import { COLOR_HUES, type ColorHueKey } from "@sanity/color";

// Gray reads as "disabled" in the UI, so it never comes up as an identity color.
const POSSIBLE_HUES: ColorHueKey[] = COLOR_HUES.filter((hue) => hue !== "gray");

/**
 * Returns the text and color for an identity marker. Hashing the id keeps its
 * color stable across sessions and across every surface that draws it.
 * Initials are at most two upper-cased characters. Names carry punctuation and
 * digits ("7-Eleven", "0xHoldings"), which a plain whitespace split reduces to
 * "7" or to nothing at all.
 * @public
 */
export function getInitials({ id, name }: { id: string; name: string }): {
  initials: string;
  color: ColorHueKey;
} {
  const hash = id.split("").reduce((acc, char) => acc + char.charCodeAt(0), 0);
  const index = hash % POSSIBLE_HUES.length;

  return {
    initials: resolveInitials(name),
    color: POSSIBLE_HUES[index],
  };
}

const SYMBOLS = /[^\p{Alpha}\p{N}\p{White_Space}]/gu;
const WHITESPACE = /\p{White_Space}+/u;
const ALPHANUMERIC_SEGMENTS = /(\p{N}+|\p{Alpha}+)/gu;
const IS_NUMERIC = /^\p{N}+$/u;

function resolveInitials(name: string): string {
  if (!name) return "";

  const namesArray = name
    .replace(SYMBOLS, "")
    .split(WHITESPACE)
    .filter(Boolean);

  if (namesArray.length === 0) return "";

  if (namesArray.length === 1) {
    const word = namesArray[0];
    const segments = word.match(ALPHANUMERIC_SEGMENTS) || [];

    if (segments.length === 0) return "";
    if (segments.length === 1) {
      if (word.length === 1) {
        return word.toUpperCase();
      }

      if (IS_NUMERIC.test(word)) {
        return `${word.charAt(0)}${word.charAt(1)}`.toUpperCase();
      }

      return word.charAt(0).toUpperCase();
    }

    return `${segments[0]!.charAt(0)}${segments[1].charAt(0)}`.toUpperCase();
  }

  return `${namesArray[0].charAt(0)}${namesArray[namesArray.length - 1].charAt(0)}`.toUpperCase();
}