/*=============================================================================
 *
 *
 * Format Numbers
 *
 *
 =============================================================================*/

/**
 * Provide `formatNumber` cross-platform number to string converter function.
 *
 * Taken from here:
 * https://github.com/client9/stringencoders/blob/master/src/modp_numtoa.c
 * Original function name: `modp_dtoa2`.
 *
 * Modified:
 * - `isnan` instead of tricky comparing and return "NaN"
 * - handle Infinity values and return "Inf" or "-Inf"
 * - return `OVF` and `-OVF` for numbers bigger than max possible, instead of using `sprintf`
 * - use `Number` instead of double
 * - if negative number rounds to zero, return just "0" instead of "-0"
 *
 * This is a replacement of `dtostrf`.
 */

#ifndef XOD_FORMAT_NUMBER_H
#define XOD_FORMAT_NUMBER_H

namespace xod {

/**
 * Powers of 10
 * 10^0 to 10^9
 */
static const Number powers_of_10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000,
    10000000, 100000000, 1000000000 };

static void strreverse(char* begin, char* end) {
    char aux;
    while (end > begin)
        aux = *end, *end-- = *begin, *begin++ = aux;
};

size_t formatNumber(Number value, int prec, char* str) {
    if (isnan(value)) {
        strcpy(str, "NaN");
        return (size_t)3;
    }

    if (isinf(value)) {
        bool isNegative = value < 0;
        strcpy(str, isNegative ? "-Inf" : "Inf");
        return (size_t)isNegative ? 4 : 3;
    }

    /* if input is larger than thres_max return "OVF" */
    const Number thres_max = (Number)(0x7FFFFFFF);

    Number diff = 0.0;
    char* wstr = str;

    if (prec < 0) {
        prec = 0;
    } else if (prec > 9) {
        /* precision of >= 10 can lead to overflow errors */
        prec = 9;
    }

    /* we'll work in positive values and deal with the
	   negative sign issue later */
    int neg = 0;
    if (value < 0) {
        neg = 1;
        value = -value;
    }

    uint32_t whole = (uint32_t)value;
    Number tmp = (value - whole) * powers_of_10[prec];
    uint32_t frac = (uint32_t)(tmp);
    diff = tmp - frac;

    if (diff > 0.5) {
        ++frac;
        /* handle rollover, e.g.  case 0.99 with prec 1 is 1.0  */
        if (frac >= powers_of_10[prec]) {
            frac = 0;
            ++whole;
        }
    } else if (diff == 0.5 && prec > 0 && (frac & 1)) {
        /* if halfway, round up if odd, OR
		   if last digit is 0.  That last part is strange */
        ++frac;
        if (frac >= powers_of_10[prec]) {
            frac = 0;
            ++whole;
        }
    } else if (diff == 0.5 && prec == 0 && (whole & 1)) {
        ++frac;
        if (frac >= powers_of_10[prec]) {
            frac = 0;
            ++whole;
        }
    }

    if (value > thres_max) {
        if (neg) {
            strcpy(str, "-OVF");
            return (size_t)4;
        }
        strcpy(str, "OVF");
        return (size_t)3;
    }

    int has_decimal = 0;
    int count = prec;
    bool notzero = frac > 0;

    while (count > 0) {
        --count;
        *wstr++ = (char)(48 + (frac % 10));
        frac /= 10;
        has_decimal = 1;
    }

    if (frac > 0) {
        ++whole;
    }

    /* add decimal */
    if (has_decimal) {
        *wstr++ = '.';
    }

    notzero = notzero || whole > 0;

    /* do whole part
	 * Take care of sign conversion
	 * Number is reversed.
	 */
    do
        *wstr++ = (char)(48 + (whole % 10));
    while (whole /= 10);

    if (neg && notzero) {
        *wstr++ = '-';
    }
    *wstr = '\0';
    strreverse(str, wstr - 1);
    return (size_t)(wstr - str);
}

} // namespace xod
#endif