/**
 * Spam SCORING for the intake handler. Pouya's ruling, 2026-09-04.
 *
 * ⚠️ **THIS MODULE NEVER REJECTS ANYTHING, AND THAT IS THE WHOLE DESIGN.** It
 * returns a score and a list of signal names. The handler stores the record and
 * sends both emails either way; above the threshold it prefixes the OPERATOR
 * notification's subject with `[Possible spam] ` and adds one line naming the
 * signals. Pouya filters in Gmail. His words: *"Nothing is dropped; a false
 * positive costs him one glance."*
 *
 * That asymmetry is why the thresholds below can be tuned aggressively. The cost
 * of a false positive is a subject-line prefix; the cost of a false negative is
 * one unlabelled email. Neither loses an inquiry — which a filter that rejected
 * would, and a legal inquiry lost silently is the one outcome this form must not
 * produce.
 *
 * ⚠️ **NOTHING HERE IS STORED.** The score and the signals do not enter the
 * DynamoDB item. `/legal/privacy/` publishes what the record holds, field by
 * field, and adding an attribute would make that list wrong — a disclosure
 * defect, not a schema change. The label lives only in the operator
 * notification. ⚠️ **THAT MAILBOX IS DELEGATED, NOT PERSONAL** — §9 Q63 and
 * `/legal/privacy/` §Who can see it both say so, and an earlier draft of this
 * comment said the label "lives in an email that only Pouya reads", which is the
 * exclusivity Q63 struck. It reaches whoever reads `info@smlcompany.ca`. If a
 * stored score is ever wanted, the page changes first.
 *
 * ⚠️ **AND THE INQUIRER NEVER SEES ANY OF THIS.** The confirmation email is
 * untouched. A person wrongly scored must not be told a machine thought they
 * were a bot.
 *
 * WHY SCORING RATHER THAN MORE REJECTION. The two submissions of 2026-09-04
 * (`docs/05` §Observed abuse) passed the honeypot. Every rule that would have
 * caught them — a foreign phone, a link in the summary, a disposable-looking
 * address — is a rule some real inquirer also trips: this practice takes
 * cross-border commercial work, so a `+44` number is a client, not a bot. A
 * rejecting rule set built from those signals would eventually discard a real
 * dispute and report success while doing it.
 */

/**
 * ⚠️ **NOT MEASURED FROM A CORPUS — THERE IS NO CORPUS.** No genuine inquiry has
 * arrived through this form yet, so there is nothing to measure a normal summary
 * length against, and a number presented as measured when it is not is the
 * defect `AGENTS.md` keeps paying for.
 *
 * It is DERIVED, and the derivation is the form's own instruction: the `summary`
 * field's hint reads *"A few sentences is enough."* This floor sits **below** what
 * that invites, so it fires on a summary that does not attempt the question
 * rather than on one that answers it briefly. `[assumed 2026-09-04]`
 *
 * ⚠️ **TUNE IT DOWN WHEN IN DOUBT, NEVER UP.** An unlabelled spam costs nothing
 * that matters; a labelled real inquiry spends the reader's trust in the label.
 * *"Shareholder dispute, two directors, Ontario CBCA company."* is 57 characters
 * and is exactly what the hint asks for — a floor above that scores the form's
 * own instruction as a spam signal.
 *
 * **Pouya can replace this with a measurement whenever he likes** — the two spam
 * records of 2026-09-04 are still in the table, and their `summary` lengths are
 * the first real data this number could rest on. §9 Q65 records that.
 */
export const SHORT_SUMMARY_CHARS = 100;

/**
 * Above this, the notification is labelled. Weights below are 1 for a signal a
 * real inquirer plausibly trips and 2 for one they rarely do, so the threshold
 * of 2 means: **one strong signal, or two weak ones.**
 *
 * Worked, because a threshold nobody has worked through is a guess with a number
 * on it:
 *   - Ontario counsel, local number, three-line summary          → 0, clean
 *   - Cross-border counsel, `+44` number, three-line summary     → 1, clean
 *   - Cross-border counsel, `+44` number, one-line summary       → 2, LABELLED
 *   - A four-part real name at gmail.com                         → 1, clean
 *   - Anyone pasting a link to a public tender document          → 2, LABELLED
 *   - foreign number + a short scraped summary carrying a link → 4, LABELLED
 *
 * The third and fourth rows are the accepted false positives. Both are real
 * shapes, both cost one glance, and both were preferred to missing the fifth.
 *
 * ⚠️ **THE LAST ROW IS A SHAPE, NOT A MEASUREMENT OF THE TWO 2026-09-04
 * SUBMISSIONS. THOSE RECORDS WERE NEVER READ.** What the attested signature
 * guarantees is a non-NANP phone — **one weak signal** — and whether either is
 * labelled turns on facts only the two rows in the table hold. §9 Q65 records
 * that they are still there and are the only real data any of these numbers
 * could rest on.
 */
export const SPAM_THRESHOLD = 2;

/** `https://…` or `www.…` only. A bare `acme.com` is NOT matched: an inquirer
 *  writing "the dispute concerns acme.com's supply contract" is describing a
 *  party, and matching that would label ordinary commercial prose. */
const URL_IN_TEXT = /\b(?:https?:\/\/|www\.)\S/i;

/**
 * NANP: an explicit `+<cc>` settles it; otherwise ten digits, or eleven
 * beginning with 1, after the tail is dropped.
 *
 * ⚠️ **A DIGIT COUNT ALONE CANNOT DO THIS.** `416-555-0123 ext 22` is twelve
 * digits, `416-555-0123 or 416-555-0124` is twenty, and both are ordinary
 * Toronto numbers that a bare count calls foreign — a signal saying the opposite
 * of the truth. The tail is dropped at the first extension marker or
 * second-number separator, and the marker list is deliberately generous.
 *
 * **The country code is read FIRST because it is the only unambiguous thing in
 * the field.** `+44 …` and `+7 …` are settled without counting anything, which
 * is what a pure shape test cannot do: `+7 912 345 6789` is grouped 3-3-4
 * exactly like a NANP number, so matching the shape would call it Canadian.
 * Only when there is no explicit country code does the digit count run, and then
 * the tail is dropped at the first extension marker or second-number separator.
 */
function looksNorthAmerican(phone) {
  const trimmed = phone.trim();
  /* An explicit international prefix is decisive in both directions. */
  const cc = trimmed.match(/^\+\s*(\d{1,3})/);
  if (cc) return cc[1] === '1';
  /* Longest alternative FIRST: regex alternation is leftmost-first, so `ext`
     placed before `extension` matches the first three letters and then relies on
     backtracking. Ordering it correctly is cheaper than depending on that.
     `\bx\b` would NOT match the `x` in `x22` — the digit after it is a word
     character, so there is no boundary — which is how `(416) 555-0123 x22` scored
     foreign for one round. The marker is matched by what FOLLOWS it. */
  const digits = trimmed
    .split(/\s*(?:extension|extn|ext|x)[.:-]?\s*\d|[#,;]|\bor\b/i)[0]
    .replace(/\D/g, '');
  return digits.length === 10 || (digits.length === 11 && digits[0] === '1');
}

/**
 * The Gmail dot trick: one mailbox, unlimited distinct-looking addresses,
 * because Gmail ignores dots in the local part.
 *
 * ⚠️ **A DOT IS NOT THE SIGNAL, AND TREATING IT AS ONE WOULD LABEL MOST REAL
 * GMAIL USERS.** `first.last@gmail.com` is the single most ordinary form a Gmail
 * address takes. What distinguishes the trick is dot DENSITY: **three or more
 * dots**, and nothing else.
 *
 * ⚠️ **AND THE WEIGHT IS 1, NOT 2, WHICH MATTERS MORE THAN THE BOUNDARY DOES.**
 * `mary.jane.o.brien@gmail.com` and `maria.de.la.cruz@gmail.com` are three-dot
 * REAL names — compound surnames and middle initials are ordinary, not rare —
 * and weight 2 is defined here as what a real inquirer rarely trips. At weight 1
 * nothing can be labelled on the shape of its owner's name alone; a genuine
 * dot-trick address reaches the threshold as soon as it trips anything else,
 * which spam reliably does. **Do not raise it back.**
 */
function looksLikeGmailDotTrick(email) {
  const at = email.lastIndexOf('@');
  if (at < 1) return false;
  const local = email.slice(0, at);
  const domain = email.slice(at + 1).toLowerCase();
  if (domain !== 'gmail.com' && domain !== 'googlemail.com') return false;
  const dots = local.split('.').length - 1;
  return dots >= 3;
}

/**
 * @param {Record<string, string>} fields  the handler's `clean` map — validated,
 *   plain-texted values, keyed by field name. Absent fields are simply absent.
 * @returns {{score: number, signals: string[]}} `signals` are written for a
 *   human reading one line of an email, not for a machine.
 */
export function scoreSubmission(fields) {
  const signals = [];
  let score = 0;
  const add = (weight, label) => {
    score += weight;
    signals.push(label);
  };

  const summary = fields.summary ?? '';
  const phone = fields.phone ?? '';
  const email = fields.email ?? '';

  /* Only when a summary exists. An absent one is a validation failure the
     handler has already turned into the failure page, so scoring an empty
     string here would be scoring a submission that never got this far. */
  if (summary !== '' && summary.length < SHORT_SUMMARY_CHARS) {
    add(1, `summary under ${SHORT_SUMMARY_CHARS} characters`);
  }
  /* `phone` is OPTIONAL. Not giving one is not a signal — most inquirers will
     not — so this fires only on a number that is present and not North
     American. Treating absence as suspicious would label the quiet majority. */
  if (phone !== '' && !looksNorthAmerican(phone)) {
    add(1, 'phone is not a Canadian or US number');
  }
  if (URL_IN_TEXT.test(summary)) {
    add(2, 'link in the dispute summary');
  }
  if (looksLikeGmailDotTrick(email)) {
    add(1, 'Gmail address using the dot trick');
  }

  return { score, signals };
}

/** True when the operator notification should carry the label. */
export const isPossibleSpam = ({ score }) => score >= SPAM_THRESHOLD;