(local lume (require "lib.lume"))
(local {: lo : hi} (require "lib.util"))

(fn inc16-stk [l h]
  [:block
    [:inc l :x]
    [:bne :done]
    [:inc h :x]
   :done])

(fn inc16 [l h]
  [:block
    [:inc l]
    [:bne :done]
    [:inc h]
   :done
  ])

(fn dec16 [l h]
  [:block
    [:lda l]
    [:bne :declow]
    [:dec h]
   :declow
    [:dec l]])

(fn add16 [l h]
  [:block
    [:clc]
    [:adc l]
    [:sta l]
    [:bcc :go]
    [:inc h]
    :go
  ])

(fn mk-vm [prg options]
  (local code1 (prg:org 0xc00))

  (fn prg.dat-parser.vm [bytecodes]
    (local block (prg:new-block))
    (each [_ bytecode (ipairs (lume.slice bytecodes 2))]
      (if
        (= (type bytecode) :number)
        (prg:parse-dats block [[:ref :lit] [:dw bytecode]])

        (= (type bytecode) :string)
        (prg:parse-dats block [[:ref bytecode]])

        (= (type bytecode) :table)
        (prg:parse-dats block [bytecode])

        (error (.. "VM can't parse " (fv bytecode)))))
    block)
  (local vm {
    :IP   :0x60
    :IPH  :0x61
    :W    :0x62
    :WH   :0x63
    :ROFF :0x64
    :TOP  :0x80
    :TOPH :0x81
    :ST1  :0x7e
    :ST1H :0x7f
    :ST2  :0x7c
    :ST2H :0x7d
    :RSTACK :0x6000
    :code code1
    :ret (fn [self] [:jmp :next])
    :reserve (fn [self] [:block [:inx] [:inx]])
    :push
    (fn [self v]
      (local l (bit.band v 0xff))
      (local h (bit.band (bit.rshift v 8) 0xff))
      [:block (self:reserve)
        [:lda l]
        [:sta self.TOP :x]
        [:lda h]
        [:sta self.TOPH :x]
      ])
    :drop (fn [self] [:block [:dex] [:dex]])
    :def
    (fn [self name ...]
      (code1:append name [:flatten ...] (self:ret)))
    :word
    (fn [self name ...]
      (code1:append name [:jsr :subroutine] [:vm ...] [:vm :ret]))
    :inline
    (fn [self ...]
      [:block [:jsr :subroutine] [:vm ...] [:vm :restore]])
    :asm
    (fn [self ...]
      [:block [:vm :native] [:block ...] [:jsr :interpret]])
  })

  (code1:append :next
    [:ldy 0]
    [:lda [vm.IP] :y]  [:sta vm.W]
    (inc16 vm.IP vm.IPH)
    [:lda [vm.IP] :y] [:sta vm.WH]
    (inc16 vm.IP vm.IPH)

  ;   [:lda vm.WH]
  ;   [:jsr mon.hexout]
  ;   [:lda vm.W]
  ;   [:jsr mon.hexout]
  ;   [:lda (achar " ")]
  ;   [:jsr mon.putchar]

    [:jmp [vm.W]])

  (code1:append :reset
    [:lda #(lo ($1:lookup-addr :quit))]
    [:sta vm.IP]
    [:lda #(hi ($1:lookup-addr :quit))]
    [:sta vm.IPH]
    [:lda 0]
    [:sta vm.ROFF]
    [:ldx 0xfe]
    [:rts])

  (vm:def
   :subroutine ; usage: [jsr :subroutine] followed by bytecode
    [:ldy vm.ROFF]
    [:lda vm.IP] [:sta vm.RSTACK :y] [:iny]
    [:lda vm.IPH] [:sta vm.RSTACK :y] [:iny]
    [:sty vm.ROFF]
   :interpret ; usage: [jsr :interpret] followed by bytecode
    [:pla] [:sta vm.IP] [:pla] [:sta vm.IPH]
    (inc16 vm.IP vm.IPH))

  (vm:def :ret
    [:ldy vm.ROFF]
    [:dey] [:lda vm.RSTACK :y] [:sta vm.IPH]
    [:dey] [:lda vm.RSTACK :y] [:sta vm.IP]
    [:sty vm.ROFF])

  (code1:append :native [:jmp [vm.IP]])
  (code1:append :quit [:rts])
  (code1:append :restore
    [:lda vm.IP]  [:sta vm.W]
    [:lda vm.IPH] [:sta vm.WH]
    [:ldy vm.ROFF]
    [:dey] [:lda vm.RSTACK :y] [:sta vm.IPH]
    [:dey] [:lda vm.RSTACK :y] [:sta vm.IP]
    [:sty vm.ROFF]
    [:jmp [vm.W]])


  (vm:def :drop (vm:drop))

  (vm:def :dup
    (vm:reserve)
    [:lda vm.ST1H :x]
    [:sta vm.TOPH :x]
    [:lda vm.ST1 :x]
    [:sta vm.TOP :x])

  (vm:def :swap
    [:lda vm.TOP :x]
    [:ldy vm.ST1 :x]
    [:sty vm.TOP :x]
    [:sta vm.ST1 :x]
    [:lda vm.TOPH :x]
    [:ldy vm.ST1H :x]
    [:sty vm.TOPH :x]
    [:sta vm.ST1H :x])

  (vm:def :over
    (vm:reserve)
    [:lda vm.ST2H :x]
    [:sta vm.TOPH :x]
    [:lda vm.ST2 :x]
    [:sta vm.TOP :x])
  (vm:word :2dup :over :over)

  (vm:def :>rot ; (a b c -- c a b)
    [:lda vm.TOP :x] ; a: c (a b c)
    [:ldy vm.ST2 :x] ; y: a (a b c)
    [:sta vm.ST2 :x] ; a: c (c b c)
    [:lda vm.ST1 :x] ; a: b (c b c)
    [:sta vm.TOP :x] ; a: b (c b b)
    [:sty vm.ST1 :x] ; y: a (c a b)
    [:lda vm.TOPH :x] ; a: c (a b c)
    [:ldy vm.ST2H :x] ; y: a (a b c)
    [:sta vm.ST2H :x] ; a: c (c b c)
    [:lda vm.ST1H :x] ; a: b (c b c)
    [:sta vm.TOPH :x] ; a: b (c b b)
    [:sty vm.ST1H :x] ; y: a (c a b)
  )
  (vm:def :<rot ; (a b c -- b c a)
    [:lda vm.TOP :x] ; a: c (a b c)
    [:ldy vm.ST1 :x] ; y: b (a b c)
    [:sta vm.ST1 :x] ; a: c (a c c)
    [:lda vm.ST2 :x] ; a: a (a c c)
    [:sta vm.TOP :x] ; a: a (a c a)
    [:sty vm.ST2 :x] ; y: b (b c a)
    [:lda vm.TOPH :x] ; a: c (a b c)
    [:ldy vm.ST1H :x] ; y: b (a b c)
    [:sta vm.ST1H :x] ; a: c (a c c)
    [:lda vm.ST2H :x] ; a: a (a c c)
    [:sta vm.TOPH :x] ; a: a (a c a)
    [:sty vm.ST2H :x] ; y: b (b c a)
  )

  (vm:def :get
    [:lda [vm.TOP :x]]
    [:tay]
    (inc16-stk vm.TOP vm.TOPH)
    [:lda [vm.TOP :x]]
    [:sta vm.TOPH :x]
    [:sty vm.TOP :x])

  (vm:def :set ; v p --
    [:lda vm.ST1 :x]
    [:sta [vm.TOP :x]]
    (inc16-stk vm.TOP vm.TOPH)
    [:lda vm.ST1H :x]
    [:sta [vm.TOP :x]]
    (vm:drop) (vm:drop))

  (vm:def :bget ; p -- b
    [:lda [vm.TOP :x]] [:sta vm.TOP :x]
    [:lda 0] [:sta vm.TOPH :x])

  (vm:def :bset ; b p --
    [:lda vm.ST1 :x] [:sta [vm.TOP :x]]
    (vm:drop) (vm:drop))

  (vm:def :lit
    (vm:reserve) [:ldy 0]
    [:lda [vm.IP] :y] [:sta vm.TOP :x]
    (inc16 vm.IP vm.IPH)
    [:lda [vm.IP] :y] [:sta vm.TOPH :x]
    (inc16 vm.IP vm.IPH))

  (vm:def :>r ; v --
    [:ldy vm.ROFF]
    [:lda vm.TOP :x]  [:sta vm.RSTACK :y] [:iny]
    [:lda vm.TOPH :x] [:sta vm.RSTACK :y] [:iny]
    [:sty vm.ROFF]
    (vm:drop))

  (vm:def :r> ; -- v
    (vm:reserve)
    [:ldy vm.ROFF]
    [:dey] [:lda vm.RSTACK :y] [:sta vm.TOPH :x]
    [:dey] [:lda vm.RSTACK :y] [:sta vm.TOP :x]
    [:sty vm.ROFF])

  (vm:def :rtop ; -- v
    (vm:reserve)
    [:ldy vm.ROFF]
    [:dey] [:lda vm.RSTACK :y] [:sta vm.TOPH :x]
    [:dey] [:lda vm.RSTACK :y] [:sta vm.TOP :x])

  (vm:def :rdrop
    [:ldy vm.ROFF] [:dey] [:dey] [:sty vm.ROFF])

  (vm:def :bz ; f --
    [:block
      [:lda vm.TOP :x]
      [:bne :skip]
      [:lda vm.TOPH :x]
      [:beq :dojmp]
     :skip
      (vm:drop)
      [:lda 2] (add16 vm.IP vm.IPH) (vm:ret)
     :dojmp (vm:drop)]
   :jmp
    ; ugh I don't have enough registers for this; a (one-byte?) relative jump would maybe be better
    [:ldy 0] [:lda [vm.IP] :y] [:sta vm.W]
    [:iny] [:lda [vm.IP] :y] [:sta vm.IPH]
    [:lda vm.W] [:sta vm.IP])

  (fn vm.while [self preamble ...]
    [:block
      :start
        [:vm (table.unpack preamble)]
        [:ref :bz] [:ref :end]
        [:vm ...]
        [:ref :jmp] [:ref :start]
      :end])

  (fn vm.until [self ...]
    [:block :start [:vm ...] [:ref :bz] [:ref :start]])

  (fn vm.for [self ...]
    [:vm :>r (vm:while [:rtop] :r> :dec :>r ...) :rdrop])

  (vm:def :+ ; a b -- c
    [:clc]
    [:lda vm.ST1 :x] [:adc vm.TOP :x] [:sta vm.ST1 :x]
    [:lda vm.ST1H :x] [:adc vm.TOPH :x] [:sta vm.ST1H :x]
    (vm:drop))

  (vm:def :- ; a b -- c
    [:sec]
    [:lda vm.ST1 :x] [:sbc vm.TOP :x] [:sta vm.ST1 :x]
    [:lda vm.ST1H :x] [:sbc vm.TOPH :x] [:sta vm.ST1H :x]
    (vm:drop))

  (vm:def :inc ; a -- a+1
    (inc16-stk vm.TOP vm.TOPH))

  (vm:def :dec ; a -- a-1
    [:block
      [:lda vm.TOP :x]
      [:bne :declow]
      [:dec vm.TOPH :x]
     :declow
      [:dec vm.TOP :x]])

  (vm:def :not ; f - !f
    [:block
      [:lda vm.TOP :x]
      [:bne :zero]
      [:lda vm.TOPH :x]
      [:bne :zero]
      [:lda 0xff] [:sta vm.TOP :x] [:sta vm.TOPH :x] (vm:ret)
     :zero
      [:lda 0] [:sta vm.TOP :x] [:sta vm.TOPH :x]])

  (vm:def := ; a b -- f
    [:block
      [:lda vm.ST1 :x]
      [:cmp vm.TOP :x]
      [:bne :noteq]
      [:lda vm.ST1H :x]
      [:cmp vm.TOP :x]
      [:bne :noteq]
      [:lda 0xff] (vm:drop) [:sta vm.TOP :x] [:sta vm.TOPH :x] (vm:ret)
     :noteq
      [:lda 0] (vm:drop) [:sta vm.TOP :x] [:sta vm.TOPH :x]])
  vm)

{:new mk-vm}