// Linear Decay
//
// decay_linear -  decay
//
// Propogates the maximum values of a function into the future for at most k periods
//
// y_i = max( x_i, y_i-1 - k )
//
// Inputs:    1
// Outputs:   1
// Constants: 0


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


typedef struct {
    uint_t k;
} ts_decay_linear_params_t;

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


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

int ts_decay_linear(
	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_decay_linear_p );
	if ( !c ) return -1;
	uint_t k = ((ts_decay_linear_params_t const *)c)->k;
	if (k == 0 || n < k) return -1;

 for (uint_t zi = 0; zi < k; ++zi) y[0][zi] = 0;

	uint_t xi = 1;

	fp_t prev = x[0][0];
	fp_t r = prev / (fp_t)k;

	for( ; xi < k; xi++ )
	{
		prev -= r;

		if( x[0][xi] > prev )
		{
			prev = x[0][xi];
			r = x[0][xi] / (fp_t)k;
		}
		else
		{
			prev = fmax( prev, 0 );
		}
	}

	for( uint_t yi = k; xi < n; xi++, yi++ )
	{
		fp_t curr = prev - r;

		if( x[0][xi] > curr )
		{
			curr = x[0][xi];
			r = x[0][xi] / (fp_t)k;
		}
		else
		{
			curr = fmax( curr, 0 );
		}

		y[0][yi] = curr;
		prev = curr;
	}
	return 0;
}