unit Myc.TaskManager;

interface

uses
    System.SysUtils,
    Myc.Signals;

type
    TTaskManager = record
        type
            ITaskManager = interface
                procedure CreateThread(const Proc: TProc);
                procedure RunTask(const Gate: TState; const Proc: TProc);
                procedure WaitFor(const State: TState);
            end;
    private
        FTaskManager: ITaskManager;

    public
        constructor Create(const ATaskManager: ITaskManager);
        class operator Implicit(const A: ITaskManager): TTaskManager; overload;
        class operator Implicit(const A: TTaskManager): ITaskManager; overload;

        // Creates and starts a new, independent thread executing Proc.
        // Returns a State to await thread completion.
        function CreateThread(const Proc: TProc): TState;

        // Run a task when the gate is opened.
        // Returns a State to await thread completion.
        function RunTask(const Gate: TState; const Proc: TFunc<TState>): TState;

        // Waits for the operation associated with State to complete.
        // Must not be called from a task of this factory.
        // After waiting, or if the state is already set, any first stored exception
        // from any worker thread of this factory will be re-raised in the calling (main) thread.
        // Raises ETaskException if called from within a worker thread.
        procedure WaitFor(const State: TState); inline;
    end;

var
    TaskManager: TTaskManager;

procedure SetupTaskManagerMock;

implementation

uses
    Myc.Core.Tasks;

type
    TMycExecMock = class(TInterfacedObject, TSignal.ISubscriber)
    private
        FProc: TProc;
    public
        constructor Create(const AProc: TProc);
        function Notify: Boolean;
    end;

    TMycTaskManagerMock = class(TInterfacedObject, TTaskManager.ITaskManager)
    public
        constructor Create;
        procedure RunTask(const Gate: TState; const Proc: TProc);
        procedure WaitFor(const State: TState);
        procedure CreateThread(const Proc: TProc);
    end;

{ TMycExecMock }

constructor TMycExecMock.Create(const AProc: TProc);
begin
    inherited Create;
    FProc := AProc;
end;

function TMycExecMock.Notify: Boolean;
begin
    Result := Assigned(FProc);
    if Result then
    begin
        FProc();
        FProc := nil;
    end;
end;

{ TMycTaskManagerMock }

constructor TMycTaskManagerMock.Create;
begin
    inherited Create;
end;

procedure TMycTaskManagerMock.CreateThread(const Proc: TProc);
begin
    Proc();
end;

procedure TMycTaskManagerMock.RunTask(const Gate: TState; const Proc: TProc);
begin
    Gate.Signal.Subscribe(TMycExecMock.Create(Proc));
end;

procedure TMycTaskManagerMock.WaitFor(const State: TState);
begin
    Assert(State.IsSet);
end;

procedure SetupTaskManagerMock;
begin
    TaskManager.Create(TMycTaskManagerMock.Create);
end;

constructor TTaskManager.Create(const ATaskManager: ITaskManager);
begin
    FTaskManager := ATaskManager;
end;

function TTaskManager.CreateThread(const Proc: TProc): TState;
begin
    // Create a latch that will be signaled when the proc finishes
    var done := TLatch.CreateLatch(1);
    Result := done.State;

    var cProc := Proc; // Capture Proc for the anonymous method
    FTaskManager.CreateThread(
        procedure
        begin
            try
                cProc(); // Execute the provided procedure
            finally
                cProc := nil; // Clear the captured proc
                done.Notify; // Signal completion via the latch's Notify method
            end;
        end
    );
end;

function TTaskManager.RunTask(const Gate: TState; const Proc: TFunc<TState>): TState;
begin
    var cProc: TFunc<TState> := Proc;
    if not Assigned(@cProc) then
        exit(TState.Null);

    var Done := TLatch.CreateLatch(1);
    Result := Done.State;

    FTaskManager.RunTask(
        Gate,
        procedure
        begin
            try
                cProc.Signal.Subscribe(Done);
            except
                Done.Notify;
                raise;
            end;
        end
    );
end;

procedure TTaskManager.WaitFor(const State: TState);
begin
    FTaskManager.WaitFor(State);
end;

class operator TTaskManager.Implicit(const A: ITaskManager): TTaskManager;
begin
    Result.Create(A);
end;

class operator TTaskManager.Implicit(const A: TTaskManager): ITaskManager;
begin
    Result := A.FTaskManager;
end;

end.