/*
 * axis.c
 *
 * Logic to deal with various axises
 *
 * Copyright (C) 2013-2021 Sylvain Munaut
 * SPDX-License-Identifier: GPL-3.0-or-later
 */

/*! \addtogroup axis
 *  @{
 */

/*! \file axis.c
 *  \brief Logic to deal with various axises
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#include "axis.h"


#define FX_MODE_COUNT		0
#define FX_MODE_RELATIVE	1
#define FX_MODE_ABSOLUTE	2


static double
_si_scaling(double val, int max_num, char *prefix, int *exp)
{
	const char prefixes[5] = { ' ', 'k', 'M', 'G', 'T' };
	int exponent = log10f(fabs(val));
	int d = exponent >= max_num ? ((exponent - max_num + 3) / 3) : 0;

	if (prefix)
		*prefix = prefixes[d];

	if (exp)
		*exp = d * 3;

	return val / powf(10.0, d * 3);
}

static int
_num_decimals(double val)
{
	int c;
	double v;

	for (c=0; c<22; c++) {
		v = val * pow(10, c);
		if ( fabs(v - round(v)) == 0.0 )
			return c;
	}

	return -1;
}


void
freq_axis_build(struct freq_axis *fx, double center, double span, int n_div)
{
	/* Basic info */
	fx->center = center;
	fx->span   = span;
	fx->step   = span / n_div;

	/* Select mode of operation */
	if (span == 0.0) {
		fx->mode = FX_MODE_COUNT;
	} else if (center == 0.0) {
		fx->mode = FX_MODE_RELATIVE;
	} else if (floor(log10f(fx->step)) < (floor(log10f(fx->center)) - 4)) {
		fx->mode = FX_MODE_RELATIVE;
	} else {
		fx->mode = FX_MODE_ABSOLUTE;
	}

	/* Select display format for abolute frequencies */
	if (center != 0.0)
	{
		double min_freq, max_freq, big_freq;
		char prefix[2] = {0, 0};
		int exp, x, y, z;

		max_freq = fx->center + (span / 2.0);
		min_freq = fx->center - (span / 2.0);

		big_freq = (fabs(max_freq) > fabs(min_freq)) ?
				fabs(max_freq) : fabs(min_freq);

		_si_scaling(big_freq, 4, prefix, &exp);

		if (prefix[0] == ' ')
			prefix[0] = '\0';

		fx->abs_scale = 1.0 / powf(10.0, exp);

		x = (int)floor(log10f(big_freq)) - exp + 1;
		y = _num_decimals(fx->center * fx->abs_scale);
		z = _num_decimals(fx->step   * fx->abs_scale);

		if (z > y)
			y = z;

		if (x + y > 6)
			y = 6 - x;

		sprintf(fx->abs_fmt, "%%.%dlf%s", y, prefix);
	}

	/* Select display format for relative mode */
	if (fx->mode == FX_MODE_RELATIVE)
	{
		double max_dev = fx->step * 5;
		char prefix[2] = {0, 0};
		int exp, x, y;

		_si_scaling(max_dev, 3, prefix, &exp);

		if (prefix[0] == ' ')
			prefix[0] = '\0';

		fx->rel_step = fx->step / powf(10.0, exp);

		x = (int)floor(log10f(max_dev)) - exp + 1;
		y = _num_decimals(fx->rel_step);

		if (x + y > 4)
			y = 4 - x;

		sprintf(fx->rel_fmt, "%%+.%dlf%s", y, prefix);
	}
}

void
freq_axis_render(struct freq_axis *fx, char *str, int step)
{
	/* Special case: count mode */
	if (step && (fx->mode == FX_MODE_COUNT)) {
		sprintf(str, "%+d", step);
		return;
	}

	/* Special case: no center frequency */
	if (!step && (fx->center == 0.0)) {
		sprintf(str, "0");
		return;
	}

	/* Relative case */
	if (step && (fx->mode == FX_MODE_RELATIVE)) {
		sprintf(str, fx->rel_fmt, step * fx->rel_step);
		return;
	}

	/* Normal full absolute frequency */
	sprintf(str, fx->abs_fmt, (fx->center + step * fx->step) * fx->abs_scale);
}

/*! @} */