Ewma.h

/*
 * EWMA Filter - Exponentially Weighted Moving Average filter used for smoothing data series readings.
 *
 *     output = alpha * reading + (1 - alpha) * lastOutput
 *
 * Where:
 *  -   alpha = factor greater than 0 and less or equal to 1
 *  -   reading = current input value
 *  -   lastOutput = last filter output value
 *  -   output = filter output value after the last reading
 * https://www.arduino.cc/reference/en/libraries/ewma/
 */

#ifndef EWMA_H_
#define EWMA_H_

class Ewma {
public:
	/*
	 * Current data output
	 */
	double output = 0;
	/*
	 * Smoothing factor, in range [0,1]. Higher the value - less smoothing (higher the latest reading impact).
	 */
	double alpha = 0;

	// Custom constructor, need alpha init
	Ewma();

	/*
	 * Creates a filter without a defined initial output. The first output will be equal to the first input.
	 */
	Ewma(double alpha);

	/*
	 * Creates a filter with a defined initial output.
	 */
	Ewma(double alpha, double initialOutput);

	void reset();

	/*
	 * Specifies a reading value.
	 * @returns current output
	 */
	double filter(double input);

private:
	bool hasInitial = false;
};

#endif /* EWMA_H_ */