BUFSIZE equ 1

dataseg segment para public
    StrInput         db "Введите имя файла: ", 0Dh, 0Ah, '$'
    StrEmpty         db "Введена пустая строка", 0Dh, 0Ah, '$'
    StrOpenError     db 0Dh, 0Ah, "Невозможно открыть файл", 0Dh,0Ah, '$'
    StrReadError     db "Ошибка чтения", 0Dh,0Ah, '$'

    Buf            db BUFSIZE  dup (?)
    HInput         dw 0
    BufInput       db 254, 255 dup (?)
    FlagEOF        db ?
    i              dw 0
    j   dw 0
    k dw 0
    Lines   dw 0
    Fd db 0
    Fu db 0
    FileSizeHigh dw 0
    FileSizeLow  dw 0
    Endl    db 0Dh, 0Ah, '$'
    Help    db 'Up - вверх   Down - вниз  Esc - выход                             ',0
dataseg ends

stackseg segment para stack
    dw 128 dup(0)
stackseg ends

codeseg segment para public
assume cs:codeseg,ds:dataseg,ss:stackseg
;=======================================
;Вход:  AX - кол-во позиций
;       BX - Handle
;=======================================
SeekBack proc
    push cx

    push ax

    mov ah, 42h
    mov al, 1
    xor cx, cx
    xor dx, dx
    ;mov bx, FileHandle
    int 21h             ; в DX:AX текущая позиция относительно начала файла

    pop cx

    sub ax, cx
    sbb dx, 0

    mov cx, dx
    mov dx, ax
    mov ah, 42h
    mov al, 0
    int 21h


    mov ah, 42h
    mov al, 1
    xor cx, cx
    xor dx, dx
    ;mov bx, FileHandle
    int 21h

    pop cx
    ret
SeekBack endp

ClrScr proc
    push ax
    mov ah, 0
    mov al, 2
    int 10h
    pop ax
    ret
ClrScr endp

ClrLine proc

    push ax
    push bx
    push dx
    push cx
    mov ah, 03
    mov bh, 0
    int 10h

    mov ax, 80
    mul dh
    mov di, ax

    push es
    mov ax, 0B800h
    mov es, ax
    mov cx, 80
    mov ax, 1020h
    rep stosw
    pop es

    pop cx
    pop dx
    pop bx
    pop ax
    ret
ClrLine endp

WriteStr proc

    push ax
    push bx
    push dx
    push cx


    mov ah, 13h
    mov al, 0
    mov cx, 79
    mov dh, 24
    mov dl, 0
    mov bh, 0
    mov bl, 01110000b
    int 10h

    pop cx
    pop dx
    pop bx
    pop ax
    ret

WriteStr endp
start:
    mov ax, dataseg
    mov ds, ax
    mov es, ax
    mov ax, stackseg
    mov ss, ax

InputRead:
    mov ah, 9
    lea dx, StrInput
    int 21h

    mov ah, 0Ah
    lea dx, BufInput
    int 21h

    cmp [BufInput+1], 0
    jne OpenFile
    mov ah, 9
    lea dx, StrEmpty
    int 21h
    jmp InputRead
OpenFile:
    xor ax, ax
    mov al, [BufInput+1]
    mov di, ax
    mov [BufInput+di+2], 0

    mov ax, 3D00h
    lea dx, [BufInput+2]
    int 21h               ;Открыть файл в режиме чтения
    jnc Process
    mov ah, 9
    lea dx, StrOpenError
    int 21h
    jmp InputRead
Process:
    mov HInput, ax
    mov i, 0

    call ClrScr

        mov FlagEOF, 0
        mov j, 0
    mov Fd, 1
    mov Fu, 0


    mov ah, 42h
    mov al, 2
    xor cx, cx
    xor dx, dx
    mov bx, hInput
    int 21h
    mov FileSizeHigh, dx
    mov FileSizeLow, ax

    mov ah, 42h
    mov al, 0
    xor cx, cx
    xor dx, dx
    mov bx, hInput
    int 21h

ReadFile:
    cmp Lines, 23
    jna Read
    lea bp, Help
    call WriteStr
    jmp WaitKey
Read:
    mov ah, 3Fh         ;чтение из файла
    mov bx, HInput
    lea dx, Buf
    mov cx, BUFSIZE
    int 21h

    jnc NoError
        mov ah, 9
        lea dx, StrReadError
        int 21h
        jmp exit
NoError:
    ;========

    mov ah, 42h
    mov al, 1
    xor cx, cx
    xor dx, dx
    mov bx, hInput
    int 21h

    cmp dx, FileSizeHigh
    jne NotEof
    cmp ax, FileSizeLow
    jne NotEOF
        mov FlagEOF, 1
        mov Fd, 0
NotEOF:
    mov ah, 02h
    mov dl, Buf
    int 21h
    inc i
    cmp FlagEOF, 1
    jne TestEndl
        mov ah, 9
        lea dx, Endl
        int 21h

        lea bp, Help
        call WriteStr

    jmp WaitKey
TestEndl:
    cmp dl, 0Ah
    jne ReadFile
    inc Lines
    cmp j, 0
    je ChangeJ
    jmp  ReadFile
ChangeJ:
    mov ax, i
    mov j, ax
    jmp ReadFile

    WaitKey:

        mov ah, 00
        int 16h
        cmp al, 27
        jne TestKeys
        jmp exit
    TestKeys:
        cmp al, 0
        jne WaitKey
        cmp ah, 50h  ;DOWN
        jne CheckUp
        cmp Fd, 1
        jne CheckUp

        mov ax, j
        mov k, ax
        mov ax, i
        sub ax, j
        mov bx, hInput
        call SeekBack

    ;L7:
        mov ah, 9
        lea dx, Endl
        int 21h

        mov i, 0
        mov j, 0
        mov Lines, 0
        mov Fu, 1
        jmp ReadFile
    CheckUp:
        cmp ah, 48h
        jne TestEOF
        cmp Fu, 1
        jne WaitKey

        mov ah, 9
        lea dx, Endl
        int 21h

        mov ax, i
        mov bx, hInput
        call SeekBack
    Seek:
        mov ax, 2
        mov bx, hInput
        call SeekBack
        add ax, dx
        cmp ax, 0
        jne L1
        mov Fu, 0
        jmp StrFound
    L1:

        mov ah, 3Fh         ;чтение из файла
        mov bx, HInput
        lea dx, Buf
        mov cx, BUFSIZE
        int 21h

        cmp Buf, 0Ah
        je StrFound
        jmp Seek

    StrFound:
        mov FlagEOF, 0
        mov i, 0
        mov j, 0
        mov Lines, 0
        mov k, 0
        mov Fd, 1
        jmp ReadFile
TestEOF:
    cmp FlagEOF, 1
    jne _WaitKey
        jmp WaitKey
_WaitKey:
    jmp ReadFile



exit:
    mov ah, 3Eh
    mov bx, HInput
    int 21h

    mov ax, 4c00h
    int 21h

codeseg ends
end start