SettingGroup.h

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// Copyright Onix Solutions Limited [OnixS]. All rights reserved.
//
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#pragma once

#include <OnixS/CME/ConflatedUDP/String.h>

ONIXS_CONFLATEDUDP_NAMESPACE_BEGIN

ONIXS_CONFLATEDUDP_LTWT_CLASS_DECL
(
    SettingGroup
);

/// Represents a service controlling assignment 
/// operations for the collections of settings. 
ONIXS_CONFLATEDUDP_EXPORTED_STRUCT 
SettingAssignController
{
    /// Begins the setting assignment operation. 
    /// 
    /// May throw an exception if assignment 
    /// is not possible for the moment or is 
    /// prohibited for a setting or a group to 
    /// which the setting being updated belongs. 
    virtual 
    void 
    beginAssign(
        const SettingGroup&, 
        const Char*) = 0;

    /// Accomplishes the setting assignment operation. 
    /// 
    /// The given member must be invoked after 
    /// successful invocation of the 'beginAssign' 
    /// member and before any other setting update. 
    virtual 
    void 
    endAssign() = 0;
};

// Default attributes and functionality. 
ONIXS_CONFLATEDUDP_EXPORTED_STRUCT
TrivialAssignController 
: SettingAssignController
{
    /// Implements base class interface. 
    void 
    beginAssign(
        const SettingGroup&, 
        const Char*)
    {
    }
    
    /// Implements base class interface. 
    void 
    endAssign()
    {
    }

    /// Returns instance of the 
    /// trivial assignment controller. 
    static 
    SettingAssignController&
    self()
    {
        static
        TrivialAssignController
        trivial;
    
        return trivial;
    }
};

/// Scope guard to update setting in the safe way. 
ONIXS_CONFLATEDUDP_LTWT_CLASS SettingAssignGuard
{
    SettingAssignController& controller_;

    SettingAssignGuard(
        const SettingAssignGuard&);

    SettingAssignGuard& 
    operator =(
        const SettingAssignGuard&);

public:
    /// Initializes the guard for the given setting update. 
    SettingAssignGuard(
        SettingAssignController& controller, 
        const SettingGroup& group, 
        const Char* details)
        : controller_(controller)
    {
        controller_.beginAssign(group, details);
    }

    /// Accomplishes setting update. 
    ~SettingAssignGuard()
    {
        controller_.endAssign();
    }
};

/// Base services for settings grouped by a certain criteria. 
ONIXS_CONFLATEDUDP_LTWT_CLASS SettingGroup
{
    // Controller for the given group of settings.
    SettingAssignController& controller_;

    SettingGroup(
        const SettingGroup&);

    SettingGroup&
    operator =(
        const SettingGroup&);

public:
    /// Initializes the group of settings 
    /// with the given validation services. 
    SettingGroup(
        SettingAssignController* 
        controller = NULL)
        : controller_
          (
            controller 
                ? *controller 
                : TrivialAssignController::
                  self()
          )
    {
    }

    /// Does actually nothing. 
    ~SettingGroup()
    {
    }

    /// Guarded assignment of the given 
    /// value to the given variable.
    template
    <
        class Assignee,
        class Value
    >
    void 
    controlAssignment(
        const Char* description, 
        Assignee& assignee, 
        Value value) const 
    {
        const 
        SettingAssignGuard 
        guard(
            controller_, 
            *this, 
            description);
        {
            assignee = value;
        }
    }

    /// Guarded invoke of the given routine 
    /// which assumes complex assignment or 
    /// update for the given object from the 
    /// given value. 
    template
    <
        class Assignee, 
        class Value, 
        class AssignRoutine
    >
    void 
    controlAssignment(
        const Char* description, 
        AssignRoutine routine, 
        Assignee& assignee,
        const Value& value) const 
    {
        const 
        SettingAssignGuard
        guard(
            controller_, 
            *this, 
            description);
        {
            (assignee.*routine)(value);
        }
    }

    /// Returns an instance 
    /// representing a null group. 
    ONIXS_CONFLATEDUDP_LTWT_EXPORTED
    static
    const SettingGroup&
    null()
    {
        static 
        const 
        SettingGroup 
        nullInstance;

        return nullInstance;
    }
};

/// Checks the two groups for equality. 
inline 
bool
operator ==(
    const SettingGroup& left,
    const SettingGroup& right)
{
    return (&left == &right);
}

/// Checks the two groups for inequality. 
inline 
bool
operator !=(
    const SettingGroup& left,
    const SettingGroup& right)
{
    return (&left != &right);
}

ONIXS_CONFLATEDUDP_NAMESPACE_END