/** \file input_common.c

Implementation file for the low level input library

*/
#include "config.h"


#include <string.h>
#include <errno.h>
#include <sys/time.h>
#include <unistd.h>
#include <list>
#include <queue>
#include <cwchar>                       // for wint_t
#include <deque>                        // for deque
#include <utility>                      // for swap, pair
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif

#include "fallback.h" // IWYU pragma: keep
#include "util.h"

#include "common.h"
#include "input_common.h"
#include "env_universal_common.h"
#include "env.h"
#include "iothread.h"

/**
   Time in milliseconds to wait for another byte to be available for
   reading after \\x1b is read before assuming that escape key was
   pressed, and not an escape sequence.

   This is the value used by the readline library.
*/
#define WAIT_ON_ESCAPE 500

/** Characters that have been read and returned by the sequence matching code */
static std::deque<wint_t> lookahead_list;

/* Queue of pairs of (function pointer, argument) to be invoked. Expected to be mostly empty. */
typedef std::pair<void (*)(void *), void *> callback_info_t;
typedef std::queue<callback_info_t, std::list<callback_info_t> > callback_queue_t;
static callback_queue_t callback_queue;
static void input_flush_callbacks(void);

static bool has_lookahead(void)
{
    return ! lookahead_list.empty();
}

static wint_t lookahead_pop(void)
{
    wint_t result = lookahead_list.front();
    lookahead_list.pop_front();
    return result;
}

static void lookahead_push_back(wint_t c)
{
    lookahead_list.push_back(c);
}

static void lookahead_push_front(wint_t c)
{
    lookahead_list.push_front(c);
}

static wint_t lookahead_front(void)
{
    return lookahead_list.front();
}

/** Callback function for handling interrupts on reading */
static int (*interrupt_handler)();

void input_common_init(int (*ih)())
{
    interrupt_handler = ih;
}

void input_common_destroy()
{

}

/**
   Internal function used by input_common_readch to read one byte from fd 0. This function should only be called by
   input_common_readch().
*/
static wint_t readb()
{
    /* do_loop must be set on every path through the loop; leaving it uninitialized allows the static analyzer to assist in catching mistakes. */
    unsigned char arr[1];
    bool do_loop;

    do
    {
        /* Flush callbacks */
        input_flush_callbacks();

        fd_set fdset;
        int fd_max = 0;
        int ioport = iothread_port();
        int res;

        FD_ZERO(&fdset);
        FD_SET(0, &fdset);
        if (ioport > 0)
        {
            FD_SET(ioport, &fdset);
            fd_max = maxi(fd_max, ioport);
        }
        
        /* Get our uvar notifier */
        universal_notifier_t &notifier = universal_notifier_t::default_notifier();
        
        /* Get the notification fd (possibly none) */
        int notifier_fd = notifier.notification_fd();
        if (notifier_fd > 0)
        {
            FD_SET(notifier_fd, &fdset);
            fd_max = maxi(fd_max, notifier_fd);
        }
        
        /* Get its suggested delay (possibly none) */
        struct timeval tv = {};
        const unsigned long usecs_delay = notifier.usec_delay_between_polls();
        if (usecs_delay > 0)
        {
            unsigned long usecs_per_sec = 1000000;
            tv.tv_sec = (int)(usecs_delay / usecs_per_sec);
            tv.tv_usec = (int)(usecs_delay % usecs_per_sec);
        }
        
        res = select(fd_max + 1, &fdset, 0, 0, usecs_delay > 0 ? &tv : NULL);
        if (res==-1)
        {
            switch (errno)
            {
                case EINTR:
                case EAGAIN:
                {
                    if (interrupt_handler)
                    {
                        int res = interrupt_handler();
                        if (res)
                        {
                            return res;
                        }
                        if (has_lookahead())
                        {
                            return lookahead_pop();
                        }

                    }


                    do_loop = true;
                    break;
                }
                default:
                {
                    /*
                      The terminal has been closed. Save and exit.
                    */
                    return R_EOF;
                }
            }
        }
        else
        {
            /* Assume we loop unless we see a character in stdin */
            do_loop = true;

            /* Check to see if we want a universal variable barrier */
            bool barrier_from_poll = notifier.poll();
            bool barrier_from_readability = false;
            if (notifier_fd > 0 && FD_ISSET(notifier_fd, &fdset))
            {
                barrier_from_readability = notifier.notification_fd_became_readable(notifier_fd);
            }
            if (barrier_from_poll || barrier_from_readability)
            {
                env_universal_barrier();
            }

            if (ioport > 0 && FD_ISSET(ioport, &fdset))
            {
                iothread_service_completion();
                if (has_lookahead())
                {
                    return lookahead_pop();
                }
            }

            if (FD_ISSET(STDIN_FILENO, &fdset))
            {
                if (read_blocked(0, arr, 1) != 1)
                {
                    /* The teminal has been closed. Save and exit. */
                    return R_EOF;
                }

                /* We read from stdin, so don't loop */
                do_loop = false;
            }
        }
    }
    while (do_loop);

    return arr[0];
}

wchar_t input_common_readch(int timed)
{
    if (! has_lookahead())
    {
        if (timed)
        {
            int count;
            fd_set fds;
            struct timeval tm=
            {
                0,
                1000 * WAIT_ON_ESCAPE
            }
            ;

            FD_ZERO(&fds);
            FD_SET(0, &fds);
            count = select(1, &fds, 0, 0, &tm);

            switch (count)
            {
                case 0:
                    return WEOF;

                case -1:
                    return WEOF;
                    break;
                default:
                    break;

            }
        }

        wchar_t res;
        mbstate_t state = {};

        while (1)
        {
            wint_t b = readb();
            char bb;

            size_t sz;

            if ((b >= R_NULL) && (b < R_NULL + 1000))
                return b;

            bb=b;

            sz = mbrtowc(&res, &bb, 1, &state);

            switch (sz)
            {
                case (size_t)(-1):
                    memset(&state, '\0', sizeof(state));
                    debug(2, L"Illegal input");
                    return R_NULL;
                case (size_t)(-2):
                    break;
                case 0:
                    return 0;
                default:
                    return res;
            }
        }
    }
    else
    {
        if (!timed)
        {
            while (has_lookahead() && lookahead_front() == WEOF)
                lookahead_pop();
            if (! has_lookahead())
                return input_common_readch(0);
        }

        return lookahead_pop();
    }
}


void input_common_queue_ch(wint_t ch)
{
    lookahead_push_back(ch);
}

void input_common_next_ch(wint_t ch)
{
    lookahead_push_front(ch);
}

void input_common_add_callback(void (*callback)(void *), void *arg)
{
    ASSERT_IS_MAIN_THREAD();
    callback_queue.push(callback_info_t(callback, arg));
}

static void input_flush_callbacks(void)
{
    /* Nothing to do if nothing to do */
    if (callback_queue.empty())
        return;

    /* We move the queue into a local variable, so that events queued up during a callback don't get fired until next round. */
    callback_queue_t local_queue;
    std::swap(local_queue, callback_queue);
    while (! local_queue.empty())
    {
        const callback_info_t &callback = local_queue.front();
        callback.first(callback.second); //cute
        local_queue.pop();
    }
}