/**
 * Detection for attempts to move a conversation off Reddit, plus the
 * transactional funnels that usually accompany them.
 *
 * This is deliberately separate from the configured `sellerKeywords` list in
 * `findSellerSignal`: that list is a lead-quality filter an operator can turn
 * off, whereas these signals are the ones that end a conversation outright. It
 * also matches on a normalized form of the text, because sellers obfuscate the
 * exact words Reddit itself filters on (`0nlyfans`, `t3l3gram`,
 * `t e l e g r a m`, zero-width joiners between letters).
 */

export type OffPlatformSignalKind =
  | 'contact-platform'
  | 'handle-ask'
  | 'payment'
  | 'seller-link'
  | 'verification-scam';

export interface OffPlatformSignal {
  kind: OffPlatformSignalKind;
  /** Stable label used in logs and the durable handoff reason. */
  label: string;
  /** The fragment that matched, kept as evidence in the audit trail. */
  matched: string;
}

const ZERO_WIDTH = /[​-‍⁠­]/g;
const COMBINING_MARKS = /[̀-ͯ]/g;

const LEET_MAP: Record<string, string> = {
  '0': 'o',
  '1': 'i',
  '3': 'e',
  '4': 'a',
  '5': 's',
  '7': 't',
  '8': 'b',
  '9': 'g',
  '@': 'a',
  $: 's',
  '!': 'i',
  '|': 'i',
  '£': 'e',
};

/**
 * Lowercased, unicode-folded text with separators intact. Word-boundary rules
 * run against this so short tokens cannot match inside unrelated words.
 */
export function normalizeSignalText(text: string): string {
  return text
    .normalize('NFKD')
    .replace(COMBINING_MARKS, '')
    .replace(ZERO_WIDTH, '')
    .toLowerCase()
    .replace(/[’‘`]/g, "'")
    .replace(/\s+/g, ' ')
    .trim();
}

/**
 * Aggressively folded text: leet characters mapped back to letters, every
 * separator removed, and long runs collapsed. `t.me` becomes `tme`, `0nly
 * f4ns` becomes `onlyfans`, `snaaaapchat` becomes `snapchat`. Only tokens long
 * enough to be unambiguous are matched here — see `FOLDED_TOKENS`.
 */
export function foldSignalText(text: string): string {
  const normalized = normalizeSignalText(text);
  let folded = '';
  for (const character of normalized) {
    folded += LEET_MAP[character] ?? character;
  }
  return folded
    .replace(/[^a-z0-9]/g, '')
    .replace(/(.)\1{2,}/g, '$1');
}

/**
 * Tokens of six characters or more that carry no innocent reading in this
 * context. Matched against the folded text, so obfuscated spellings are caught.
 */
const FOLDED_TOKENS: ReadonlyArray<{ kind: OffPlatformSignalKind; label: string; token: string }> = [
  { kind: 'contact-platform', label: 'Telegram', token: 'telegram' },
  { kind: 'contact-platform', label: 'WhatsApp', token: 'whatsapp' },
  { kind: 'contact-platform', label: 'Snapchat', token: 'snapchat' },
  { kind: 'contact-platform', label: 'Discord', token: 'discord' },
  { kind: 'contact-platform', label: 'Wickr', token: 'wickr' },
  { kind: 'contact-platform', label: 'Skype', token: 'skype' },
  { kind: 'contact-platform', label: 'Viber', token: 'viber' },
  { kind: 'contact-platform', label: 'Instagram', token: 'instagram' },
  { kind: 'seller-link', label: 'OnlyFans', token: 'onlyfans' },
  { kind: 'seller-link', label: 'Fansly', token: 'fansly' },
  { kind: 'seller-link', label: 'Fanvue', token: 'fanvue' },
  { kind: 'seller-link', label: 'LoyalFans', token: 'loyalfans' },
  { kind: 'seller-link', label: 'ManyVids', token: 'manyvids' },
  { kind: 'seller-link', label: 'JustForFans', token: 'justforfans' },
  { kind: 'seller-link', label: 'FanCentro', token: 'fancentro' },
  { kind: 'seller-link', label: 'AdmireMe', token: 'admireme' },
  { kind: 'seller-link', label: 'Linktree', token: 'linktree' },
  { kind: 'seller-link', label: 'AllMyLinks', token: 'allmylinks' },
  { kind: 'seller-link', label: 'Beacons', token: 'beacons' },
  { kind: 'seller-link', label: 'Chaturbate', token: 'chaturbate' },
  { kind: 'seller-link', label: 'MyFreeCams', token: 'myfreecams' },
  { kind: 'seller-link', label: 'premium Snapchat', token: 'premiumsnap' },
  { kind: 'seller-link', label: 'Throne', token: 'throne' },
  { kind: 'payment', label: 'Cash App', token: 'cashapp' },
  { kind: 'payment', label: 'Venmo', token: 'venmo' },
  { kind: 'payment', label: 'PayPal', token: 'paypal' },
  { kind: 'payment', label: 'Zelle', token: 'zelle' },
];

/**
 * Rules for short or ambiguous tokens. These need surrounding context because
 * the bare word has an innocent meaning in this domain — `snap` is a photo,
 * `signal` is a sign, `sc` and `ig` appear inside ordinary words.
 */
const CONTEXT_RULES: ReadonlyArray<{ kind: OffPlatformSignalKind; label: string; pattern: RegExp }> = [
  // Link shorteners for the messaging apps, which appear without the app name.
  { kind: 'contact-platform', label: 'Telegram', pattern: /\bt\.me\b/ },
  { kind: 'contact-platform', label: 'Telegram', pattern: /\btelegra?\.ph\b/ },
  { kind: 'contact-platform', label: 'WhatsApp', pattern: /\bwa\.me\b/ },
  { kind: 'contact-platform', label: 'Telegram', pattern: /\btg\b[^.\n]{0,12}\b(?:is|handle|user|username|@)/ },
  { kind: 'contact-platform', label: 'Telegram', pattern: /\b(?:add|my|your|on)\b[^.\n]{0,12}\btg\b/ },
  { kind: 'contact-platform', label: 'Kik', pattern: /\bkik\b/ },
  // `snap` alone is a photo in this context, so only handle-shaped uses count.
  { kind: 'contact-platform', label: 'Snapchat', pattern: /\bsnap\s*(?:chat)?\s*(?:code|handle|id|user|username)\b/ },
  { kind: 'contact-platform', label: 'Snapchat', pattern: /\bmy snap\s+(?:is|=|:)/ },
  { kind: 'contact-platform', label: 'Snapchat', pattern: /\b(?:add|find|message|msg|dm)\s+me\s+(?:up\s+)?on\s+(?:the\s+)?snap\b/ },
  { kind: 'contact-platform', label: 'Snapchat', pattern: /\bwhat'?s? (?:your|ur) snap\b/ },
  { kind: 'contact-platform', label: 'Snapchat', pattern: /\bsc\b[^.\n]{0,10}\b(?:is|handle|user|username)\b/ },
  { kind: 'contact-platform', label: 'Instagram', pattern: /\binsta\b/ },
  { kind: 'contact-platform', label: 'Instagram', pattern: /\big\b[^.\n]{0,10}\b(?:is|handle|user|username)\b/ },
  { kind: 'contact-platform', label: 'Instagram', pattern: /\b(?:add|dm|message|msg|find)\s+me\s+(?:up\s+)?on\s+(?:the\s+)?ig\b/ },
  { kind: 'contact-platform', label: 'Signal', pattern: /\b(?:on|to|via|use|using|my|get)\s+signal\b/ },
  { kind: 'contact-platform', label: 'Signal', pattern: /\bsignal\s+(?:app|handle|username|number)\b/ },
  // Generic "continue this somewhere else" asks, whatever the platform.
  {
    kind: 'handle-ask',
    label: 'off-platform contact request',
    pattern: /\b(?:add|find|message|msg|text|dm|hit)\s+me\s+(?:up\s+)?(?:on|at|@)\b(?![^.\n]{0,10}\breddit\b)/,
  },
  {
    kind: 'handle-ask',
    label: 'off-platform contact request',
    pattern: /\bwhat'?s? (?:your|ur)\s+(?:@|handle|username|user name)\b/,
  },
  { kind: 'handle-ask', label: 'off-platform contact request', pattern: /\bmy\s+(?:@|handle|username)\s+(?:is|=|:)/ },
  {
    kind: 'handle-ask',
    label: 'off-platform contact request',
    pattern: /\b(?:let'?s|lets|wanna|want to|shall we|we should|can we)\s+(?:chat|talk|continue|move|take this|carry on)\b[^.\n]{0,20}\b(?:elsewhere|off|somewhere else|another app|different app)\b/,
  },
  {
    kind: 'handle-ask',
    label: 'off-platform contact request',
    pattern: /\b(?:take|move|moving|continue|chat|talk|talking|go|get)\b[^.\n]{0,20}\boff (?:of )?reddit\b/,
  },
  { kind: 'handle-ask', label: 'off-platform contact request', pattern: /\breddit (?:chat )?(?:is )?(?:sucks|glitch(?:y|es)|broken|keeps? (?:crashing|deleting))\b[^.\n]{0,40}\b(?:instead|another|other) (?:app|platform)\b/ },
  // Money rails. Cash App cashtags are matched on un-folded text so `$` survives.
  { kind: 'payment', label: 'Cash App cashtag', pattern: /(?:^|[\s(])\$[a-z][a-z0-9_]{2,}\b/ },
  { kind: 'payment', label: 'payment request', pattern: /\bpay\s*pal\b/ },
  { kind: 'payment', label: 'payment request', pattern: /\bcash\s*app\b/ },
  { kind: 'payment', label: 'payment request', pattern: /\bgift\s*card\b/ },
  // Link-in-bio funnels. "check my profile" is deliberately absent: genuine
  // users say it too, and it is not itself a move off the platform.
  { kind: 'seller-link', label: 'link-in-bio funnel', pattern: /\b(?:link|links)\s+(?:is\s+|are\s+)?in\s+(?:my\s+|the\s+)?(?:bio|profile|about)\b/ },
  { kind: 'seller-link', label: 'link-in-bio funnel', pattern: /\bbio\s+link\b/ },
  // The age/bot "verification" scam, which always ends on a third-party site.
  { kind: 'verification-scam', label: 'verification scam', pattern: /\b(?:age|id|identity)\s*verif(?:y|ied|ication)\b/ },
  {
    kind: 'verification-scam',
    label: 'verification scam',
    pattern: /\bverify\s+(?:that\s+)?(?:you|your|yourself|u)\b[^.\n]{0,25}\b(?:not a bot|human|real|age|18|adult)\b/,
  },
  { kind: 'verification-scam', label: 'verification scam', pattern: /\bverification\s+(?:site|link|page|process|code|card)\b/ },
];

/**
 * Returns the first signal that a conversation is being pulled off Reddit, or
 * null. Order is stable: unambiguous platform and funnel names first, then the
 * context-dependent rules, so the recorded evidence names the strongest match.
 */
export function findOffPlatformSignal(text: string): OffPlatformSignal | null {
  if (!text || !text.trim()) return null;
  const normalized = normalizeSignalText(text);
  const folded = foldSignalText(text);

  for (const rule of FOLDED_TOKENS) {
    if (folded.includes(rule.token)) {
      return { kind: rule.kind, label: rule.label, matched: rule.token };
    }
  }
  for (const rule of CONTEXT_RULES) {
    const match = normalized.match(rule.pattern);
    if (match) {
      return { kind: rule.kind, label: rule.label, matched: match[0].trim() };
    }
  }
  return null;
}

/** Human-readable reason recorded against a killed conversation. */
export function offPlatformSignalReason(signal: OffPlatformSignal): string {
  switch (signal.kind) {
    case 'contact-platform':
      return `Off-platform contact push detected (${signal.label}: "${signal.matched}").`;
    case 'handle-ask':
      return `Off-platform contact push detected ("${signal.matched}").`;
    case 'payment':
      return `Payment solicitation detected (${signal.label}: "${signal.matched}").`;
    case 'seller-link':
      return `Seller funnel detected (${signal.label}: "${signal.matched}").`;
    case 'verification-scam':
      return `Verification scam detected ("${signal.matched}").`;
  }
}