// dbmessage.h

/**
*    Copyright (C) 2008 10gen 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/static_assert.h"
#include "mongo/bson/bson_validate.h"
#include "mongo/client/constants.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/server_options.h"
#include "mongo/util/net/message.h"

namespace mongo {

class OperationContext;

/* db response format

   Query or GetMore: // see struct QueryResult
      int resultFlags;
      int64 cursorID;
      int startingFrom;
      int nReturned;
      list of marshalled JSObjects;
*/

/* db request message format

   unsigned opid;         // arbitary; will be echoed back
   byte operation;
   int options;

   then for:

   dbInsert:
      std::string collection;
      a series of JSObjects
   dbDelete:
      std::string collection;
      int flags=0; // 1=DeleteSingle
      JSObject query;
   dbUpdate:
      std::string collection;
      int flags; // 1=upsert
      JSObject query;
      JSObject objectToUpdate;
        objectToUpdate may include { $inc: <field> } or { $set: ... }, see struct Mod.
   dbQuery:
      std::string collection;
      int nToSkip;
      int nToReturn; // how many you want back as the beginning of the cursor data (0=no limit)
                     // greater than zero is simply a hint on how many objects to send back per
                     // "cursor batch".
                     // a negative number indicates a hard limit.
      JSObject query;
      [JSObject fieldsToReturn]
   dbGetMore:
      std::string collection; // redundant, might use for security.
      int nToReturn;
      int64 cursorID;
   dbKillCursors=2007:
      int n;
      int64 cursorIDs[n];

   Note that on Update, there is only one object, which is different
   from insert where you can pass a list of objects to insert in the db.
   Note that the update field layout is very similar layout to Query.
*/

namespace QueryResult {
#pragma pack(1)
/* see http://dochub.mongodb.org/core/mongowireprotocol
*/
struct Layout {
    MsgData::Layout msgdata;
    int64_t cursorId;
    int32_t startingFrom;
    int32_t nReturned;
};
#pragma pack()

class ConstView {
public:
    ConstView(const char* storage) : _storage(storage) {}

    const char* view2ptr() const {
        return storage().view();
    }

    MsgData::ConstView msgdata() const {
        return storage().view(offsetof(Layout, msgdata));
    }

    int64_t getCursorId() const {
        return storage().read<LittleEndian<int64_t>>(offsetof(Layout, cursorId));
    }

    int32_t getStartingFrom() const {
        return storage().read<LittleEndian<int32_t>>(offsetof(Layout, startingFrom));
    }

    int32_t getNReturned() const {
        return storage().read<LittleEndian<int32_t>>(offsetof(Layout, nReturned));
    }

    const char* data() const {
        return storage().view(sizeof(Layout));
    }

    int32_t dataLen() const {
        return msgdata().getLen() - sizeof(Layout);
    }

protected:
    const ConstDataView& storage() const {
        return _storage;
    }

private:
    ConstDataView _storage;
};

class View : public ConstView {
public:
    View(char* data) : ConstView(data) {}

    using ConstView::view2ptr;
    char* view2ptr() {
        return storage().view();
    }

    using ConstView::msgdata;
    MsgData::View msgdata() {
        return storage().view(offsetof(Layout, msgdata));
    }

    void setCursorId(int64_t value) {
        storage().write(tagLittleEndian(value), offsetof(Layout, cursorId));
    }

    void setStartingFrom(int32_t value) {
        storage().write(tagLittleEndian(value), offsetof(Layout, startingFrom));
    }

    void setNReturned(int32_t value) {
        storage().write(tagLittleEndian(value), offsetof(Layout, nReturned));
    }

    int32_t getResultFlags() {
        return DataView(msgdata().data()).read<LittleEndian<int32_t>>();
    }

    void setResultFlags(int32_t value) {
        DataView(msgdata().data()).write(tagLittleEndian(value));
    }

    void setResultFlagsToOk() {
        setResultFlags(ResultFlag_AwaitCapable);
    }

    void initializeResultFlags() {
        setResultFlags(0);
    }

private:
    DataView storage() const {
        return const_cast<char*>(ConstView::view2ptr());
    }
};

class Value : public EncodedValueStorage<Layout, ConstView, View> {
public:
    Value() {
        MONGO_STATIC_ASSERT(sizeof(Value) == sizeof(Layout));
    }

    Value(ZeroInitTag_t zit) : EncodedValueStorage<Layout, ConstView, View>(zit) {}
};

}  // namespace QueryResult

/* For the database/server protocol, these objects and functions encapsulate
   the various messages transmitted over the connection.

   See http://dochub.mongodb.org/core/mongowireprotocol
*/
class DbMessage {
    // Assume sizeof(int) == 4 bytes
    MONGO_STATIC_ASSERT(sizeof(int) == 4);

public:
    // Note: DbMessage constructor reads the first 4 bytes and stores it in reserved
    DbMessage(const Message& msg);

    // Indicates whether this message is expected to have a ns
    bool messageShouldHaveNs() const {
        return (_msg.operation() >= dbUpdate) & (_msg.operation() <= dbDelete);
    }

    /** the 32 bit field before the ns
     * track all bit usage here as its cross op
     * 0: InsertOption_ContinueOnError
     * 1: fromWriteback
     */
    int reservedField() const {
        return _reserved;
    }

    const char* getns() const;
    int getQueryNToReturn() const;

    int pullInt();
    long long pullInt64();
    const char* getArray(size_t count) const;

    /* for insert and update msgs */
    bool moreJSObjs() const {
        return _nextjsobj != 0 && _nextjsobj != _theEnd;
    }

    BSONObj nextJsObj();

    const Message& msg() const {
        return _msg;
    }

    const char* markGet() const {
        return _nextjsobj;
    }

    void markSet() {
        _mark = _nextjsobj;
    }

    void markReset(const char* toMark);

private:
    // Check if we have enough data to read
    template <typename T>
    void checkRead(const char* start, size_t count = 0) const;

    // Read some type without advancing our position
    template <typename T>
    T read() const;

    // Read some type, and advance our position
    template <typename T>
    T readAndAdvance();

    const Message& _msg;
    int _reserved;  // flags or zero depending on packet, starts the packet

    const char* _nsStart;    // start of namespace string, +4 from message start
    const char* _nextjsobj;  // current position reading packet
    const char* _theEnd;     // end of packet

    const char* _mark;

    unsigned int _nsLen;
};


/* a request to run a query, received from the database */
class QueryMessage {
public:
    const char* ns;
    int ntoskip;
    int ntoreturn;
    int queryOptions;
    BSONObj query;
    BSONObj fields;

    /**
     * parses the message into the above fields
     * Warning: constructor mutates DbMessage.
     */
    explicit QueryMessage(DbMessage& d) {
        ns = d.getns();
        ntoskip = d.pullInt();
        ntoreturn = d.pullInt();
        query = d.nextJsObj();
        if (d.moreJSObjs()) {
            fields = d.nextJsObj();
        }
        queryOptions = DataView(d.msg().header().data()).read<LittleEndian<int32_t>>();
    }

    /**
     * A non-muting constructor from the whole message.
     */
    explicit QueryMessage(const Message& message) {
        DbMessage dbm(message);
        *this = QueryMessage(dbm);
    }
};

/**
 * A response to a DbMessage.
 *
 * Order of fields makes DbResponse{funcReturningMessage()} valid.
 */
struct DbResponse {
    Message response;       // If empty, nothing will be returned to the client.
    std::string exhaustNS;  // Namespace of cursor if exhaust mode, else "".
};

/**
 * Prepares query replies to legacy finds (opReply to dbQuery) in place. This is also used for
 * command responses that don't use the new dbCommand protocol.
 */
class OpQueryReplyBuilder {
    MONGO_DISALLOW_COPYING(OpQueryReplyBuilder);

public:
    OpQueryReplyBuilder();

    /**
     * Returns the BufBuilder that should be used for placing result objects. It will be positioned
     * where the first (or next) object should go.
     *
     * You must finish the BSONObjBuilder that uses this (by destruction or calling doneFast())
     * before calling any more methods on this object.
     */
    BufBuilder& bufBuilderForResults() {
        return _buffer;
    }

    /**
     * Finishes the reply and returns the message buffer.
     */
    Message toQueryReply(int queryResultFlags,
                         int nReturned,
                         int startingFrom = 0,
                         long long cursorId = 0);

    /**
     * Similar to toQueryReply() but used for replying to a command.
     */
    Message toCommandReply() {
        return toQueryReply(0, 1);
    }

private:
    BufBuilder _buffer;
};

/**
 * Helper to build a DbResponse from a buffer containing an OP_QUERY response.
 */
DbResponse replyToQuery(int queryResultFlags,
                        const void* data,
                        int size,
                        int nReturned,
                        int startingFrom = 0,
                        long long cursorId = 0);


/**
 * Helper to build a DbRespose for OP_QUERY with a single reply object.
 */
inline DbResponse replyToQuery(const BSONObj& obj, int queryResultFlags = 0) {
    return replyToQuery(queryResultFlags, obj.objdata(), obj.objsize(), /*nReturned*/ 1);
}
}  // namespace mongo