/*
 * events.c - Epoll-based event loops for WebSocket I/O and signal dispatch
 *
 * Two-thread architecture:
 *   HOT thread:  epoll_wait on WebSocket fds + timer fd for keep-alive pings
 *   EXECUTOR thread: polls SPSC signal queue + fill wake fd, executes triangles
 *
 * Signals flow: evaluate.c -> SPSC queue -> executor thread (direct execution)
 */

#include "log.h"
#include "events.h"
#include "evaluate.h"
#include "executor.h"
#include <stdio.h>
#include <time.h>

static int64_t now_mono_ms(void) {
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    return (int64_t)ts.tv_sec * 1000 + (int64_t)ts.tv_nsec / 1000000;
}
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <time.h>
#include <pthread.h>
#include <sys/timerfd.h>
#include <sys/eventfd.h>
#include <sys/socket.h>
#include <arpa/inet.h>

/* Set O_NONBLOCK on an fd. Returns 0 on success, -1 on error. */
static int set_nonblocking(int fd) {
    int flags = fcntl(fd, F_GETFL, 0);
    if (flags < 0) return -1;
    return fcntl(fd, F_SETFL, flags | O_NONBLOCK);
}

/* Register an fd with the epoll set. If the fd is already tracked, modify
   its events instead of re-adding. Returns 0 on success, -1 on error. */
int event_loops_add_fd(epoll_set_t *set, int fd, fd_type_t type,
                       uint32_t ws_idx, void *user_data, uint32_t events) {
    if (set->fd_count >= MAX_EPOLL_FDS) {
        log_write("[EVENTS] epoll set full\n");
        return -1;
    }

    // If fd already tracked, modify instead of re-adding
    for (uint32_t i = 0; i < set->fd_count; i++) {
        if (set->fds[i].fd == fd) {
            struct epoll_event ev = {
                .events = events,
                .data.ptr = &set->fds[i]
            };
            return epoll_ctl(set->epoll_fd, EPOLL_CTL_MOD, fd, &ev);
        }
    }

    tracked_fd_t *tf = &set->fds[set->fd_count++];
    tf->fd = fd;
    tf->type = type;
    tf->ws_conn_idx = ws_idx;
    tf->user_data = user_data;

    struct epoll_event ev = {
        .events = events,
        .data.ptr = tf
    };
    return epoll_ctl(set->epoll_fd, EPOLL_CTL_ADD, fd, &ev);
}

/* Remove an fd from the epoll set and mark its tracked entry as unused. */
void event_loops_remove_fd(epoll_set_t *set, int fd) {
    epoll_ctl(set->epoll_fd, EPOLL_CTL_DEL, fd, NULL);
    for (uint32_t i = 0; i < set->fd_count; i++) {
        if (set->fds[i].fd == fd) {
            set->fds[i].fd = -1;
            return;
        }
    }
}

/* Initialise an epoll set: create epoll fd, zero the tracked fd array. */
static void epoll_set_init(epoll_set_t *set) {
    memset(set, 0, sizeof(*set));
    set->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
    if (set->epoll_fd < 0) {
        perror("epoll_create1");
        exit(1);
    }
}

/* Initialise both epoll sets (hot + cold), timer fd, and wakeup fd.
   The cold epoll set monitors the wakeup eventfd for SPSC drain signals. */
int event_loops_init(event_loops_t *loops, ws_client_t *ws_client,
                     const config_t *cfg, executor_slot_t *slots, int n_slots) {
    memset(loops, 0, sizeof(*loops));
    loops->ws_client = ws_client;
    loops->slots = slots;
    loops->n_slots = n_slots;
    loops->running = true;

    loops->executor_shared = calloc(1, sizeof(executor_shared_t));
    if (loops->executor_shared) {
        pthread_mutex_init(&loops->executor_shared->lock, NULL);
    }

    epoll_set_init(&loops->hot_epoll);
    epoll_set_init(&loops->cold_epoll);

    loops->timer_fd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
    if (loops->timer_fd < 0) {
        perror("timerfd_create");
        return -1;
    }

    return 0;
}

/* Stop the event loops and close all fds (timer, eventfd, sockets, epolls). */
void event_loops_destroy(event_loops_t *loops) {
    loops->running = false;
    if (loops->timer_fd >= 0) close(loops->timer_fd);
    if (loops->executor_shared) {
        pthread_mutex_destroy(&loops->executor_shared->lock);
        free(loops->executor_shared);
        loops->executor_shared = NULL;
    }
    if (loops->hot_epoll.epoll_fd >= 0) close(loops->hot_epoll.epoll_fd);
    if (loops->cold_epoll.epoll_fd >= 0) close(loops->cold_epoll.epoll_fd);
}

static void arm_ping_timer(event_loops_t *loops, uint64_t interval_ms) {
    if (interval_ms == 0) return;
    struct itimerspec its = {0};
    its.it_value.tv_sec = interval_ms / 1000;
    its.it_value.tv_nsec = (interval_ms % 1000) * 1000000;
    timerfd_settime(loops->timer_fd, 0, &its, NULL);
}

/*
 * HOT thread: epoll-driven WebSocket I/O.
 * Monitors WS connection fds for incoming data and ping timer for keep-alive.
 * Sends ping frames to all connected WS connections on timer expiry.
 */
void *event_hot_thread(void *arg) {
    event_loops_t *loops = (event_loops_t *)arg;
    ws_client_t *ws = loops->ws_client;

    log_write("[HOT] Thread started\n");

    for (uint32_t i = 0; i < ws->connection_count; i++) {
        ws_connection_t *conn = &ws->connections[i];
        if (conn->fd >= 0) {
            set_nonblocking(conn->fd);
            event_loops_add_fd(&loops->hot_epoll, conn->fd, FD_TYPE_WS, i, NULL, EPOLLIN);
        }
    }

    if (ws->connections[0].ping_interval_ms > 0) {
        event_loops_add_fd(&loops->hot_epoll, loops->timer_fd, FD_TYPE_TIMER,
                           0, NULL, EPOLLIN);
        arm_ping_timer(loops, ws->connections[0].ping_interval_ms);
    }

    while (loops->running) {
        int nfds = epoll_wait(loops->hot_epoll.epoll_fd,
                              loops->hot_epoll.events, MAX_EPOLL_FDS, 100);
        if (nfds < 0) {
            if (errno == EINTR) continue;
            perror("epoll_wait hot");
            break;
        }

        for (int i = 0; i < nfds; i++) {
            tracked_fd_t *tf = (tracked_fd_t *)loops->hot_epoll.events[i].data.ptr;
            if (!tf || tf->fd < 0) continue;

            if (tf->type == FD_TYPE_WS) {
                ws_client_read(ws, tf->ws_conn_idx);
            } else if (tf->type == FD_TYPE_TIMER) {
                uint64_t expirations = 0;
                if (read(loops->timer_fd, &expirations, sizeof(expirations)) < 0) {}

                for (uint32_t c = 0; c < ws->connection_count; c++) {
                    ws_connection_t *conn = &ws->connections[c];
                    if (conn->state == WS_STATE_CONNECTED) {
                        ws_client_send_ping(conn);
                    }
                }

                if (ws->connections[0].ping_interval_ms > 0) {
                    arm_ping_timer(loops, ws->connections[0].ping_interval_ms);
                }
            }
        }
    }

    log_write("[HOT] Thread exited\n");
    return NULL;
}

/*
 * Per-executor-thread entry point: creates its own executor_thread_t,
 * polls its private slot eventfd + the shared fill channel eventfd,
 * and executes one triangle per signal.
 */
void *event_executor_thread(void *arg) {
    executor_thread_arg_t *ta = (executor_thread_arg_t *)arg;
    event_loops_t *loops = ta->loops;
    executor_slot_t *slot = ta->slot;

    executor_thread_t *exec = executor_thread_create(loops->ws_client->cfg,
                                                       loops->ws_client->fill_ch,
                                                       loops->ws_client,
                                                       loops->executor_shared,
                                                       slot);
    if (!exec) {
        log_write("[EXEC] Failed to create executor\n");
        return NULL;
    }

    int fill_wake_fd = fill_channel_wake_fd(loops->ws_client->fill_ch);
    struct pollfd pfds[2];
    memset(pfds, 0, sizeof(pfds));
    pfds[0].fd = slot->eventfd;
    pfds[0].events = POLLIN;
    pfds[1].fd = fill_wake_fd;
    pfds[1].events = POLLIN;

    int64_t last_keepalive_ms = 0;

    while (loops->running) {
        /* Fast path: check slot state without poll */
        if (atomic_load_explicit(&slot->state, memory_order_acquire) == EXECUTOR_SLOT_READY) {
            signal_entry_t sig = slot->signal;
            atomic_store_explicit(&slot->state, EXECUTOR_SLOT_FREE, memory_order_release);
            /* Drain eventfd so poll can block next time */
            uint64_t val;
            if (read(slot->eventfd, &val, sizeof(val)) < 0) {}

            executor_execute_triangle(exec, &sig);

            int64_t now = now_mono_ms();
            if (last_keepalive_ms == 0 || now - last_keepalive_ms >= 30000) {
                executor_keepalive(exec);
                last_keepalive_ms = now_mono_ms();
            }
            continue;
        }

        /* Slow path: poll with 30s timeout for keepalive */
        int poll_timeout = 30000;
        if (last_keepalive_ms == 0) poll_timeout = 100;

        int nfds = poll(pfds, 2, poll_timeout);
        if (nfds < 0) {
            if (errno == EINTR) continue;
            log_write("[EXEC] poll error: %s\n", strerror(errno));
            break;
        }

        /* Drain slot eventfd */
        if (pfds[0].revents & POLLIN) {
            uint64_t val;
            if (read(slot->eventfd, &val, sizeof(val)) < 0) {}
        }
        /* Drain fill channel wake */
        if (pfds[1].revents & POLLIN) {
            uint64_t val;
            if (read(fill_wake_fd, &val, sizeof(val)) < 0) {}
        }

        /* Keepalive */
        int64_t now = now_mono_ms();
        if (last_keepalive_ms == 0 || now - last_keepalive_ms >= 30000) {
            executor_keepalive(exec);
            last_keepalive_ms = now_mono_ms();
        }
    }

    executor_thread_destroy(exec);
    log_write("[EXEC] Thread exited\n");
    return NULL;
}

/* Legacy single-thread entry point — delegates to event_executor_thread semantics
   but creates its own shared state. */
void *event_cold_thread(void *arg) {
    return event_executor_thread(arg);
}