import { empty }                from '../constants';
import { formatNumber }         from '../formatNumber';
import isNil                    from 'lodash/isNil';
import round                    from 'lodash/round';

export type Options = {
    /**
     * format specification to pass to @link{formatNumber}
     */
    format?: string;
    /**
     * left padding to apply to numeric value
     */
    pad?: number;
    /**
     * Array of suffixes to use for large values (default: ['K', 'M', 'B', 'T', 'P', 'E', 'Z', 'Y'])
     */
    macro?: ArrayLike<string>;
    /**
     * Array of suffixed to use for small values (default: ['m', 'µ', 'n', 'p', 'f', 'a', 'z', 'y'])
     */
    micro?: ArrayLike<string>;
    /**
     * Multiplier for each level of suffixes (default: 1000)
     */
    unit?: number;
    /**
     * Number of digits after the decimal point to display
     */
    precision?: number;
};

/**
 * Abbreviate a number by adding a suffix for metric units (i.e. 1000 => 1K, .0001 = 1m)
 *
 * @param input The number to abbreviate
 * @param __namedParameters {@link MetricUnitOptions}
 */
export function metricUnits(
    input: number,
    {
        format,
        pad,
        macro = [ 'K', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y' ],
        micro = [ 'm', 'µ', 'n', 'p', 'f', 'a', 'z', 'y' ],
        unit = 1000,
        precision = 2,
    }:  Options = {},
):  string {
    let number  = Math.abs(input);
    let suffix  = empty;
    let index   = 0;

    if(number < 1) {
        while((number + Number.EPSILON) < 1 && index < micro.length) {
            suffix = micro[index++];
            number = number * unit;
        }
    } else {
        while((number + Number.EPSILON) >= unit && index < macro.length) {
            suffix = macro[index++];
            number = number / unit;
        }
    }

    return (isNil(format) ? round(number, precision).toString() : formatNumber(round(number, precision), format)).padStart(pad ?? 0) + suffix;
}

export default metricUnits;