// Fisher Transform
//
// fisher_transform - FT
//
// 0.5 * log(price_position / (1 - price_position)), normalized to range
//
// Inputs:    4 (OHLC)
// Outputs:   2 (Transform, Trigger)
// Constants: 1 (period)

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

typedef struct {
    uint_t k;
} ts_fisher_transform_params_t;

ts_parameter_t const ts_fisher_transform_p = { .n_inputs = 4, .n_outputs = 2, .n_constants = 1, .params_size = sizeof(ts_fisher_transform_params_t) };

uint_t ts_fisher_transform_offset( ts_constant_t const *c )
{
	( void )c;
	return ( c ? ((ts_fisher_transform_params_t const *)c)->k - 1 : 0 );
}

int ts_fisher_transform(
	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_fisher_transform_p );
	if ( !c ) return -1;
    uint_t k = ((ts_fisher_transform_params_t const *)c)->k;
    if (k == 0 || n < k) return -1;

    for (uint_t i = k - 1; i < n; ++i)
    {
        /* Find high and low over window */
        fp_t hh = x[1][i - k + 1];
        fp_t ll = x[2][i - k + 1];
        for (uint_t j = i - k + 2; j <= i; ++j)
        {
            if (x[1][j] > hh) hh = x[1][j];
            if (x[2][j] < ll) ll = x[2][j];
        }

        fp_t range = hh - ll;
        fp_t val = range != 0 ? (x[3][i] - ll) / range : 0.5;

        /* Clamp to [0.01, 0.99] to avoid log(0) */
        if (val < 0.01) val = 0.01;
        if (val > 0.99) val = 0.99;

        fp_t fisher = 0.5 * log(val / (1.0 - val));

        /* Smooth with previous value (skip first output) */
        uint_t out_i = i;
        if (i > k - 1)
        {
            fisher = fisher + 0.5 * y[0][out_i - 1];
        }
        y[0][out_i] = fisher;

        /* Trigger line = previous fisher */
        if (out_i > 0)
        {
            y[1][out_i] = y[0][out_i - 1];
        }
        else
        {
            y[1][out_i] = 0;
        }
    }
	return 0;
}