; ʕ·ᴥ·ʔ- fuzzy v0 rev 0: parse program text and spit out binary representation @ $4000

    .include "./macro.inc"

n = $05 ; temporary storage for data stack operations
base = $00
result_binary_base = base ; pointer to where the next byte of binary data should be stored0
binary_base_index = result_binary_base + 2 ; offset for that pointer
binary_subroutine_address = binary_base_index + 1 ; pointer to a subroutine to be written to the binary

    .org $8000
    .include "./subroutines.inc"

program_text:
    .asciiz '2 3 +'

reset:
    sei
    lda #0
    ldx #0
    ldy #0

main:
    stz binary_base_index
    lda #$40
    sta result_binary_base + 1 ; set where to store resulting binary
    stz binary_subroutine_address 
    lda #$80
    sta binary_subroutine_address + 1 ; available subroutines start at $8000
    jsr compile_values
    stp

; parser loop, eventually this will be able to handle longer program strings, but indexing by y is fine for now
compile_values:
    ldy #0
parser_loop:
    lda program_text, y ; get character at index
    cmp #0 ; is eof?
    beq .end ; yes, exit loop
    cmp #20 ; is space?
    beq parser_loop ; yes, skip this char
    cmp #12 ; is newline?
    beq .newline ; yes, handle newline
    jsr compile_values_op
    jsr compile_values_nat
    .newline: ; we reached a newline, y is program string index
       iny ; WARN: don't accidentally iny in this loop w/out handling a character
       lda program_text, y ; load next char
       cmp #12 ; is newline?
       bne parser_loop ; no, keep parsing tokens
       rts ; yes, no more tokens in body (see syntax.md for info)
    .end:
        rts
         
; a holds character value, y program text index, only iny if you find a matching character & consume it
compile_values_op:
    cmp #"+" ; i personally think this syntax is really silly but whatever, one of these days i'm gonna write my own assembler and document everything cause vasm documentation is kinda terrible
    bne .next
    .is_plus: 
        lda #1
        jsr store_subroutine
        rts
    .next:
        rts
    ; cmp #"!" ; commenting these out for now to handle a single simple case
    ; cmp #"&"
    ; cmp #"|"
    ; cmp #"-"
    ; cmp #"*"
    ; cmp #"/"
    ; cmp #"="
    ; cmp #">"
    ; cmp #"<"
    ; cmp #"#"

; a holds character value, y program text index, only iny if you find a matching character & consume it
compile_values_nat:
    ; TODO:
    ; cmp #"$" ; is hex?
    ; bne .decimal ; no, try decimal
    ; cmp  
    ; rts 
    cmp #47 ; less than (before) start of 0-9 georgescii range?
    bcc .not_nat 
    cmp #57 ; greater than end of 0-9 georgescii range?
    bcs .not_nat
    jsr georgescii_decimal_to_value
    jsr store_binary
    iny
    rts
    .not_nat:
        rts

; georgescii decmal value in a register, return equivalent plain value in a register
georgescii_decimal_to_value:
    clc
    sbc #$30 ; decimal digits start at georgescii $30
    rts

; we have binary in the a register we want to store
store_binary:
    phy  
    ldy binary_base_index
    sta (result_binary_base), y
    inc binary_base_index
    bne .not_overflow ; did we roll over?
    inc result_binary_base + 1 ; yes, roll over base address
    .not_overflow: ; no, carry on as normal
        ply
        rts

; binary_subroutine_address is a pointer to a subroutine that we want to store
; the first byte at the subroutine's address is its length
store_contiguous_binary:
    pha ; just to be safe
    phy
    phx
    lda (binary_subroutine_address) ; get the subroutine length
    tax ; loop counter
    ldy #0 ; index into subroutine
    .loop:
        lda (binary_subroutine_address), y
        jsr store_binary
        iny
        dex
        bne .loop
    .end:
        phx
        ply
        pla
        rts

; this wouldn't be necessary if we could get the 
; address of a label in vasm, but that's for another time
; (when i feel like writing an assembler lol)
; for now, pass the index of the subroutine (in subroutines.asm)
; to a and it will get written to binary_subroutine_address
get_subroutine_address:
   tax  ; set up counter
   bne .loop ; first subrotine? 
   stz binary_subroutine_address ; yes, store its address
   lda #$80
   sta binary_subroutine_address + 1
   rts
   .loop: ; loop through
       lda (binary_subroutine_address) ; no, load length of subroutine
       inc ; distance from next subroutine
       clc
       adc binary_subroutine_address ; add it to the current address
       sta binary_subroutine_address
       bcs .no_carry
       lda binary_subroutine_address + 1 ; add the carry to the high byte of address
       adc #0 
       sta binary_subroutine_address + 1
       .no_carry:
           dex ; is this our address?
           bne .loop ; yes, we're done
       rts


; pass subroutine index to a and it will get written into the binary
; TODO: stabilize subroutine location & just write a `jsr $subroutine` to the binary
store_subroutine:
    jsr get_subroutine_address
    jsr store_contiguous_binary
    rts


isr: ; interrupt service routine
    pha
    phx
    phy
    ply
    plx
    pla
    rti

    

    .org $fffc
    .word reset
    .word isr