import fs from 'node:fs';
import { google } from 'googleapis';
import config from './config.js';
import db from './db.js';
import { localStamp } from './util.js';

/**
 * The spreadsheet is an evacuation list and nothing else.
 *
 * One tab, rewritten in full whenever anyone signs in or out, holding only the
 * people currently in the building. It is never appended to, so there is no
 * history to scroll past while standing in a car park counting heads.
 *
 * The full visit history stays in the application's own database, where it is
 * searchable in the admin console and exportable as CSV.
 */

const HEADER = [
  'Site',
  'First name',
  'Last name',
  'Company',
  'Visiting',
  'Phone',
  'Email',
  'Check',
  'Signed in',
  'On site for',
  'Visit ID',
];

const MAX_ROWS = 1000;

let client = null;
let tabPromise = null;
let dirty = false;
let syncing = false;

export const status = {
  lastOk: null,
  lastError: null,
  onSiteCount: null,
};

/* ----------------------------------------------------------- connection */

function loadCredentials() {
  if (config.sheets.credentialsB64) {
    return JSON.parse(Buffer.from(config.sheets.credentialsB64, 'base64').toString('utf8'));
  }
  if (config.sheets.credentialsPath && fs.existsSync(config.sheets.credentialsPath)) {
    return JSON.parse(fs.readFileSync(config.sheets.credentialsPath, 'utf8'));
  }
  throw new Error('No Google service account credentials found.');
}

function getClient() {
  if (client) return client;
  const creds = loadCredentials();
  const auth = new google.auth.JWT({
    email: creds.client_email,
    key: creds.private_key,
    scopes: ['https://www.googleapis.com/auth/spreadsheets'],
  });
  client = google.sheets({ version: 'v4', auth });
  return client;
}

/**
 * The service account's own address. Nothing works until the spreadsheet is
 * shared with it, and it is buried in a JSON key file nobody wants to open on a
 * server, so the admin console shows it.
 */
export function serviceAccountEmail() {
  try {
    return loadCredentials().client_email || null;
  } catch {
    return null;
  }
}

/**
 * Google's own wording for these failures says what went wrong but never what to
 * do about it, so the common ones are rewritten with the actual next step.
 */
function explain(err) {
  const code = err?.code || err?.response?.status;
  const raw = String(err?.message || '');
  const email = serviceAccountEmail();

  if (code === 403 && /caller does not have permission|permission/i.test(raw)) {
    return (
      `The service account cannot open this spreadsheet. Share the sheet with ` +
      `${email || 'the service account address'} and give it Editor access.`
    );
  }
  if (code === 403 && /has not been used|accessNotConfigured|disabled/i.test(raw)) {
    return 'The Google Sheets API is not enabled on that Google Cloud project. Enable it, then wait a minute and retry.';
  }
  if (code === 404) {
    return 'No spreadsheet was found with that ID. Check SHEETS_SPREADSHEET_ID against the sheet URL.';
  }
  if (code === 400 && /Unable to parse range/i.test(raw)) {
    return `The tab "${config.sheets.onSiteTab}" could not be addressed. Check SHEETS_ONSITE_TAB matches the tab name exactly.`;
  }
  if (/invalid_grant|Invalid JWT|clock/i.test(raw)) {
    return "Google rejected the credentials. Check the server's clock is correct and the service account key has not been deleted.";
  }
  return raw || 'Unknown error talking to Google Sheets.';
}

export function isEnabled() {
  return Boolean(config.sheets.enabled && config.sheets.spreadsheetId);
}

/**
 * Creates the tab if it is missing. Memoised as a promise rather than a boolean:
 * two syncs starting at once would otherwise both decide it was missing.
 */
function ensureTab(sheets, { force = false } = {}) {
  if (force) tabPromise = null;
  if (!tabPromise) {
    tabPromise = doEnsureTab(sheets).catch((err) => {
      tabPromise = null;
      throw err;
    });
  }
  return tabPromise;
}

async function doEnsureTab(sheets) {
  const meta = await sheets.spreadsheets.get({ spreadsheetId: config.sheets.spreadsheetId });
  const titles = meta.data.sheets.map((s) => s.properties.title);
  if (!titles.includes(config.sheets.onSiteTab)) {
    await sheets.spreadsheets.batchUpdate({
      spreadsheetId: config.sheets.spreadsheetId,
      requestBody: {
        requests: [{ addSheet: { properties: { title: config.sheets.onSiteTab } } }],
      },
    });
    console.log(`[sheets] created tab "${config.sheets.onSiteTab}"`);
  }
}

/* --------------------------------------------------------- who is here */

function humanDuration(fromIso) {
  const minutes = Math.max(0, Math.round((Date.now() - new Date(fromIso).getTime()) / 60000));
  if (minutes < 60) return `${minutes} min`;
  const hours = Math.floor(minutes / 60);
  return `${hours}h ${String(minutes % 60).padStart(2, '0')}m`;
}

function onSiteRows() {
  return db
    .prepare('SELECT * FROM visits WHERE signed_out_at IS NULL ORDER BY site_name, signed_in_at')
    .all()
    .slice(0, MAX_ROWS)
    .map((v) => [
      v.site_name || '',
      v.first_name,
      v.last_name,
      v.company || '',
      v.host_name,
      v.phone || '',
      v.email || '',
      v.check_type === 'NONE' ? 'None' : `${v.check_type} ${v.check_number || ''}`.trim(),
      localStamp(v.signed_in_at),
      humanDuration(v.signed_in_at),
      String(v.id),
    ]);
}

/**
 * Replaces the whole tab with the current state. Rewriting rather than patching
 * means a missed update can never leave a stale name on the evacuation list:
 * whatever is on the tab is what the database says right now.
 */
export async function syncOnSite() {
  if (!isEnabled()) return { skipped: true };
  if (syncing) {
    dirty = true;
    return { skipped: true };
  }
  syncing = true;
  try {
    const sheets = getClient();
    await ensureTab(sheets);
    const rows = onSiteRows();
    const banner = `On site now — ${rows.length} ${rows.length === 1 ? 'person' : 'people'} — updated ${localStamp(new Date().toISOString())}`;

    await sheets.spreadsheets.values.clear({
      spreadsheetId: config.sheets.spreadsheetId,
      range: `${config.sheets.onSiteTab}!A1:K${MAX_ROWS + 10}`,
    });
    await sheets.spreadsheets.values.update({
      spreadsheetId: config.sheets.spreadsheetId,
      range: `${config.sheets.onSiteTab}!A1`,
      valueInputOption: 'RAW',
      requestBody: { values: [[banner], HEADER, ...rows] },
    });

    dirty = false;
    status.lastOk = new Date().toISOString();
    status.lastError = null;
    status.onSiteCount = rows.length;
    return { rows: rows.length };
  } catch (err) {
    dirty = true;
    status.lastError = explain(err);
    const wrapped = new Error(status.lastError);
    wrapped.cause = err;
    throw wrapped;
  } finally {
    syncing = false;
  }
}

/**
 * Called after every sign in and sign out. Fire and forget: a Sheets outage must
 * never hold up someone standing at the front desk. A failure leaves the tab
 * marked stale and the worker retries.
 */
export function mirror() {
  if (!isEnabled()) return;
  dirty = true;
  syncOnSite().catch((err) => console.error('[sheets] sync failed, will retry:', err.message));
}

export async function testConnection() {
  if (!isEnabled()) throw new Error('Google Sheets mirroring is turned off in the environment.');
  try {
    const sheets = getClient();
    const meta = await sheets.spreadsheets.get({ spreadsheetId: config.sheets.spreadsheetId });
    await ensureTab(sheets, { force: true });
    await syncOnSite();
    status.lastError = null;
    return { title: meta.data.properties.title, tab: config.sheets.onSiteTab };
  } catch (err) {
    status.lastError = explain(err);
    throw new Error(status.lastError);
  }
}

export function tabName() {
  return config.sheets.onSiteTab;
}

export function isStale() {
  return dirty;
}

export function startWorker() {
  if (!isEnabled()) {
    console.log('[sheets] mirroring disabled');
    return;
  }
  console.log(
    `[sheets] mirroring who is on site to ${config.sheets.spreadsheetId} ("${config.sheets.onSiteTab}")`
  );

  // Rows left over from the older append-only log are no longer sent anywhere.
  const stale = db.prepare('SELECT COUNT(*) AS n FROM sheet_queue').get().n;
  if (stale) {
    db.prepare('DELETE FROM sheet_queue').run();
    console.log(
      `[sheets] discarded ${stale} queued history row(s): the sheet now holds only who is on site. ` +
        'The full history is still in the visit log.'
    );
  }

  // Retry anything that failed, and keep the "on site for" column honest.
  setInterval(() => {
    if (dirty) {
      syncOnSite().catch((err) => console.error('[sheets] retry failed:', err.message));
    }
  }, config.sheets.retryIntervalMs).unref();

  setInterval(() => {
    syncOnSite().catch(() => {
      /* the retry above will pick it up */
    });
  }, 15 * 60 * 1000).unref();

  syncOnSite().catch((err) => console.error('[sheets] initial sync failed:', err.message));
}