#include "DNSResolver.h"
#include <base/CachedFn.h>
#include <Common/Exception.h>
#include <Common/ProfileEvents.h>
#include <Core/Names.h>
#include <base/types.h>
#include <Poco/Net/IPAddress.h>
#include <Poco/Net/DNS.h>
#include <Poco/Net/NetException.h>
#include <Poco/NumberParser.h>
#include <arpa/inet.h>
#include <atomic>
#include <optional>
#include <string_view>

namespace ProfileEvents
{
    extern const Event DNSError;
}

namespace std
{
template<> struct hash<Poco::Net::IPAddress>
{
    size_t operator()(const Poco::Net::IPAddress & address) const noexcept
    {
        std::string_view addr(static_cast<const char *>(address.addr()), address.length());
        std::hash<std::string_view> hash_impl;
        return hash_impl(addr);
    }
};
}

namespace DB
{

namespace ErrorCodes
{
    extern const int BAD_ARGUMENTS;
    extern const int DNS_ERROR;
}


/// Slightly altered implementation from https://github.com/pocoproject/poco/blob/poco-1.6.1/Net/src/SocketAddress.cpp#L86
static void splitHostAndPort(const std::string & host_and_port, std::string & out_host, UInt16 & out_port)
{
    String port_str;
    out_host.clear();

    auto it = host_and_port.begin();
    auto end = host_and_port.end();

    if (*it == '[') /// Try parse case '[<IPv6 or something else>]:<port>'
    {
        ++it;
        while (it != end && *it != ']')
            out_host += *it++;
        if (it == end)
            throw Exception("Malformed IPv6 address", ErrorCodes::BAD_ARGUMENTS);
        ++it;
    }
    else /// Case '<IPv4 or domain name or something else>:<port>'
    {
        while (it != end && *it != ':')
            out_host += *it++;
    }

    if (it != end && *it == ':')
    {
        ++it;
        while (it != end)
            port_str += *it++;
    }
    else
        throw Exception("Missing port number", ErrorCodes::BAD_ARGUMENTS);

    unsigned port;
    if (Poco::NumberParser::tryParseUnsigned(port_str, port) && port <= 0xFFFF)
    {
        out_port = static_cast<UInt16>(port);
    }
    else
        throw Exception("Port must be numeric", ErrorCodes::BAD_ARGUMENTS);
}

static DNSResolver::IPAddresses hostByName(const std::string & host)
{
    /// Family: AF_UNSPEC
    /// AI_ALL is required for checking if client is allowed to connect from an address
    auto flags = Poco::Net::DNS::DNS_HINT_AI_V4MAPPED | Poco::Net::DNS::DNS_HINT_AI_ALL;
    /// Do not resolve IPv6 (or IPv4) if no local IPv6 (or IPv4) addresses are configured.
    /// It should not affect client address checking, since client cannot connect from IPv6 address
    /// if server has no IPv6 addresses.
    flags |= Poco::Net::DNS::DNS_HINT_AI_ADDRCONFIG;

    DNSResolver::IPAddresses addresses;

    try
    {
        addresses = Poco::Net::DNS::hostByName(host, flags).addresses();
    }
    catch (const Poco::Net::DNSException & e)
    {
        LOG_ERROR(&Poco::Logger::get("DNSResolver"), "Cannot resolve host ({}), error {}: {}.", host, e.code(), e.name());
        addresses.clear();
    }

    if (addresses.empty())
    {
        ProfileEvents::increment(ProfileEvents::DNSError);
        throw Exception("Not found address of host: " + host, ErrorCodes::DNS_ERROR);
    }

    return addresses;
}

static DNSResolver::IPAddresses resolveIPAddressImpl(const std::string & host)
{
    Poco::Net::IPAddress ip;

    /// NOTE:
    /// - Poco::Net::DNS::resolveOne(host) doesn't work for IP addresses like 127.0.0.2
    /// - Poco::Net::IPAddress::tryParse() expect hex string for IPv6 (without brackets)
    if (host.starts_with('['))
    {
        assert(host.ends_with(']'));
        if (Poco::Net::IPAddress::tryParse(host.substr(1, host.size() - 2), ip))
            return DNSResolver::IPAddresses(1, ip);
    }
    else
    {
        if (Poco::Net::IPAddress::tryParse(host, ip))
            return DNSResolver::IPAddresses(1, ip);
    }

    DNSResolver::IPAddresses addresses = hostByName(host);

    return addresses;
}

static String reverseResolveImpl(const Poco::Net::IPAddress & address)
{
    Poco::Net::SocketAddress sock_addr(address, 0);

    /// Resolve by hand, because Poco::Net::DNS::hostByAddress(...) does getaddrinfo(...) after getnameinfo(...)
    char host[1024];
    int err = getnameinfo(sock_addr.addr(), sock_addr.length(), host, sizeof(host), nullptr, 0, NI_NAMEREQD);
    if (err)
        throw Exception("Cannot getnameinfo(" + address.toString() + "): " + gai_strerror(err), ErrorCodes::DNS_ERROR);
    return host;
}

struct DNSResolver::Impl
{
    using HostWithConsecutiveFailures = std::unordered_map<String, UInt32>;
    using AddressWithConsecutiveFailures = std::unordered_map<Poco::Net::IPAddress, UInt32>;

    CachedFn<&resolveIPAddressImpl> cache_host;
    CachedFn<&reverseResolveImpl> cache_address;

    std::mutex drop_mutex;
    std::mutex update_mutex;

    /// Cached server host name
    std::optional<String> host_name;

    /// Store hosts, which was asked to resolve from last update of DNS cache.
    HostWithConsecutiveFailures new_hosts;
    AddressWithConsecutiveFailures new_addresses;

    /// Store all hosts, which was whenever asked to resolve
    HostWithConsecutiveFailures known_hosts;
    AddressWithConsecutiveFailures known_addresses;

    /// If disabled, will not make cache lookups, will resolve addresses manually on each call
    std::atomic<bool> disable_cache{false};
};


DNSResolver::DNSResolver() : impl(std::make_unique<DNSResolver::Impl>()), log(&Poco::Logger::get("DNSResolver")) {}

Poco::Net::IPAddress DNSResolver::resolveHost(const std::string & host)
{
    return resolveHostAll(host).front();
}

DNSResolver::IPAddresses DNSResolver::resolveHostAll(const std::string & host)
{
    if (impl->disable_cache)
        return resolveIPAddressImpl(host);

    addToNewHosts(host);
    return impl->cache_host(host);
}

Poco::Net::SocketAddress DNSResolver::resolveAddress(const std::string & host_and_port)
{
    if (impl->disable_cache)
        return Poco::Net::SocketAddress(host_and_port);

    String host;
    UInt16 port;
    splitHostAndPort(host_and_port, host, port);

    addToNewHosts(host);
    return Poco::Net::SocketAddress(impl->cache_host(host).front(), port);
}

Poco::Net::SocketAddress DNSResolver::resolveAddress(const std::string & host, UInt16 port)
{
    if (impl->disable_cache)
        return Poco::Net::SocketAddress(host, port);

    addToNewHosts(host);
    return  Poco::Net::SocketAddress(impl->cache_host(host).front(), port);
}

std::vector<Poco::Net::SocketAddress> DNSResolver::resolveAddressList(const std::string & host, UInt16 port)
{
    if (Poco::Net::IPAddress ip; Poco::Net::IPAddress::tryParse(host, ip))
        return std::vector<Poco::Net::SocketAddress>{{ip, port}};

    std::vector<Poco::Net::SocketAddress> addresses;

    if (!impl->disable_cache)
        addToNewHosts(host);

    std::vector<Poco::Net::IPAddress> ips = impl->disable_cache ? hostByName(host) : impl->cache_host(host);
    auto ips_end = std::unique(ips.begin(), ips.end());

    addresses.reserve(ips_end - ips.begin());
    for (auto ip = ips.begin(); ip != ips_end; ++ip)
        addresses.emplace_back(*ip, port);

    return addresses;
}

String DNSResolver::reverseResolve(const Poco::Net::IPAddress & address)
{
    if (impl->disable_cache)
        return reverseResolveImpl(address);

    addToNewAddresses(address);
    return impl->cache_address(address);
}

void DNSResolver::dropCache()
{
    impl->cache_host.drop();
    impl->cache_address.drop();

    std::scoped_lock lock(impl->update_mutex, impl->drop_mutex);

    impl->known_hosts.clear();
    impl->known_addresses.clear();
    impl->new_hosts.clear();
    impl->new_addresses.clear();
    impl->host_name.reset();
}

void DNSResolver::setDisableCacheFlag(bool is_disabled)
{
    impl->disable_cache = is_disabled;
}

String DNSResolver::getHostName()
{
    if (impl->disable_cache)
        return Poco::Net::DNS::hostName();

    std::lock_guard lock(impl->drop_mutex);

    if (!impl->host_name.has_value())
        impl->host_name.emplace(Poco::Net::DNS::hostName());

    return *impl->host_name;
}

static const String & cacheElemToString(const String & str) { return str; }
static String cacheElemToString(const Poco::Net::IPAddress & addr) { return addr.toString(); }

template <typename UpdateF, typename ElemsT>
bool DNSResolver::updateCacheImpl(
    UpdateF && update_func,
    ElemsT && elems,
    UInt32 max_consecutive_failures,
    const String & notfound_log_msg,
    const String & dropped_log_msg)
{
    bool updated = false;
    String lost_elems;
    using iterators = typename std::remove_reference_t<decltype(elems)>::iterator;
    std::vector<iterators> elements_to_drop;
    for (auto it = elems.begin(); it != elems.end(); it++)
    {
        try
        {
            updated |= (this->*update_func)(it->first);
            it->second = 0;
        }
        catch (const DB::Exception & e)
        {
            if (e.code() != ErrorCodes::DNS_ERROR)
            {
                tryLogCurrentException(log, __PRETTY_FUNCTION__);
                continue;
            }
            if (!lost_elems.empty())
                lost_elems += ", ";
            lost_elems += cacheElemToString(it->first);
            if (max_consecutive_failures)
            {
                it->second++;
                if (it->second >= max_consecutive_failures)
                    elements_to_drop.emplace_back(it);
            }
        }
        catch (...)
        {
            tryLogCurrentException(log, __PRETTY_FUNCTION__);
        }
    }

    if (!lost_elems.empty())
        LOG_INFO(log, fmt::runtime(notfound_log_msg), lost_elems);
    if (elements_to_drop.size())
    {
        updated = true;
        String deleted_elements;
        for (auto it : elements_to_drop)
        {
            if (!deleted_elements.empty())
                deleted_elements += ", ";
            deleted_elements += cacheElemToString(it->first);
            elems.erase(it);
        }
        LOG_INFO(log, fmt::runtime(dropped_log_msg), deleted_elements);
    }

    return updated;
}

bool DNSResolver::updateCache(UInt32 max_consecutive_failures)
{
    LOG_DEBUG(log, "Updating DNS cache");

    {
        String updated_host_name = Poco::Net::DNS::hostName();

        std::lock_guard lock(impl->drop_mutex);

        for (const auto & host : impl->new_hosts)
            impl->known_hosts.insert(host);
        impl->new_hosts.clear();

        for (const auto & address : impl->new_addresses)
            impl->known_addresses.insert(address);
        impl->new_addresses.clear();

        impl->host_name.emplace(updated_host_name);
    }

    /// FIXME Updating may take a long time because we cannot manage timeouts of getaddrinfo(...) and getnameinfo(...).
    /// DROP DNS CACHE will wait on update_mutex (possibly while holding drop_mutex)
    std::lock_guard lock(impl->update_mutex);

    bool hosts_updated = updateCacheImpl(
        &DNSResolver::updateHost, impl->known_hosts, max_consecutive_failures, "Cached hosts not found: {}", "Cached hosts dropped: {}");
    updateCacheImpl(
        &DNSResolver::updateAddress,
        impl->known_addresses,
        max_consecutive_failures,
        "Cached addresses not found: {}",
        "Cached addresses dropped: {}");

    LOG_DEBUG(log, "Updated DNS cache");
    return hosts_updated;
}

bool DNSResolver::updateHost(const String & host)
{
    /// Usage of updateHost implies that host is already in cache and there is no extra computations
    auto old_value = impl->cache_host(host);
    impl->cache_host.update(host);
    return old_value != impl->cache_host(host);
}

bool DNSResolver::updateAddress(const Poco::Net::IPAddress & address)
{
    auto old_value = impl->cache_address(address);
    impl->cache_address.update(address);
    return old_value == impl->cache_address(address);
}

void DNSResolver::addToNewHosts(const String & host)
{
    std::lock_guard lock(impl->drop_mutex);
    UInt8 consecutive_failures = 0;
    impl->new_hosts.insert({host, consecutive_failures});
}

void DNSResolver::addToNewAddresses(const Poco::Net::IPAddress & address)
{
    std::lock_guard lock(impl->drop_mutex);
    UInt8 consecutive_failures = 0;
    impl->new_addresses.insert({address, consecutive_failures});
}

DNSResolver::~DNSResolver() = default;

DNSResolver & DNSResolver::instance()
{
    static DNSResolver ret;
    return ret;
}

}