"use client";

// Settings panel for the desktop shell's encrypted local search index.
//
// Deliberately small: the index's PRIMARY trigger is the live push connection
// (see lib/mail-index-client.ts's indexOnStateChange, wired into
// stores/email-store.ts's handleStateChange), so this panel is a status readout
// plus a manual catch-up button - not the mechanism.
//
// Renders nothing at all outside the Electron shell, where the routes 404.

import { useCallback, useEffect, useState } from 'react';
import { Button } from '@/components/ui/button';
import { SettingsSection, SettingItem } from './settings-section';
import { isElectronShell } from '@/lib/electron-bridge';
import { useAccountStore } from '@/stores/account-store';
import {
  catchUpIndex, fetchIndexStats, getRetentionDays, setRetentionDays, type IndexStats,
} from '@/lib/mail-index-client';
import {
  chainSync, fetchReplicaStatus, purgeReplica, updateRetentionPolicy,
  type ReplicaStatus, type RetentionPolicy,
} from '@/lib/offline-replica-client';

const TYPE_LABELS: Record<string, string> = {
  mail: 'Mail',
  calendar: 'Calendar',
  contact: 'Contacts',
  file: 'Files',
};

export function LocalIndexSettings() {
  const slot = useAccountStore((s) => s.accounts.find((a) => a.id === s.activeAccountId)?.cookieSlot);
  const [stats, setStats] = useState<IndexStats[] | null>(null);
  const [busy, setBusy] = useState(false);
  const [message, setMessage] = useState<string | null>(null);
  // `null` until the first probe resolves, so we don't flash a panel that then
  // vanishes on a non-desktop build.
  const [available, setAvailable] = useState<boolean | null>(null);
  // `null` = keep everything. Read once on mount; the setter writes through.
  const [retentionDays, setRetentionDaysState] = useState<number | null>(365);

  useEffect(() => { setRetentionDaysState(getRetentionDays()); }, []);

  const refreshStats = useCallback(async () => {
    const next = await fetchIndexStats(slot);
    setStats(next);
    setAvailable(next !== null);
  }, [slot]);

  useEffect(() => {
    if (!isElectronShell()) {
      setAvailable(false);
      return;
    }
    void refreshStats();
  }, [refreshStats]);

  const handleRebuild = async () => {
    setBusy(true);
    setMessage(null);
    try {
      const result = await catchUpIndex(slot, retentionDays);
      if (result.unavailable) {
        setAvailable(false);
        setMessage(result.error ?? 'The encrypted index is unavailable on this system.');
        return;
      }
      if (!result.ok) {
        setMessage(result.error ?? 'Indexing failed.');
        return;
      }
      const written = Object.entries(result.written ?? {})
        .map(([type, n]) => `${TYPE_LABELS[type] ?? type}: ${n}`)
        .join(', ');
      const failed = (result.errors ?? []).map((e) => `${e.contentType} (${e.message})`).join('; ');
      setMessage(
        [
          written ? `Indexed ${written}.` : 'Nothing to index.',
          result.skipped?.length ? `Not supported: ${result.skipped.join(', ')}.` : '',
          failed ? `Problems: ${failed}` : '',
        ]
          .filter(Boolean)
          .join(' '),
      );
      await refreshStats();
    } finally {
      setBusy(false);
    }
  };

  if (available === false || available === null) return null;

  const total = (stats ?? []).reduce((sum, s) => sum + s.count, 0);

  return (
    <SettingsSection
      title="Local search index"
      description={
        'An encrypted index of your recent mail, calendar events, contacts and file names, ' +
        'stored on this device only. It updates automatically as items arrive, and powers ' +
        'local search and AI answers about your own data. Files are indexed by name and ' +
        'location, not by their contents.'
      }
    >
      <SettingItem
        label="Indexed items"
        description={
          total > 0
            ? (stats ?? [])
                .map((s) => `${TYPE_LABELS[s.contentType] ?? s.contentType}: ${s.count}`)
                .join(' · ')
            : 'Nothing indexed yet.'
        }
      >
        <span className="text-sm text-muted-foreground tabular-nums">{total}</span>
      </SettingItem>

      <SettingItem
        label="Keep AI search history for"
        description={
          'How far back the AI assistant can search your mail. This also PRUNES: mail older ' +
          'than the window is removed from the local index on the next update, so a short ' +
          'window means questions about older mail cannot be answered. Only ever covers the ' +
          'mailbox you are signed in to.'
        }
      >
        <select
          className="h-9 rounded-md border border-border bg-background px-2 text-sm"
          value={retentionDays === null ? 'forever' : String(retentionDays)}
          onChange={(e) => {
            const next = e.target.value === 'forever' ? null : Number.parseInt(e.target.value, 10);
            setRetentionDaysState(next);
            setRetentionDays(next);
            setMessage('Saved. Choose "Update index" to apply it now.');
          }}
        >
          <option value="30">30 days</option>
          <option value="90">3 months</option>
          <option value="365">1 year</option>
          <option value="forever">Everything</option>
        </select>
      </SettingItem>

      <SettingItem
        label="Update now"
        description={
          message ??
          'Catches up on anything that changed while the app was closed. Normally not needed - ' +
            'the index updates itself when mail, events, contacts or files change.'
        }
      >
        <Button variant="outline" size="sm" onClick={handleRebuild} disabled={busy}>
          {busy ? 'Indexing…' : 'Update index'}
        </Button>
      </SettingItem>

      <OfflineMailSettings slot={slot} />
    </SettingsSection>
  );
}

function formatBytes(bytes: number): string {
  if (bytes < 1024) return `${bytes} B`;
  const units = ['KB', 'MB', 'GB'];
  let value = bytes / 1024;
  let unit = 0;
  while (value >= 1024 && unit < units.length - 1) { value /= 1024; unit++; }
  return `${value.toFixed(value >= 10 ? 0 : 1)} ${units[unit]}`;
}

const PHASE_LABELS: Record<string, string> = {
  'never-run': 'not started',
  scanning: 'downloading history',
  reconciling: 'rebuilding',
  complete: 'up to date',
};

/**
 * Controls for the offline mail replica (lib/offline-replica/**).
 *
 * Lives inside the same panel as the search index because they share one
 * encrypted file, one key and one purge - presenting them as two unrelated
 * features would misrepresent what "delete" deletes.
 */
function OfflineMailSettings({ slot }: { slot: number | undefined }) {
  const [status, setStatus] = useState<ReplicaStatus | null>(null);
  const [busy, setBusy] = useState<null | 'sync' | 'purge' | 'policy'>(null);
  const [message, setMessage] = useState<string | null>(null);

  const refresh = useCallback(async () => {
    setStatus(await fetchReplicaStatus(slot));
  }, [slot]);

  useEffect(() => { void refresh(); }, [refresh]);

  const savePolicy = async (patch: Partial<RetentionPolicy>) => {
    if (!status) return;
    const next: RetentionPolicy = { ...status.policy, ...patch };
    setBusy('policy');
    setMessage(null);
    try {
      const ok = await updateRetentionPolicy(next, slot);
      if (!ok) { setMessage('Could not save the retention setting.'); return; }
      // The change is applied by the next cycle - a widen re-scans, a narrow
      // evicts - so run one now rather than leaving the number looking wrong.
      await chainSync({ slot, max: 2 });
      await refresh();
    } finally {
      setBusy(null);
    }
  };

  const handleSync = async () => {
    setBusy('sync');
    setMessage(null);
    try {
      const report = await chainSync({ slot });
      if (!report) { setMessage('Offline mail is unavailable on this system.'); return; }
      setMessage(
        report.ok
          ? `Synced ${report.envelopesWritten} messages and ${report.bodiesWritten} bodies.` +
            (report.unfinishedWork ? ' More will download in the background.' : '') +
            (report.warnings.length > 0 ? ` Notes: ${report.warnings.join('; ')}` : '')
          : `Sync failed: ${report.error ?? 'unknown error'}`,
      );
      await refresh();
    } finally {
      setBusy(null);
    }
  };

  const handlePurge = async () => {
    setBusy('purge');
    setMessage(null);
    try {
      const ok = await purgeReplica(slot);
      setMessage(ok ? 'Offline mail deleted from this device.' : 'Could not delete offline mail.');
      await refresh();
    } finally {
      setBusy(null);
    }
  };

  if (!status) return null;

  const stats = status.stats;
  const total = stats ? stats.fileBytes : 0;

  return (
    <>
      <SettingItem
        label="Offline mail"
        description={
          stats
            ? `${stats.envelopes} messages listed, ${stats.bodies} readable offline · ` +
              `${formatBytes(stats.bodyBytes)} of message content · ` +
              `status: ${PHASE_LABELS[status.coveragePhase] ?? status.coveragePhase}` +
              (status.resyncRequired ? ' (a rebuild is queued)' : '') +
              (stats.wantedBodies > 0 ? ` · ${stats.wantedBodies} still downloading` : '')
            : 'Nothing stored yet. Mail downloads automatically as it arrives.'
        }
      >
        <span className="text-sm text-muted-foreground tabular-nums">{formatBytes(total)}</span>
      </SettingItem>

      <SettingItem
        label="Keep message list for"
        description={
          'How far back the offline message list goes. Listed messages are tiny (about a ' +
          'kilobyte each), so a wide window here costs very little and means a message never ' +
          'disappears from the offline list just because its content was removed to save space.'
        }
      >
        <select
          className="h-9 rounded-md border border-border bg-background px-2 text-sm"
          value={status.policy.envelopeDays}
          disabled={busy !== null}
          onChange={(e) => void savePolicy({ envelopeDays: Number(e.target.value) })}
        >
          {[30, 90, 180, 365, 730, 1825].map((d) => (
            <option key={d} value={d}>
              {d >= 365 ? `${Math.round(d / 365)} year${d >= 730 ? 's' : ''}` : `${d} days`}
            </option>
          ))}
        </select>
      </SettingItem>

      <SettingItem
        label="Keep full messages for"
        description={
          'How far back complete messages - including formatted content - are stored so they ' +
          'can be read with no network. Attachments are not downloaded; they still need a ' +
          'connection.'
        }
      >
        <select
          className="h-9 rounded-md border border-border bg-background px-2 text-sm"
          value={status.policy.bodyDays}
          disabled={busy !== null}
          onChange={(e) => void savePolicy({ bodyDays: Number(e.target.value) })}
        >
          {[7, 14, 30, 90, 180, 365].map((d) => (
            <option key={d} value={d}>{d >= 365 ? '1 year' : `${d} days`}</option>
          ))}
        </select>
      </SettingItem>

      <SettingItem
        label="Storage limit for message content"
        description={
          'The oldest stored content is removed first when this is reached. Messages stay in ' +
          'the offline list either way - only their content is removed.'
        }
      >
        <select
          className="h-9 rounded-md border border-border bg-background px-2 text-sm"
          value={status.policy.maxBodyMB}
          disabled={busy !== null}
          onChange={(e) => void savePolicy({ maxBodyMB: Number(e.target.value) })}
        >
          {[100, 250, 500, 1000, 2000, 5000].map((mb) => (
            <option key={mb} value={mb}>{mb >= 1000 ? `${mb / 1000} GB` : `${mb} MB`}</option>
          ))}
        </select>
      </SettingItem>

      <SettingItem
        label="Offline mail actions"
        description={message ?? 'Download now, or delete everything stored offline on this device.'}
      >
        <div className="flex gap-2">
          <Button variant="outline" size="sm" onClick={handleSync} disabled={busy !== null}>
            {busy === 'sync' ? 'Downloading…' : 'Download now'}
          </Button>
          <Button variant="outline" size="sm" onClick={handlePurge} disabled={busy !== null}>
            {busy === 'purge' ? 'Deleting…' : 'Delete offline mail'}
          </Button>
        </div>
      </SettingItem>
    </>
  );
}