banks)
   #:transparent)

(define (make-memory)
   (memory (make-regvec) (make-statevec) (make-bank)))

(define (make-regvec)
   (make-vector 8))

(define (make-statevec)
   (make-vector 2))

(define (make-bank [init 0])
   (make-vector (expt 2 16)))

(define (deref-state sym)
   (case sym
      [(state-PC) 0]
      [(state-SP) 1]
      [else (error "invalid state:" sym)]))

(define (deref-reg sym)
  (case sym
      [(reg-A) 0]
      [(reg-F) 1]
      [(reg-B) 2]
      [(reg-C) 3]
      [(reg-D) 4]
      [(reg-E) 5]
      [(reg-H) 6]
      [(reg-L) 7]
      [else (error "invalid register:" sym)]))

(define (get-reg sym memory)
   (vector-ref (memory-registers memory) (deref-reg sym)))

(define (get-state sym memory)
   (vector-ref (memory-state memory) (deref-state sym)))

(define (get-byte addr bank memory)
   (if (and (>= addr 0)
            (< addr 65536))
       (vector-ref (memory-banks memory) addr)
       (error (format "ERROR: address ~a out of bounds" addr))))

(define (set-reg! sym memory val)
   (vector-set! (memory-registers memory) (deref-reg sym) (mod-8bit val)))

(define (set-state! sym memory val)
   (vector-set! (memory-state memory) (deref-state sym) (mod-16bit val)))

(define (set-byte! addr bank memory val)
   (if (and (>= addr 0)
            (< addr 65536))
       (vector-set! (memory-banks memory) addr (mod-8bit val))
       (error (format "ERROR: address ~a out of bounds" addr))))

;----------------------------
; define-8bit & define-16bit
;----------------------------
; composes operations with a modulo in order
; to keep numbers within 8 bits
;----------------------------

(define (mod-8bit x)
   (modulo x 256))

(define (mod-16bit x)
   (modulo x 65536))

(provide (all-defined-out))