/**
 * Copyright since 2025 Mifos Initiative
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/**
 * Casing for client names: the name is stored exactly as the officer typed it, except that a word
 * starting with a lower-case letter has that first letter raised. Nothing else is touched.
 *
 *   'keshav Singh sisodiya'                  →  'Keshav Singh Sisodiya'
 *   'lincpay lTD'                            →  'Lincpay LTD'
 *   'Technoludium Solutions Private Limited' →  unchanged
 *   'TECHNOLUDIUM SOLUTIONS'                 →  unchanged
 *
 * Deliberately NOT full title-casing. Lower-casing the rest of each word would rewrite an entity
 * name the officer entered as it appears on the certificate — 'TECHNOLUDIUM' becoming
 * 'Technoludium', 'Ltd' becoming a forced 'LTD'. That name is matched character-for-character
 * against the PAN holder's registered name during KYC verification, so the typed spelling is the
 * thing to preserve; only an unintended lower-case first letter is corrected.
 */

/** Characters after which a new word starts: 'jean-marie' → 'Jean-Marie'. */
const SEGMENT_STARTERS = new Set([
  '-',
  "'",
  '’'
]);

/**
 * Raises the first letter of each word in a single space-delimited token, leaving every other
 * character as typed.
 */
function capitalizeWord(word: string): string {
  let result = '';
  for (let i = 0; i < word.length; i++) {
    const previous = i === 0 ? '' : word[i - 1];
    let startsWord = i === 0 || SEGMENT_STARTERS.has(previous);
    if (previous === "'" || previous === '’') {
      // 'o'brien' / 'd'souza' capitalise after the apostrophe, but a possessive
      // ('lincpay's') must not — only a single leading letter marks the name prefix.
      startsWord = i === 2;
    }
    result += startsWord ? word[i].toUpperCase() : word[i];
  }
  return result;
}

/**
 * Applies the casing rule above to a person or entity name.
 * Trims and collapses runs of whitespace; non-string input yields ''.
 */
export function toProperNameCase(value: string | null | undefined): string {
  if (typeof value !== 'string') {
    return '';
  }
  const collapsed = value.trim().replace(/\s+/g, ' ');
  if (!collapsed) {
    return '';
  }
  return collapsed.split(' ').map(capitalizeWord).join(' ');
}