// Copyright 2014-2021 Sindre Sorhus. All rights reserved. MIT license.
// Copyright 2021 Yoshiya Hinosawa. All rights reserved. MIT license.
// Copyright 2021 Giuseppe Eletto. All rights reserved. MIT license.
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

type LocaleOptions = {
  minimumFractionDigits?: number;
  maximumFractionDigits?: number;
};

/** Options for {@linkcode format}. */
export interface FormatOptions {
  /**
   * Uses bits representation.
   *
   * @default {false}
   */
  bits?: boolean;
  /**
   * Uses binary bytes (e.g. kibibyte).
   *
   * @default {false}
   */
  binary?: boolean;
  /**
   * Include plus sign for positive numbers.
   *
   * @default {false}
   */
  signed?: boolean;
  /**
   * Uses localized number formatting. If it is set to true, uses default
   * locale on the system. If it's set to string, uses that locale. The given
   * string should be a
   * {@link https://en.wikipedia.org/wiki/IETF_language_tag | BCP 47 language tag}.
   * You can also give the list of language tags.
   */
  locale?: boolean | string | string[];
  /**
   * The minimum number of fraction digits to display. If neither
   * {@linkcode minimumFractionDigits} or {@linkcode maximumFractionDigits}
   * are set, the default behavior is to round to 3 significant digits.
   */
  minimumFractionDigits?: number;
  /**
   * The maximum number of fraction digits to display. If neither
   * {@linkcode minimumFractionDigits} or {@linkcode maximumFractionDigits}
   * are set, the default behavior is to round to 3 significant digits.
   */
  maximumFractionDigits?: number;
}

/**
 * Convert bytes to a human-readable string: 1337 → 1.34 kB
 *
 * Based on {@link https://github.com/sindresorhus/pretty-bytes | pretty-bytes}.
 * A utility for displaying file sizes for humans.
 *
 * This module is browser compatible.
 *
 * @example
 * ```ts
 * import { format } from "@std/fmt/bytes";
 *
 * format(1337);
 * //=> '1.34 kB'
 *
 * format(100);
 * //=> '100 B'
 *
 * // Display with units of bits
 * format(1337, { bits: true });
 * //=> '1.34 kbit'
 *
 * // Display file size differences
 * format(42, { signed: true });
 * //=> '+42 B'
 *
 * // Localized output using German locale
 * format(1337, { locale: "de" });
 * //=> '1,34 kB'
 * ```
 */
export function format(
  num: number,
  options: FormatOptions = {},
): string {
  if (!Number.isFinite(num)) {
    throw new TypeError(`Expected a finite number, got ${typeof num}: ${num}`);
  }

  const UNITS_FIRSTLETTER = (options.bits ? "b" : "B") + "kMGTPEZY";

  if (options.signed && num === 0) {
    return ` 0 ${UNITS_FIRSTLETTER[0]}`;
  }

  const prefix = num < 0 ? "-" : (options.signed ? "+" : "");
  num = Math.abs(num);

  const localeOptions = getLocaleOptions(options);

  if (num < 1) {
    const numberString = toLocaleString(num, options.locale, localeOptions);
    return prefix + numberString + " " + UNITS_FIRSTLETTER[0];
  }

  const exponent = Math.min(
    Math.floor(
      options.binary ? Math.log(num) / Math.log(1024) : Math.log10(num) / 3,
    ),
    UNITS_FIRSTLETTER.length - 1,
  );
  num /= Math.pow(options.binary ? 1024 : 1000, exponent);

  if (!localeOptions) {
    num = Number(num.toPrecision(3));
  }

  const numberString = toLocaleString(
    num,
    options.locale,
    localeOptions,
  );

  let unit = UNITS_FIRSTLETTER[exponent];
  if (exponent > 0) {
    unit += options.binary ? "i" : "";
    unit += options.bits ? "bit" : "B";
  }

  return prefix + numberString + " " + unit;
}

function getLocaleOptions(
  { maximumFractionDigits, minimumFractionDigits }: FormatOptions,
): LocaleOptions | undefined {
  if (maximumFractionDigits || minimumFractionDigits) {
    return {
      maximumFractionDigits,
      minimumFractionDigits,
    };
  }
}

/**
 * Formats the given number using `Number#toLocaleString`.
 * - If locale is a string, the value is expected to be a locale-key (for example: `de`).
 * - If locale is true, the system default locale is used for translation.
 * - If no value for locale is specified, the number is returned unmodified.
 */
function toLocaleString(
  num: number,
  locale: boolean | string | string[] | undefined,
  options: LocaleOptions | undefined,
): string {
  if (typeof locale === "string" || Array.isArray(locale)) {
    return num.toLocaleString(locale, options);
  } else if (locale === true || options !== undefined) {
    return num.toLocaleString(undefined, options);
  }

  return num.toString();
}