rebreak-monorepo/backend/server/utils/mail-classifier.ts

/**
 * Mail-Klassifikations-Pipeline (deterministisch, ohne LLM).
 *
 * Architektur:
 *   Layer 0   — Skip-Guard (bereits geblockt / kein Consent)
 *   Layer 1   — Whitelist (wetter, wettkampf …) → PASS
 *   Layer 2   — Domain-Hard-Block (Blocklist)
 *   Layer 2.5 — Brand+Random-Token-Detection (Hard-Block, fängt Apple Hide-My-Email)
 *   Layer 3   — Score 0–100 (deterministisch); ≥50 → BLOCK, sonst PASS
 *   Layer 5   — MailClassificationSample-Insert (immer, außer Layer 0)
 *
 * Alle Layer-Logiken sind pure Funktionen → vollständig unit-testbar ohne DB-Mocks.
 *
 * DSGVO-Hinweise:
 *   - Mail-Inhalte (Body) werden nie persistiert (Art. 9).
 *   - Keine Daten verlassen mehr den Server (kein LLM-Drittland-Transfer).
 *   - userId in Logs nur wenn absolut nötig (Datenminimierung Art. 5).
 *   - MailClassificationSample: Cascade-Delete via userId-Relation (Art. 17).
 */

// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-ignore — .mjs ohne types, Exports sind string[]
import { GAMBLING_KEYWORDS, GAMBLING_WHITELIST } from "./gambling-keywords.mjs";

// ─── Typen ─────────────────────────────────────────────────────────────────────

export type ClassificationAction = "blocked" | "passed";

export type TriggerSource =
  | "domain"
  | "relay-decoded"
  | "brand+random"
  | "custom-display-name"
  | `score:${number}`
  | "whitelist"
  | "no-signal";

export interface MailInput {
  /** Sender-E-Mail-Adresse (lowercase, wie von IMAP geliefert) */
  senderEmail: string;
  /** Display-Name des Absenders (kann leer sein) */
  senderName: string | null;
  /** Betreff-Zeile */
  subject: string;
}

export interface ClassificationResult {
  action: ClassificationAction;
  triggerSource: TriggerSource;
  score: number;
  /** Aus Relay-Adressen extrahierte echte Domain (z.B. gamblezen.com) */
  relayDecodedDomain: string | null;
  /** Score-Komponenten für MailClassificationSample.features */
  features: ClassificationFeatures;
}

export interface ClassificationFeatures {
  score: number;
  domainBlocked: boolean;
  relayDecoded: boolean;
  brandMatch: boolean;
  randomTokens: boolean;
  keywordHitsSubject: string[];
  keywordHitsDomain: string[];
  keywordHitsName: string[];
  styleFlags: string[];
  whitelistHit: boolean;
}

// ─── Score-Weights (TS-Constants, kein Config-File-Overhead) ──────────────────

export const SCORE_WEIGHTS = {
  // Domain-Indikatoren
  DOMAIN_GAMBLING_KEYWORD: 40,    // Domain enthält Gambling-Begriff (bet, casino, slots …)
  DOMAIN_SHORT_RANDOM: 15,        // Domain-Root < 6 Zeichen und zufällig wirkend (betx, 1win)

  // Subject-Indikatoren
  SUBJECT_GAMBLING_KEYWORD: 35,   // Keyword im Betreff (casino, jackpot, freispiel …)
  SUBJECT_MONEY_PATTERN: 20,      // €/$ + Zahl (z.B. "100€ Bonus")
  SUBJECT_URGENCY: 15,            // "Nur heute", "Letzte Chance", "Ablaufdatum"
  SUBJECT_ALL_CAPS_WORD: 5,       // EINZELNES ALL-CAPS-WORT im Betreff

  // Display-Name-Indikatoren
  SENDER_NAME_GAMBLING_KEYWORD: 30, // Gambling-Begriff im Absender-Namen
  SENDER_NAME_BRAND_MATCH: 20,      // Name matcht bekannten Gambling-Brand (normalisiert)

  // Layer 2.5 Score-Ergänzungen (wenn kein Hard-Block ausgelöst)
  BRAND_MATCH_NO_RANDOM: 35,      // Brand-Match ohne Random-Tokens (kein Hard-Block)
  RANDOM_TOKENS_NO_BRAND: 10,     // Random-Tokens ohne Brand-Match
} as const;

// Hard-Block-Threshold: Score >= 80 → BLOCK
const SCORE_HARD_BLOCK_THRESHOLD = 80;
// Pass-Below: Score < 25 → PASS (no-signal)
const SCORE_PASS_BELOW = 25;
// Mid-range Block-Threshold: Score in [25, 80) → BLOCK ab 50, sonst PASS
const SCORE_BLOCK_MIDRANGE = 50;

// ─── Bekannte Gambling-Brands (für Brand-Match-Normalisierung) ─────────────────
// Abgeleitet aus GAMBLING_KEYWORDS + typischen Blocklist-Domains.
// Normalisierungsregel: lowercase, alle Sonder- und Leerzeichen entfernt.
const GAMBLING_BRANDS: string[] = [
  "casino", "bet365", "bwin", "tipico", "unibet", "betway", "888casino",
  "pokerstars", "interwetten", "netbet", "leovegas", "mrgreen",
  "betsson", "neobet", "mybet", "lottoland", "betano", "williamhill",
  "paddypower", "betfair", "stake", "rolletto", "vbet", "1xbet", "melbet",
  "mostbet", "luckyvibe", "spinz", "casinoly", "rabona",
  "justcasino", "getslots", "rocketplay", "freshcasino",
  "nomnomcasino", "gamblezen", "betandplay",
];

// ─── Relay-Decoder ─────────────────────────────────────────────────────────────

/**
 * Extrahiert die echte Ziel-Domain aus einer E-Mail-Relay-Adresse.
 *
 * Muster die wir kennen:
 *   bounces+user=example.com@sendgrid.net    → example.com
 *   track.user=gamblezen.com@mailchimp.com   → gamblezen.com
 *   a1b2c3_user_at_betandplay.com@em.em.xyz  → betandplay.com
 *   user=betandplay.com@bounce.em.example    → betandplay.com
 *
 * Pattern: Sucht nach `=domain.tld` oder `_at_domain.tld` im local-part.
 */
export function extractRelayedDomain(senderEmail: string): string | null {
  if (!senderEmail.includes("@")) return null;
  const [localPart] = senderEmail.split("@");

  // Pattern 1: user=domain.tld (SendGrid, Mailchimp, SES-Bounces)
  const eqMatch = localPart.match(/=([a-z0-9][\w-]*\.[a-z]{2,}(?:\.[a-z]{2,})?)(?:[+_&]|$)/i);
  if (eqMatch) return eqMatch[1].toLowerCase();

  // Pattern 2: _at_domain.tld (weniger häufig, einige Custom-Relay-Setups)
  const atMatch = localPart.match(/_at_([a-z0-9][\w-]*\.[a-z]{2,}(?:\.[a-z]{2,})?)(?:[_+]|$)/i);
  if (atMatch) return atMatch[1].toLowerCase();

  return null;
}

// ─── Brand-Normalisierung ──────────────────────────────────────────────────────

/**
 * Normalisiert einen String für Brand-Vergleiche.
 * "BetandPlay" → "betandplay", "bet-and-play.com" → "betandplay" (nach Strip)
 */
export function normalizeBrand(s: string): string {
  return s.toLowerCase().replace(/[\s\-._]/g, "");
}

/**
 * Prüft ob ein normalisierter String mit einem bekannten Gambling-Brand übereinstimmt.
 * Mindestlänge 4 Zeichen um False-Positives zu vermeiden ("bet" alleine → zu kurz).
 */
export function matchesGamblingBrand(normalized: string): boolean {
  if (normalized.length < 4) return false;
  return GAMBLING_BRANDS.some((brand) => normalized === brand || normalized.includes(brand));
}

/**
 * Extrahiert Brand-Kandidaten aus einer Domain für den Match-Check.
 * "betand-play.com" → ["betandplay", "betand"] (root + normalisiert)
 */
function domainToBrandCandidates(domain: string): string[] {
  const root = domain.split(".")[0] ?? "";
  return [normalizeBrand(root), normalizeBrand(domain)];
}

// ─── Random-Token-Detection ───────────────────────────────────────────────────

/**
 * Erkennt zufällig wirkende Tokens im Local-Part einer E-Mail-Adresse.
 *
 * Definition "random token": >= 6 Zeichen, Mix aus Buchstaben + Ziffern,
 * kein bekanntes Funktions-Wort (info, admin, noreply, support …).
 *
 * Ein Local-Part mit >= 2 solchen Tokens gilt als "random-looking" —
 * typisch für Massen-Mailer mit trackierbaren User-IDs.
 */
export function hasRandomTokens(localPart: string): boolean {
  const FUNCTION_WORDS = new Set([
    "info", "admin", "noreply", "no-reply", "support", "hello",
    "news", "marketing", "sales", "contact", "newsletter", "service",
    "offers", "promotions", "promo", "team", "mail", "email",
    "reply", "bounce", "return", "postmaster", "mailer",
  ]);

  const tokens = localPart.split(/[_\-.+]+/);
  const randomLooking = tokens.filter((t) => {
    if (t.length < 6) return false;
    if (!/[a-z]/i.test(t) || !/[0-9]/.test(t)) return false; // muss Letters+Digits haben
    const lower = t.toLowerCase();
    if (FUNCTION_WORDS.has(lower)) return false;
    return true;
  });

  return randomLooking.length >= 2;
}

// ─── Score-Berechnung (Layer 3) ───────────────────────────────────────────────

interface ScoreResult {
  score: number;
  keywordHitsSubject: string[];
  keywordHitsDomain: string[];
  keywordHitsName: string[];
  styleFlags: string[];
  whitelistHit: boolean;
}

export function computeScore(
  senderEmail: string,
  senderName: string | null,
  subject: string,
  brandMatchFound: boolean,
  randomTokensFound: boolean,
): ScoreResult {
  let score = 0;
  const keywordHitsSubject: string[] = [];
  const keywordHitsDomain: string[] = [];
  const keywordHitsName: string[] = [];
  const styleFlags: string[] = [];

  const subjectLower = subject.toLowerCase();
  const senderEmailLower = senderEmail.toLowerCase();
  const senderNameLower = (senderName ?? "").toLowerCase();
  const domain = senderEmailLower.split("@")[1] ?? "";
  const domainRoot = domain.split(".")[0] ?? "";

  // ── Whitelist-Check (Layer 1) ──
  for (const w of GAMBLING_WHITELIST as string[]) {
    if (subjectLower.includes(w) || senderEmailLower.includes(w) || senderNameLower.includes(w)) {
      return {
        score: 0,
        keywordHitsSubject: [],
        keywordHitsDomain: [],
        keywordHitsName: [],
        styleFlags: [],
        whitelistHit: true,
      };
    }
  }

  // ── Domain-Keywords ──
  for (const kw of GAMBLING_KEYWORDS as string[]) {
    if (domain.includes(kw) || domainRoot.includes(kw)) {
      keywordHitsDomain.push(kw);
      score += SCORE_WEIGHTS.DOMAIN_GAMBLING_KEYWORD;
      break; // einmal reicht
    }
  }

  // ── Subject-Keywords ──
  for (const kw of GAMBLING_KEYWORDS as string[]) {
    if (subjectLower.includes(kw)) {
      keywordHitsSubject.push(kw);
      score += SCORE_WEIGHTS.SUBJECT_GAMBLING_KEYWORD;
      break;
    }
  }

  // ── Sender-Name-Keywords ──
  for (const kw of GAMBLING_KEYWORDS as string[]) {
    if (senderNameLower.includes(kw)) {
      keywordHitsName.push(kw);
      score += SCORE_WEIGHTS.SENDER_NAME_GAMBLING_KEYWORD;
      break;
    }
  }

  // ── Geld-Pattern im Betreff (€/$ + Zahl) ──
  if (/[€$£]\s*\d|\d\s*[€$£]/.test(subject)) {
    styleFlags.push("money-pattern");
    score += SCORE_WEIGHTS.SUBJECT_MONEY_PATTERN;
  }

  // ── Urgency-Wörter im Betreff ──
  const URGENCY_PATTERNS = [
    "nur heute", "letzte chance", "läuft ab", "ablaufdatum",
    "expires", "last chance", "limited time", "jetzt einlösen",
    "sofort", "nur noch", "endet heute",
  ];
  if (URGENCY_PATTERNS.some((p) => subjectLower.includes(p))) {
    styleFlags.push("urgency");
    score += SCORE_WEIGHTS.SUBJECT_URGENCY;
  }

  // ── ALL-CAPS-Wort im Betreff ──
  if (/\b[A-Z]{4,}\b/.test(subject)) {
    styleFlags.push("all-caps");
    score += SCORE_WEIGHTS.SUBJECT_ALL_CAPS_WORD;
  }

  // ── Short-Random-Domain ──
  if (domainRoot.length > 0 && domainRoot.length <= 5 && /[a-z]/.test(domainRoot) && /[0-9]/.test(domainRoot)) {
    styleFlags.push("short-random-domain");
    score += SCORE_WEIGHTS.DOMAIN_SHORT_RANDOM;
  }

  // ── Layer 2.5 Score-Ergänzungen ──
  if (brandMatchFound && !randomTokensFound) {
    score += SCORE_WEIGHTS.BRAND_MATCH_NO_RANDOM;
  }
  if (!brandMatchFound && randomTokensFound) {
    score += SCORE_WEIGHTS.RANDOM_TOKENS_NO_BRAND;
  }

  return {
    score: Math.min(score, 100),
    keywordHitsSubject,
    keywordHitsDomain,
    keywordHitsName,
    styleFlags,
    whitelistHit: false,
  };
}

// ─── Haupt-Pipeline ───────────────────────────────────────────────────────────

export interface ClassifyMailParams {
  mail: MailInput;
  /** Menge der geblockten Domains (aus getBlocklistedDomainsSet) */
  blockedDomainSet: Set<string>;
  /**
   * User-spezifische Display-Name-Patterns (aus getCustomMailDisplayNames).
   * Layer 2.6: case-insensitive Substring-Match gegen senderName.
   * Leer-Array wenn User keine Display-Name-Patterns gesetzt hat.
   *
   * DSGVO: keine PII — reine Heuristik-Muster (z.B. ["EXTRASPIN"]).
   */
  customDisplayNames?: string[];
}

/**
 * Klassifiziert eine einzelne Mail durch alle Layer.
 * Komplett deterministisch — keine externen Calls, keine PII verlässt den Server.
 * DB-Writes (MailBlocked, MailClassificationSample) liegen beim Aufrufer.
 */
export async function classifyMail(params: ClassifyMailParams): Promise<ClassificationResult> {
  const { mail, blockedDomainSet, customDisplayNames } = params;
  const { senderEmail, senderName, subject } = mail;

  const senderEmailLower = senderEmail.toLowerCase();
  const domain = senderEmailLower.split("@")[1] ?? "";
  const localPart = senderEmailLower.split("@")[0] ?? "";

  // ── Layer 1: Whitelist ──────────────────────────────────────────────────────
  const haystack = `${senderEmailLower} ${subject} ${senderName ?? ""}`.toLowerCase();
  for (const w of GAMBLING_WHITELIST as string[]) {
    if (haystack.includes(w)) {
      return {
        action: "passed",
        triggerSource: "whitelist",
        score: 0,
        relayDecodedDomain: null,
        features: {
          score: 0,
          domainBlocked: false,
          relayDecoded: false,
          brandMatch: false,
          randomTokens: false,
          keywordHitsSubject: [],
          keywordHitsDomain: [],
          keywordHitsName: [],
          styleFlags: [],
          whitelistHit: true,
        },
      };
    }
  }

  // ── Layer 2: Domain-Hard-Block ──────────────────────────────────────────────
  if (domain && blockedDomainSet.has(domain)) {
    return {
      action: "blocked",
      triggerSource: "domain",
      score: 100,
      relayDecodedDomain: null,
      features: {
        score: 100,
        domainBlocked: true,
        relayDecoded: false,
        brandMatch: false,
        randomTokens: false,
        keywordHitsSubject: [],
        keywordHitsDomain: [],
        keywordHitsName: [],
        styleFlags: [],
        whitelistHit: false,
      },
    };
  }

  // ── Layer 2: Relay-Decoded Domain-Block ─────────────────────────────────────
  const relayDecodedDomain = extractRelayedDomain(senderEmailLower);
  if (relayDecodedDomain && blockedDomainSet.has(relayDecodedDomain)) {
    return {
      action: "blocked",
      triggerSource: "relay-decoded",
      score: 100,
      relayDecodedDomain,
      features: {
        score: 100,
        domainBlocked: false,
        relayDecoded: true,
        brandMatch: false,
        randomTokens: false,
        keywordHitsSubject: [],
        keywordHitsDomain: [],
        keywordHitsName: [],
        styleFlags: [],
        whitelistHit: false,
      },
    };
  }

  // ── Layer 2.5: Brand+Random-Token-Hard-Block ────────────────────────────────
  // Normalisiere Absender-Name und Domain-Root für Brand-Vergleich
  const displayNameNorm = normalizeBrand(senderName ?? "");
  const domainCandidates = domainToBrandCandidates(domain);
  const relayDomainCandidates = relayDecodedDomain ? domainToBrandCandidates(relayDecodedDomain) : [];
  const allBrandCandidates = [displayNameNorm, ...domainCandidates, ...relayDomainCandidates];

  const brandMatch = allBrandCandidates.some((c) => c.length >= 4 && matchesGamblingBrand(c));
  const randomTokens = hasRandomTokens(localPart);

  if (brandMatch && randomTokens) {
    return {
      action: "blocked",
      triggerSource: "brand+random",
      score: 100,
      relayDecodedDomain,
      features: {
        score: 100,
        domainBlocked: false,
        relayDecoded: !!relayDecodedDomain,
        brandMatch: true,
        randomTokens: true,
        keywordHitsSubject: [],
        keywordHitsDomain: [],
        keywordHitsName: [],
        styleFlags: [],
        whitelistHit: false,
      },
    };
  }

  // ── Layer 2.6: User-Custom-Display-Name-Hard-Block ──────────────────────────
  // User-eigene Patterns (z.B. "EXTRASPIN") matchen case-insensitiv als Substring
  // gegen den Sender-Display-Name. Kein Score — direkter Hard-Block wenn Match.
  //
  // Substring-Match (nicht exact) damit "EXTRASPIN Casino" und "ExtraSpin Bonus"
  // beide von Pattern "EXTRASPIN" erfasst werden.
  //
  // Gambling-Brands rotieren aktiv Capitalization → case-insensitive ist Pflicht.
  if (customDisplayNames && customDisplayNames.length > 0 && senderName) {
    const senderNameLower = senderName.toLowerCase();
    const matchedPattern = customDisplayNames.find(
      (pattern) => pattern.length > 0 && senderNameLower.includes(pattern.toLowerCase()),
    );
    if (matchedPattern) {
      return {
        action: "blocked",
        triggerSource: "custom-display-name",
        score: 100,
        relayDecodedDomain,
        features: {
          score: 100,
          domainBlocked: false,
          relayDecoded: !!relayDecodedDomain,
          brandMatch,
          randomTokens,
          keywordHitsSubject: [],
          keywordHitsDomain: [],
          keywordHitsName: [],
          styleFlags: [],
          whitelistHit: false,
        },
      };
    }
  }

  // ── Layer 3: Score ──────────────────────────────────────────────────────────
  const scoreResult = computeScore(
    senderEmailLower,
    senderName,
    subject,
    brandMatch,
    randomTokens,
  );

  if (scoreResult.whitelistHit) {
    return {
      action: "passed",
      triggerSource: "whitelist",
      score: 0,
      relayDecodedDomain,
      features: {
        ...scoreResult,
        score: 0,
        domainBlocked: false,
        relayDecoded: !!relayDecodedDomain,
        brandMatch,
        randomTokens,
      },
    };
  }

  const score = scoreResult.score;

  // Score >= 80 → Hard-Block, kein LLM
  if (score >= SCORE_HARD_BLOCK_THRESHOLD) {
    const triggerSource: TriggerSource = `score:${score}`;
    return {
      action: "blocked",
      triggerSource,
      score,
      relayDecodedDomain,
      features: {
        ...scoreResult,
        domainBlocked: false,
        relayDecoded: !!relayDecodedDomain,
        brandMatch,
        randomTokens,
      },
    };
  }

  // Score < 25 → PASS
  if (score < SCORE_PASS_BELOW) {
    return {
      action: "passed",
      triggerSource: "no-signal",
      score,
      relayDecodedDomain,
      features: {
        ...scoreResult,
        domainBlocked: false,
        relayDecoded: !!relayDecodedDomain,
        brandMatch,
        randomTokens,
      },
    };
  }

  // Score 25-79 → PASS bei < 50, BLOCK bei >= 50 (deterministisch, kein LLM)
  const midAction: ClassificationAction =
    score >= SCORE_BLOCK_MIDRANGE ? "blocked" : "passed";
  const midTrigger: TriggerSource = `score:${score}`;
  return {
    action: midAction,
    triggerSource: midTrigger,
    score,
    relayDecodedDomain,
    features: {
      ...scoreResult,
      domainBlocked: false,
      relayDecoded: !!relayDecodedDomain,
      brandMatch,
      randomTokens,
    },
  };
}