module picoev

$if windows {
    #include <winsock2.h>
    #include <ws2tcpip.h>
} $else {
    #include <sys/select.h>
}

pub struct SelectLoop {
mut:
    id  int
    now i64
}

type LoopType = SelectLoop

// create_select_loop creates a new `SelectLoop` struct with the given `id`.
pub fn create_select_loop(id int) !&SelectLoop {
    return &SelectLoop{
        id: id
    }
}

// updates the events associated with a file descriptor in the event loop.
@[direct_array_access]
fn (mut pv Picoev) update_events(fd int, events int) int {
    // check if fd is in range
    assert fd < max_fds

    pv.file_descriptors[fd].events = u32(events & picoev_readwrite)
    return 0
}

// performs a single iteration of the select-based event loop.
@[direct_array_access]
fn (mut pv Picoev) poll_once(max_wait_in_sec int) int {
    // Initializes sets for read, write, and error events
    readfds, writefds, errorfds := C.fd_set{}, C.fd_set{}, C.fd_set{}

    // setup
    C.FD_ZERO(&readfds)
    C.FD_ZERO(&writefds)
    C.FD_ZERO(&errorfds)

    mut maxfd := 0

    // finds the maximum file descriptor and adds sockets to the sets `fd_sets`.
    for target in pv.file_descriptors {
        if target.loop_id == pv.loop.id {
            if target.events & picoev_read != 0 {
                C.FD_SET(target.fd, &readfds)
                if maxfd < target.fd {
                    maxfd = target.fd
                }
            }
            if target.events & picoev_write != 0 {
                C.FD_SET(target.fd, &writefds)
                if maxfd < target.fd {
                    maxfd = target.fd
                }
            }
        }
    }

    // select and handle sockets if any
    tv := C.timeval{
        tv_sec:  u64(max_wait_in_sec)
        tv_usec: 0
    }
    r := C.select(maxfd + 1, &readfds, &writefds, &errorfds, &tv)
    if r == -1 {
        // timeout
        return -1
    } else if r > 0 {
        // Iterates through file descriptors and calls their callbacks for triggered events
        for target in pv.file_descriptors {
            if target.loop_id == pv.loop.id {
                mut read_events := 0
                if C.FD_ISSET(target.fd, &readfds) != 0 {
                    read_events |= picoev_read
                }
                if C.FD_ISSET(target.fd, &writefds) != 0 {
                    read_events |= picoev_write
                }
                if read_events != 0 {
                    trace_fd('do callback ${target.fd}')
                    // do callback!
                    unsafe { target.cb(target.fd, read_events, &pv) }
                }
            }
        }
    }
    return 0
}