// Elder Force Index
//
// elder_force_index - EFI
//
// EMA((Close - PrevClose) * Volume), volume-weighted price change
//
// Inputs:    5 (OHLCV)
// Outputs:   1 (EFI)
// Constants: 1 (period)

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

typedef struct {
    uint_t k;
} ts_elder_force_index_params_t;

ts_parameter_t const ts_elder_force_index_p = { .n_inputs = 5, .n_outputs = 1, .n_constants = 1, .params_size = sizeof(ts_elder_force_index_params_t) };

uint_t ts_elder_force_index_offset( ts_constant_t const *c )
{
	( void )c;
	return ( 1 );
}

int ts_elder_force_index(
	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_elder_force_index_p );
	if ( !c ) return -1;
    uint_t k = ((ts_elder_force_index_params_t *)c)->k;
	if (k == 0 || n < k) return -1;
    fp_t a = 1.0 / k;

    fp_t fi = 0;
    if ( n > 1 )
        fi = ( ts_c( x, 1 ) - ts_c( x, 0 ) ) * ts_v( x, 1 );
    y[0][0] = fi;

    for( uint_t i = 1; i < n; ++i )
    {
        fi = ( ts_c( x, i ) - ts_c( x, i - 1 ) ) * ts_v( x, i );
        y[0][i] = y[0][i - 1] + a * ( fi - y[0][i - 1] );
    }

	return 0;
}