import { Router, Request, Response } from 'express';
import { pool } from '../db';
import { asyncRoute } from '../asyncRoute';
import {
  TEMPLATES,
  TemplateKey,
  StoredTemplate,
  missingPlaceholders,
  renderTemplate,
  formatDuration,
  greeting,
  SAMPLE_VALUES
} from '../emailTemplates';
import { getSettings } from '../adminSettings';

/** A row of the admin_settings key/value store. */
interface SettingRow {
  key: string;
  value: string;
}

const router = Router();

const KEYS = Object.keys(TEMPLATES) as TemplateKey[];

// Stored in admin_settings rather than a table of their own: it is already a
// key/value store with a settled read/write shape, and five templates is not a
// schema.
const settingKey = (key: TemplateKey, part: 'subject' | 'body') => `email_${key}_${part}`;

function isTemplateKey(value: unknown): value is TemplateKey {
  return typeof value === 'string' && (KEYS as string[]).includes(value);
}

export async function loadStoredTemplate(key: TemplateKey): Promise<StoredTemplate> {
  const { rows } = await pool.query<SettingRow>(`SELECT key, value FROM admin_settings WHERE key = ANY($1)`, [
    [settingKey(key, 'subject'), settingKey(key, 'body')]
  ]);
  const stored: StoredTemplate = {};
  for (const row of rows) {
    if (row.key === settingKey(key, 'subject')) stored.subject = row.value;
    if (row.key === settingKey(key, 'body')) stored.body = row.value;
  }
  return stored;
}

// Returns the definitions alongside whatever is stored, so the admin screen can
// show the placeholders a template accepts and which of them it must keep,
// rather than the editor having to know.
router.get('/', asyncRoute(async (_req: Request, res: Response) => {
  const { rows } = await pool.query<SettingRow>(
    `SELECT key, value FROM admin_settings WHERE key LIKE 'email\\_%'`
  );
  const stored = new Map<string, string>(rows.map((r) => [r.key, r.value]));

  res.json(
    KEYS.map((key) => ({
      key,
      label: TEMPLATES[key].label,
      required: TEMPLATES[key].required,
      available: TEMPLATES[key].available,
      defaultSubject: TEMPLATES[key].defaultSubject,
      defaultBody: TEMPLATES[key].defaultBody,
      // Null rather than the default, so the admin can tell "not customised"
      // from "customised to exactly the default text".
      subject: stored.get(settingKey(key, 'subject')) ?? null,
      body: stored.get(settingKey(key, 'body')) ?? null
    }))
  );
}));

// Renders what an email would look like, from the subject and body in the
// editor rather than from what is stored — so an admin sees the effect of an
// edit before committing to it.
//
// Rendered here rather than in the browser, deliberately. renderTemplate is the
// only thing that turns this markdown into HTML, and markdown-it is configured
// with html: false, which is what stops an admin putting script into a
// customer's inbox. A second renderer in the frontend would be a second place
// for that setting to be wrong, and a preview that differs from the mailer is
// worse than no preview.
//
// Deliberately does not enforce required placeholders. Saving refuses a body
// that dropped one; previewing it is how an admin sees what they have done.
/**
 * The sample values, with the three duration placeholders replaced by what the
 * settings actually hold.
 *
 * The preview exists so an admin sees the email that will be sent. A duration
 * drawn from a static sample would show "one hour" while the setting said two,
 * which is the precise failure this placeholder was added to remove.
 */
async function previewValues(key: TemplateKey): Promise<Record<string, string>> {
  const {
    cartExpiryHours,
    verifyTokenHours,
    passwordResetHours,
    greetingFormat,
    greetingFallback
  } = await getSettings();
  // `expiresIn` names one placeholder but two different lifetimes, so the value
  // depends on which template is being previewed. The route knows the key.
  const expiresIn = key === 'passwordReset' ? passwordResetHours : verifyTokenHours;
  return {
    ...SAMPLE_VALUES,
    holdDuration: formatDuration(cartExpiryHours),
    expiresIn: formatDuration(expiresIn),
    // Built from the configured format for the same reason as the durations:
    // the preview is meant to show the email that will be sent.
    greeting: greeting(SAMPLE_VALUES.firstName, greetingFormat, greetingFallback, SAMPLE_VALUES.lastName)
  };
}

router.post('/:key/preview', asyncRoute(async (req: Request, res: Response) => {
  const key = req.params.key;
  if (!isTemplateKey(key)) {
    return res.status(404).json({ error: 'unknown template' });
  }

  const { subject, body } = req.body ?? {};
  const rendered = renderTemplate(
    key,
    {
      subject: typeof subject === 'string' ? subject : null,
      body: typeof body === 'string' ? body : null
    },
    await previewValues(key)
  );

  res.json(rendered);
}));

router.put('/:key', asyncRoute(async (req: Request, res: Response) => {
  const key = req.params.key;
  if (!isTemplateKey(key)) {
    return res.status(404).json({ error: 'unknown template' });
  }

  const subject = typeof req.body?.subject === 'string' ? req.body.subject.trim() : '';
  const body = typeof req.body?.body === 'string' ? req.body.body.trim() : '';

  if (!subject) {
    return res.status(400).json({ error: 'a subject is required' });
  }
  if (!body) {
    return res.status(400).json({ error: 'a body is required' });
  }

  // The rule that makes this feature safe rather than a way to break password
  // resets from a settings screen. A body without its link still sends, still
  // looks correct in the log, and is useless to everyone who receives it — so
  // the save is refused rather than warned about.
  const missing = missingPlaceholders(key, body);
  if (missing.length) {
    const named = missing.map((name) => '{{' + name + '}}').join(' and ');
    return res.status(400).json({ error: `the body must keep ${named}` });
  }

  for (const [part, value] of [
    ['subject', subject],
    ['body', body]
  ] as const) {
    await pool.query(
      `INSERT INTO admin_settings (key, value, updated_at) VALUES ($1, $2, now())
       ON CONFLICT (key) DO UPDATE SET value = $2, updated_at = now()`,
      [settingKey(key, part), value]
    );
  }

  res.json({ key, subject, body });
}));

// Restores the built-in copy by removing the stored rows, rather than by
// writing the default into them — so "not customised" stays distinguishable
// from "customised back to the original wording".
router.delete('/:key', asyncRoute(async (req: Request, res: Response) => {
  const key = req.params.key;
  if (!isTemplateKey(key)) {
    return res.status(404).json({ error: 'unknown template' });
  }

  await pool.query(`DELETE FROM admin_settings WHERE key = ANY($1)`, [
    [settingKey(key, 'subject'), settingKey(key, 'body')]
  ]);

  res.json({ key, subject: null, body: null });
}));

export default router;