import 'dart:io';

import 'package:collection/collection.dart';
import 'package:rimworld_modman/logger.dart';
import 'package:rimworld_modman/mod.dart';
import 'package:xml/xml.dart';

class LoadOrder {
  final List<Mod> order = [];
  final List<String> errors = [];
  List<String> get loadOrder => order.map((e) => e.id).toList();

  LoadOrder();

  bool get hasErrors => errors.isNotEmpty;
}

class ModList {
  String configPath = '';
  String modsPath = '';
  // O(1) lookup
  Map<String, Mod> activeMods = {};
  Map<String, Mod> mods = {};

  ModList({this.configPath = '', this.modsPath = ''});

  ModList copyWith({
    String? configPath,
    String? modsPath,
    Map<String, Mod>? mods,
    Map<String, bool>? activeMods,
  }) {
    final newModlist = ModList(
      configPath: configPath ?? this.configPath,
      modsPath: modsPath ?? this.modsPath,
    );
    newModlist.mods = Map.from(mods ?? this.mods);
    newModlist.activeMods = Map.from(activeMods ?? this.activeMods);
    return newModlist;
  }

  Stream<Mod> loadAvailable() async* {
    final logger = Logger.instance;
    final stopwatch = Stopwatch()..start();

    final directory = Directory(modsPath);

    if (!directory.existsSync()) {
      logger.error('Error: Mods root directory does not exist: $modsPath');
      return;
    }

    final List<FileSystemEntity> entities = directory.listSync();
    // TODO: Count only the latest version of each mod and not all versions
    final List<String> modDirectories =
        entities.whereType<Directory>().map((dir) => dir.path).toList();

    logger.info(
      'Found ${modDirectories.length} mod directories (${stopwatch.elapsedMilliseconds}ms)',
    );

    for (final modDir in modDirectories) {
      try {
        final modStart = stopwatch.elapsedMilliseconds;

        // Check if this directory contains a valid mod
        final aboutFile = File('$modDir/About/About.xml');
        if (!aboutFile.existsSync()) {
          logger.warning('No About.xml found in directory: $modDir');
          continue;
        }

        final mod = Mod.fromDirectory(modDir);
        logger.info('Loaded mod from directory: ${mod.name} (ID: ${mod.id})');

        if (mods.containsKey(mod.id)) {
          logger.warning(
            'Mod $mod.id already exists in mods list, overwriting',
          );
          final existingMod = mods[mod.id]!;
          mods[mod.id] = Mod(
            name: mod.name,
            id: mod.id,
            path: mod.path,
            versions: mod.versions,
            description: mod.description,
            dependencies: mod.dependencies,
            loadAfter: mod.loadAfter,
            loadBefore: mod.loadBefore,
            incompatibilities: mod.incompatibilities,
            size: mod.size,
            enabled: existingMod.enabled,
            isBaseGame: existingMod.isBaseGame,
            isExpansion: existingMod.isExpansion,
          );
          logger.info('Updated existing mod: ${mod.name} (ID: ${mod.id})');
        } else {
          mods[mod.id] = mod;
          logger.info('Added new mod: ${mod.name} (ID: ${mod.id})');
        }

        final modTime = stopwatch.elapsedMilliseconds - modStart;
        logger.info(
          'Loaded mod from directory: ${mod.name} (ID: ${mod.id}) in $modTime ms',
        );
        yield mod;
      } catch (e) {
        logger.error('Error loading mod from directory: $modDir');
        logger.error('Error: $e');
      }
    }
  }

  Stream<Mod> loadActive() async* {
    final logger = Logger.instance;
    final file = File(configPath);
    logger.info('Loading configuration from: $configPath');

    try {
      final xmlString = file.readAsStringSync();
      logger.info('XML content read successfully.');

      final xmlDocument = XmlDocument.parse(xmlString);
      logger.info('XML document parsed successfully.');

      final modConfigData = xmlDocument.findElements("ModsConfigData").first;
      logger.info('Found ModsConfigData element.');

      final modsElement = modConfigData.findElements("activeMods").first;
      logger.info('Found activeMods element.');

      final modElements = modsElement.findElements("li");
      logger.info('Found ${modElements.length} active mods.');

      // Get the list of known expansions
      final knownExpansionsElement =
          modConfigData.findElements("knownExpansions").firstOrNull;
      final knownExpansionIds =
          knownExpansionsElement != null
              ? knownExpansionsElement
                  .findElements("li")
                  .map((e) => e.innerText.toLowerCase())
                  .toList()
              : <String>[];

      logger.info('Found ${knownExpansionIds.length} known expansions.');

      // Clear and recreate the mods list
      for (final modElement in modElements) {
        final modId = modElement.innerText.toLowerCase();

        // Check if this is a special Ludeon mod
        final isBaseGame = modId == 'ludeon.rimworld';
        final isExpansion =
            !isBaseGame &&
            modId.startsWith('ludeon.rimworld.') &&
            knownExpansionIds.contains(modId);

        final existingMod = mods[modId];
        final mod = Mod(
          name:
              existingMod?.name ??
              (isBaseGame
                  ? "RimWorld"
                  : isExpansion
                  ? "RimWorld ${_expansionNameFromId(modId)}"
                  : modId),
          id: existingMod?.id ?? modId,
          path: existingMod?.path ?? '',
          versions: existingMod?.versions ?? [],
          description:
              existingMod?.description ??
              (isBaseGame
                  ? "RimWorld base game"
                  : isExpansion
                  ? "RimWorld expansion"
                  : ""),
          dependencies: existingMod?.dependencies ?? [],
          loadAfter:
              existingMod?.loadAfter ??
              (isExpansion ? ['ludeon.rimworld'] : []),
          loadBefore: existingMod?.loadBefore ?? [],
          incompatibilities: existingMod?.incompatibilities ?? [],
          enabled: existingMod?.enabled ?? false,
          size: existingMod?.size ?? 0,
          isBaseGame: isBaseGame,
          isExpansion: isExpansion,
        );
        if (mods.containsKey(modId)) {
          logger.warning('Mod $modId already exists in mods list, overwriting');
        }
        mods[modId] = mod;
        setEnabled(modId, true);
        yield mod;
      }

      logger.info('Loaded ${modElements.length} mods from config file.');
    } catch (e) {
      logger.error('Error loading configuration file: $e');
      throw Exception('Failed to load config file: $e');
    }
  }

  void setEnabled(String modId, bool enabled) {
    if (mods.containsKey(modId)) {
      final mod = mods[modId]!;
      mod.enabled = enabled;
      if (enabled) {
        activeMods[modId] = mod;
      } else {
        activeMods.remove(modId);
      }
    }
  }

  void enableAll() {
    for (final mod in mods.values) {
      setEnabled(mod.id, true);
    }
  }

  void disableAll() {
    for (final mod in mods.values) {
      setEnabled(mod.id, false);
    }
  }

  void enableMods(List<String> modIds) {
    for (final modId in modIds) {
      setEnabled(modId, true);
    }
  }

  void disableMods(List<String> modIds) {
    for (final modId in modIds) {
      setEnabled(modId, false);
    }
  }

  //LoadOrder loadRequired([LoadOrder? loadOrder]) {
  //  loadOrder ??= LoadOrder();
  //  final toEnable = <String>[];
  //  for (final modid in activeMods.keys) {
  //    loadDependencies(modid, loadOrder, toEnable);
  //  }
  //  for (final modid in toEnable) {
  //    setEnabled(modid, true);
  //  }
  //  return generateLoadOrder(loadOrder);
  //}

  LoadOrder generateLoadOrder([LoadOrder? loadOrder]) {
    loadOrder ??= LoadOrder();
    final modMap = {for (final m in activeMods.values) m.id: m};
    final errors = _validateIncompatibilities(modMap);
    if (errors.isNotEmpty) {
      loadOrder.errors.addAll(errors);
    }

    // Hard dependency graph
    final inDegree = <String, int>{};
    final adjacency = <String, List<String>>{};

    // Soft constraint reverse mappings
    final reverseLoadBefore = <String, List<Mod>>{};
    final reverseLoadAfter = <String, List<Mod>>{};

    // Initialize data structures
    for (final mod in activeMods.values) {
      mod.loadBeforeNotPlaced = mod.loadBefore.length;
      mod.loadAfterPlaced = 0;

      reverseLoadBefore[mod.id] = [];
      reverseLoadAfter[mod.id] = [];
      inDegree[mod.id] = 0;
      adjacency[mod.id] = [];
    }

    // Build dependency graph and reverse soft constraints
    for (final mod in activeMods.values) {
      for (final depId in mod.dependencies) {
        adjacency[depId]!.add(mod.id);
        inDegree[mod.id] = (inDegree[mod.id] ?? 0) + 1;
      }

      for (final targetId in mod.loadBefore) {
        final target = modMap[targetId];
        if (target != null) {
          reverseLoadBefore[targetId]!.add(mod);
        }
      }

      for (final targetId in mod.loadAfter) {
        final target = modMap[targetId];
        if (target != null) {
          reverseLoadAfter[targetId]!.add(mod);
        }
      }
    }

    final heap = PriorityQueue<Mod>((a, b) {
      // 1. Base game first
      if (a.isBaseGame != b.isBaseGame) {
        return a.isBaseGame ? -1 : 1;
      }
      // 2. Expansions next
      if (a.isExpansion != b.isExpansion) {
        return a.isExpansion ? -1 : 1;
      }
      // 3. Soft constraints: Prioritize mods that need to be placed earlier
      final aUnmetBefore = a.loadBeforeNotPlaced;
      final bUnmetBefore = b.loadBeforeNotPlaced;
      if (aUnmetBefore != bUnmetBefore) {
        return bUnmetBefore.compareTo(aUnmetBefore); // Higher unmetBefore first
      }
      // If tied, deprioritize mods with more unmet `loadAfter`
      final aUnmetAfter = a.loadAfter.length - a.loadAfterPlaced;
      final bUnmetAfter = b.loadAfter.length - b.loadAfterPlaced;
      if (aUnmetAfter != bUnmetAfter) {
        return aUnmetAfter.compareTo(bUnmetAfter); // Lower unmetAfter first
      }
      // 4. Smaller size last
      return b.size.compareTo(a.size);
    });

    // Initialize heap with available mods
    for (final mod in activeMods.values) {
      if (inDegree[mod.id] == 0) {
        heap.add(mod);
      }
    }

    while (heap.isNotEmpty) {
      final current = heap.removeFirst();
      loadOrder.order.add(current);

      // Update dependents' in-degree
      for (final neighborId in adjacency[current.id]!) {
        inDegree[neighborId] = inDegree[neighborId]! - 1;
        if (inDegree[neighborId] == 0) {
          heap.add(modMap[neighborId]!);
        }
      }

      // Update soft constraints
      _updateReverseConstraints(
        current,
        reverseLoadBefore,
        loadOrder,
        heap,
        (mod) => mod.loadBeforeNotPlaced--,
      );
      _updateReverseConstraints(
        current,
        reverseLoadAfter,
        loadOrder,
        heap,
        (mod) => mod.loadAfterPlaced++,
      );
    }

    if (loadOrder.order.length != activeMods.length) {
      loadOrder.errors.add("Cyclic dependencies detected");
    }

    return loadOrder;
  }

  List<String> _validateIncompatibilities(Map<String, Mod> modMap) {
    final errors = <String>[];
    for (final mod in modMap.values) {
      for (final incompatibleId in mod.incompatibilities) {
        if (modMap.values.any((m) => m.id == incompatibleId)) {
          errors.add("Incompatible mods: ${mod.id} and $incompatibleId");
        }
      }
    }
    return errors;
  }

  void _updateReverseConstraints(
    Mod current,
    Map<String, List<Mod>> reverseMap,
    LoadOrder loadOrder,
    PriorityQueue<Mod> heap,
    void Function(Mod) update,
  ) {
    reverseMap[current.id]?.forEach((affectedMod) {
      if (!loadOrder.order.contains(affectedMod)) {
        update(affectedMod);
        // If mod is already in heap, re-add to update position
        if (heap.contains(affectedMod)) {
          heap.remove(affectedMod);
          heap.add(affectedMod);
        }
      }
    });
  }

  LoadOrder loadDependencies(
    String modId, [
    LoadOrder? loadOrder,
    List<String>? toEnable,
    Map<String, bool>? seen,
    List<String>? cyclePath,
  ]) {
    final mod = mods[modId]!;
    loadOrder ??= LoadOrder();
    toEnable ??= <String>[];
    seen ??= <String, bool>{};
    cyclePath ??= <String>[];

    // Add current mod to cycle path
    cyclePath.add(modId);

    for (final dep in mod.dependencies) {
      if (!mods.containsKey(dep)) {
        loadOrder.errors.add(
          'Missing dependency: ${mod.name} requires mod with ID $dep',
        );
        continue;
      }
      final depMod = mods[dep]!;
      if (seen[dep] == true) {
        // Find the start of the cycle
        int cycleStart = cyclePath.indexOf(dep);
        if (cycleStart >= 0) {
          // Extract the cycle part
          List<String> cycleIds = [...cyclePath.sublist(cycleStart), modId];
          loadOrder.errors.add(
            'Cyclic dependency detected: ${cycleIds.join(' -> ')}',
          );
        } else {
          loadOrder.errors.add('Cyclic dependency detected: $modId -> $dep');
        }
        continue;
      }
      seen[dep] = true;
      toEnable.add(depMod.id);
      loadDependencies(
        depMod.id,
        loadOrder,
        toEnable,
        seen,
        List.from(cyclePath),
      );
    }

    return loadOrder;
  }

  LoadOrder loadRequired([LoadOrder? loadOrder]) {
    loadOrder ??= LoadOrder();
    final toEnable = <String>[];
    for (final modid in activeMods.keys) {
      loadDependencies(modid, loadOrder, toEnable);
    }
    for (final modid in toEnable) {
      setEnabled(modid, true);
    }
    return generateLoadOrder(loadOrder);
  }
}

String _expansionNameFromId(String id) {
  final parts = id.split('.');
  if (parts.length < 3) return id;

  final expansionPart = parts[2];
  return expansionPart.substring(0, 1).toUpperCase() +
      expansionPart.substring(1);
}