// Percentage Change
//
// change - pct_change
//
// (x[t] - x[t-k]) / x[t-k] * 100
//
// Inputs:    1
// Outputs:   1 (Change %)
// Constants: 1 (period)

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

typedef struct {
    uint_t k;
} ts_change_params_t;

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

uint_t ts_change_offset( ts_constant_t const *c )
{
	( void )c;
	return ( c ? ((ts_change_params_t *)c)->k : 0 );
}

int ts_change(
	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_change_p );
	if ( !c ) return -1;
	uint_t k = ((ts_change_params_t *)c)->k;
	if (k == 0 || n < k) return -1;

	for( uint_t i = k; i < n; ++i )
	{
		if( x[0][i - k] == 0 ) { y[0][i] = 0; continue; }
		y[0][i] = ( x[0][i] - x[0][i - k] ) / x[0][i - k] * 100;
	}

	return 0;
}