global _start

; constants
SYS_READ        equ 0
SYS_WRITE       equ 1
SYS_POLL        equ 7
SYS_SENDFILE    equ 40
SYS_SOCKET      equ 41
SYS_ACCEPT      equ 43
SYS_BIND        equ 49
SYS_LISTEN      equ 50
SYS_EXIT        equ 60
SYS_FCNTL       equ 72
SYS_UNLINK      equ 87
STDOUT          equ 1
AF_UNIX         equ 1
SOCK_STREAM     equ 1
F_GETFL         equ 3
F_SETFL         equ 4
O_NONBLOCK      equ 2048
POLLIN          equ 1
POLLOUT         equ 4

pollfd_size equ 4 + 2 + 2  ; $ man 2 poll
pollfds_capacity equ 100

SECTION .data
hello           db "Hello world!", 0x0a
hello_len       equ $ - hello
server_path     db "server.sock", 0x00
server_path_len equ $ - hello
sockaddr_size   equ 2 + 108  ; $ man 7 unix

SECTION .bss
sockaddr    resb sockaddr_size
pollfds     resb pollfd_size * pollfds_capacity

SECTION .text

_start:
    mov rax, SYS_WRITE
    mov rdi, STDOUT
    mov rsi, hello
    mov rdx, hello_len
    syscall

    call make_server
    mov rbx, 0  ; pollfd array length
    mov ebp, eax  ; server fd

    mov rax, rbx
    mov edi, ebp
    mov si, POLLIN
    call pollfds__append
    mov rbx, rax

    mov rax, SYS_POLL
    mov rdi, pollfds
    mov rsi, rbx
    mov rdx, 5000
    syscall

exit:
    mov rax, SYS_EXIT
    mov rdi, 0
    syscall

accept:
    mov rdi, rax
    mov rax, SYS_ACCEPT
    mov rsi, 0
    mov rdx, 0
    syscall
    ret

; rax - array length
; edi - fd
; si - events
; Returns new array length in rax
pollfds__append:
    mov [pollfds + rax], edi
    mov [pollfds + rax + 4], si
    add rax, 1
    ret

; Returns new array length in rax
; rax - array length
; edi - fd
pollfds__remove:
    mov r10d, edi
    mov rdi, 0

; Variables:
; rax - array length
; rdi - array index
; r10d - fd
; r11d - pollfds[rdi].fd
pollfds__remove__loop:
    cmp rdi, rax
    jge return  ; fd was not found
    mov r11d, [pollfds + rdi * pollfd_size]
    add rdi, 1
    cmp r11d, r10d
    jne pollfds__remove__loop
    sub rdi, 1

; Returns new array length in rax
; rax - array length
; rdi - array index to remove
pollfds__remove_index:
    cmp rax, 1
    jle pollfds__clear
    mov r10d, [pollfds + (rax - 1) * pollfd_size]
    mov [pollfds + rdi * pollfd_size], r10d
    sub rax, 1
    ret

; Returns new array length in rax
; rax - array length
pollfds__clear:
    mov rax, 0
    ret

; Returns (in rax) the server's file descriptor
make_server:
    mov rax, SYS_UNLINK
    mov rdi, server_path
    syscall

    mov rax, SYS_SOCKET
    mov rdi, AF_UNIX
    mov rsi, SOCK_STREAM
    mov rdx, 0
    syscall
    push rax

    call nonblocking
    call make_sockaddr
    pop r10

    mov rax, SYS_BIND
    mov rdi, r10
    mov rsi, sockaddr
    mov rdx, sockaddr_size
    syscall

    mov rax, SYS_LISTEN
    mov rdi, r10
    mov rsi, 100
    syscall

    mov rax, r10
    ret

nonblocking:
    mov r10, rax

    mov rax, SYS_FCNTL
    mov rdi, r10
    mov rsi, F_GETFL
    syscall

    mov r11, rax
    xor r11, O_NONBLOCK

    mov rax, SYS_FCNTL
    mov rdi, r10
    mov rsi, F_SETFL
    mov rdx, r11
    syscall

    ret

make_sockaddr:
    mov word [sockaddr], AF_UNIX
    mov rax, 0

make_sockaddr__copy_server_path:
    cmp rax, server_path_len
    jge return
    mov r10, [server_path + rax]
    mov [sockaddr + rax + 2], r10
    add rax, 8
    jmp make_sockaddr__copy_server_path

return:
    ret