unit Myc.Signals;

interface

uses
    System.SysUtils;

type
    IMycSubscriber = interface
        // Interface for an entity that can be notified by a TState or TState.
        // Returns true if this subscriber expects further notifications from the source, false otherwise.
        function Notify: Boolean;
    end;

    IMycState = interface
        // Represents a subscribable TState that can be queried.
        {$REGION 'property access'}
        function GetIsSet: Boolean;
        {$ENDREGION}
        // Subscribes a given subscriber to this TState.
        function Subscribe(Subscriber: IMycSubscriber): Pointer;
        procedure Unsubscribe(Tag: Pointer);
        // IsSet is true if the TState has been reached or the condition is met.
        property IsSet: Boolean read GetIsSet;
    end;

    TState = record // helper for IMycState
        type
            TSubscription = record
            private
                FState: IMycState;
                FTag: Pointer; // Tag identifying this subscription within the notifier list.
                constructor Create(const AState: IMycState; ATag: Pointer);
            public
                class operator Initialize(out Dest: TSubscription);
                // Unsubscribes from the associated TState.
                procedure Unsubscribe;
            end;

    strict private
        class var
            FNull: IMycState;
        class constructor ClassCreate;
    private
        FState: IMycState;
        function GetIsSet: Boolean; inline;
    public
        constructor Create(const AState: IMycState);

        class operator Implicit(const A: IMycState): TState; overload;
        class operator Implicit(const A: TState): IMycState; overload;

        class function All(const States: TArray<TState>): TState; static;
        class function Any(const States: TArray<TState>): TState; static;

        class property Null: IMycState read FNull;

        function Subscribe(Subscriber: IMycSubscriber): TSubscription; inline;
        procedure Unsubscribe(Tag: Pointer); inline;

        property IsSet: Boolean read GetIsSet;
    end;

    IMycEvent = interface(IMycSubscriber)
        function GetState: TState;
        property State: TState read GetState;
    end;

    TEvent = record
    strict private
        class var
            FNull: IMycEvent;
        class constructor ClassCreate;
    private
        FLatch: IMycEvent;
        function GetState: TState; inline;

    public
        constructor Create(const ALatch: IMycEvent);
        class operator Initialize(out Dest: TEvent);
        class operator Implicit(const A: IMycEvent): TEvent; overload;
        class operator Implicit(const A: TEvent): IMycEvent; overload;

        // A notifier is an event that acts as a multi-cast event. Its state is always set and it forwards all notifications the all subscribers.
        class function CreateNotifier: TEvent; static;

        // A latch is a specific type of event that, once set, remains set (non-resettable).
        // It becomes set when the internal countdown reaches zero.
        class function CreateLatch(Count: Integer): TEvent; static;

        class function Enqueue(var Gate: TEvent; Count: Integer = 1): TState; static;

        class property Null: IMycEvent read FNull;

        function Notify: Boolean; inline;

        property State: TState read GetState;
    end;

    // IMycFlag represents a resettable flag, typically indicating if a State is "dirty" (requiring attention) or "clean".
    IMycFlag = interface(IMycSubscriber)
        function GetState: TState;
        // Resets the flag to its "clean" (not set / not dirty) State.
        // Returns true if the flag was actually dirty before this reset, false otherwise.
        function Reset: Boolean;
        property State: TState read GetState;
    end;

    TFlag = record
    strict private
        class var
            FNull: IMycFlag;
        class constructor ClassCreate;

    private
        FDirty: IMycFlag;
        function GetState: TState; inline;

    public
        constructor Create(const ADirty: IMycFlag);
        class operator Implicit(const A: IMycFlag): TFlag; overload;
        class operator Implicit(const A: TFlag): IMycFlag; overload;
        class operator Initialize(out Dest: TFlag);

        class function CreateFlag: IMycFlag; static;
        class property Null: IMycFlag read FNull;

        function Notify: Boolean; inline;
        function Reset: Boolean;

        property State: TState read GetState;
    end;

implementation

uses
    Myc.Core.Notifier,
    Myc.Core.Signals;

{ TState.TSubscription }

constructor TState.TSubscription.Create(const AState: IMycState; ATag: TMycNotifyList<IMycSubscriber>.TTag);
begin
    Assert(Assigned(AState));
    FState := AState;
    FTag := ATag;
end;

procedure TState.TSubscription.Unsubscribe;
begin
    FState.Unsubscribe(FTag);
    FState := TState.Null;
    FTag := nil;
end;

class operator TState.TSubscription.Initialize(out Dest: TSubscription);
begin
    Dest.FState := TState.Null;
    Dest.FTag := nil;
end;

{ TState }

constructor TState.Create(const AState: IMycState);
begin
    FState := AState;
    if not Assigned(FState) then
        FState := FNull;
end;

class constructor TState.ClassCreate;
begin
    // Create a singleton null latch instance that is initially (and always) set.
    FNull := TMycNullState.Create(); // Calls the instance constructor
end;

class function TState.All(const States: TArray<TState>): TState;
var
    Latch: IMycEvent;
begin
    Latch := TEvent.CreateLatch(Length(States));
    for var i := 0 to High(States) do
        States[i].Subscribe(Latch);
    Result := Latch.State;
end;

class function TState.Any(const States: TArray<TState>): TState;
var
    Latch: IMycEvent;
begin
    if Length(States) = 0 then
    begin
        Result := TState.Null;
    end
    else
    begin
        Latch := TEvent.CreateLatch(1);
        for var i := 0 to High(States) do
            States[i].Subscribe(Latch);
        Result := Latch.State;
    end;
end;

function TState.GetIsSet: Boolean;
begin
    Result := FState.IsSet;
end;

function TState.Subscribe(Subscriber: IMycSubscriber): TSubscription;
begin
    Result := TSubscription.Create(FState, FState.Subscribe(Subscriber));
end;

procedure TState.Unsubscribe(Tag: Pointer);
begin
    FState.Unsubscribe(Tag);
end;

class operator TState.Implicit(const A: TState): IMycState;
begin
    Result := A.FState;
end;

class operator TState.Implicit(const A: IMycState): TState;
begin
    Result.Create(A);
end;

{ TFlag }

class constructor TFlag.ClassCreate;
begin
    FNull := TMycNullFlag.Create;
end;

{ TFlag }

constructor TFlag.Create(const ADirty: IMycFlag);
begin
    FDirty := ADirty;
    if not Assigned(FDirty) then
        FDirty := FNull;
end;

class function TFlag.CreateFlag: IMycFlag;
begin
    Result := TMycFlag.Create;
end;

function TFlag.GetState: TState;
begin
    Result := FDirty.State;
end;

function TFlag.Notify: Boolean;
begin
    Result := FDirty.Notify;
end;

function TFlag.Reset: Boolean;
begin
    Result := FDirty.Reset;
end;

class operator TFlag.Implicit(const A: IMycFlag): TFlag;
begin
    Result.Create(A);
end;

class operator TFlag.Implicit(const A: TFlag): IMycFlag;
begin
    Result := A.FDirty;
end;

class operator TFlag.Initialize(out Dest: TFlag);
begin
    Dest.FDirty := FNull;
end;

{ TEvent }

class constructor TEvent.ClassCreate;
begin
    // Create a singleton null latch instance that is initially (and always) set.
    FNull := TMycNullEvent.Create;
end;

{ TEvent }

constructor TEvent.Create(const ALatch: IMycEvent);
begin
    FLatch := ALatch;
    if not Assigned(FLatch) then
        FLatch := FNull;
end;

class function TEvent.CreateLatch(Count: Integer): TEvent;
begin
    if Count > 0 then
        Result := TMycLatch.Create(Count)
    else
        Result := FNull;
end;

class function TEvent.CreateNotifier: TEvent;
begin
    Result := TMycNotifyEvent.Create;
end;

class function TEvent.Enqueue(var Gate: TEvent; Count: Integer = 1): TState;
begin
    var gateState := Gate.State;
    Gate := TMycLatch.Create(Count);
    gateState.Subscribe(Gate);
    exit(Gate.State);
end;

function TEvent.GetState: TState;
begin
    Result := FLatch.State;
end;

function TEvent.Notify: Boolean;
begin
    Result := FLatch.Notify;
end;

class operator TEvent.Implicit(const A: IMycEvent): TEvent;
begin
    Result.Create(A);
end;

class operator TEvent.Implicit(const A: TEvent): IMycEvent;
begin
    Result := A.FLatch;
end;

class operator TEvent.Initialize(out Dest: TEvent);
begin
    Dest.FLatch := FNull;
end;

end.