// Implementation file for the low level input library.
#include "config.h"

#include <errno.h>
#include <string.h>
#include <unistd.h>
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/types.h>
#include <wchar.h>

#include <deque>
#include <list>
#include <memory>
#include <type_traits>

#include "common.h"
#include "env.h"
#include "env_universal_common.h"
#include "fallback.h"  // IWYU pragma: keep
#include "input_common.h"
#include "iothread.h"
#include "util.h"
#include "wutil.h"

/// Time in milliseconds to wait for another byte to be available for reading
/// after \e is read before assuming that escape key was pressed, and not an
/// escape sequence.
#define WAIT_ON_ESCAPE_DEFAULT 300
static int wait_on_escape_ms = WAIT_ON_ESCAPE_DEFAULT;

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

// Queue of pairs of (function pointer, argument) to be invoked. Expected to be mostly empty.
typedef std::list<std::function<void(void)>> 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) {
            if (errno == EINTR || errno == EAGAIN) {
                if (interrupt_handler) {
                    int res = interrupt_handler();
                    if (res) return res;
                    if (has_lookahead()) return lookahead_pop();
                }

                do_loop = true;
            } else {
                // 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];
}

// Update the wait_on_escape_ms value in response to the fish_escape_delay_ms user variable being
// set.
void update_wait_on_escape_ms() {
    env_var_t escape_time_ms = env_get_string(L"fish_escape_delay_ms");
    if (escape_time_ms.missing_or_empty()) {
        wait_on_escape_ms = WAIT_ON_ESCAPE_DEFAULT;
        return;
    }

    long tmp = fish_wcstol(escape_time_ms.c_str());
    if (errno || tmp < 10 || tmp >= 5000) {
        fwprintf(stderr,
                 L"ignoring fish_escape_delay_ms: value '%ls' "
                 L"is not an integer or is < 10 or >= 5000 ms\n",
                 escape_time_ms.c_str());
    } else {
        wait_on_escape_ms = (int)tmp;
    }
}

wchar_t input_common_readch(int timed) {
    if (!has_lookahead()) {
        if (timed) {
            fd_set fds;
            FD_ZERO(&fds);
            FD_SET(0, &fds);
            struct timeval tm = {wait_on_escape_ms / 1000, 1000 * (wait_on_escape_ms % 1000)};
            int count = select(1, &fds, 0, 0, &tm);
            if (count <= 0) {
                return R_TIMEOUT;
            }
        }

        wchar_t res;
        mbstate_t state = {};

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

            if (b >= R_NULL && b <= R_MAX) return b;

            if (MB_CUR_MAX == 1) {
                // return (unsigned char)b;  // single-byte locale, all values are legal
                return b;  // single-byte locale, all values are legal
            }

            char bb = b;
            size_t 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() == R_TIMEOUT) 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(std::function<void(void)> callback) {
    ASSERT_IS_MAIN_THREAD();
    callback_queue.push_back(std::move(callback));
}

static void input_flush_callbacks(void) {
    // We move the queue into a local variable, so that events queued up during a callback don't get
    // fired until next round.
    ASSERT_IS_MAIN_THREAD();
    callback_queue_t local_queue;
    std::swap(local_queue, callback_queue);
    for (auto &f : local_queue) {
        f();
    }
}
