%include "CONSTANTS.h"

section .data
    prompt: db `Enter a phrase: `,0
    fmtString1: db `You entered '%s' \n`,0
    endl: db `\n`,0

section .bss
    MAX_LEN equ 10
    phrase: resb  MAX_LEN+1

section .text

global main
main:

    ; r12 will hold the end of the string.
    ; r13 will hold the lcv

    ; prompt for a phrase
    mov rdi, prompt
    call CallPrintf

    ; flush the buffer, fflush needs to be called.
    mov rdi, 0
    call Flush

    ; call read to read up to MAX_LEN into the buffer
    ; this will read until the end of line, or MAX_LEN is read
    ; and will store it into buffer, inclding the newline
    mov rax, SYS_READ
    mov rdi, STDIN 
    mov rsi, phrase
    mov rdx, MAX_LEN
    syscall

     
    ; this will  check to see if less then the max characters have been input
    mov r12, rax
    cmp r12, MAX_LEN 
    jl fix

    ; we have max characters, is the last one an endl?  
    mov al, byte [phrase+r12-1]
    cmp al, [endl]

    ; if the last character is not an endl don't remove it.
    jne skip

fix:
    ; if it is a newline, remove it
    dec r12

skip:
    ; this make sure that the string is null terminated.
    mov byte [phrase + r12], 0

    ; print it out.
    mov rdi, fmtString1
    mov rsi, phrase
    call CallPrintf

    ; set the index to be 0
    mov r13,0
FixerLoopTop:
    cmp r13, r12
    je  FixerLoopDone 

    ; load the letter into the al
    mov al, byte [phrase + r13]

    ; skip changing the letter if it is less than 'a'
    cmp al, 'a'
    jl  FixerLoopBottom

    ; also don't mess with it if it is more than z
    cmp al, 'z'
    jg  FixerLoopBottom

    ; must be between a and z so subtract 20 to make it upper case
    sub al, 0x20
    mov byte [phrase + r13], al

FixerLoopBottom:

    ; increment the loop control variable
    inc r13
    jmp FixerLoopTop

FixerLoopDone:

    ; print it out.
    mov rdi, fmtString1
    mov rsi, phrase
    call CallPrintf
   
    jmp Exit