import 'dart:convert';
import 'dart:io';

import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';
import 'package:trainhub_flutter/core/constants/ai_constants.dart';

enum AiServerStatus { offline, starting, ready, error }

/// Manages the two llama.cpp server processes that provide AI features.
///
/// Both processes are kept alive for the lifetime of the app and must be
/// killed on shutdown to prevent zombie processes from consuming RAM.
///
/// - Qwen3 4B    → port 8080  (chat / completions)
/// - Nomic Embed → port 8081  (embeddings)
///
/// Startup strategy: first attempt offloads all layers to the GPU (Vulkan).
/// If the chat server does not become healthy in time — first-run pipeline
/// compilation can be very slow, and some GPUs hang outright — everything is
/// restarted in CPU-only mode, which loads via mmap and is reliably fast.
class AiProcessManager extends ChangeNotifier {
  Process? _qwenProcess;
  Process? _nomicProcess;
  AiServerStatus _status = AiServerStatus.offline;
  String? _lastError;
  String? _statusDetail;

  // Last stderr lines per server — llama.cpp prints its actual failure
  // reason (bad model file, out of memory, …) there, so keep a short tail
  // to show the user instead of a generic "crashed" message.
  final List<String> _qwenStderrTail = [];
  final List<String> _nomicStderrTail = [];
  static const int _stderrTailLines = 8;

  // -------------------------------------------------------------------------
  // Public API
  // -------------------------------------------------------------------------

  AiServerStatus get status => _status;
  bool get isRunning => _status == AiServerStatus.ready;
  String? get errorMessage => _lastError;

  /// Live progress line while [status] is [AiServerStatus.starting],
  /// e.g. "Loading AI model on GPU… 45s".
  String? get statusDetail => _statusDetail;

  /// Starts both inference servers.  No-ops if already running or starting.
  Future<void> startServers() async {
    if (_status == AiServerStatus.starting || _status == AiServerStatus.ready) {
      return;
    }

    _updateStatus(AiServerStatus.starting);
    _lastError = null;

    final dir = await getApplicationDocumentsDirectory();
    final base = dir.path;
    final serverBin = p.join(base, AiConstants.serverBinaryName);

    if (!File(serverBin).existsSync()) {
      _lastError = 'llama-server executable not found.';
      _updateStatus(AiServerStatus.error);
      return;
    }

    try {
      // Attempt 1: full GPU offload.
      final gpuReady = await _startAttempt(
        serverBin,
        base,
        gpuLayers: AiConstants.gpuLayerOffload,
        timeout: AiConstants.serverStartupTimeout,
        detailLabel: 'GPU',
      );
      if (gpuReady) {
        _updateStatus(AiServerStatus.ready);
        return;
      }

      // Attempt 2: CPU only. Covers GPUs where Vulkan hangs, crashes
      // (e.g. out of VRAM) or pipeline compilation never finishes.
      await _killProcesses();
      _lastError = null;
      _qwenStderrTail.clear();
      _nomicStderrTail.clear();
      final cpuReady = await _startAttempt(
        serverBin,
        base,
        gpuLayers: 0,
        timeout: AiConstants.serverStartupTimeoutCpu,
        detailLabel: 'CPU',
      );
      if (cpuReady) {
        _updateStatus(AiServerStatus.ready);
        return;
      }

      throw Exception(
        _lastError ??
            'The AI server did not become ready (tried GPU, then CPU).'
                '${_diagnostics()}',
      );
    } catch (e) {
      // Clean up any partially-started processes before returning error.
      await _killProcesses();
      _lastError = e.toString();
      _updateStatus(AiServerStatus.error);
    } finally {
      _statusDetail = null;
    }
  }

  /// Kills both processes and resets the running flag.
  /// Safe to call even if servers were never started.
  Future<void> stopServers() async {
    await _killProcesses();

    if (Platform.isWindows) {
      try {
        await Process.run('taskkill', [
          '/F',
          '/IM',
          AiConstants.serverBinaryName,
        ]);
      } catch (_) {}
    } else if (Platform.isMacOS || Platform.isLinux) {
      try {
        await Process.run('pkill', ['-f', 'llama-server']);
      } catch (_) {}
    }

    _updateStatus(AiServerStatus.offline);
  }

  // -------------------------------------------------------------------------
  // Internals
  // -------------------------------------------------------------------------

  /// Spawns both servers with the given GPU offload and waits for health.
  /// Returns false on timeout; rethrows nothing — a crashed process is
  /// reported through [_lastError] by the exit watcher and detected here.
  Future<bool> _startAttempt(
    String serverBin,
    String base, {
    required int gpuLayers,
    required Duration timeout,
    required String detailLabel,
  }) async {
    _qwenProcess = await _spawn(
      serverBin,
      [
        '-m', p.join(base, AiConstants.qwenModelFile),
        '--port', '${AiConstants.chatServerPort}',
        '--ctx-size', '${AiConstants.qwenContextSize}',
        '-ngl', '$gpuLayers',
        // Use the chat template embedded in the GGUF (required for
        // correct Qwen3 formatting).
        '--jinja',
      ],
      label: 'QWEN',
      stderrTail: _qwenStderrTail,
      crashMessage: 'Qwen Chat Server crashed',
    );

    _nomicProcess = await _spawn(
      serverBin,
      [
        '-m',
        p.join(base, AiConstants.nomicModelFile),
        '--port',
        '${AiConstants.embeddingServerPort}',
        '--ctx-size',
        '${AiConstants.nomicContextSize}',
        '--embedding',
      ],
      label: 'NOMIC',
      stderrTail: _nomicStderrTail,
      crashMessage: 'Nomic Embedding Server crashed',
    );

    // llama-server binds its port almost immediately but returns 503 until
    // the model is fully loaded, so poll /health rather than the TCP port.
    final started = DateTime.now();
    final deadline = started.add(timeout);
    var qwenReady = false;
    var nomicReady = false;

    while (DateTime.now().isBefore(deadline) && (!qwenReady || !nomicReady)) {
      // A crashed process will never become healthy — give up on this
      // attempt right away (the caller may retry on CPU).
      if (_lastError != null) return false;

      await Future.delayed(AiConstants.healthPollInterval);
      if (!qwenReady) {
        qwenReady = await _isHealthy(AiConstants.chatHealthUrl);
      }
      if (!nomicReady) {
        nomicReady = await _isHealthy(AiConstants.embeddingHealthUrl);
      }

      final elapsed = DateTime.now().difference(started).inSeconds;
      _statusDetail =
          'Loading AI model on $detailLabel… ${elapsed}s '
          '(first run can take a few minutes)';
      notifyListeners();
    }

    return qwenReady && nomicReady;
  }

  Future<void> _killProcesses() async {
    // Detach before killing so the exit watchers recognise an intentional
    // shutdown and don't flag it as a crash.
    final qwen = _qwenProcess;
    final nomic = _nomicProcess;
    _qwenProcess = null;
    _nomicProcess = null;
    qwen?.kill();
    nomic?.kill();
  }

  Future<Process> _spawn(
    String binary,
    List<String> args, {
    required String label,
    required List<String> stderrTail,
    required String crashMessage,
  }) async {
    final process = await Process.start(binary, args, runInShell: false);

    process.stdout.transform(utf8.decoder).listen((text) {
      if (kDebugMode) debugPrint('[$label STDOUT] $text');
    });
    process.stderr.transform(utf8.decoder).listen((text) {
      for (final line in const LineSplitter().convert(text)) {
        if (line.trim().isEmpty) continue;
        stderrTail.add(line);
        if (stderrTail.length > _stderrTailLines) stderrTail.removeAt(0);
      }
      if (kDebugMode) debugPrint('[$label STDERR] $text');
    });

    // Monitor for unexpected crash. Intentional kills (retry, shutdown)
    // null out the process reference first, so they are ignored here.
    process.exitCode.then((code) {
      final isCurrent =
          identical(process, _qwenProcess) || identical(process, _nomicProcess);
      if (!isCurrent) return;
      if (_status == AiServerStatus.ready ||
          _status == AiServerStatus.starting) {
        _lastError = '$crashMessage (exit code $code).${_diagnostics()}';
        if (_status == AiServerStatus.ready) {
          _updateStatus(AiServerStatus.error);
        }
      }
    });

    return process;
  }

  Future<bool> _isHealthy(String url) async {
    try {
      final response = await http
          .get(Uri.parse(url))
          .timeout(const Duration(seconds: 2));
      return response.statusCode == 200;
    } catch (_) {
      return false;
    }
  }

  String _diagnostics() {
    final buffer = StringBuffer();
    if (_qwenStderrTail.isNotEmpty) {
      buffer.write('\n\nChat server log:\n${_qwenStderrTail.join('\n')}');
    }
    if (_nomicStderrTail.isNotEmpty) {
      buffer.write('\n\nEmbedding server log:\n${_nomicStderrTail.join('\n')}');
    }
    return buffer.toString();
  }

  void _updateStatus(AiServerStatus newStatus) {
    if (_status != newStatus) {
      _status = newStatus;
      notifyListeners();
    }
  }
}