export function text(value) { return String(value ?? '').trim(); }
function number(value) { const parsed = Number(value); return Number.isFinite(parsed) ? parsed : 0; }
function legacyId(row) { return number(row.legacyUserId || row.legacyUserData?.UserID); }
function normalizePhone(value) {
  const digits = text(value).replace(/\D/g, '');
  if (/^86\d{11}$/.test(digits)) return digits.slice(2);
  return /^1\d{10}$/.test(digits) ? digits : '';
}
function phones(row) {
  return new Set([
    row.mobile, row.phone, row.mobilePhoneNumber, row.username,
    row.legacyUserData?.Mobile, row.legacyUserData?.UserName,
  ].map(normalizePhone).filter(Boolean));
}
function normalizeName(value) {
  return text(value).toLowerCase().replace(/[\s\p{P}\p{S}]+/gu, '');
}
function names(row) {
  return new Set([
    row.nickname, row.nickName, row.realName, row.name,
    row.legacyUserData?.HoneyName, row.legacyUserData?.TrueName,
  ].map(normalizeName).filter((value) => value.length >= 2));
}
function intersects(left, right) { return [...left].some((value) => right.has(value)); }
export function isCanonical(row) { return text(row.sourceKey).startsWith('legacy-sync:user:') && !row.isDeleted; }
export function isReadingImport(row) {
  return !text(row.sourceKey) && !legacyId(row) && row.isAdmin !== true && !row.isDeleted;
}

export function buildPlan(users) {
  const targets = users.filter(isCanonical);
  const sources = users.filter(isReadingImport);
  const targetsByPhone = new Map();
  for (const target of targets) {
    for (const phone of phones(target)) {
      const values = targetsByPhone.get(phone) || [];
      values.push(target);
      targetsByPhone.set(phone, values);
    }
  }

  const merge = [];
  const promote = []; // Never allocate old-system IDs for reading accounts.
  const held = [];
  let nameResolved = 0;
  let ambiguous = 0;
  let unmatched = 0;
  for (const source of sources) {
    if (source.legacyUserData?.ReadingSourceVerified !== 'xiaoshu') {
      held.push({ objectId: source.objectId, reason: 'unverified-source' });
      continue;
    }
    const candidates = new Map();
    for (const phone of phones(source)) {
      for (const candidate of targetsByPhone.get(phone) || []) candidates.set(candidate.objectId, candidate);
    }
    let possible = [...candidates.values()];
    if (possible.length > 1) {
      const sourceNames = names(source);
      const nameMatches = possible.filter((candidate) => intersects(sourceNames, names(candidate)));
      if (nameMatches.length === 1) { possible = nameMatches; nameResolved += 1; }
    }
    if (possible.length === 1) {
      merge.push({ source: source.objectId, target: possible[0].objectId });
    } else {
      held.push({ objectId: source.objectId, reason: possible.length > 1 ? 'ambiguous-identity' : 'unmatched-identity' });
      if (possible.length > 1) ambiguous += 1;
      else unmatched += 1;
    }
  }
  return { targets, sources, merge, promote, held, nameResolved, ambiguous, unmatched };
}