%define SYS_read 0
%define SYS_write 1
%define SYS_poll 7
%define SYS_exit 60

%define FD_stdin 0
%define FD_stdout 1
%define FD_stderr 2

%define POLLIN 1

section .text
global _start
_start:
prompt_weight:
    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,weight_prompt_text
    mov rdx,weight_prompt_length
    syscall
    
    call read_float
    cmp rax,0
    jne good_weight

    call clear_stdin
    jmp prompt_weight

good_weight:
    ; convert weight to kg
    divss xmm0,[lb_kg_scale]
    movq r15,xmm0 ; weight

prompt_height:
    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,height_prompt_text
    mov rdx,height_prompt_length
    syscall

    call read_float
    cmp rax,0
    jne good_height

    call clear_stdin
    jmp prompt_height
    
good_height:
    ; convert height to cm
    mulss xmm0,[inch_cm_scale]
    movq r14,xmm0 ; height

    ; print metric weight
    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,weight_notice_pre_text
    mov rdx,weight_notice_pre_length
    syscall

    movq xmm0,r15
    mov rdi,3
    call print_float

    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,weight_notice_post_text
    mov rdx,weight_notice_post_length
    syscall

    ; print metric height
    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,height_notice_pre_text
    mov rdx,height_notice_pre_length
    syscall

    movq xmm0,r14
    mov rdi,3
    call print_float

    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,height_notice_post_text
    mov rdx,height_notice_post_length
    syscall

    ; calculate bmi (kg/(m^2))
    movq xmm1,r14 ; height
    divss xmm1,[_100f] ; cm to m
    mulss xmm1,xmm1
    movq xmm0,r15 ; weight
    divss xmm0,xmm1
    movq r15,xmm0 ; bmi

    ; write bmi
    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,bmi_notice_text
    mov rdx,bmi_notice_length
    syscall

    movq xmm0,r15
    mov rdi,3
    call print_float

    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,newline_char
    mov rdx,1
    syscall

    call clear_stdin

    ; exit
    xor rdi,rdi
    mov rax,SYS_exit
    syscall

clear_stdin:
    ; 16 - read buff
    ; 4 - pollfd.fd
    ; 2 - pollfd.events
    ; 2 - pollfd.revents
    sub rsp,24
    mov DWORD [rsp+16],FD_stdin
    mov WORD [rsp+20],POLLIN
clear_stdin_loop:
    mov rax,SYS_poll
    lea rdi,[rsp+16]
    mov rsi,1
    xor rdx,rdx
    syscall

    cmp rax,0
    jle clear_stdin_end

    mov rax,SYS_read
    mov rdi,FD_stdin
    mov rsi,rsp
    mov rdx,16
    syscall

    jmp clear_stdin_loop

clear_stdin_end:
    add rsp,24
    ret

print_float: ; void print_float(float f, int percission)
    sub rsp,24
    movss xmm1,[_10f]
    mov rcx,rdi
print_float_scale_loop:
    mulss xmm0,xmm1
    loop print_float_scale_loop

    ; put digits in memory
    cvtss2si rax,xmm0
    mov rcx,23
    mov rbx,10
print_float_reverse_loop:
    xor rdx,rdx
    div rbx
    add rdx,'0'
    mov [rsp+rcx],dl
    dec rcx

    cmp rax,0
    jne print_float_reverse_loop

    push rcx
    push rdi

    add rcx,17

    ; number to write
    mov rdx,rcx
    sub rdx,40
    imul rdx,-1
    sub rdx,rdi

    mov rax,SYS_write
    mov rdi,FD_stdout
    lea rsi,[rsp+rcx]
    syscall

    mov rax,SYS_write
    mov rdi,FD_stdout
    mov rsi,period_char
    mov rdx,1
    syscall

    pop rdi
    pop rcx

    lea rsi,[rsp+24]
    sub rsi,rdi
    mov rdx,rdi
    mov rax,SYS_write
    mov rdi,FD_stdout
    syscall

    add rsp,24
    ret


; on error, return 0 in rax. otherwise, return 1 in rax 
; and the result in xmm0
read_float: ; float read_float()
    push r15 ; read count
    push r14 ; whole part

    sub rsp,21 ; read buffer
    xor r15,r15
    mov r14,-1
read_float_loop:
    cmp r15,20
    je read_float_size_error

    mov rax,SYS_read
    mov rdi,FD_stdin
    lea rsi,[rsp+20]
    mov rdx,1
    syscall

    mov dil,[rsp+20]

    cmp r15,0 
    sete ah

    cmp dil,'0'
    sete al
    and al,ah
    jnz read_float_loop

    cmp dil,' '
    sete al
    and al,ah
    jnz read_float_loop

    cmp dil,0xA ; \n
    je read_float_convert

    cmp dil,'.'
    je read_float_start_decimal

    call is_number ; dil is preserved
    cmp rax,0
    je read_float_num_error

    sub dil,'0'
    mov [rsp+r15],dil
    inc r15

    xor rax,rax
    cmp r14,-1
    setne al
    add r14,rax

    jmp read_float_loop

read_float_start_decimal:
    cmp r14,-1
    jne read_float_num_error

    xor r14,r14
    jmp read_float_loop

read_float_convert:
    ; zero r14 if it is -1
    xor rax,rax
    cmp r14,-1
    cmove r14,rax

    ; invert scale
    sub r14,r15
    imul r14,-1

    mov rax,0
    movq xmm0,rax

    xor rcx,rcx
read_float_convert_whole_loop:
    cmp rcx,r14
    je read_float_convert_dec_prepare

    mulss xmm0,[_10f]

    xor eax,eax
    mov al,[rsp+rcx]
    cvtsi2ss xmm1,eax

    addss xmm0,xmm1

    inc rcx
    jmp read_float_convert_whole_loop

read_float_convert_dec_prepare:
    mov rax,1 ; return value
    movss xmm7,[_0.1f]
    movss xmm6,[_10f]
read_float_convert_dec_loop:
    cmp rcx,r15
    je read_float_end

    xor ebx,ebx
    mov bl,[rsp+rcx]
    cvtsi2ss xmm1,ebx

    mulss xmm1,xmm7
    addss xmm0,xmm1
    divss xmm7,xmm6
    
    inc rcx
    jmp read_float_convert_dec_loop

read_float_end:
    add rsp,21
    pop r14
    pop r15
    ret

read_float_num_error:
    mov rax,SYS_write
    mov rdi,FD_stderr
    mov rsi,num_error_text
    mov rdx,num_error_length
    syscall

    mov rax,0
    jmp read_float_end

read_float_size_error:
    mov rax,SYS_write
    mov rdi,FD_stderr
    mov rsi,size_error_text
    mov rdx,size_error_length
    syscall

    mov rax,0
    jmp read_float_end

; dil is preserved across calls
is_number: ; bool is_number(char n)
    cmp dil,'0'
    jl is_number_fail

    cmp dil,'9'
    jg is_number_fail

    mov rax,1
    ret

is_number_fail:
    xor rax,rax
    ret

section .data
num_error_text: db "Invalid number!",0xA
num_error_length: equ $ - num_error_text
size_error_text: db "Number too long!",0xA
size_error_length: equ $ - size_error_text
period_char: db "."
newline_char: db 0xA
_10f: dd 10.0
_0.1f: dd 0.1
_100f: dd 100.0

inch_cm_scale: dd 2.54
lb_kg_scale: dd 2.20462

weight_prompt_text: db "Enter weight (pounds): "
weight_prompt_length: equ $ - weight_prompt_text
height_prompt_text: db "Enter height (inches): "
height_prompt_length: equ $ - height_prompt_text
height_notice_pre_text: db "Your metric height: "
height_notice_pre_length: equ $ - height_notice_pre_text
height_notice_post_text: db "cm",0xA
height_notice_post_length: equ $ - height_notice_post_text
weight_notice_pre_text: db "Your metric weight: "
weight_notice_pre_length: equ $ - weight_notice_pre_text
weight_notice_post_text: db "kg",0xA
weight_notice_post_length: equ $ - weight_notice_post_text
bmi_notice_text: db "Your BMI: "
bmi_notice_length: equ $ - bmi_notice_text