added support for multiple accounts with an account switcher in settings

lib/api/cache_store.dart

@@ -5,6 +5,7 @@ import 'dart:io';
 import 'package:flutter/foundation.dart';
 import 'package:path_provider/path_provider.dart';
 
+import '../session/session_manager.dart';
 import '../utils/directory_size.dart';
 
 /// One cached response: the raw JSON payload and when it was stored.
@@ -22,6 +23,9 @@ class CacheEntry {
 /// in memory for the whole session and JSON-encodes payloads a second time.
 /// Here every access is async and touches exactly one file, and the payload is
 /// stored verbatim behind a one-line header (`<lastUpdate>\n<json>`).
+///
+/// Every account has its own directory; all access goes to the one of the
+/// active account, in every isolate.
 class CacheStore {
   CacheStore._();
 
@@ -30,15 +34,30 @@ class CacheStore {
   /// Payloads above this size are decoded on a background isolate.
   static const int isolateDecodeThreshold = 64 * 1024;
 
-  Future<Directory>? _dir;
+  static const _directoryPrefix = 'request_cache';
+
+  final Map<String, Future<Directory>> _dirs = {};
   final Map<String, Future<void>> _writes = {};
 
-  Future<Directory> _directory() => _dir ??= () async {
-    final base = await getApplicationCacheDirectory();
-    final dir = Directory('${base.path}/request_cache');
-    await dir.create(recursive: true);
-    return dir;
-  }();
+  /// Directory name for an account's storage [namespace]; null while no
+  /// account is active. The account from before multi-account support
+  /// (namespace '') keeps the original directory.
+  @visibleForTesting
+  static String directoryName(String? namespace) => switch (namespace) {
+    null => '$_directoryPrefix-signed-out',
+    '' => _directoryPrefix,
+    _ => '$_directoryPrefix-$namespace',
+  };
+
+  Future<Directory> _directory() {
+    final name = directoryName(SessionManager().activeAccount?.namespace);
+    return _dirs[name] ??= () async {
+      final base = await getApplicationCacheDirectory();
+      final dir = Directory('${base.path}/$name');
+      await dir.create(recursive: true);
+      return dir;
+    }();
+  }
 
   Future<File> _file(String key) async =>
       File('${(await _directory()).path}/${_safeName(key)}');
@@ -49,8 +68,9 @@ class CacheStore {
 
   Future<CacheEntry?> read(String key) async {
     try {
-      await _writes[key];
-      return parse(await (await _file(key)).readAsString());
+      final file = await _file(key);
+      await _writes[file.path];
+      return parse(await file.readAsString());
     } on Object {
       // Missing (PathNotFoundException) or unreadable: a cache miss.
       return null;
@@ -64,18 +84,21 @@ class CacheStore {
     return {for (var i = 0; i < keys.length; i++) keys[i]: ?entries[i]};
   }
 
-  Future<void> write(String key, String json) {
-    final previous = _writes[key] ?? Future<void>.value();
+  Future<void> write(String key, String json) async {
+    // Resolved up front: a queued write must not follow an account switch
+    // into the next account's directory.
+    final file = await _file(key);
+    final path = file.path;
+    final previous = _writes[path] ?? Future<void>.value();
     late final Future<void> current;
-    current = previous.then((_) => _write(key, json)).whenComplete(() {
-      if (identical(_writes[key], current)) _writes.remove(key);
+    current = previous.then((_) => _write(file, json)).whenComplete(() {
+      if (identical(_writes[path], current)) _writes.remove(path);
     });
-    return _writes[key] = current;
+    return _writes[path] = current;
   }
 
-  Future<void> _write(String key, String json) async {
+  Future<void> _write(File file, String json) async {
     try {
-      final file = await _file(key);
       // Write-then-rename so a reader (or the widget background isolate)
       // never sees a half-written file.
       final tmp = File('${file.path}.tmp');
@@ -85,19 +108,21 @@ class CacheStore {
       );
       await tmp.rename(file.path);
     } on Object catch (e) {
-      debugPrint('CacheStore.write($key) failed: $e');
+      debugPrint('CacheStore.write(${file.path}) failed: $e');
     }
   }
 
   Future<void> delete(String key) async {
     try {
-      await _writes[key];
-      await (await _file(key)).delete();
+      final file = await _file(key);
+      await _writes[file.path];
+      await file.delete();
     } on Object {
       // A missing or locked file is as good as deleted for a cache.
     }
   }
 
+  /// Empties the active account's cache.
   Future<void> clear() async {
     try {
       final dir = await _directory();
@@ -105,7 +130,20 @@ class CacheStore {
     } on Object catch (e) {
       debugPrint('CacheStore.clear failed: $e');
     }
-    _dir = null;
+    _dirs.clear();
+  }
+
+  /// Removes the cache of the account with [namespace], active or not.
+  Future<void> deleteNamespace(String namespace) async {
+    final name = directoryName(namespace);
+    try {
+      final base = await getApplicationCacheDirectory();
+      final dir = Directory('${base.path}/$name');
+      if (dir.existsSync()) await dir.delete(recursive: true);
+    } on Object catch (e) {
+      debugPrint('CacheStore.deleteNamespace failed: $e');
+    }
+    _dirs.removeWhere((key, _) => key == name);
   }
 
   /// All stored keys, optionally filtered by [prefix].
@@ -124,17 +162,22 @@ class CacheStore {
     }
   }
 
-  /// Removes entries not written for [maxAge], judged by file mtime so nothing
-  /// has to be read or decoded.
+  /// Removes entries not written for [maxAge] from every account's cache,
+  /// judged by file mtime so nothing has to be read or decoded.
   Future<void> deleteOlderThan(Duration maxAge) async {
     try {
-      final dir = await _directory();
+      final base = await getApplicationCacheDirectory();
       final cutoff = DateTime.now().subtract(maxAge);
-      await for (final entity in dir.list()) {
-        if (entity is! File) continue;
-        // ignore: avoid_slow_async_io
-        final modified = (await entity.stat()).modified;
-        if (modified.isBefore(cutoff)) await entity.delete();
+      await for (final dir in base.list()) {
+        if (dir is! Directory) continue;
+        final name = dir.uri.pathSegments.lastWhere((s) => s.isNotEmpty);
+        if (!name.startsWith(_directoryPrefix)) continue;
+        await for (final entity in dir.list()) {
+          if (entity is! File) continue;
+          // ignore: avoid_slow_async_io
+          final modified = (await entity.stat()).modified;
+          if (modified.isBefore(cutoff)) await entity.delete();
+        }
       }
     } on Object catch (e) {
       debugPrint('CacheStore.deleteOlderThan failed: $e');