#include <c_TcpEpollReactor.h>
#include "c_TcpServer.h"

#if defined(__linux__)
#include <sys/epoll.h>
#include <unistd.h>
#include <string.h>

#define MAX_EPOLL_EVENTS 1024

typedef struct {
    c_TcpReactor_t base;
    int            epoll_fd;      /* Raw Linux epoll kernel handle instance descriptor */
    struct epoll_event events[MAX_EPOLL_EVENTS]; /* Pre-allocated active kernel alerts buffer */
    c_Allocator_t  allocator;     /* Deep copy of the user-provided allocator */
} c_EPollReactorImpl_t;

static c_err_t EPoll_Add(c_TcpReactor_t* self, c_socket_t sock, uint32_t events) {
    c_EPollReactorImpl_t* impl = (c_EPollReactorImpl_t*)self;

    struct epoll_event ev;
    memset(&ev, 0, sizeof(ev));
    /* Map incoming events to POLLIN / read data availability triggers */
    ev.events = (events ? EPOLLIN : 0) | EPOLLERR | EPOLLHUP;
    ev.data.fd = (int)sock;

    if (epoll_ctl(impl->epoll_fd, EPOLL_CTL_ADD, (int)sock, &ev) < 0) {
        return C_ERR_FAIL;
    }
    return C_SUCCESS;
}

static c_err_t EPoll_Remove(c_TcpReactor_t* self, c_socket_t sock) {
    c_EPollReactorImpl_t* impl = (c_EPollReactorImpl_t*)self;

    /* Passing NULL for the epoll_event structure is valid for deletions since Linux 2.6.9 */
    if (epoll_ctl(impl->epoll_fd, EPOLL_CTL_DEL, (int)sock, NULL) < 0) {
        return C_ERR_NOTFOUND;
    }
    return C_SUCCESS;
}

static c_err_t EPoll_Poll(c_TcpReactor_t* self, int timeout_ms, c_TcpServer_t* server, void* args) {
    c_EPollReactorImpl_t* impl = (c_EPollReactorImpl_t*)self;
    if (!server->is_running) return C_SUCCESS;

    /* Intercept readiness frames directly out of the epoll kernel tree instance */
    int ret = epoll_wait(impl->epoll_fd, impl->events, MAX_EPOLL_EVENTS, timeout_ms);

    if (ret < 0) {
        if (server->fnOnError) {
            server->fnOnError(server, server->listen_sock, C_TCPSERVER_ERR_ON_POLL, args);
        }
        return C_SUCCESS;
    }
    if (ret == 0) return C_SUCCESS; /* Timeout pass, exit cleanly */

    /*
     * Iterative Forward Processing Pass:
     * Unlike arrays, epoll_wait packs active ready elements sequentially into indices 0 to ret-1.
     * This provides a strict O(1) loop traversal path that is entirely immune to index mutations.
     */
    for (int i = 0; i < ret; ++i) {
        struct epoll_event* current_ev = &impl->events[i];
        c_socket_t active_sock = (c_socket_t)current_ev->data.fd;

        /* Channel A: Master server listener handles incoming connection handshakes */
        if (active_sock == server->listen_sock) {
            if (current_ev->events & EPOLLIN) {
                c_SockAddr_t peer_addr;
                socklen_t addr_len = sizeof(peer_addr);
                c_socket_t client = accept(server->listen_sock, (struct sockaddr*)&peer_addr, &addr_len);

                if (c_Socket_IsValid(client)) {
                    bool keep = true;
                    if (server->fnOnConnect) {
                        keep = server->fnOnConnect(server, client, &peer_addr, args);
                    }
                    if (keep) {
                        EPoll_Add(self, client, 1); /* Inject new client into the red-black tree watchlist */
                    } else {
                        c_Socket_Close(client);
                    }
                } else if (server->fnOnError) {
                    server->fnOnError(server, server->listen_sock, C_TCPSERVER_ERR_ON_ACCEPT, args);
                }
            }
            if (current_ev->events & (EPOLLERR | EPOLLHUP)) {
                if (server->fnOnError) {
                    server->fnOnError(server, server->listen_sock, C_TCPSERVER_ERR_ON_POLLERR, args);
                }
            }
        }
        /* Channel B: Connected active client descriptors processing data readiness loops */
        else {
            c_bool_t keep_alive = C_TRUE;

            /* Intercept hardware-level operational error signals first */
            if (current_ev->events & EPOLLERR) {
                if (server->fnOnError) {
                    server->fnOnError(server, active_sock, C_TCPSERVER_ERR_ON_POLLERR, args);
                }
                keep_alive = C_FALSE;
            }

            if (keep_alive && (current_ev->events & EPOLLIN)) {
                /* Identify clean socket EOF drops via zero-byte peeks */
                char peek_buf;
                ssize_t peek_res = recv(active_sock, &peek_buf, 1, MSG_PEEK);

                if (peek_res == 0 || peek_res < 0) {
                    keep_alive = C_FALSE; /* Connection explicitly severed by remote peer node */
                } else if (server->fnOnRequest) {
                    keep_alive = server->fnOnRequest(server, active_sock, args);
                }
            }

            /* Clean up active client descriptor tracking states if loop signaling drops or errors out */
            if (!keep_alive || (current_ev->events & EPOLLHUP)) {
                /*
                 * Remove explicitly from epoll tracking first.
                 * Closing the socket handle automatically removes it from epoll,
                 * but manual synchronization ensures clean deterministic state tracking.
                 */
                EPoll_Remove(self, active_sock);

                if (server->fnOnDisconnect) {
                    server->fnOnDisconnect(server, active_sock, args);
                }
                c_Socket_Close(active_sock);
            }
        }
    }
    return C_SUCCESS;
}

static void EPoll_Destroy(c_TcpReactor_t* self) {
    c_EPollReactorImpl_t* impl = (c_EPollReactorImpl_t*)self;
    c_Allocator_t alloc = impl->allocator;

    if (impl->epoll_fd >= 0) {
        close(impl->epoll_fd);
    }
    c_Allocator_Free(&alloc, impl);
}

static const c_TcpReactorVtbl_t g_EPollReactorVtbl = { EPoll_Add, EPoll_Remove, EPoll_Poll, EPoll_Destroy };

/* ------------------------------------------------------------------------------------------------------------------ */
/*  */


c_err_t c_TcpEPollReactor_Create(c_TcpReactor_t** out_reactor, c_Allocator_t* allocator) {
    if (!out_reactor) return C_ERR_PARAM;
    c_Allocator_t alloc = allocator ? *allocator : c_DefaultAllocator;

    c_EPollReactorImpl_t* impl = (c_EPollReactorImpl_t*)c_Allocator_Calloc(&alloc, 1, sizeof(c_EPollReactorImpl_t));
    if (!impl) return C_ERR_NOMEM;

    /* Create the epoll instance handle (Size parameter must be > 0; ignored since Linux 2.6.8) */
    impl->epoll_fd = epoll_create(1);
    if (impl->epoll_fd < 0) {
        c_Allocator_Free(&alloc, impl);
        return C_ERR_FAIL;
    }

    impl->base.vtbl = &g_EPollReactorVtbl;
    impl->allocator = alloc;
    *out_reactor = &impl->base;
    return C_SUCCESS;
}

#endif /* __linux__ */