locals
.model tiny
.code
org 100h
.386


start:
jmp main

delay       db  12h
cur_teak    db  0h

m08_handler proc
    pusha
    mov al, cur_teak
    cmp al, delay
    je @@move
    inc cur_teak
    jmp @@end

@@move:
    call move_snake
    mov cur_teak, 0h
@@end:
    popa
    iret
m08_handler endp

move_snake proc
    cmp direct, 0
    jne @@is_up
    sub head_x, 1
    jmp @@end
@@is_up:
    cmp direct, 1
    jne @@is_right
    sub head_y, 1
    jmp @@end

@@is_right:
    cmp direct, 2
    jne @@down
    add head_x, 1
    jmp @@end
@@down:
    add head_y, 1
@@end:
    mov di, offset map
    add di, word ptr(head_x)
    mov al, head_y
    mov bl, 64
    mul bl
    add di, ax
    mov al, 1
    stosb
    call draw_head

    call draw_tail
    cmp direct_tail, 0
    jne @@is_up_t
    sub tail_x, 1
    jmp @@end_t
@@is_up_t:
    cmp direct_tail, 1
    jne @@is_right_t
    sub tail_y, 1
    jmp @@end_t

@@is_right_t:
    cmp direct_tail, 2
    jne @@down_t
    add tail_x, 1
    jmp @@end_t
@@down_t:
    add tail_y, 1
@@end_t:
    mov di, offset map
    add di, word ptr(tail_x)
    mov al, tail_y
    mov bl, 64
    mul bl
    add di, ax
    mov al, 0
    stosb
    ret
move_snake endp

draw_head proc
    mov al, head_x
    mov bl, 05h
    mul bl
    mov start_x, ax
    mov al, head_y
    mul bl
    mov start_y, ax

    mov ax, snake_point_size
    mov cur_point_size, ax

    mov al, snake_color
    mov cur_color, al

    call draw_point
    ret
draw_head endp

draw_tail proc
    mov al, tail_x
    mov bl, 05h
    mul bl
    mov start_x, ax
    mov al, tail_y
    mul bl
    mov start_y, ax

    mov ax, snake_point_size
    mov cur_point_size, ax

    mov al, 00h
    mov cur_color, al

    call draw_point
    ret
draw_tail endp


m09_handler proc
    pusha
    in al, 60h
    push ax

    in al, 61h
    mov ah, al
    or al, 80h
    out 61H, al
    xchg ah, al
    out 61H, al

    cmp al, 1
    jnz non_esc
    mov ext_flag, 1
    jmp interrupt_end

non_esc:
    cmp al, 4bh
    je @@left

    cmp al, 48h
    je @@up

    cmp al, 4dh
    je @@right

    cmp al, 50h
    je @@down

    jmp @@end

@@left:
    mov direct, 0
@@up:
    mov direct, 1
@@right:
    mov direct, 2
@@down:
    mov direct, 3
@@end:
interrupt_end:
    mov al, 20h
    out 20h, al
    popa
    iret
m09_handler endp
old_09_code         db  0eah, 00, 00, 00, 00

get_old_mode proc
    push    ax
    push    bx
    push    ds

    xor     ax,ax
    mov     ds, ax
    mov     bh, ds:449h

    pop     ds
    mov     [old_vm], bh
    pop     bx
    pop     ax
    ret
get_old_mode endp


get_old_page proc
    push    ax
    push    bx
    push    ds

    xor     ax,ax
    mov     ds, ax
    mov     bh, ds:462h

    pop     ds
    mov     [old_page], bh
    pop     bx
    pop     ax
    ret
get_old_page endp

change_vm proc
    push bp
    mov bp, sp
    push ax

    ; в стеке vm -> ap -> bp -> ax
    mov ah, 00h
    mov al, [bp+6] ;vm
    int 10h

    mov ah, 05h
    mov al, [bp+4] ;ap
    int 10h

    pop ax
    pop bp
    ret 4
change_vm endp

change_mode proc
    call get_old_mode
    call get_old_page

    xor ax, ax
    mov al, our_vm
    push ax
    mov al, our_page
    push ax

    call change_vm

    ret
change_mode endp

draw_point proc
    ;   устанавливаем размер клетки в cur_point_size,
    ;   цвет клетки в cur_color,
    ;   начальную позицию в start_y, start_x
    pusha; ax sp bp si di
    mov ax, cur_point_size
    mov temp_size_x, ax
    mov temp_size_y, ax

    mov ax, start_y
    mov temp_line, ax
    mov ax, start_x
    mov temp_column, ax

    mov ah, 0ch
    mov al, cur_color
    mov bh, our_page
@@loop:
    mov cx, temp_column
    mov dx, temp_line
    int 10h

    dec temp_size_x
    inc temp_column
    cmp temp_size_x, 0
    jnz @@loop

    dec temp_size_y
    inc temp_line
    mov cx, cur_point_size
    mov temp_size_x, cx

    mov cx, start_x
    mov temp_column, cx

    cmp temp_size_y, 0
    jnz @@loop

    popa; di si bp sp ax

    ret
draw_point endp


draw_snake proc
    mov cl, snake_length
    xor ch, ch
@@loop:
    call draw_point
    cmp is_vertical_snake, 00h
    jne @@vert_snake
    add start_x, 5
    jmp @@next
@@vert_snake:
    add start_y, 5

@@next:
    mov ax, 4
    mov cur_point_size, ax
    dec cx
    test cx, cx
    jne @@loop
    ret
draw_snake endp

init_snake proc
    mov al, 1
    mov di, offset map
    add di, 30
    add di, 20*64
    stosb
    stosb
    stosb
    stosb

    mov head_x, 30
    mov head_y, 20
    mov tail_x, 33
    mov tail_y, 20


    mov al, head_x
    mov bl, 05h
    mul bl
    mov start_x, ax
    mov al, head_y
    mul bl
    mov start_y, ax

    mov ax, snake_point_size
    mov cur_point_size, ax

    mov al, snake_color
    mov cur_color, al
    call draw_snake
    ret
init_snake endp

main:
    call change_mode

    call init_snake

    push es
    mov ah, 35h
    mov al, 09h
    int 21h
    mov word ptr old_09_code + 1, bx
    mov word ptr old_09_code + 3, es
    mov dx, offset m09_handler
    mov ah, 25h
    mov al, 09h
    int 21h
    pop es

    push es
    mov ah, 35h
    mov al, 1ch
    int 21h
    mov word ptr old_08_code + 1, bx
    mov word ptr old_08_code + 3, es
    mov dx, offset m08_handler
    mov ah, 25h
    mov al, 1ch
    int 21h
    pop es

    main_loop:
    mov al, ext_flag
    test al, al
    jz main_loop

    push ds
    mov dx, word ptr old_08_code + 1
    mov ds, word ptr old_08_code + 3
    mov ah, 25h
    mov al, 1ch
    int 21h
    pop ds

    push ds
    mov dx, word ptr old_09_code + 1
    mov ds, word ptr old_09_code + 3
    mov ah, 25h
    mov al, 09h
    int 21h
    pop ds

    xor ax, ax
    mov al, [old_vm]
    push ax
    mov al, [old_page]
    push ax
    call change_vm

ret
snake_length        db  4h
snake_color         db  07h
snake_point_size    dw  0004h
cur_point_size      dw  ?
cur_color           db  ?
temp_size_x         dw  ?
temp_size_y         dw  ?
temp_point          db  ?
start_x             dw  ?
start_y             dw  ?
is_vertical_snake   db  00h
temp_line           dw  ?
temp_column         dw  ?

map:                db 40*64 dup(0)
direct              db  0   ; 0  <-
                            ; 1 up
                            ; 2 ->
                            ; 3 down
direct_tail         db  0
head_x              db  ?
head_y              db  ?
tail_x              db  ?
tail_y              db  ?

ext_flag            db  0

old_vm              db  ?
old_page            db  ?
old_08_code         db  0eah, 00, 00, 00, 00
our_vm              db  13h
our_page            db  00h
;размер экрана - 320*200
;размер карты - 40*64

end start