LOAD_ADDR equ 0x00010000 ; address this program is loaded at

TOKEN_TABLE_ADDR equ 0x00060000 ; address the token table is loaded at
TOKEN_TABLE_SIZE equ 0x1000     ; max length of table

TEST_ARENA_ADDR equ 0x00060000 ; address to run tests at
TEST_ARENA_SIZE equ 0x1000     ; maximum size tests can use

OUTPUT_ADDR equ 0x00070000 ; address of outputed binary
OUTPUT_SIZE equ 0x1000     ; max length of outputed binary

STACK_ADDR equ 0x00060000 ; address to put the 64-bit stack at

[bits 64]
[org LOAD_ADDR]

start:
  mov rsp, STACK_ADDR ; we might need more stack space, let's just be safe

  mov rsi, msg_welcome
  call print

  call run_tests

  jmp halt

; ------------------------------------------------------------------------------
; tokenising
; ------------------------------------------------------------------------------

; ------------------------------------------------------------------------------
; copy_token 
;
; description:
; copies a token from one spot in memory to another
;
; parameters:
; rdi -> start of buffer to be read
; rsi -> start of buffer to be written
;
; returned:
; rax -> last byte read
; rdx -> last byte written
; ------------------------------------------------------------------------------

copy_token:
  .loop:

    mov dl, [rdi] ; move bit to compare to current byte in read buffer

    push rdi ; push incrementors to call elemb
    push rsi ;

    mov rdi, 8                  ; length of terminator list
    mov rsi, token_terminator_8 ; start of terminator list
                                ; dl set before pushing rdi
    call elemb

    pop rsi ;
    pop rdi ; pop incrementors after call

    cmp rax, 1 ; check if the next character is a token terminator
    je .break  ; > if so, break the function

    ; rdi and rsi set from previous loop iteration
    call copy_byte ; if not, copy the current byte in read buffer

    inc rdi ; read pointer
    inc rsi ; write pointer

    jmp .loop

  .break:
    mov rax, rdi ; -> last byte read
    mov rdx, rsi ; -> last byte written
    ret
    
; ------------------------------------------------------------------------------
; copy_byte
;
; description:
; copies a byte from one spot in memory to another
;
; parameters:
; rdi -> word to be read
; rsi -> word to be written
;
; returned:
; al = byte that was read; the rest of rax is zeroed
; ------------------------------------------------------------------------------

copy_byte:
  xor rax, rax ; zero out so it returns fine
  mov al, [rdi]
  mov [rsi], al
  ret

; ------------------------------------------------------------------------------
; utilities
; ------------------------------------------------------------------------------

; ------------------------------------------------------------------------------
; print
;
; description:
; prints a null-terminated string
;
; parameters:
; rsi -> start of null-terminated string
; ------------------------------------------------------------------------------

print:
  push rdx
  mov rdx, 0x3F8
  .loop:
    mov al, [rsi]
    test al, al
    jz .done
    out dx, al
    inc rsi
    jmp .loop
  .done:
    pop rdx
    ret

; ------------------------------------------------------------------------------
; halt
;
; description:
; halts the program, silly :)
; ------------------------------------------------------------------------------

halt:
  mov rsi, msg_halt
  call print
  hlt
  jmp halt

; ------------------------------------------------------------------------------
; elemb
;
; description:
; checks if given byte is element of the specified list
;
; parameters:
; rdi = size of list
; rsi -> start of list
; dl =  given byte
;
; returned:
; rax = 0: is not an element
;       1: is an element
; ------------------------------------------------------------------------------

elemb:
  .loop
    cmp rdi, 0    ; check if remaining length 0
    je .not_found ; if so, break; dl not an element of list

    mov al, [rsi]
    cmp al, dl    ; check if current byte in list is the desired byte
    je .found     ; if so, break; dl an element of list

    inc rsi ; move to next byte
    dec rdi ; and reduce remaining length

    jmp .loop

  .not_found
    xor rax, rax ; return 0; dl not an element of list
    ret

  .found
    xor rax, rax
    mov rax, 1 ; return 1; dl an element of list
    ret

  .f db "found", 0x0D, 0x0A, 0x00
  .nf db "not found", 0x0D, 0x0A, 0x00

; ------------------------------------------------------------------------------
; tests
; ------------------------------------------------------------------------------

; ------------------------------------------------------------------------------
; run_tests
;
; description:
; runs all tests
; ------------------------------------------------------------------------------

run_tests:
  mov rsi, .msg
  call print

  call test_copy_byte
  call test_copy_token
  call test_elemb

  ret
  .msg db "running test suite...", 0x0D, 0x0A, 0x00

; ------------------------------------------------------------------------------
; test_copy_byte
;
; description:
; tests copy_byte described functionality
; ------------------------------------------------------------------------------

test_copy_byte:
  mov rsi, .msg
  call print

  mov rdi, test_byte       ; byte to be copied
  mov rsi, TEST_ARENA_ADDR ; location of test
  call copy_byte

  mov cx, [rsi]
  and ax, 0xFF ; only compare bottom byte
  and cx, 0xFF
  cmp ax, cx ; compare returned byte to copied byte
  jne .fail
  cmp al, [test_byte] ; compare returned byte to expected byte
  jne .fail

  .pass:
    mov rsi, msg_pass
    call print
    ret
  .fail:
    mov rsi, msg_fail
    call print
    ret
  .msg db "test_copy_byte...", 0x00

; ------------------------------------------------------------------------------
; test_copy_token
;
; description:
; tests copy_token described functionality
; ------------------------------------------------------------------------------

test_copy_token:
  mov rsi, .msg
  call print

  ; test case: space terminated

  mov rdi, test_token_space ; read buffer
  mov rsi, TEST_ARENA_ADDR  ; write buffer
  call copy_token

  ; check reported final indicies with the expected final indicies
  cmp rax, test_token_space + 8 ; last byte read
  jne .fail
  cmp rdx, TEST_ARENA_ADDR + 8 ; last byte written
  jne .fail

  mov rsi, TEST_ARENA_ADDR
  mov rcx, [rsi]
  cmp rcx, [test_token_space] ; check if copied token matches expected token
  jne .fail                   ; if not, fail

  ; test case: null terminated

  mov rdi, test_token_null ; read buffer
  mov rsi, TEST_ARENA_ADDR ; write buffer
  call copy_token

  ; check reported final indicies with the expected final indicies
  cmp rax, test_token_null + 8 ; last byte read
  jne .fail
  cmp rdx, TEST_ARENA_ADDR + 8 ; last byte written
  jne .fail

  mov rsi, TEST_ARENA_ADDR
  mov rcx, [rsi]
  cmp rcx, [test_token_null] ; check if copied token matches expected token
  jne .fail                  ; if not, fail

  .pass:
    mov rsi, msg_pass
    call print
    ret
  .fail:
    mov rsi, msg_fail
    call print
    ret
  .msg db "test_copy_token...", 0x00

; ------------------------------------------------------------------------------
; test_elemb
;
; description:
; tests elemb described functionality
; ------------------------------------------------------------------------------

test_elemb:
  mov rsi, .msg
  call print

  ; [0]
  mov rdi, 5
  mov rsi, test_elemb_5
  mov dl, [test_elemb_5]
  call elemb
  cmp al, 1
  jne .fail

  ; [n - 1]
  mov rdi, 5
  mov rsi, test_elemb_5
  mov dl, [test_elemb_5 + 4]
  call elemb
  cmp al, 1
  jne .fail

  ; [1]
  mov rdi, 5
  mov rsi, test_elemb_5
  mov dl, [test_elemb_5 + 1]
  call elemb
  cmp al, 1
  jne .fail

  ; not present
  mov rdi, 5
  mov rsi, test_elemb_5
  mov dl, 0xDA
  call elemb
  cmp al, 0
  jne .fail

  ; 0 length list
  mov rdi, 0
  mov rsi, test_elemb_0
  mov dl, 0x34
  call elemb
  cmp al, 0
  jne .fail

  .pass:
    mov rsi, msg_pass
    call print
    ret
  .fail:
    mov rsi, msg_fail
    call print
    ret
  .msg db "test_elemb...", 0x00

; ------------------------------------------------------------------------------
; data
; ------------------------------------------------------------------------------

msg_welcome db "Welcome to Twasm", 0x0D, 0x0A, 0x00
msg_halt db "halted.", 0x0D, 0x0A, 0x00
msg_pass db "passed.", 0x0D, 0x0A, 0x00
msg_fail db "failed.", 0x0D, 0x0A, 0x00

test_byte db "Q" ; unterminated, just a byte chillin
test_token_null db "TestTokn", 0x00 ; followed by null terminator. Quad word
test_token_space db "TestTokn " ; followed by space. Quad word
test_elemb_0
test_elemb_5 db 0x54, 0x00, 0x21, 0x20, 0x34

token_terminator_8 db 0x00, " ", 0x0A, 0x0D, 0x00, 0x00, 0x00, 0x00

debug_string db "debug_string", 0x0D, 0x0A, 0x00