import '../../ai/tools/tool_definition.dart';

/// Abstract LLM backend.
///
/// Concrete impls: `GemmaLlmService` (flutter_gemma) and `MockLlmService` (tests).
/// Contract:
/// - After [load], [isLoaded] is true.
/// - [generateStructured] throws [StateError] when not loaded.
/// - [generateStructured] returns a parsed JSON map matching the schema.
///   On schema/parse failure throws [FormatException].
/// - [unload] is idempotent.
/// - [startChat] opens a multi-turn chat session for tool calling (#260).
abstract class LlmService {
  bool get isLoaded;

  Future<void> load();

  Future<void> unload();

  /// Calls the model with a function-calling [schema] and returns the parsed
  /// JSON arguments map. Caller is responsible for applying `.timeout(...)`.
  Future<Map<String, dynamic>> generateStructured(
    String prompt,
    Map<String, dynamic> schema,
  );

  /// Opens a chat session that supports multi-turn user input + tool result
  /// submission with the supplied [tools]. See ADR-0005.
  Future<LlmChatSession> startChat({
    required List<ToolDefinition> tools,
  });
}

/// Streaming chat session for the tool-calling loop.
///
/// Lifecycle: created by [LlmService.startChat], lives for a single chat
/// screen, must be [close]d when the user dismisses the screen. Each
/// `send*` call returns a stream of [LlmChatEvent]s until the model yields
/// control (text done or a function call requested).
abstract class LlmChatSession {
  Stream<LlmChatEvent> sendUser(String text);

  Stream<LlmChatEvent> sendToolResult({
    required String toolName,
    required Map<String, dynamic> result,
  });

  Future<void> close();
}

/// Events emitted by [LlmChatSession]. See ADR-0005 §C.
sealed class LlmChatEvent {
  const LlmChatEvent();
}

final class LlmTextChunk extends LlmChatEvent {
  final String text;
  const LlmTextChunk(this.text);
}

final class LlmFunctionCall extends LlmChatEvent {
  final String name;
  final Map<String, dynamic> args;
  const LlmFunctionCall(this.name, this.args);
}

/// Programmable stub for tests. Use [enqueueResponse] / [enqueueError].
class MockLlmService implements LlmService {
  final List<_Response> _queue = [];
  bool _loaded = false;
  int callCount = 0;
  String? lastPrompt;
  Map<String, dynamic>? lastSchema;
  Duration responseDelay = Duration.zero;

  /// #311 test helpers. Simulate cold-load latency / failure so the warm-up
  /// controller can be exercised. Mirrors the Gemma path:
  /// - `loadDelay > 0`  → load completes after the delay
  /// - `loadThrows`     → load throws this error
  /// - `loadCount`      → observed by concurrent-load tests
  Duration loadDelay = Duration.zero;
  Object? loadThrows;
  int loadCount = 0;
  Future<void>? _loadingFuture;

  /// Queues consumed by [startChat] in order. Each entry is the event list
  /// returned for a single `send*` call.
  final List<List<LlmChatEvent>> chatScript = [];
  int chatStartCount = 0;
  MockLlmChatSession? lastChat;

  @override
  bool get isLoaded => _loaded;

  /// #311 AC7: same concurrent-call guard as [GemmaLlmService]. Repeated
  /// in-flight `load()` calls share a single Future, so test assertions on
  /// `loadCount` reflect the number of native-init attempts (1), not the
  /// number of callers.
  @override
  Future<void> load() {
    if (_loaded) return Future.value();
    final existing = _loadingFuture;
    if (existing != null) return existing;
    final future = _doLoad();
    _loadingFuture = future;
    return future.whenComplete(() {
      _loadingFuture = null;
    });
  }

  Future<void> _doLoad() async {
    loadCount += 1;
    if (loadDelay > Duration.zero) {
      await Future<void>.delayed(loadDelay);
    }
    final err = loadThrows;
    if (err != null) throw err;
    _loaded = true;
  }

  @override
  Future<void> unload() async {
    _loaded = false;
  }

  void enqueueResponse(Map<String, dynamic> response) {
    _queue.add(_Response.value(response));
  }

  void enqueueError(Object error) {
    _queue.add(_Response.error(error));
  }

  /// Enqueue one batch of events that will be emitted on the next
  /// `sendUser` or `sendToolResult` call. Items are streamed in order.
  void enqueueChatEvents(List<LlmChatEvent> events) {
    chatScript.add(events);
  }

  @override
  Future<Map<String, dynamic>> generateStructured(
    String prompt,
    Map<String, dynamic> schema,
  ) async {
    callCount += 1;
    lastPrompt = prompt;
    lastSchema = schema;
    if (!_loaded) {
      throw StateError('LlmService not loaded');
    }
    if (responseDelay > Duration.zero) {
      await Future<void>.delayed(responseDelay);
    }
    if (_queue.isEmpty) {
      throw StateError('MockLlmService: no queued response');
    }
    final r = _queue.removeAt(0);
    if (r.error != null) throw r.error!;
    return r.value!;
  }

  @override
  Future<LlmChatSession> startChat({
    required List<ToolDefinition> tools,
  }) async {
    if (!_loaded) {
      throw StateError('LlmService not loaded');
    }
    chatStartCount += 1;
    final session = MockLlmChatSession(chatScript);
    lastChat = session;
    return session;
  }
}

/// Mock chat session that replays pre-queued events from [MockLlmService].
class MockLlmChatSession implements LlmChatSession {
  final List<List<LlmChatEvent>> _script;
  int sendCount = 0;
  final List<String> userInputs = [];
  final List<(String, Map<String, dynamic>)> toolResults = [];
  bool closed = false;

  MockLlmChatSession(this._script);

  Stream<LlmChatEvent> _emitNext() async* {
    sendCount += 1;
    if (_script.isEmpty) {
      throw StateError('MockLlmChatSession: no queued events');
    }
    final batch = _script.removeAt(0);
    for (final ev in batch) {
      yield ev;
    }
  }

  @override
  Stream<LlmChatEvent> sendUser(String text) {
    userInputs.add(text);
    return _emitNext();
  }

  @override
  Stream<LlmChatEvent> sendToolResult({
    required String toolName,
    required Map<String, dynamic> result,
  }) {
    toolResults.add((toolName, result));
    return _emitNext();
  }

  @override
  Future<void> close() async {
    closed = true;
  }
}

class _Response {
  final Map<String, dynamic>? value;
  final Object? error;
  const _Response._(this.value, this.error);
  factory _Response.value(Map<String, dynamic> v) => _Response._(v, null);
  factory _Response.error(Object e) => _Response._(null, e);
}