/**
	simple low-pass filter that averages successive samples by:
	saving the value of the last sample in a vector
	averaging it with the first sample of the next vector
*/

/**
	include files	
*/

#include "ext.h" // should always be first
#include "ext_obex.h" // followed by ext_obex.h
#include "z_dsp.h" // ONLY MSP

/**
	structure declaration	
*/

typedef struct _myfilter
{
	t_pxobject f_obj; // t_pbxobject in MSP, for Max use t_object
	t_float f_sample; // internal state
} t_myfilter;

/**
	initialization routine	
*/

void *myfilter_class;
void *myfilter_new(double val);
t_int *myfilter_perform(t_int *w);
void myfilter_dsp(t_myfilter *x, t_signal **sp, short *count);

int main(void)
{
	t_class *c; // always first
	
	c = class_new("myfilter", (method)myfilter_new, (method)dsp_free, sizeof(t_myfilter), NULL, 0);
	// creating the class with the new instance routine and the free function dsp_free
	
	class_addmethod(c, (method)myfilter_dsp, "dsp", A_CANT, 0);// respond to the dsp message 
    // (sent to MSP objects when audio is turned on/off)
	// binds C method myfilter_dsp  to the text symbol "dsp"
	
	class_dspinit(c); // ONLY DSP
	// adds some standard method handlers for internal messages used by all signal objects
	
	class_register(CLASS_BOX, c);
	// will be searched when typing it into a Max object box
	
	myfilter_class = c;
	// assign the class we’ve created to a global variable so we can use it when creating new instances
	
	return 0;
}

/**
	new instance routine	
*/

void *myfilter_new(double val)
{
    t_myfilter *x = object_alloc(myfilter_class);
    dsp_setup((t_pxobject *)x, 1); // creating one signal inlet
    outlet_new((t_object *)x, "signal"); // creating one signal outlet
    return (x);
}

/**
	dsp method	
*/

void myfilter_dsp(t_myfilter *x, t_signal **sp, short *count)
{
	dsp_add(myfilter_perform, 4, x, sp[0]->s_vec, sp[1]->s_vec, sp[0]->s_n);
	x->f_sample = 0; // initialize internal state
}

/**
	perform routine	
*/

t_int *myfilter_perform(t_int *w)
{
	t_myfilter *x = (t_myfilter *)w[1];
	t_float *in = (t_float *)w[2];
	t_float *out = (t_float *)w[3];
	int n = (int)w[4];
	t_float samp = x->f_sample;	// samp float reads from internal state
	t_float val;
	
	while (n--) { // loop that performs the average continously
		val = *in++; // reads new sample
		*out++ = (val + samp) * 0.5; // average
		samp = val;
	}
	x->f_sample = samp;	// save to internal state
	
	return w + 5;
}