{
  :: X2UtSettings provides a generic access mechanism for application settings.
  :: Include one of the extensions (X2UtSettingsINI, X2UtSettingsRegistry) for
  :: an implementation.
  ::
  :: Last changed:    $Date$
  :: Revision:        $Rev$
  :: Author:          $Author$
}
unit X2UtSettings;

interface
uses
  Classes,
  SysUtils,
  Variants,
  X2UtHashes;

type
  //:$ Raised when an unregistered setting is requested without providing a
  //:$ default value.
  EX2SettingsUndefined  = class(Exception);

  //:$ Raised when trying to read a registered setting as a different type than
  //:$ it was registered with.
  EX2SettingsType       = class(Exception);

  //:$ Raised when the specified range is invalid.
  EX2SettingsRange      = class(Exception);

  //:$ Raised when the specified define already exists
  EX2SettingsExists     = class(Exception);

  //:$ Callback method for defines
  TX2SettingsCallback   = procedure(const ASection, AName: String;
                                    var AValue: Variant) of object;

  {
    :$ Internal representation of a persistent setting
  }
  TX2SettingsRanges     = array of array[0..1] of Variant;

  TX2SettingsDefine     = class(TObject)
  private
    FCallback:      TX2SettingsCallback;
    FRanges:        TX2SettingsRanges;
    FValue:         Variant;
  public
    constructor Create(const AValue: Variant;
                       const ARanges: array of const;
                       const ACallback: TX2SettingsCallback);

    property Callback:  TX2SettingsCallback read FCallback;
    property Ranges:    TX2SettingsRanges   read FRanges;
    property Value:     Variant             read FValue;
  end;


  // Forward declaration
  TX2SettingsFactory    = class;

  {
    :$ Abstract settings object.

    :: Provides access to the settings regardless of the storage backend.
  }
  TX2Settings           = class(TObject)
  private
    FFactory:         TX2SettingsFactory;
    FSection:         String;
  protected
    function InternalReadBool(const AName: String; out AValue: Boolean): Boolean; virtual; abstract;
    function InternalReadFloat(const AName: String; out AValue: Double): Boolean; virtual; abstract;
    function InternalReadInteger(const AName: String; out AValue: Integer): Boolean; virtual; abstract;
    function InternalReadString(const AName: String; out AValue: String): Boolean; virtual; abstract;

    property Factory:         TX2SettingsFactory  read FFactory;
    property Section:         String              read FSection;
  public
    constructor Create(const AFactory: TX2SettingsFactory;
                       const ASection: String); virtual;

    //:$ Reads a boolean value from the settings.
    //:: If the ADefault parameter is used, that value will be returned if the
    //:: setting could not be found. Otherwise the setting must have been
    //:: registered with the factory's Register() method.
    function ReadBool(const AName: String): Boolean; overload; virtual;
    function ReadBool(const AName: String; const ADefault: Boolean): Boolean; overload; virtual;

    //:$ Reads a floating point value from the settings.
    //:: If the ADefault parameter is used, that value will be returned if the
    //:: setting could not be found. Otherwise the setting must have been
    //:: registered with the factory's Register() method.
    function ReadFloat(const AName: String): Double; overload; virtual;
    function ReadFloat(const AName: String; const ADefault: Double): Double; overload; virtual;

    //:$ Reads an integer value from the settings.
    //:: If the ADefault parameter is used, that value will be returned if the
    //:: setting could not be found. Otherwise the setting must have been
    //:: registered with the factory's Register() method.
    function ReadInteger(const AName: String): Integer; overload; virtual;
    function ReadInteger(const AName: String; const ADefault: Integer): Integer; overload; virtual;

    //:$ Reads a string value from the settings.
    //:: If the ADefault parameter is used, that value will be returned if the
    //:: setting could not be found. Otherwise the setting must have been
    //:: registered with the factory's Register() method.
    function ReadString(const AName: String): String; overload; virtual;
    function ReadString(const AName, ADefault: String): String; overload; virtual;

    //:$ Writes a boolean value to the settings.
    procedure WriteBool(const AName: String; AValue: Boolean); virtual; abstract;

    //:$ Writes a floating point value to the settings.
    procedure WriteFloat(const AName: String; AValue: Double); virtual; abstract;

    //:$ Writes an integer value to the settings.
    procedure WriteInteger(const AName: String; AValue: Integer); virtual; abstract;

    //:$ Writes a string value to the settings.
    procedure WriteString(const AName, AValue: String); virtual; abstract;

    //:$ Checks if the specified setting exists.
    function ValueExists(const AName: String): Boolean; virtual; abstract;

    //:$ Retrieves the list of sub-sections for this section.
    procedure GetSectionNames(const ADest: TStrings); virtual; abstract;

    //:$ Retrieves the list of values for this section.
    procedure GetValueNames(const ADest: TStrings); virtual; abstract;

    //:$ Deletes this section.
    procedure DeleteSection(); virtual; abstract;

    //:$ Deletes the specified value.
    procedure DeleteValue(const AName: String); virtual; abstract;
  end;

  {
    :$ Settings factory.

    :: Extensions must implement a factory descendant which an application can
    :: create to provide application-wide access to the same settings.
  }
  TX2SettingsFactory    = class(TObject)
  private
    FDefines:         TX2ObjectHash;
  protected
    function GetSection(const ASection: String): TX2Settings; virtual; abstract;
  public
    constructor Create();
    destructor Destroy(); override;

    //:$ Loads a section from the settings.
    //:: Sub-sections are indicated by seperating the sections with a dot ('.')
    //:: characters, ex: Sub.Section. The underlying extension will translate
    //:: this into a compatible section.
    //:! The application is responsible for freeing the returned class.
    property Sections[const ASection: String]:    TX2Settings read GetSection; default;

    //:$ Defines a persistent setting
    //:: Persistent settings are a way for the application to register it's
    //:: configuration settings on startup with a default value and a range.
    //:: When reading a setting it will be checked against the specified range
    //:: (if supplied), or if not found, the registered default value will be
    //:: returned. This allows the setting to be read in many places without
    //:: having to do all the checks every time. In addition you may provide
    //:: a callback method to handle more advanced checks.
    //:: /n/n
    //:: Ranges must be specified as an array where each pair of values
    //:: specifies the minimum and maximum value of that range. The type
    //:: of the values in the ranges must be the same as the type of the
    //:: value, and is used later on for type checking. The only exception
    //:: to this rule is that you are allowed to specify integer ranges for
    //:: a floating value.
    procedure Define(const ASection, AName: String; const AValue: Variant;
                     const ARanges: array of const;
                     const ACallback: TX2SettingsCallback = nil);
  end;


implementation
resourcestring
  RSInvalidRange  = 'Invalid range!';
  RSInvalidType   = 'Invalid type!';
  RSUndefined     = 'Undefined setting: %s!';
  RSDefineExists  = 'Define already exists!';


{============================ TX2Settings
  Initialization
========================================}
constructor TX2Settings.Create;
begin
  inherited Create();

  FFactory  := AFactory;
  FSection  := ASection;
end;


{============================ TX2Settings
  Read
========================================}
function TX2Settings.ReadBool(const AName: String): Boolean;
begin
  if not InternalReadBool(AName, Result) then
    raise EX2SettingsUndefined.CreateFmt(RSUndefined, [AName]);
end;

function TX2Settings.ReadBool(const AName: String;
                              const ADefault: Boolean): Boolean;
begin
  if not InternalReadBool(AName, Result) then
    Result  := ADefault;
end;

function TX2Settings.ReadFloat(const AName: String): Double;
begin
  if not InternalReadFloat(AName, Result) then
    raise EX2SettingsUndefined.CreateFmt(RSUndefined, [AName]);
end;

function TX2Settings.ReadFloat(const AName: String;
                               const ADefault: Double): Double;
begin
  if not InternalReadFloat(AName, Result) then
    Result  := ADefault;
end;

function TX2Settings.ReadInteger(const AName: String): Integer;
begin
  if not InternalReadInteger(AName, Result) then
    raise EX2SettingsUndefined.CreateFmt(RSUndefined, [AName]);
end;

function TX2Settings.ReadInteger(const AName: String;
                                 const ADefault: Integer): Integer;
begin
  if not InternalReadInteger(AName, Result) then
    Result  := ADefault;
end;

function TX2Settings.ReadString(const AName: String): String;
begin
  if not InternalReadString(AName, Result) then
    raise EX2SettingsUndefined.CreateFmt(RSUndefined, [AName]);
end;

function TX2Settings.ReadString(const AName, ADefault: String): String;
begin
  if not InternalReadString(AName, Result) then
    Result  := ADefault;
end;


{===================== TX2SettingsFactory
  Defines
========================================}
constructor TX2SettingsFactory.Create;
begin
  inherited;

  FDefines  := TX2ObjectHash.Create();
end;

destructor TX2SettingsFactory.Destroy;
begin
  FreeAndNil(FDefines);

  inherited;
end;


procedure TX2SettingsFactory.Define;
  function CheckVarType(const AValue: Variant): TVarType;
  begin
    case VarType(AValue) of
      varBoolean:     break;
      varByte,
      varSmallint,
      varInteger,
      varWord,
      varLongWord:    Result  := varInteger;
      varSingle,
      varDouble,
      varDate:        Result  := varDouble;
      varOleStr,
      varStrArg,
      varString:      Result  := varString;
    else
      raise EX2SettingsType.Create(RSInvalidType);
    end;
  end;

var
  iIndex:         Integer;
  sHash:          String;
  vtValue:        TVarType;

begin
  sHash := ASection + #0 + AName;
  if FDefines.Exists(sHash) then
    raise EX2SettingsExists.Create(RSDefineExists);

  // Validate type
  vtValue         := CheckVarType(AValue);

  // Validate ranges
  if High(ARanges) mod 2 <> 0 then
    raise EX2SettingsRange.Create(RSInvalidRange);

  for iIndex  := 0 to High(ARanges) do
    case ARanges[iIndex].VType of
      vtBoolean:
        if vtValue <> varBoolean then
          raise EX2SettingsType.Create(RSInvalidType);
      vtInteger:
        if not (vtValue in [varInteger, varDouble]) then
          raise EX2SettingsType.Create(RSInvalidType);
      vtExtended:
        if vtValue <> varDouble then
          raise EX2SettingsType.Create(RSInvalidType);
      vtString,
      vtPChar,
      vtChar,
      vtWideChar,
      vtPWideChar,
      vtWideString,
      vtAnsiString:
        if vtValue <> varString then
          raise EX2SettingsType.Create(RSInvalidType);
      vtVariant:
        if vtValue <> CheckVarType(ARanges[iIndex].VVariant^) then
          raise EX2SettingsType.Create(RSInvalidType);
    end;

  FDefines[sHash] := TX2SettingsDefine.Create(VarAsType(AValue, vtValue),
                                              ARanges, ACallback);
end;


{====================== TX2SettingsDefine
  Initialization
========================================}
constructor TX2SettingsDefine.Create;
  function VarRecToVariant(const AVarRec: TVarRec): Variant;
  begin
    case AVarRec.VType of
      vtBoolean:    Result  := AVarRec.VBoolean;
      vtInteger:    Result  := AVarRec.VInteger;
      vtExtended:   Result  := VarAsType(AVarRec.VExtended^, varDouble);
      vtString:     Result  := AVarRec.VString^;
      vtPChar:      Result  := String(AVarRec.VPChar);
      vtPWideChar:  Result  := String(AVarRec.VPWideChar^);
      vtWideChar:   Result  := String(AVarRec.VWideChar);
      vtWideString: Result  := String(AVarRec.VWideString^);
      vtAnsiString: Result  := String(AVarRec.VAnsiString^);
      vtVariant:    Result  := AVarRec.VVariant^;
    end;
  end;

var
  iCount:         Integer;
  iIndex:         Integer;
  iRange:         Integer;

begin
  FValue    := AValue;
  FCallback := ACallback;

  // Copy ranges
  iCount    := (High(ARanges) + 1) div 2;
  iIndex    := 0;

  SetLength(FRanges, iCount);

  for iRange  := 0 to iCount - 1 do
  begin
    FRanges[iRange][0]  := VarRecToVariant(ARanges[iIndex]);
    FRanges[iRange][1]  := VarRecToVariant(ARanges[iIndex + 1]);

    Inc(iIndex, 2);
  end;
end;

end.