// Minus Directional Indicator
//
// di_minus - DI-
//
// 100 * EMA(-DM) / (EMA(+DM) + EMA(-DM)), measures downward pressure
//
// Inputs:    4 (OHLC)
// Outputs:   1 (DI-)
// Constants: 1 (period)

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

typedef struct {
    uint_t k;
} ts_di_minus_params_t;

ts_parameter_t const ts_di_minus_p = { .n_inputs = 4, .n_outputs = 1, .n_constants = 1, .params_size = sizeof(ts_di_minus_params_t) };

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

int ts_di_minus(
	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_di_minus_p );
	if ( !c ) return -1;
	uint_t k = ((ts_di_minus_params_t *)c)->k;
	if (k == 0 || n < 2) return -1;
	fp_t *ema_minus = calloc( n, sizeof( fp_t ) );
	fp_t *ema_plus = calloc( n, sizeof( fp_t ) );
	if( !ema_minus || !ema_plus ) { free( ema_minus ); free( ema_plus ); return -1; }

	for( uint_t i = 1; i < n; ++i )
	{
		fp_t hdmd = ts_h( x, i ) - ts_h( x, i - 1 );
		fp_t ldml = ts_l( x, i - 1 ) - ts_l( x, i );

		fp_t minus_dm = ldml > hdmd && ldml > 0 ? ldml : 0;
		fp_t plus_dm = hdmd > ldml && hdmd > 0 ? hdmd : 0;

		ema_minus[i] = i == 1 ? minus_dm
		                      : ema_minus[i - 1] + ( 1.0 / k ) * ( minus_dm - ema_minus[i - 1] );
		ema_plus[i] = i == 1 ? plus_dm
		                     : ema_plus[i - 1] + ( 1.0 / k ) * ( plus_dm - ema_plus[i - 1] );
	}

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

	for( uint_t i = k; i < n; ++i )
	{
		fp_t denom = ema_minus[i] + ema_plus[i];
		y[0][i] = denom != 0 ? 100.0 * ema_minus[i] / denom : 0;
	}

	free( ema_minus );
	free( ema_plus );
	return 0;
}