// Copyright (C) 2013-2021 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/.

#ifndef D2_UPDATE_MGR_H
#define D2_UPDATE_MGR_H

/// @file d2_update_mgr.h This file defines the class D2UpdateMgr.

#include <asiolink/io_service.h>
#include <d2/d2_queue_mgr.h>
#include <d2srv/nc_trans.h>
#include <d2srv/d2_cfg_mgr.h>
#include <d2srv/d2_log.h>
#include <exceptions/exceptions.h>

#include <boost/noncopyable.hpp>
#include <boost/shared_ptr.hpp>
#include <map>

namespace isc {
namespace d2 {

/// @brief Thrown if the update manager encounters a general error.
class D2UpdateMgrError : public isc::Exception {
public:
    D2UpdateMgrError(const char* file, size_t line, const char* what) :
        isc::Exception(file, line, what) { };
};

/// @brief Defines a list of transactions.
typedef std::map<TransactionKey, NameChangeTransactionPtr> TransactionList;

/// @brief D2UpdateMgr creates and manages update transactions.
///
/// D2UpdateMgr is the DHCP_DDNS task master, instantiating and then supervising
/// transactions that execute the DNS updates needed to fulfill the requests
/// (NameChangeRequests) received from DHCP_DDNS clients (e.g. DHCP servers).
///
/// D2UpdateMgr uses the services of D2QueueMgr to monitor the queue of
/// NameChangeRequests and select and dequeue requests for processing.
/// When a request is dequeued for processing it is removed from the queue and
/// wrapped in NameChangeTransaction and added to the D2UpdateMgr's list of
/// transactions.
///
/// As part of the process of forming transactions, D2UpdateMgr matches each
/// request with the appropriate list of DNS servers.  This matching is  based
/// upon request attributes, primarily the FQDN and update direction (forward
/// or reverse).  D2UpdateMgr uses the services of D2CfgMgr to match requests
/// to DNS server lists.
///
/// Once created, each transaction is responsible for carrying out the steps
/// required to fulfill its specific request.  These steps typically consist of
/// one or more DNS packet exchanges with the appropriate DNS server.  As
/// transactions complete,  D2UpdateMgr removes them from the transaction list,
/// replacing them with new transactions.
///
/// D2UpdateMgr carries out each of the above steps, with a method called
/// sweep().  This method is intended to be called as IO events complete.
/// The upper layer(s) are responsible for calling sweep in a timely and cyclic
/// manner.
///
class D2UpdateMgr : public boost::noncopyable {
public:
    /// @brief Maximum number of concurrent transactions
    /// NOTE that 32 is an arbitrary choice picked for the initial
    /// implementation.
    static const size_t MAX_TRANSACTIONS_DEFAULT = 32;

    /// @brief Constructor
    ///
    /// @param queue_mgr reference to the queue manager receiving requests
    /// @param cfg_mgr reference to the configuration manager
    /// @param io_service IO service used by the upper layer(s) to manage
    /// IO events
    /// @param max_transactions the maximum number of concurrent transactions
    ///
    /// @throw D2UpdateMgrError if either the queue manager or configuration
    /// managers are NULL, or max transactions is less than one.
    D2UpdateMgr(D2QueueMgrPtr& queue_mgr, D2CfgMgrPtr& cfg_mgr,
                asiolink::IOServicePtr& io_service,
                const size_t max_transactions = MAX_TRANSACTIONS_DEFAULT);

    /// @brief Destructor
    virtual ~D2UpdateMgr();

    /// @brief Check current transactions; start transactions for new requests.
    ///
    /// This method is the primary public interface used by the upper layer. It
    /// should be called as IO events complete.  During each invocation it does
    /// the following:
    ///
    /// - Removes all completed transactions from the transaction list.
    ///
    /// - If the request queue is not empty and the number of transactions
    /// in the transaction list has not reached maximum allowed, then select
    /// a request from the queue.
    ///
    /// - If a request was selected, start a new transaction for it and
    /// add the transaction to the list of transactions.
    void sweep();

protected:
    /// @brief Performs post-completion cleanup on completed transactions.
    ///
    /// Iterates through the list of transactions and removes any that have
    /// reached completion.  This method may expand in complexity or even
    /// disappear altogether as the implementation matures.
    void checkFinishedTransactions();

    /// @brief Starts a transaction for the next eligible request in the queue.
    ///
    /// This method will scan the request queue for the next request to
    /// dequeue.  The current implementation starts at the front of the queue
    /// and looks for the first request for whose DHCID there is no current
    /// transaction in progress.
    ///
    /// If a request is selected, it is removed from the queue and transaction
    /// is constructed for it.
    ///
    /// It is possible that no such request exists, though this is likely to be
    /// rather rare unless a system is frequently seeing requests for the same
    /// clients in quick succession.
    void pickNextJob();

    /// @brief Create a new transaction for the given request.
    ///
    /// This method will attempt to match the request to suitable DNS servers.
    /// If matching servers are found, it will instantiate a transaction for
    /// the requests, add the transaction to the transaction list, and start
    /// the transaction.
    ///
    /// If updates in a given direction are disabled requests for updates in
    /// that direction will be ignored.  For example: If a request is received
    /// which asks for updates in both directions but only forward updates are
    /// enabled; only the forward update will be attempted.  Effectively, the
    /// request will be treated as if it only asked for forward updates.
    ///
    /// If updates in a given direction are enabled, and a request asks for
    /// updates in that direction, failing to match the request to a list
    /// of servers is an error which will be logged and the request will be
    /// discarded.
    ///
    /// Finally, If conflict resolution is enabled, it will instantiate either
    /// a NameAddTransaction or a NameRemoveTransaction. If disabled it will
    /// instantiate either a SimpleAddTransaction or a SimpleRemoveTransaction.
    ///
    /// @param ncr the NameChangeRequest for which to create a transaction.
    ///
    /// @throw D2UpdateMgrError if a transaction for this DHCID already
    /// exists. Note this would be programmatic error.
    void makeTransaction(isc::dhcp_ddns::NameChangeRequestPtr& ncr);

public:
    /// @brief Gets the D2UpdateMgr's IOService.
    ///
    /// @return returns a reference to the IOService
    const asiolink::IOServicePtr& getIOService() {
        return (io_service_);
    }

    /// @brief Returns the maximum number of concurrent transactions.
    size_t getMaxTransactions() const {
        return (max_transactions_);
    }

    /// @brief Sets the maximum number of entries allowed in the queue.
    ///
    /// @param max_transactions is the new maximum number of transactions
    ///
    /// @throw Throws D2QueueMgrError if the new value is less than one or if
    /// the new value is less than the number of entries currently in the
    /// queue.
    void setMaxTransactions(const size_t max_transactions);

    /// @brief Search the transaction list for the given key.
    ///
    /// @param key the transaction key value for which to search.
    ///
    /// @return Iterator pointing to the entry found.  If no entry is
    /// it will point to the list end position.
    TransactionList::iterator findTransaction(const TransactionKey& key);

    /// @brief Returns the transaction list end position.
    TransactionList::iterator transactionListEnd();

    /// @brief Returns the transaction list beg position.
    TransactionList::iterator transactionListBegin();

    /// @brief Convenience method that checks transaction list for the given key
    ///
    /// @param key the transaction key value for which to search.
    ///
    /// @return Returns true if the key is found within the list, false
    /// otherwise.
    bool hasTransaction(const TransactionKey& key);

    /// @brief Removes the entry pointed to by key from the transaction list.
    ///
    /// Removes the entry referred to by key if it exists.  It has no effect
    /// if the entry is not found.
    ///
    /// @param key of the transaction to remove
    void removeTransaction(const TransactionKey& key);

    /// @brief Immediately discards all entries in the transaction list.
    ///
    /// @todo For now this just wipes them out. We might need something
    /// more elegant, that allows a cancel first.
    void clearTransactionList();

    /// @brief Convenience method that returns the number of requests queued.
    size_t getQueueCount() const;

    /// @brief Returns the current number of transactions.
    size_t getTransactionCount() const;

private:
    /// @brief Pointer to the queue manager.
    D2QueueMgrPtr queue_mgr_;

    /// @brief Pointer to the configuration manager.
    D2CfgMgrPtr cfg_mgr_;

    /// @brief Primary IOService instance.
    /// This is the IOService that the upper layer(s) use for IO events, such
    /// as shutdown and configuration commands.  It is the IOService that is
    /// passed into transactions to manager their IO events.
    /// (For future reference, multi-threaded transactions would each use their
    /// own IOService instance.)
    asiolink::IOServicePtr io_service_;

    /// @brief Maximum number of concurrent transactions.
    size_t max_transactions_;

    /// @brief List of transactions.
    TransactionList transaction_list_;
};

/// @brief Defines a pointer to a D2UpdateMgr instance.
typedef boost::shared_ptr<D2UpdateMgr> D2UpdateMgrPtr;


} // namespace isc::d2
} // namespace isc
#endif