/// Locally-stored GitHub sync configuration, ported from `~/src/todo`'s
/// `sync/sync_settings.dart`, including the OAuth device-flow fields: the
/// "Connect GitHub" button is the primary path, with a pasted PAT kept as a
/// manual fallback.
library;

import 'package:diet_guard_app/services/token_vault.dart';
import 'package:diet_guard_app/services/token_vault_factory.dart';
import 'package:shared_preferences/shared_preferences.dart';

/// The GitHub token is kept out of `SharedPreferences`, which holds only the
/// non-secret owner/repo: on Android it lives in the OS keystore, and in the
/// desktop web build it lives in the wrapper process rather than the browser
/// at all (see [TokenVault]). Older builds stored the token in plaintext
/// prefs; [load]/[save] migrate it transparently and never drop the plaintext
/// copy until a vault write is confirmed (so we degrade to -- never below --
/// the old behaviour when no secure store is available).
class SyncSettings {
  /// Creates a [SyncSettings] from its owner/repo/token.
  const SyncSettings({
    required this.owner,
    required this.repo,
    required this.token,
    this.clientId = '',
  });

  /// The repo owner/org (e.g. `"kuhyx"`).
  final String owner;

  /// The repo name (e.g. `"syncs"`).
  final String repo;

  /// A GitHub PAT with contents read/write on [owner]/[repo].
  final String token;

  /// GitHub OAuth App client id used by the device-flow "Connect" button.
  /// Not a secret (device flow needs no client secret), so it is safe to
  /// ship as a compile-time default and commit to source — see
  /// [defaultClientId].
  final String clientId;

  /// The app's own GitHub OAuth App (device-flow enabled) client id, baked
  /// in so "Connect GitHub" works with zero setup. Registered 2026-06-23 at
  /// github.com/settings/developers, device flow enabled — distinct from
  /// the sibling notes app's OAuth App, which belongs to a different
  /// product.
  static const defaultClientId = 'Ov23li8wIQBai3qtbsqa';

  /// True when enough is set to attempt a sync.
  bool get isConfigured =>
      owner.isNotEmpty && repo.isNotEmpty && token.isNotEmpty;

  /// True when device-flow "Connect GitHub" can be offered.
  bool get canUseDeviceFlow => clientId.isNotEmpty;

  static const _kOwner = 'sync.owner';
  static const _kRepo = 'sync.repo';
  static const _kClientId = 'sync.clientId';
  // Legacy plaintext location for the token; read-only now and removed once
  // the token has been migrated into secure storage.
  static const _kToken = 'sync.token';

  static final TokenVault _vault = openTokenVault();

  /// True when this platform can show the stored token back to the user.
  static bool get exposesTokenValue => _vault.exposesTokenValue;

  /// Loads settings, defaulting the owner/repo to `kuhyx/syncs`
  /// (matching the PC's `SYNC_REPO_OWNER`/`SYNC_REPO_NAME` constants) and the
  /// client id to the baked-in [defaultClientId], so a fresh install needs
  /// only "Connect GitHub" (once an OAuth App is registered) or a pasted PAT.
  ///
  /// A device that already persisted the old standalone `diet-guard-sync`
  /// repo name (before it was folded into the shared `syncs` monorepo) is
  /// migrated to `syncs` here and the corrected value is written straight
  /// back to prefs, so this only ever runs once per device.
  static Future<SyncSettings> load() async {
    final prefs = await SharedPreferences.getInstance();
    var repo = prefs.getString(_kRepo) ?? 'syncs';
    if (repo == 'diet-guard-sync') {
      repo = 'syncs';
      await prefs.setString(_kRepo, repo);
    }
    return SyncSettings(
      owner: prefs.getString(_kOwner) ?? 'kuhyx',
      repo: repo,
      token: await _loadToken(prefs),
      clientId: prefs.getString(_kClientId) ?? defaultClientId,
    );
  }

  /// Reads the token, preferring the vault and falling back to the legacy
  /// plaintext value. A legacy value is migrated into the vault on read, but
  /// only dropped from prefs once that write succeeds.
  static Future<String> _loadToken(SharedPreferences prefs) async {
    final stored = await _vault.read();
    if (stored.isNotEmpty) return stored;

    final legacy = prefs.getString(_kToken) ?? '';
    if (legacy.isNotEmpty && await _vault.write(legacy)) {
      await prefs.remove(_kToken);
    }
    return legacy;
  }

  /// Persists [owner]/[repo] to prefs and [token] to the vault (or plaintext
  /// prefs as a fallback -- see [_loadToken]).
  Future<void> save() async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_kOwner, owner);
    await prefs.setString(_kRepo, repo);
    await prefs.setString(_kClientId, clientId);
    // Confirm-before-delete: only remove the plaintext copy once the vault
    // write succeeds; otherwise keep persisting it to prefs as before.
    if (await _vault.write(token)) {
      await prefs.remove(_kToken);
    } else {
      await prefs.setString(_kToken, token);
    }
  }

  /// Returns a copy of this with only the given fields replaced.
  SyncSettings copyWith({
    String? owner,
    String? repo,
    String? token,
    String? clientId,
  }) {
    return SyncSettings(
      owner: owner ?? this.owner,
      repo: repo ?? this.repo,
      token: token ?? this.token,
      clientId: clientId ?? this.clientId,
    );
  }
}