// @ts-check
/**
 * Klammertext's character codes, for typing letters a keyboard lacks:
 * `^o"` is ö, `^s^` is ß, `^a1` is ā, `^00E9^` is é, `^130ED^` an
 * Egyptian hieroglyph, `^9053 53EF^` two characters from one pair of
 * carets, and `^^` is a caret.  The text field replaces a code as soon
 * as the keystroke that completes it is typed (text_editor.js), like a
 * compose key.
 *
 * The tables and the rules are those of Klammertext's K/mac/character.h,
 * character.cpp and katom_process.cpp (the live tree; K/src is
 * deprecated), copied 2026-10-13; `kdesc -c` lists the tables.  Left
 * out, since a text block is not a document: the `^'...'^` literal span
 * (a code is replaced only at the caret here, so nothing needs
 * protecting), and the one-hex-digit form `^a^`, which makes a control
 * character.  A single character standing for itself inside a sequence
 * (`^9053 a^` is 道a) applies only when at least one member is a code
 * point (Andy, 2026-10-13), so that a typed `x^2 + y^2` stays.  An
 * invalid code point, which is an error in a document, stays as typed.
 * The result is normalized to its precomposed form, as Klammertext's
 * `compose` does, so that ö is one character in the page file and to
 * Backspace.
 */

/** The diacritic each mark letter stands for, as a combining character. */
export const DIACRITICS = {
  '`': '̀',   // grave accent
  "'": '́',   // acute accent
  'h': '̂',   // circumflex (hat)
  '~': '̃',   // tilde
  '-': '̄',   // macron
  '"': '̈',   // dieresis
  'b': '̆',   // breve
  'd': '̇',   // dot above
  'r': '̊',   // ring above
  'w': '̌',   // wedge (caron)
  'c': '̧',   // cedilla
  'a': '̋',   // double acute accent
};

/** Letters outside the Roman alphabet and ligatures, `^code^`. */
export const EXTENDED_LATIN = {
  's': 'ß',   // Eszett
  'i': 'ı',   // dotless i
  'I': 'İ',   // capital dotted i
  't': 'þ',   // thorn
  'T': 'Þ',   // thorn capital
  'e': 'ð',   // eth
  'E': 'Ð',   // eth capital
  'o': 'ø',   // o stroke
  'O': 'Ø',   // o stroke capital
  'd': 'đ',   // d stroke
  'D': 'Đ',   // d stroke capital
  'ae': 'æ',  // ae ligature
  'AE': 'Æ',  // ae ligature capital
  'oe': 'œ',  // oe ligature
  'OE': 'Œ',  // oe ligature capital
};

/** Mandarin pinyin tones on a vowel, `^a1` to `^a4`. */
export const PINYIN_TONES = {
  '1': '̄',   // high
  '2': '́',   // rising
  '3': '̌',   // falling-rising
  '4': '̀',   // falling
};

/** A code point in hex: 4 to 6 digits (2 and 3 would collide with the mnemonics). */
const HEX = '[0-9A-Fa-f]{4,6}';

/**
 * Whether the number is a code point a character can be made of
 * (Klammertext's `valid_codepoint`): in range, not a surrogate, not a
 * noncharacter.
 * @param {number} cp
 * @returns {boolean}
 */
export function validCodePoint(cp) {
  if (cp < 0 || cp > 0x10FFFF) return false;
  if (0xD800 <= cp && cp <= 0xDFFF) return false;
  if (0xFDD0 <= cp && cp <= 0xFDEF) return false;
  if ((cp & 0xFFFE) === 0xFFFE) return false;
  return true;
}

/**
 * What a sequence's members stand for: a hex member its code point, any
 * other, a single character, itself; or null when no member is a code
 * point (the run is not a sequence) or one is not a valid code point.
 * @param {string[]} members
 * @returns {string | null}
 */
function charactersOf(members) {
  const hexRe = new RegExp(`^${HEX}$`, 'u');
  if (!members.some((m) => hexRe.test(m))) return null;
  let result = '';
  for (const member of members) {
    if (hexRe.test(member)) {
      const cp = parseInt(member, 16);
      if (!validCodePoint(cp)) return null;
      result += String.fromCodePoint(cp);
    } else {
      result += member;
    }
  }
  return result;
}

/**
 * The code that the text ends with, if it ends with a complete one.
 * Checked in Klammertext's order: an extended Latin letter, a code point
 * or a sequence, the caret itself, a diacritic, a pinyin tone.
 * @param {string} text
 * @returns {{length: number, character: string} | null}
 *     How many characters of the text the code takes, and what it means.
 */
export function codeAtEnd(text) {
  const extended = /\^(ae|AE|oe|OE|[siItTeEoOdD])\^$/u.exec(text);
  if (extended) {
    const name = /** @type {keyof typeof EXTENDED_LATIN} */ (extended[1]);
    return { length: name.length + 2, character: EXTENDED_LATIN[name] };
  }
  // One pair of carets around members separated by spaces, on one line,
  // no space inside the carets: code points of 4 to 6 hex digits and,
  // once one of those is present, single characters standing for
  // themselves (a caret cannot be one: it would close the sequence).
  const member = `(?:${HEX}|[^\\s^])`;
  const sequence = new RegExp(`\\^(${member}(?: +${member})*)\\^$`, 'u').exec(text);
  if (sequence) {
    const character = charactersOf(sequence[1].split(/ +/));
    if (character !== null) return { length: sequence[0].length, character };
  }
  if (text.endsWith('^^')) return { length: 2, character: '^' };
  // The base is a letter of any alphabet: not a space, a digit or ASCII
  // punctuation (Klammertext's rule).
  const diacritic = /\^([^\s0-9!-/:-@[-`{-~])([-'`h~"cbrdwa])$/u.exec(text);
  if (diacritic) {
    const mark = /** @type {keyof typeof DIACRITICS} */ (diacritic[2]);
    return { length: diacritic[0].length, character: (diacritic[1] + DIACRITICS[mark]).normalize('NFC') };
  }
  const tone = /\^([aeiou])([1-4])$/u.exec(text);
  if (tone) {
    const number = /** @type {keyof typeof PINYIN_TONES} */ (tone[2]);
    return { length: 3, character: (tone[1] + PINYIN_TONES[number]).normalize('NFC') };
  }
  return null;
}