unit Myc.Core.Futures;

interface

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

type
    TMycFuture<T> = class abstract( TInterfacedObject, IMycFuture<T> )
    protected
        function GetResult: T; virtual; abstract;
        function GetDone: TState; virtual; abstract;
    end;

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

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

implementation

{ TMycNullFuture<T> }

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

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

{ TMycGateFuncFuture<T> }

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

    FDone := TLatch.Construct( 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 );

    FInit.Unsubscribe;
    inherited Destroy;
end;

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

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

end.