#include <arpa/inet.h>
#include <chrono>
#include <cstring>
#include <filesystem>
#include <fstream>
#include <netinet/in.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <unistd.h>
#include <vector>

#include <nxst/service/transfer_service.hpp>

#ifdef __SWITCH__
#include <switch.h>

#include <nxst/domain/account.hpp>
#include <nxst/domain/util.hpp>
#include <nxst/infra/fs/io.hpp>
#endif

#include <nxst/domain/protocol.hpp>
#include <nxst/infra/net/socket.hpp>

namespace fs = std::filesystem;

namespace nxst {

// ─── File-transfer helpers ────────────────────────────────────────────────────

static bool sendAll(int sock, const void* buf, size_t len) {
    size_t sent = 0;
    while (sent < len) {
        ssize_t n = send(sock, static_cast<const char*>(buf) + sent, len - sent, 0);
        if (n <= 0)
            return false;
        sent += n;
    }
    return true;
}

static bool recvAll(int sock, void* buf, size_t len) {
    size_t got = 0;
    while (got < len) {
        ssize_t n = read(sock, static_cast<char*>(buf) + got, len - got);
        if (n <= 0)
            return false;
        got += n;
    }
    return true;
}

static bool sendFile(int sock, const fs::path& filepath, TransferState& state) {
    std::ifstream infile(filepath, std::ios::binary | std::ios::ate);
    if (!infile.is_open())
        return false;

    uint32_t filename_len = (uint32_t)filepath.string().size();
    uint64_t file_size = (uint64_t)infile.tellg();
    infile.seekg(0, std::ios::beg);

    if (!sendAll(sock, &filename_len, sizeof(filename_len)))
        return false;
    if (!sendAll(sock, filepath.c_str(), filename_len))
        return false;
    if (!sendAll(sock, &file_size, sizeof(file_size)))
        return false;

    std::vector<char> buffer(proto::BUF_SIZE);
    uint64_t remaining = file_size;
    while (remaining > 0) {
        size_t to_read = (size_t)std::min(remaining, (uint64_t)proto::BUF_SIZE);
        infile.read(buffer.data(), (std::streamsize)to_read);
        std::streamsize count = infile.gcount();
        if (count <= 0)
            break;
        if (!sendAll(sock, buffer.data(), (size_t)count))
            return false;
        state.bytes_done.fetch_add((uint64_t)count);
        remaining -= (uint64_t)count;
    }
    return true;
}

static void mkdirs(const std::string& path) {
    for (size_t i = 1; i < path.size(); i++) {
        if (path[i] == '/') {
            std::string component = path.substr(0, i);
            mkdir(component.c_str(), 0777);
        }
    }
    mkdir(path.c_str(), 0777);
}

static void receiveFile(int sock, const std::string& rel_path, uint64_t file_size, TransferState& state) {
    size_t last_slash = rel_path.rfind('/');
    if (last_slash != std::string::npos) {
        std::string dir = rel_path.substr(0, last_slash);
        if (!dir.empty())
            mkdirs(dir);
    }

    FILE* outfile = fopen(rel_path.c_str(), "wb");
    if (!outfile) {
        std::vector<char> drain(proto::BUF_SIZE);
        uint64_t remaining = file_size;
        while (remaining > 0) {
            size_t to_read = (size_t)std::min(remaining, (uint64_t)proto::BUF_SIZE);
            ssize_t n = read(sock, drain.data(), to_read);
            if (n <= 0)
                break;
            remaining -= (uint64_t)n;
        }
        return;
    }

    state.bytes_total.store(file_size);
    state.bytes_done.store(0);

    std::vector<char> buffer(proto::BUF_SIZE);
    uint64_t total = 0;
    while (total < file_size) {
        size_t to_read = (size_t)std::min(file_size - total, (uint64_t)proto::BUF_SIZE);
        ssize_t n = read(sock, buffer.data(), to_read);
        if (n <= 0)
            break;
        fwrite(buffer.data(), 1, (size_t)n, outfile);
        total += (uint64_t)n;
        state.bytes_done.store(total);
    }
    fclose(outfile);
}

// ─── Sender ──────────────────────────────────────────────────────────────────

void TransferService::failSend(const std::string& reason) {
    sender_state.fail_reason = reason;
    sender_state.connection_failed.store(true);
    sender_state.done.store(true);
}

int TransferService::findServer(char* out_ip) {
    int udp_fd = socket(AF_INET, SOCK_DGRAM, 0);
    if (udp_fd < 0)
        return -1;
    sender_udp_sock.store(udp_fd);

    auto releaseUdp = [&]() {
        int owned = sender_udp_sock.exchange(-1);
        if (owned == udp_fd)
            close(udp_fd);
    };

    sockaddr_in addr{};
    addr.sin_family = AF_INET;
    addr.sin_port = htons(proto::MULTICAST_PORT);
    addr.sin_addr.s_addr = inet_addr(proto::MULTICAST_GROUP);

    if (sendto(udp_fd, "DISCOVER_SERVER", 15, 0, (sockaddr*)&addr, sizeof(addr)) < 0) {
        releaseUdp();
        return -1;
    }

    // Poll in 100ms slices so cancel races within 100ms
    auto deadline = std::chrono::steady_clock::now() + std::chrono::seconds(3);
    while (std::chrono::steady_clock::now() < deadline) {
        if (sender_state.cancelled.load()) {
            releaseUdp();
            return -1;
        }
        struct timeval tv{0, 100000};
        fd_set fds;
        FD_ZERO(&fds);
        FD_SET(udp_fd, &fds);
        if (select(udp_fd + 1, &fds, nullptr, nullptr, &tv) > 0) {
            sockaddr_in from{};
            socklen_t fromlen = sizeof(from);
            char buf[256];
            ssize_t n = recvfrom(udp_fd, buf, sizeof(buf) - 1, 0, (sockaddr*)&from, &fromlen);
            if (n > 0) {
                buf[n] = '\0';
                if (strcmp(buf, "SERVER_HERE") == 0) {
                    inet_ntop(AF_INET, &from.sin_addr, out_ip, INET_ADDRSTRLEN);
                    releaseUdp();
                    return 0;
                }
            }
        }
    }
    releaseUdp();
    return -1;
}

void* TransferService::senderEntry(void* arg) {
    auto* a = static_cast<SenderArgs*>(arg);
    TransferService* svc = a->svc;
    size_t idx = a->title_index;
    AccountUid uid = a->uid;
    delete a;
    svc->runSender(idx, uid);
    return nullptr;
}

void TransferService::runSender(size_t title_index, AccountUid uid) {
    sender_active.store(true);

    auto finish = [this]() {
        sender_state.done.store(true);
        sender_active.store(false);
    };

    char server_ip[INET_ADDRSTRLEN];
    if (findServer(server_ip) != 0) {
        if (!sender_state.cancelled.load())
            failSend("No receiver found.\nMake sure the other Switch is in Receive mode.");
        return finish();
    }
    if (sender_state.cancelled.load())
        return finish();

    sender_state.setStatus("Creating backup...");
#ifdef __SWITCH__
    auto backup_result = io::backup(title_index, uid);
    if (!backup_result.isOk()) {
        failSend("Failed to create backup:\n" + backup_result.error());
        return finish();
    }
    fs::path directory = backup_result.value();
#else
    fs::path directory = ".";
    (void)title_index;
    (void)uid;
#endif

    if (sender_state.cancelled.load())
        return finish();

    sender_state.setStatus("Connecting...");
    int tcp_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (tcp_fd < 0) {
        failSend("Failed to open socket.");
        return finish();
    }
    sender_tcp_sock.store(tcp_fd);

    auto releaseTcp = [&]() {
        int owned = sender_tcp_sock.exchange(-1);
        if (owned == tcp_fd)
            close(tcp_fd);
    };

    sockaddr_in serv{};
    serv.sin_family = AF_INET;
    serv.sin_port = htons(proto::TCP_PORT);
    if (inet_pton(AF_INET, server_ip, &serv.sin_addr) <= 0 ||
        connect(tcp_fd, (sockaddr*)&serv, sizeof(serv)) < 0) {
        if (!sender_state.cancelled.load())
            failSend("Failed to connect to receiver.");
        releaseTcp();
        return finish();
    }

    uint64_t total = 0;
    for (const auto& entry : fs::recursive_directory_iterator(directory))
        if (fs::is_regular_file(entry.path()))
            total += fs::file_size(entry.path());
    sender_state.bytes_total.store(total);

    for (const auto& entry : fs::recursive_directory_iterator(directory)) {
        if (sender_state.cancelled.load())
            break;
        const fs::path& p = entry.path();
        if (fs::is_regular_file(p)) {
            sender_state.setStatus(p.filename().string());
            if (!sendFile(tcp_fd, p, sender_state))
                break;
        }
    }

    uint32_t sentinel = proto::EOF_SENTINEL;
    sendAll(tcp_fd, &sentinel, sizeof(sentinel));

    releaseTcp();
    sender_state.setStatus("");
    return finish();
}

int TransferService::startSend(size_t title_index, AccountUid uid) {
    sender_state.reset();
    sender_state.setStatus("Searching for receiver...");

    auto* arg = new SenderArgs{this, title_index, uid};
    pthread_t thread;
    if (pthread_create(&thread, nullptr, senderEntry, arg) != 0) {
        delete arg;
        return -1;
    }
    pthread_detach(thread);
    return 0;
}

void TransferService::cancelSend() {
    sender_state.cancelled.store(true);
    int udp = sender_udp_sock.exchange(-1);
    if (udp >= 0) {
        shutdown(udp, SHUT_RDWR);
        close(udp);
    }
    int tcp = sender_tcp_sock.exchange(-1);
    if (tcp >= 0) {
        shutdown(tcp, SHUT_RDWR);
        close(tcp);
    }
}

// ─── Receiver ────────────────────────────────────────────────────────────────

std::string TransferService::replaceUsername(const std::string& file_path) const {
#ifdef __SWITCH__
    std::string username =
        StringUtils::removeNotAscii(StringUtils::removeAccents(Account::username(restore_uid)));
    size_t last_slash = file_path.rfind('/');
    if (last_slash == std::string::npos)
        return file_path;
    size_t prev_slash = file_path.rfind('/', last_slash - 1);
    if (prev_slash == std::string::npos)
        return username + file_path.substr(last_slash);
    return file_path.substr(0, prev_slash + 1) + username + file_path.substr(last_slash);
#else
    return file_path;
#endif
}

void* TransferService::broadcastEntry(void* arg) {
    static_cast<TransferService*>(arg)->runBroadcast();
    return nullptr;
}

void TransferService::runBroadcast() {
    receiver_broadcast_active.store(true);
    pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, nullptr);
    pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, nullptr);

    int udp = socket(AF_INET, SOCK_DGRAM, 0);
    if (udp < 0) {
        receiver_broadcast_active.store(false);
        return;
    }
    receiver_bcast_sock.store(udp);

    auto releaseUdp = [&]() {
        int owned = receiver_bcast_sock.exchange(-1);
        if (owned == udp)
            close(udp);
    };

    struct timeval tv{0, 20000};  // 20ms poll so cancel/exit wins race with socketExit
    setsockopt(udp, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));

    sockaddr_in addr{};
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_port = htons(proto::MULTICAST_PORT);

    if (bind(udp, (sockaddr*)&addr, sizeof(addr)) < 0) {
        releaseUdp();
        receiver_broadcast_active.store(false);
        return;
    }

    ip_mreq group{};
    group.imr_multiaddr.s_addr = inet_addr(proto::MULTICAST_GROUP);
    group.imr_interface.s_addr = htonl(INADDR_ANY);
    if (setsockopt(udp, IPPROTO_IP, IP_ADD_MEMBERSHIP, &group, sizeof(group)) < 0) {
        releaseUdp();
        receiver_broadcast_active.store(false);
        return;
    }

    char buf[256];
    sockaddr_in from{};
    socklen_t fromlen = sizeof(from);
    while (true) {
        ssize_t n = recvfrom(udp, buf, sizeof(buf) - 1, 0, (sockaddr*)&from, &fromlen);
        if (n < 0) {
            if (receiver_state.cancelled.load())
                break;
            continue;
        }
        buf[n] = '\0';
        if (strcmp(buf, "DISCOVER_SERVER") == 0) {
            sendto(udp, "SERVER_HERE", 11, 0, (sockaddr*)&from, fromlen);
            break;
        }
    }

    releaseUdp();
    receiver_broadcast_active.store(false);
}

void* TransferService::acceptEntry(void* arg) {
    auto* a = static_cast<AcceptArgs*>(arg);
    TransferService* svc = a->svc;
    int server_fd = a->server_fd;
    delete a;
    svc->runAccept(server_fd);
    return nullptr;
}

void TransferService::runAccept(int server_fd) {
    receiver_accept_active.store(true);
    receiver_listen_sock.store(server_fd);

    sockaddr_in client_addr{};
    socklen_t client_len = sizeof(client_addr);
    int client_sock = accept(server_fd, (sockaddr*)&client_addr, &client_len);

    int owned_listen = receiver_listen_sock.exchange(-1);
    if (owned_listen == server_fd)
        close(server_fd);

    if (client_sock >= 0) {
        receiver_client_sock.store(client_sock);

        while (true) {
            uint32_t filename_len = 0;
            if (!recvAll(client_sock, &filename_len, sizeof(filename_len)))
                break;
            if (filename_len == proto::EOF_SENTINEL)
                break;
            if (filename_len > proto::MAX_FILENAME)
                break;

            std::vector<char> filename_buf(filename_len + 1, '\0');
            if (!recvAll(client_sock, filename_buf.data(), filename_len))
                break;
            std::string filename_str(filename_buf.data(), filename_len);
            filename_str = replaceUsername(filename_str);

            {
                size_t sl = filename_str.rfind('/');
                receiver_state.setStatus(sl != std::string::npos ? filename_str.substr(sl + 1)
                                                                 : filename_str);
            }

            uint64_t file_size = 0;
            if (!recvAll(client_sock, &file_size, sizeof(file_size)))
                break;
            receiveFile(client_sock, filename_str, file_size, receiver_state);
        }

        int owned = receiver_client_sock.exchange(-1);
        if (owned == client_sock)
            close(client_sock);

        if (!receiver_state.cancelled.load()) {
#ifdef __SWITCH__
            receiver_state.setStatus("Restoring...");
            auto result = io::restore(restore_title_index, restore_uid, 0, restore_title_name);
            restore_ok = result.isOk();
            restore_error = result.isOk() ? "" : result.error();
#else
            restore_ok = true;
#endif
        }
    }

    receiver_state.done.store(true);
    receiver_accept_active.store(false);
}

int TransferService::startReceive(size_t title_index, AccountUid uid, std::string title_name) {
    receiver_state.reset();
    receiver_state.setStatus("Waiting for connection...");
    restore_title_index = title_index;
    restore_uid = uid;
    restore_title_name = std::move(title_name);
    restore_ok = false;
    restore_error.clear();

    pthread_t bcast_thread;
    if (pthread_create(&bcast_thread, nullptr, broadcastEntry, this) != 0)
        return 1;
    receiver_bcast_thread = bcast_thread;
    pthread_detach(bcast_thread);

    Socket server(socket(AF_INET, SOCK_STREAM, 0));
    if (!server.valid()) {
        cancelReceive();
        return 1;
    }

    int yes = 1;
    setsockopt(server, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));

    sockaddr_in addr{};
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = INADDR_ANY;
    addr.sin_port = htons(proto::TCP_PORT);

    if (bind(server, (sockaddr*)&addr, sizeof(addr)) < 0 || listen(server, 3) < 0) {
        cancelReceive();
        return 1;
    }

    auto* acc_args = new AcceptArgs{this, server.fd};
    pthread_t accept_thread;
    if (pthread_create(&accept_thread, nullptr, acceptEntry, acc_args) != 0) {
        delete acc_args;
        cancelReceive();
        return 1;
    }
    pthread_detach(accept_thread);
    server.release();
    return 0;
}

void TransferService::cancelReceive() {
    receiver_state.cancelled.store(true);
    int sock = receiver_client_sock.exchange(-1);
    if (sock >= 0) {
        shutdown(sock, SHUT_RDWR);
        close(sock);
    }
    int lsock = receiver_listen_sock.exchange(-1);
    if (lsock >= 0) {
        shutdown(lsock, SHUT_RDWR);
        close(lsock);
    }
    int bsock = receiver_bcast_sock.exchange(-1);
    if (bsock >= 0) {
        shutdown(bsock, SHUT_RDWR);
        close(bsock);
    }
    if (receiver_broadcast_active.load())
        pthread_cancel(receiver_bcast_thread);
}

}  // namespace nxst