unit Myc.Core.Futures;

interface

uses
    System.SysUtils,
    Myc.Signals,
    Myc.TaskManager,
    Myc.Futures;

type
    TMycFuture<T> = class abstract(TInterfacedObject, TFuture<T>.IFuture)
    protected
        function GetValue: T; virtual; abstract;
        function GetDone: TState; virtual; abstract;
    end;

    TMycNullFuture<T> = class(TMycFuture<T>)
    protected
        function GetValue: T; override;
        function GetDone: TState; override;
    end;

    TMycGateFuncFuture<T> = class(TMycFuture<T>)
    private
        FInit: TSignal.TSubscription;
        FDone: TLatch.ILatch;
        FResult: T;
    protected
        function GetValue: T; override;
        function GetDone: TState; override;
    public
        constructor Create(const ATaskManager: IMycTaskManager; const AGate: TState.IState; AProc: TFunc<T>);
        destructor Destroy; override;
    end;

implementation

{ TMycNullFuture<T> }

function TMycNullFuture<T>.GetDone: TState;
begin
    Result := TState.Null;
end;

function TMycNullFuture<T>.GetValue: T;
begin
    Result := Default(T);
end;

{ TMycGateFuncFuture<T> }

constructor TMycGateFuncFuture<T>.Create(const ATaskManager: IMycTaskManager; const AGate: TState.IState; AProc: TFunc<T>);
begin
    inherited Create;

    FDone := TLatch.CreateLatch(1);

    // Subscribe the job execution to AGate.
    // The job will run when AGate notifies the subscriber returned by Run.
    FInit :=
        ATaskManager.CreateTask(
            AGate,
            procedure
            begin
                try
                    try
                        Self.FResult := AProc();
                    except
                        Self.FResult := Default(T); // Set result to Default(T) on error
                        raise; // Re-raise for TaskFactory to handle
                    end;
                finally
                    Self.FDone.Notify; // Signal that this future is done (successfully or with error)
                end;
            end
        );
end;

destructor TMycGateFuncFuture<T>.Destroy;
begin
    Assert(FDone.State.IsSet, 'Future not done');

    FInit.Unsubscribe;
    inherited Destroy;
end;

function TMycGateFuncFuture<T>.GetDone: TState;
begin
    Result := FDone.State;
end;

function TMycGateFuncFuture<T>.GetValue: T;
begin
    Assert(FDone.State.IsSet, 'Result is not yet available.');
    Result := FResult;
end;

end.