const UNITS =      ['','K','M','G','T','P'];
const FRACTIONAL = ['','m','u','n','p','f']; // milli micro nano pico femto

export function formatSi(inValue, increment=1000, suffix=null, firstSuffix=null, startingExponent=0, minExponent=0)
{
  var val = inValue;
  var exp = startingExponent;
  while ( val >= increment && exp+1 < UNITS.length || exp < minExponent ) {
    val = val/increment;
    exp++;
  }

  var out = '';
  if ( (val < 1) || ( val < 10 ) ) {
    out = Math.round(val*100)/100;
  } else if ( val < 100 ) {
    out = Math.round(val*10)/10;
  } else {
    out = Math.round(val);
  }

  if ( exp === 0 && firstSuffix !== null) {
    out += " " + firstSuffix;
  } else {
    out += " " + UNITS[exp] + suffix||'';
  }

  return out;
}

export function exponentNeeded(val, increment=1000) {
  let exp = 0;
  while ( val >= increment ) {
    val = val/increment;
    exp++;
  }

  return exp;
}

export function parseSi(inValue, increment=null, allowFractional=true) {
  if ( !inValue || typeof inValue !== 'string' || !inValue.length ) {
    return NaN;
  }

  inValue = inValue.replace(/,/g,'')

  let [, valStr, unit, incStr] = inValue.match(/^([0-9.-]+)\s*([^0-9.-]?)([^0-9.-]?)/);
  const val = parseFloat(valStr);

  if ( !unit ) {
    return val;
  }

  // micro "mu" symbol -> u
  if ( unit.charCodeAt(0) === 181 ) {
    unit = 'u';
  }

  const divide = FRACTIONAL.includes(unit);
  const multiply = UNITS.includes(unit.toUpperCase());

  if ( increment === null ) {
    // Automatically handle 1 KB = 1000B, 1 KiB = 1024B if no increment set
    if ( (multiply || divide) && incStr === 'i' ) {
      increment = 1024;
    } else {
      increment = 1000;
    }
  }

  if ( divide && allowFractional ) {
    const exp = FRACTIONAL.indexOf(unit);
    return val / Math.pow(increment, exp);
  }

  if ( multiply ) {
    const exp = UNITS.indexOf(unit.toUpperCase());
    return val * Math.pow(increment, exp);
  }

  // Unrecognized unit character
  return val;
}