FlatFieldRefAndKey.h

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* Copyright Onix Solutions Limited [OnixS]. All rights reserved.
*
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* and international copyright treaties.
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*
* Except as otherwise granted within the terms of the Agreement, copying or reproduction of any part
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*/

#pragma once

#include <cstdlib>

namespace OnixS {
namespace FIX {

struct KnownFlatFieldKeys;

/// Represents a temporary reference to a field in an editable serialized message.
///
/// @note Reference remains valid since the moment it is obtained till the moment any other field of the same Serialized message is modified.
class FlatFieldRef
{
public:
    /// Initializes as a references to nothing.
    FlatFieldRef()
        : valueOffset_(0),
          valueSize_(0) {
    }

    /// Message only should use this constructor to initialize a valid reference.
    FlatFieldRef(size_t valueOffset, size_t valueSize)
        : valueOffset_(valueOffset), valueSize_(valueSize) {
    }

    /// Gets value offset.
    size_t valueOffset() const {
        return valueOffset_;
    }

    /// Gets value size.
    size_t valueSize() const {
        return valueSize_;
    }

    /// Indicates whether the instance refers to the field or not.
    operator bool() const {
        return (0 != valueOffset_);
    }

    /// Compares the instance with the given one.
    bool
    operator == (
        const FlatFieldRef & other) const {
        return (
                   valueOffset_ == other.valueOffset_ &&
                   valueSize_ == other.valueSize_);
    }

    /// Compares the instance with the given one.
    bool
    operator != (
        const FlatFieldRef & other) const {
        return (
                   valueOffset_ != other.valueOffset_ ||
                   valueSize_ != other.valueSize_);
    }

private:

    size_t valueOffset_;
    size_t valueSize_;
};

typedef FlatFieldRef SerializedFieldRef;

/// Key to a serialized field - represents another way of accessing fields in an editable serialized message.
///
/// In contrast to FlatFieldRef, FlatFieldKey remains constant and valid during all the life of serialized message object.
/// So they are suitable in case of multiple modifications of the same field.
class FlatFieldKey
{
public:
    /// Initializes as a non-valid key.
    FlatFieldKey()
        : key_(static_cast<size_t>(-1)) {
    }

    // Initializes valid key.
    explicit FlatFieldKey(size_t key)
        : key_(key) {
    }

    /// Implicit conversion to the index value.
    operator size_t() const {
        return key_;
    }

    /// Compares to the given instance.
    bool
    operator ==(
        const FlatFieldKey & other) const {
        return (key_ == other.key_);
    }

    /// Compares to the given instance.
    bool
    operator !=(
        const FlatFieldKey & other) const {
        return (key_ != other.key_);
    }

private:

    friend
    struct
        KnownFlatFieldKeys;

    // Numeric value of the key.
    size_t key_;
};

typedef FlatFieldKey SerializedFieldKey;

/// Keys are constant during the serialized message lifetime.
/// However, keys are allocated privately by each particular
/// message instance and thus may differ for same fields in
/// different instances. For commonly used fields, there are
/// pre-allocated keys which are same for all messages.
struct KnownFlatFieldKeys {
    /// Key to access the BodyLength field.
    static
    FlatFieldKey
    bodyLength() {
        return FlatFieldKey(0);
    }

    /// Key to access the MsgType field.
    static
    FlatFieldKey
    msgType() {
        return FlatFieldKey(1);
    }

    /// Key to access the MsgSeqNum field.
    static
    FlatFieldKey
    seqNumber() {
        return FlatFieldKey(2);
    }

    /// Key to access the SendingTime field.
    static
    FlatFieldKey
    sendingTime() {
        return FlatFieldKey(3);
    }

    /// Value of the first key to be allocated dynamically.
    static
    FlatFieldKey
    dynamic() {
        return FlatFieldKey(4);
    }
};

typedef KnownFlatFieldKeys KnownSerializedFieldKeys;

}
}