unit Myc.Core.Lazy;

interface

uses
    System.SysUtils,
    Myc.Signals,
    Myc.Lazy;

type
    TMycLazy<T> = class abstract(TInterfacedObject, IMycLazy<T>)
    protected
        function GetChanged: IMycState; virtual; abstract;
    public
        function Pop(out Res: T): Boolean; virtual; abstract;
    end;

    TMycNullLazy<T> = class(TMycLazy<T>)
    protected
        function GetChanged: IMycState; override;
    public
        function Pop(out Res: T): Boolean; override;
    end;

    TMycFuncLazy<T> = class(TMycLazy<T>)
    private
        FChanged: IMycDirty;
        FChangeState: TState.TSubscription;
        FProc: TFunc<T>;
    protected
        function GetChanged: IMycState; override;
    public
        constructor Create(const AChanged: TState; const AProc: TFunc<T>);
        destructor Destroy; override;
        function Pop(out Res: T): Boolean; override;
    end;

implementation

{ TMycNullLazy<T> }

function TMycNullLazy<T>.GetChanged: IMycState;
begin
    Result := TState.Null;
end;

function TMycNullLazy<T>.Pop(out Res: T): Boolean;
begin
    Res := Default(T);
    Result := true;
end;

{ TMycFuncLazy<T> }

constructor TMycFuncLazy<T>.Create(const AChanged: TState; const AProc: TFunc<T>);
begin
    inherited Create;
    FChanged := TDirty.Construct;
    FProc := AProc;
    FChangeState := AChanged.Subscribe(FChanged);
end;

destructor TMycFuncLazy<T>.Destroy;
begin
    FChangeState.Unsubscribe;
    inherited;
end;

function TMycFuncLazy<T>.GetChanged: IMycState;
begin
    Result := FChanged.State;
end;

function TMycFuncLazy<T>.Pop(out Res: T): Boolean;
begin
    Result := FChanged.State.IsSet;
    if Result then
    begin
        if Assigned(FProc) then
            Res := FProc;
        FChanged.Reset;
    end;
end;

end.