%include "rw32-2017.inc"

section .data
    my_string db "ahoj svete a lide!", 0

    replaced_string dd 0, 0, 0, 0, 0



section .text
main:
    mov ebp, esp

    mov eax, my_string
    call my_string_len
    call WriteUInt32

    push "e"
    push my_string
    push eax
    push replaced_string
    call my_char_replace

    xor eax, eax
    ret

my_char_replace:
    push ebp ; stack frame enter
    mov ebp, esp
    push edi
    push ebx
    push edx
    push esi
    push ecx

    ; ebp+20 char to replace
    ; ebp+16 input
    ; ebp+12 len
    ; ebp+8 output

    xor ecx, ecx
    xor edx, edx
    mov edi, [ebp+16] ; input adress
    mov esi, [ebp+8] ; output adress
    mov al, [ebp+20] ; char to replace

do_while:
    cmp [edi+ecx], al ; compare with replacement char
    je _replace_char
        mov ebx, [edi+ecx]
        mov [esi+ecx], ebx
        jmp _move_char

        _replace_char:
            mov [edi+ecx], byte "_"
            inc edx

        _move_char:
        inc ecx
    cmp ecx, [ebp+12]
    jne do_while ; loop, if we're before end

    mov eax, edx ; store replaced chars

    pop ecx
    pop esi
    pop edx
    pop ebx
    pop edi
    mov esp, ebp ; stack frame leave
    pop ebp

    ret 32

my_string_len:
    push ebx
    xor ebx, ebx

    while:  cmp [eax + ebx], byte 0
            je end
            inc ebx
            jmp while

    end:    mov eax, ebx
            pop ebx
            ret