/**
 * Gmail "folder" routing — map a ticket's Gmail thread into a managed set of
 * labels with exclusive-folder semantics.
 *
 * Gmail labels are additive; we synthesize folders by, on every move, adding the
 * target label and removing every *other* managed label plus INBOX + UNREAD
 * (removing an absent label is a no-op, so this is idempotent). "Spam" maps to
 * the built-in system SPAM label, which is never created.
 *
 * Acyclic require graph: this module depends on services/gmail (getGmailClient);
 * gmail.js does not depend back on this file.
 */
'use strict';

const { CONFIG } = require('../config');
const { getGmailClient } = require('./gmail');

// Logical folder key -> how to resolve its label. User folders read their display
// name from CONFIG (env-configurable); SPAM is the Gmail system label.
const FOLDER_DEFS = {
  TRIAGE:             { configKey: 'GMAIL_LABEL_TRIAGE' },
  AWAITING_REPLY:     { configKey: 'GMAIL_LABEL_AWAITING_REPLY' },
  NEEDS_RESPONSE:     { configKey: 'GMAIL_LABEL_NEEDS_RESPONSE' },
  ESCALATED:          { configKey: 'GMAIL_LABEL_ESCALATED' },
  RESOLVED:           { configKey: 'GMAIL_LABEL_RESOLVED' },
  FOR_JAKE:           { configKey: 'GMAIL_LABEL_FOR_JAKE' },
  DASHBOARD_ERRORS:   { configKey: 'GMAIL_LABEL_DASHBOARD_ERRORS' },
  PARTNERSHIP_OFFERS: { configKey: 'GMAIL_LABEL_PARTNERSHIP_OFFERS' },
  SPAM:               { system: 'SPAM' }
};

// User-managed folder keys (everything but the system SPAM label).
const MANAGED_USER_KEYS = Object.keys(FOLDER_DEFS).filter(k => !FOLDER_DEFS[k].system);

// Folders staff file into by hand. The reply-cycle auto-flow (autoAdvanceFolder)
// never moves a thread out of one of these — a customer reply to something filed
// under "For Jake" or "Spam" stays put. Everything else (Triage, Awaiting Reply,
// Needs Response, Escalated, Resolved) is auto-cycle eligible.
const MANUAL_KEYS = ['FOR_JAKE', 'SPAM', 'PARTNERSHIP_OFFERS', 'DASHBOARD_ERRORS'];

// Always stripped on a move so the thread leaves the inbox and is marked read.
const ALWAYS_REMOVE = ['INBOX', 'UNREAD'];

// Cache: Gmail label display name -> label ID. Populated lazily; cleared on a
// stale-label error so a label recreated in Gmail is re-resolved.
const labelIdByName = new Map();

/** Display name for a user folder key (null for the system SPAM label). */
function folderDisplayName(key) {
  const def = FOLDER_DEFS[key];
  if (!def) throw new Error(`Unknown folder key: ${key}`);
  if (def.system) return null;
  return CONFIG[def.configKey];
}

async function ensureLabelCache(gmail) {
  if (labelIdByName.size > 0) return;
  const res = await gmail.users.labels.list({ userId: 'me' });
  for (const label of res.data.labels || []) {
    labelIdByName.set(label.name, label.id);
  }
}

/**
 * Resolve a folder key to a Gmail label ID, creating a missing *user* label.
 * SPAM short-circuits to the system id and is never created.
 */
async function resolveLabelId(gmail, key) {
  const def = FOLDER_DEFS[key];
  if (!def) throw new Error(`Unknown folder key: ${key}`);
  if (def.system) return def.system;

  const name = folderDisplayName(key);
  await ensureLabelCache(gmail);
  if (labelIdByName.has(name)) return labelIdByName.get(name);

  const created = await gmail.users.labels.create({
    userId: 'me',
    requestBody: { name, labelListVisibility: 'labelShow', messageListVisibility: 'show' }
  });
  labelIdByName.set(name, created.data.id);
  return created.data.id;
}

/**
 * Pure: given the target key and a key->id map of every managed label, build the
 * add/remove sets for an exclusive-folder move. The target label is added; every
 * other managed label plus INBOX + UNREAD is removed.
 */
function computeLabelMutation(targetKey, idByKey) {
  const targetId = idByKey[targetKey];
  if (!targetId) throw new Error(`Missing resolved id for target folder: ${targetKey}`);

  const removeLabelIds = [];
  for (const key of Object.keys(idByKey)) {
    if (key === targetKey) continue;
    const id = idByKey[key];
    if (id) removeLabelIds.push(id);
  }
  for (const sys of ALWAYS_REMOVE) removeLabelIds.push(sys);

  return { addLabelIds: [targetId], removeLabelIds };
}

function isInvalidLabelError(err) {
  const status = err && ((err.response && err.response.status) || err.code);
  const msg = (err && err.message) || '';
  return status === 400 || /invalid label|labelId not found/i.test(msg);
}

/**
 * Move a Gmail thread into a managed folder with exclusive-folder semantics.
 * Resolves (and creates) every managed label, then issues one threads.modify.
 * On a stale cached label id (400 invalid label), clears the cache and retries
 * once.
 *
 * @param {string} threadId   Gmail thread id (ticket.gmailThreadId)
 * @param {string} targetKey  one of FOLDER_DEFS keys
 * @param {object} [gmail]    optional Gmail client (poll loop passes its own)
 */
async function moveThreadToFolder(threadId, targetKey, gmail = getGmailClient()) {
  if (!threadId) throw new Error('moveThreadToFolder: threadId required');
  if (!FOLDER_DEFS[targetKey]) throw new Error(`Unknown folder key: ${targetKey}`);

  const applyOnce = async () => {
    const idByKey = {};
    for (const key of Object.keys(FOLDER_DEFS)) {
      idByKey[key] = await resolveLabelId(gmail, key);
    }
    const mutation = computeLabelMutation(targetKey, idByKey);
    await gmail.users.threads.modify({
      userId: 'me',
      id: threadId,
      requestBody: mutation
    });
  };

  try {
    await applyOnce();
  } catch (err) {
    if (isInvalidLabelError(err)) {
      labelIdByName.clear();
      await applyOnce();
    } else {
      throw err;
    }
  }
}

/**
 * Read-only: which managed folder does this thread currently sit in? Returns a
 * FOLDER_DEFS key, or null if none of the managed labels are present.
 *
 * Unlike resolveLabelId this never *creates* a label — a label that doesn't exist
 * yet can't be on the thread, so it's simply skipped.
 */
async function getManagedFolderKey(threadId, gmail = getGmailClient()) {
  if (!threadId) throw new Error('getManagedFolderKey: threadId required');

  const thread = await gmail.users.threads.get({ userId: 'me', id: threadId, format: 'minimal' });
  const threadLabelIds = new Set();
  for (const m of thread.data.messages || []) {
    for (const id of m.labelIds || []) threadLabelIds.add(id);
  }

  await ensureLabelCache(gmail);
  for (const key of Object.keys(FOLDER_DEFS)) {
    const def = FOLDER_DEFS[key];
    const id = def.system ? def.system : labelIdByName.get(folderDisplayName(key));
    if (id && threadLabelIds.has(id)) return key;
  }
  return null;
}

/**
 * Advance a thread to `targetKey` as part of the reply cycle — UNLESS it is
 * currently filed in a manual folder (MANUAL_KEYS), in which case it is left
 * untouched. Threads with no managed label (or an auto-cycle label) advance.
 *
 * @returns {Promise<boolean>} true if the thread was moved, false if left in place.
 */
async function autoAdvanceFolder(threadId, targetKey, gmail = getGmailClient()) {
  if (!threadId) throw new Error('autoAdvanceFolder: threadId required');
  if (!FOLDER_DEFS[targetKey]) throw new Error(`Unknown folder key: ${targetKey}`);

  const current = await getManagedFolderKey(threadId, gmail);
  if (current && MANUAL_KEYS.includes(current)) return false;

  await moveThreadToFolder(threadId, targetKey, gmail);
  return true;
}

module.exports = {
  FOLDER_DEFS,
  MANAGED_USER_KEYS,
  MANUAL_KEYS,
  ALWAYS_REMOVE,
  folderDisplayName,
  resolveLabelId,
  computeLabelMutation,
  moveThreadToFolder,
  getManagedFolderKey,
  autoAdvanceFolder,
  // test seam: clear the name->id cache between cases
  __clearLabelCache: () => labelIdByName.clear()
};