/**
 *    Copyright (C) 2014 MongoDB Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include "mongo/base/disallow_copying.h"
#include "mongo/base/status.h"
#include "mongo/db/storage/recovery_unit.h"
#include "mongo/db/concurrency/locker.h"
#include "mongo/db/concurrency/d_concurrency.h"

namespace mongo {

class Client;
class CurOp;
class ProgressMeter;
class StringData;

/**
 * This class encompasses the state required by an operation.
 *
 * TODO(HK): clarify what this means.  There's one OperationContext for one user operation...
 *           but is this true for getmore?  Also what about things like fsyncunlock / internal
 *           users / etc.?
 *
 * On construction, an OperationContext associates itself with the current client, and only on
 * destruction it deassociates itself. At any time a client can be associated with at most one
 * OperationContext.
 */
class OperationContext {
    MONGO_DISALLOW_COPYING(OperationContext);

public:
    virtual ~OperationContext() {}

    /**
     * Interface for durability.  Caller DOES NOT own pointer.
     */
    virtual RecoveryUnit* recoveryUnit() const = 0;

    /**
     * Returns the RecoveryUnit (same return value as recoveryUnit()) but the caller takes
     * ownership of the returned RecoveryUnit, and the OperationContext instance relinquishes
     * ownership.  Sets the RecoveryUnit to NULL.
     *
     * Used to transfer ownership of storage engine state from OperationContext
     * to ClientCursor for getMore-able queries.
     *
     * Note that we don't allow the top-level locks to be stored across getMore.
     * We rely on active cursors being killed when collections or databases are dropped,
     * or when collection metadata changes.
     */
    virtual RecoveryUnit* releaseRecoveryUnit() = 0;

    virtual void setRecoveryUnit(RecoveryUnit* unit) = 0;

    /**
     * Interface for locking.  Caller DOES NOT own pointer.
     */
    virtual Locker* lockState() const = 0;

    // --- operation level info? ---

    /**
     * If the thread is not interrupted, returns Status::OK(), otherwise returns the cause
     * for the interruption. The throw variant returns a user assertion corresponding to the
     * interruption status.
     */
    virtual void checkForInterrupt() const = 0;
    virtual Status checkForInterruptNoAssert() const = 0;

    /**
     * Delegates to CurOp, but is included here to break dependencies.
     * Caller does not own the pointer.
     */
    virtual ProgressMeter* setMessage(const char* msg,
                                      const std::string& name = "Progress",
                                      unsigned long long progressMeterTotal = 0,
                                      int secondsBetween = 3) = 0;

    /**
     * Delegates to CurOp, but is included here to break dependencies.
     *
     * TODO: We return a string because of hopefully transient CurOp thread-unsafe insanity.
     */
    virtual std::string getNS() const = 0;

    /**
     * Returns the client under which this context runs.
     */
    virtual Client* getClient() const = 0;

    /**
     * Returns CurOp. Caller does not own pointer
     */
    virtual CurOp* getCurOp() const = 0;

    /**
     * Returns the operation ID associated with this operation.
     * WARNING: Due to SERVER-14995, this OpID is not guaranteed to stay the same for the
     * lifetime of this OperationContext.
     */
    virtual unsigned int getOpID() const = 0;

    /**
     * @return true if this instance is primary for this namespace
     */
    virtual bool isPrimaryFor(const StringData& ns) = 0;

protected:
    OperationContext() {}
};

class WriteUnitOfWork {
    MONGO_DISALLOW_COPYING(WriteUnitOfWork);

public:
    WriteUnitOfWork(OperationContext* txn) : _txn(txn), _ended(false) {
        _txn->lockState()->beginWriteUnitOfWork();
        _txn->recoveryUnit()->beginUnitOfWork(_txn);
    }

    ~WriteUnitOfWork() {
        _txn->recoveryUnit()->endUnitOfWork();

        if (!_ended) {
            _txn->lockState()->endWriteUnitOfWork();
        }
    }

    void commit() {
        invariant(!_ended);

        _txn->recoveryUnit()->commitUnitOfWork();
        _txn->lockState()->endWriteUnitOfWork();

        _ended = true;
    }

private:
    OperationContext* const _txn;

    bool _ended;
};


/**
 * RAII-style class to mark the scope of a transaction. ScopedTransactions may be nested.
 * An outermost ScopedTransaction calls commitAndRestart() on destruction, so that the storage
 * engine can release resources, such as snapshots or locks, that it may have acquired during
 * the transaction. Note that any writes are committed in nested WriteUnitOfWork scopes,
 * so write conflicts cannot happen on completing a ScopedTransaction.
 *
 * TODO: The ScopedTransaction should hold the global lock
 */
class ScopedTransaction {
    MONGO_DISALLOW_COPYING(ScopedTransaction);

public:
    /**
     * The mode for the transaction indicates whether the transaction will write (MODE_IX) or
     * only read (MODE_IS), or needs to run without other writers (MODE_S) or any other
     * operations (MODE_X) on the server.
     */
    ScopedTransaction(OperationContext* txn, LockMode mode) : _txn(txn) {}

    ~ScopedTransaction() {
        if (!_txn->lockState()->isLocked()) {
            _txn->recoveryUnit()->commitAndRestart();
        }
    }

private:
    OperationContext* _txn;
};

}  // namespace mongo