// Triangular Moving Average
//
// average_triangle - tma
//
// A moving average of moving averages
//
// y[i] = 
// 
// Inputs:    1
// Outputs:   1
// Constants: 1
//
// 012345678901234567890123456789
// ---------01234567890123456
// ------------------0


#include <stdlib.h>
#include "ts.h"


typedef struct {
    uint_t k;
} ts_average_triangle_params_t;

ts_parameter_t const ts_average_triangle_p = { .n_inputs = 1, .n_outputs = 1, .n_constants = 1, .params_size = sizeof(ts_average_triangle_params_t) };


uint_t ts_average_triangle_offset( ts_constant_t const *c )
{
	( void )c;
	return ( c ? 2 * ( ((ts_average_triangle_params_t *)c)->k - 1 ) : 0 );
}

int ts_average_triangle(
	fp_t * const *y, uint_t y_n,
	fp_t const * const *x, uint_t x_n,
	uint_t n, ts_constant_t const *c
)
{
	TS_PROLOGUE( ts_average_triangle_p );
	if ( !c ) return -1;
	uint_t k = ((ts_average_triangle_params_t *)c)->k;
	if (k == 0 || n < k) return -1;

	fp_t rk2 = _ts_reciprocal( _ts_square( k ) );
	uint_t xi = 0;
	uint_t yi = 2 * ( k - 1 );

	fp_t *xsum = malloc(k * sizeof(fp_t));
	if (!xsum) return -1;
	uint_t xsumi = 0;

	fp_t sum_of_xsum = 0;

   xsum[0] = 0;

	for (uint_t j = 0; j < n && j < 2 * (k - 1); ++j) y[0][j] = 0;

	fp_t last_sum = 0;

	for( ; xi < k; xi++ )
	{
		xsum[xsumi] += x[0][xi];
		last_sum = xsum[xsumi];
	}

    sum_of_xsum = xsum[xsumi];
    xsumi++;

	for( ; xi < 2 * k - 1; xi++ )
	{
	    xsum[xsumi] = xsum[xsumi - 1] + x[0][xi] - x[0][xi - k];
	    last_sum = xsum[xsumi];
	    sum_of_xsum += xsum[xsumi];
    	xsumi++;
	}

	y[0][yi++] = sum_of_xsum * rk2;

	for( ; xi < n; ++xi, ++yi )
	{
	    if( xsumi == k )
	    {
	        xsumi = 0;
       	    sum_of_xsum -= xsum[xsumi];
	        xsum[xsumi] = last_sum + x[0][xi] - x[0][xi - k];
	    }
	    else
	    {
     	    sum_of_xsum -= xsum[xsumi];
	        xsum[xsumi] = last_sum + x[0][xi] - x[0][xi - k];
	    }

        last_sum = xsum[xsumi];
        sum_of_xsum += xsum[xsumi];
		y[0][yi] = sum_of_xsum * rk2;

		xsumi++;
	}

	free(xsum);
	return 0;
}