text: /*
   *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
   *
   *  Use of this source code is governed by a BSD-style license
   *  that can be found in the LICENSE file in the root of the source
   *  tree. An additional intellectual property rights grant can be found
   *  in the file PATENTS.  All contributing project authors may
   *  be found in the AUTHORS file in the root of the source tree.
   */
  
  #ifndef API_DTMFSENDERINTERFACE_H_
  #define API_DTMFSENDERINTERFACE_H_
  
  #include <string>
  
  #include "api/mediastreaminterface.h"
  #include "rtc_base/refcount.h"
  
  namespace webrtc {
  
  // DtmfSender callback interface, used to implement RTCDtmfSender events.
  // Applications should implement this interface to get notifications from the
  // DtmfSender.
  class DtmfSenderObserverInterface {
   public:
    // Triggered when DTMF |tone| is sent.
    // If |tone| is empty that means the DtmfSender has sent out all the given
    // tones.
    virtual void OnToneChange(const std::string& tone) = 0;
  
   protected:
    virtual ~DtmfSenderObserverInterface() = default;
  };
  
  // The interface of native implementation of the RTCDTMFSender defined by the
  // WebRTC W3C Editor's Draft.
  // See: https://www.w3.org/TR/webrtc/#peer-to-peer-dtmf
  class DtmfSenderInterface : public rtc::RefCountInterface {
   public:
    // Used to receive events from the DTMF sender. Only one observer can be
    // registered at a time. UnregisterObserver should be called before the
    // observer object is destroyed.
    virtual void RegisterObserver(DtmfSenderObserverInterface* observer) = 0;
    virtual void UnregisterObserver() = 0;
  
    // Returns true if this DtmfSender is capable of sending DTMF. Otherwise
    // returns false. To be able to send DTMF, the associated RtpSender must be
    // able to send packets, and a "telephone-event" codec must be negotiated.
    virtual bool CanInsertDtmf() = 0;
  
    // Queues a task that sends the DTMF |tones|. The |tones| parameter is treated
    // as a series of characters. The characters 0 through 9, A through D, #, and
    // * generate the associated DTMF tones. The characters a to d are equivalent
    // to A to D. The character ',' indicates a delay of 2 seconds before
    // processing the next character in the tones parameter.
    //
    // Unrecognized characters are ignored.
    //
    // The |duration| parameter indicates the duration in ms to use for each
    // character passed in the |tones| parameter. The duration cannot be more
    // than 6000 or less than 70.
    //
    // The |inter_tone_gap| parameter indicates the gap between tones in ms. The
    // |inter_tone_gap| must be at least 50 ms but should be as short as
    // possible.
    //
    // If InsertDtmf is called on the same object while an existing task for this
    // object to generate DTMF is still running, the previous task is canceled.
    // Returns true on success and false on failure.
    virtual bool InsertDtmf(const std::string& tones,
                            int duration,
                            int inter_tone_gap) = 0;
  
    // Returns the tones remaining to be played out.
    virtual std::string tones() const = 0;
  
    // Returns the current tone duration value in ms.
    // This value will be the value last set via the InsertDtmf() method, or the
    // default value of 100 ms if InsertDtmf() was never called.
    virtual int duration() const = 0;
  
    // Returns the current value of the between-tone gap in ms.
    // This value will be the value last set via the InsertDtmf() method, or the
    // default value of 50 ms if InsertDtmf() was never called.
    virtual int inter_tone_gap() const = 0;
  
   protected:
    ~DtmfSenderInterface() override = default;
  };
  
  }  // namespace webrtc
  
  #endif  // API_DTMFSENDERINTERFACE_H_
  