// Copyright (C) 2014-2015 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#include <config.h>

#include <asiolink/asiolink.h>
#include <dhcpsrv/cfgmgr.h>
#include <dhcpsrv/parsers/dhcp_config_parser.h>
#include <dhcp6/json_config_parser.h>
#include <dhcp6/ctrl_dhcp6_srv.h>
#include <dhcp6/dhcp6_log.h>
#include <exceptions/exceptions.h>

#include <signal.h>

#include <string>

using namespace isc::asiolink;
using namespace isc::dhcp;
using namespace std;

namespace {

/// @brief Configure DHCPv6 server using the configuration file specified.
///
/// This function is used to both configure the DHCP server on its startup
/// and dynamically reconfigure the server when SIGHUP signal is received.
///
/// It fetches DHCPv6 server's configuration from the 'Dhcp6' section of
/// the JSON configuration file.
///
/// @param file_name Configuration file location.
void configure(const std::string& file_name) {
    // This is a configuration backend implementation that reads the
    // configuration from a JSON file.

    // We are starting the configuration process so we should remove any
    // staging configuration that has been created during previous
    // configuration attempts.
    CfgMgr::instance().rollback();

    isc::data::ConstElementPtr json;
    isc::data::ConstElementPtr dhcp6;
    isc::data::ConstElementPtr logger;
    isc::data::ConstElementPtr result;

    // Basic sanity check: file name must not be empty.
    try {
        if (file_name.empty()) {
            // Basic sanity check: file name must not be empty.
            isc_throw(isc::BadValue, "JSON configuration file not specified. Please "
                      "use -c command line option.");
        }

        // Read contents of the file and parse it as JSON
        json = isc::data::Element::fromJSONFile(file_name, true);
        if (!json) {
            isc_throw(isc::BadValue, "no configuration found");
        }

        // Let's do sanity check before we call json->get() which
        // works only for map.
        if (json->getType() != isc::data::Element::map) {
            isc_throw(isc::BadValue, "Configuration file is expected to be "
                      "a map, i.e., start with { and end with } and contain "
                      "at least an entry called 'Dhcp6' that itself is a map. "
                      << file_name
                      << " is a valid JSON, but its top element is not a map."
                      " Did you forget to add { } around your configuration?");
        }

        // Use parsed JSON structures to configure the server
        result = ControlledDhcpv6Srv::processCommand("set-config", json);
        if (!result) {
            // Undetermined status of the configuration. This should never
            // happen, but as the configureDhcp6Server returns a pointer, it is
            // theoretically possible that it will return NULL.
            isc_throw(isc::BadValue, "undefined result of "
                      "processCommand(\"set-config\", dhcp6)");
        }

        // Now check is the returned result is successful (rcode=0) or not
        // (see @ref isc::config::parseAnswer).
        int rcode;
        isc::data::ConstElementPtr comment =
            isc::config::parseAnswer(rcode, result);
        if (rcode != 0) {
            string reason = comment ? comment->stringValue() :
                "no details available";
            isc_throw(isc::BadValue, reason);
        }
    }  catch (const std::exception& ex) {
        // If configuration failed at any stage, we drop the staging
        // configuration and continue to use the previous one.
        CfgMgr::instance().rollback();

        LOG_ERROR(dhcp6_logger, DHCP6_CONFIG_LOAD_FAIL)
            .arg(file_name).arg(ex.what());
        isc_throw(isc::BadValue, "configuration error using file '"
                  << file_name << "': " << ex.what());
    }
}

/// @brief Signals handler for DHCPv6 server.
///
/// This signal handler handles the following signals received by the DHCPv6
/// server process:
/// - SIGHUP - triggers server's dynamic reconfiguration.
/// - SIGTERM - triggers server's shut down.
/// - SIGINT - triggers server's shut down.
///
/// @param signo Signal number received.
void signalHandler(int signo) {
    // SIGHUP signals a request to reconfigure the server.
    if (signo == SIGHUP) {
        // Get configuration file name.
        std::string file = ControlledDhcpv6Srv::getInstance()->getConfigFile();
        try {
            LOG_INFO(dhcp6_logger, DHCP6_DYNAMIC_RECONFIGURATION).arg(file);
            configure(file);
        } catch (const std::exception& ex) {
            // Log the unsuccessful reconfiguration. The reason for failure
            // should be already logged. Don't rethrow an exception so as
            // the server keeps working.
            LOG_ERROR(dhcp6_logger, DHCP6_DYNAMIC_RECONFIGURATION_FAIL)
                .arg(file);
        }
    } else if ((signo == SIGTERM) || (signo == SIGINT)) {
        isc::data::ElementPtr params(new isc::data::MapElement());
        ControlledDhcpv6Srv::processCommand("shutdown", params);
    }
}

}

namespace isc {
namespace dhcp {

void
ControlledDhcpv6Srv::init(const std::string& file_name) {
    // Configure the server using JSON file.
    configure(file_name);

    // We don't need to call openActiveSockets() or startD2() as these
    // methods are called in processConfig() which is called by
    // processCommand("reload-config", ...)

    // Set signal handlers. When the SIGHUP is received by the process
    // the server reconfiguration will be triggered. When SIGTERM or
    // SIGINT will be received, the server will start shutting down.
    signal_set_.reset(new isc::util::SignalSet(SIGINT, SIGHUP, SIGTERM));
    // Set the pointer to the handler function.
    signal_handler_ = signalHandler;
}

void ControlledDhcpv6Srv::cleanup() {
    // Nothing to do here. No need to disconnect from anything.
}

};
};