#ifndef STK_ENVELOPE_H
#define STK_ENVELOPE_H

#include "Generator.h"

namespace stk {

/***************************************************/
/*! \class Envelope
    \brief STK linear line envelope class.

    This class implements a simple linear line envelope generator
    which is capable of ramping to an arbitrary target value by a
    specified \e rate.  It also responds to simple \e keyOn and \e
    keyOff messages, ramping to a specified target (default = 1.0) on
    keyOn and to a specified target (default = 0.0) on keyOff.

    by Perry R. Cook and Gary P. Scavone, 1995--2021.
*/
/***************************************************/

class Envelope : public Generator
{
 public:

  //! Default constructor.
  Envelope( void );

  //! Class destructor.
  ~Envelope( void );

  //! Assignment operator.
  Envelope& operator= ( const Envelope& e );

  //! Start ramping to specified target (default = 1).
  void keyOn( StkFloat target = 1.0 ) { this->setTarget( target ); };

  //! Start ramping to specified target (default = 0).
  void keyOff(  StkFloat target = 0.0 ) { this->setTarget( target ); };

  //! Set the \e rate.
  /*!
    The \e rate must be positive (though a value of 0.0 is allowed).
   */
  void setRate( StkFloat rate );

  //! Set the \e rate based on a positive time duration (seconds).
  /*!
    The \e rate is calculated such that the envelope will ramp from
    the current value to the current target in the specified time duration.
   */
  void setTime( StkFloat time );

  //! Set the target value.
  void setTarget( StkFloat target );

  //! Set current and target values to \e value.
  void setValue( StkFloat value );

  //! Return the current envelope \e state (0 = at target, 1 otherwise).
  int getState( void ) const { return state_; };

  //! Return the last computed output value.
  StkFloat lastOut( void ) const { return lastFrame_[0]; };

  //! Compute and return one output sample.
  StkFloat tick( void );

  //! Fill a channel of the StkFrames object with computed outputs.
  /*!
    The \c channel argument must be less than the number of
    channels in the StkFrames argument (the first channel is specified
    by 0).  However, range checking is only performed if _STK_DEBUG_
    is defined during compilation, in which case an out-of-range value
    will trigger an StkError exception.
  */
  StkFrames& tick( StkFrames& frames, unsigned int channel = 0 );

 protected:

  void sampleRateChanged( StkFloat newRate, StkFloat oldRate );

  StkFloat value_;
  StkFloat target_;
  StkFloat rate_;
  int state_;
};

inline StkFloat Envelope :: tick( void )
{
  if ( state_ ) {
    if ( target_ > value_ ) {
      value_ += rate_;
      if ( value_ >= target_ ) {
        value_ = target_;
        state_ = 0;
      }
    }
    else {
      value_ -= rate_;
      if ( value_ <= target_ ) {
        value_ = target_;
        state_ = 0;
      }
    }
    lastFrame_[0] = value_;
  }

  return value_;
}

inline StkFrames& Envelope :: tick( StkFrames& frames, unsigned int channel )
{
#if defined(_STK_DEBUG_)
  if ( channel >= frames.channels() ) {
    oStream_ << "Envelope::tick(): channel and StkFrames arguments are incompatible!";
    handleError( StkError::FUNCTION_ARGUMENT );
  }
#endif

  StkFloat *samples = &frames[channel];
  unsigned int hop = frames.channels();
  for ( unsigned int i=0; i<frames.frames(); i++, samples += hop )
    *samples = tick();

  return frames;
}

} // stk namespace

#endif
