/* eslint-disable stylistic/lines-around-comment -- Need the comment! */
/**
 * @file Number formatting utilities for Elysium.
 * @copyright nhcarrigan
 * @license Naomi's Public License
 * @author Naomi Carrigan
 */
import type { NumberFormat } from "@elysium/types";

// Named suffixes up to 1e33 (Decillion). Letter-based suffixes take over from 1e36 onwards.
const namedSuffixes: Array<{ threshold: number; suffix: string }> = [
  // Decillion
  { suffix: "Dc", threshold: 1e33 },
  // Nonillion
  { suffix: "No", threshold: 1e30 },
  // Octillion
  { suffix: "Oc", threshold: 1e27 },
  // Septillion
  { suffix: "Sp", threshold: 1e24 },
  // Sextillion
  { suffix: "Sx", threshold: 1e21 },
  // Quintillion
  { suffix: "Qi", threshold: 1e18 },
  // Quadrillion
  { suffix: "Qa", threshold: 1e15 },
  // Trillion
  { suffix: "T", threshold: 1e12 },
  // Billion
  { suffix: "B", threshold: 1e9 },
  // Million
  { suffix: "M", threshold: 1e6 },
  // Thousand
  { suffix: "K", threshold: 1e3 },
];

// Letter suffixes start at 1e36 ("a"), stepping by 1000 each time (i.e. +3 exponent per letter).
const letterBaseExp = 36;

/**
 * Generates an alphabetic suffix for a given index:
 * 0 → "a", 1 → "b", ..., 25 → "z",
 * 26 → "aa", 27 → "ab", ..., 701 → "zz", 702 → "aaa", ...
 * @param index - The zero-based index to convert to a letter suffix.
 * @returns The alphabetic suffix string.
 */
const getLetterSuffix = (index: number): string => {
  let result = "";
  let n = index;
  do {
    const percent = n % 26;
    result = String.fromCodePoint(97 + percent) + result;
    n = Math.floor(n / 26) - 1;
  } while (n >= 0);
  return result;
};

/**
 * Formats a number with a named or letter-based suffix.
 * @param value - The number to format.
 * @returns The formatted string with suffix.
 */
const formatSuffix = (value: number): string => {
  if (value >= Math.pow(10, letterBaseExp)) {
    const exp = Math.floor(Math.log10(value));
    const stepsAboveBase = Math.floor((exp - letterBaseExp) / 3);
    const steps = stepsAboveBase * 3;
    const divisorExp = letterBaseExp + steps;
    const divisor = Math.pow(10, divisorExp);
    return `${(value / divisor).toFixed(2)}${getLetterSuffix(stepsAboveBase)}`;
  }
  for (const { threshold, suffix } of namedSuffixes) {
    if (value >= threshold) {
      return `${(value / threshold).toFixed(2)}${suffix}`;
    }
  }
  return value < 1
    ? value.toFixed(2)
    : value.toFixed(1);
};

/**
 * Formats a number in scientific notation: e.g. 1.23e15.
 * Falls back to K/M/B/T style below 1 million.
 * @param value - The number to format.
 * @returns The formatted string in scientific notation.
 */
const formatScientific = (value: number): string => {
  if (value < 1e6) {
    return formatSuffix(value);
  }
  // ToExponential handles all magnitudes JS can represent (up to ~1.8e308)
  return value.toExponential(2).replace("e+", "e");
};

/**
 * Formats a number in engineering notation (exponent always a multiple of 3):
 * e.g. 12.35E12, 1.23E300. Falls back to K/M/B/T style below 1 million.
 * @param value - The number to format.
 * @returns The formatted string in engineering notation.
 */
const formatEngineering = (value: number): string => {
  if (value < 1e6) {
    return formatSuffix(value);
  }
  const exp = Math.floor(Math.log10(value));
  const engExp = Math.floor(exp / 3) * 3;
  const mantissa = value / Math.pow(10, engExp);
  return `${mantissa.toFixed(2)}E${String(engExp)}`;
};

/**
 * Formats a number for display using the player's chosen notation style.
 * Negative values are formatted with a leading minus sign.
 * @param value - The number to format.
 * @param format - The notation style to use.
 * @returns The formatted number string.
 */
export const formatNumber = (
  value: number,
  format: NumberFormat = "suffix",
): string => {
  if (!Number.isFinite(value) || Number.isNaN(value)) {
    return "0";
  }
  if (value < 0) {
    return `-${formatNumber(-value, format)}`;
  }

  switch (format) {
    case "scientific":
      return formatScientific(value);
    case "engineering":
      return formatEngineering(value);
    case "suffix":
      return formatSuffix(value);
    default: {
      /* V8 ignore next -- @preserve */
      return formatSuffix(value);
    }
  }
};