import { v4 as uuidv4 } from 'uuid';
import {
  User,
  Medication,
  UserSettings,
  TakenDoses,
  CustomReminder,
  CouchDBDocument,
  UserRole,
} from '../types';
import { AccountStatus } from './auth/auth.constants';

// This is a mock CouchDB service that uses localStorage for persistence.
// It mimics the async nature of a real database API and includes robust error handling and conflict resolution.

const latency = () =>
  new Promise(res => setTimeout(res, Math.random() * 200 + 50));

export class CouchDBError extends Error {
  status: number;
  constructor(message: string, status: number) {
    super(message);
    this.name = 'CouchDBError';
    this.status = status;
  }
}

class CouchDBService {
  private async getDb<T>(dbName: string): Promise<T[]> {
    await latency();
    const db = localStorage.getItem(dbName);
    return db ? JSON.parse(db) : [];
  }

  private async saveDb<T>(dbName: string, data: T[]): Promise<void> {
    await latency();
    localStorage.setItem(dbName, JSON.stringify(data));
  }

  private async getDoc<T extends CouchDBDocument>(
    dbName: string,
    id: string
  ): Promise<T | null> {
    const allDocs = await this.getDb<T>(dbName);
    return allDocs.find(doc => doc._id === id) || null;
  }

  private async query<T>(
    dbName: string,
    predicate: (doc: T) => boolean
  ): Promise<T[]> {
    const allDocs = await this.getDb<T>(dbName);
    return allDocs.filter(predicate);
  }

  private async putDoc<T extends CouchDBDocument>(
    dbName: string,
    doc: Omit<T, '_rev'> & { _rev?: string }
  ): Promise<T> {
    const allDocs = await this.getDb<T>(dbName);
    const docIndex = allDocs.findIndex(d => d._id === doc._id);

    if (docIndex > -1) {
      // Update
      const existingDoc = allDocs[docIndex];
      if (existingDoc._rev !== doc._rev) {
        throw new CouchDBError('Document update conflict', 409);
      }
      const newRev = parseInt(existingDoc._rev.split('-')[0], 10) + 1;
      const updatedDoc = {
        ...doc,
        _rev: `${newRev}-${Math.random().toString(36).substr(2, 9)}`,
      } as T;
      allDocs[docIndex] = updatedDoc;
      await this.saveDb(dbName, allDocs);
      return updatedDoc;
    } else {
      // Create
      const newDoc = {
        ...doc,
        _rev: `1-${Math.random().toString(36).substr(2, 9)}`,
      } as T;
      allDocs.push(newDoc);
      await this.saveDb(dbName, allDocs);
      return newDoc;
    }
  }

  private async deleteDoc<T extends CouchDBDocument>(
    dbName: string,
    doc: T
  ): Promise<void> {
    let docs = await this.getDb<T>(dbName);
    const docIndex = docs.findIndex(d => d._id === doc._id);
    if (docIndex > -1) {
      if (docs[docIndex]._rev !== doc._rev) {
        throw new CouchDBError('Document update conflict', 409);
      }
      docs = docs.filter(m => m._id !== doc._id);
      await this.saveDb(dbName, docs);
    } else {
      throw new CouchDBError('Document not found', 404);
    }
  }

  // Generic update function with conflict resolution
  private async updateDocWithConflictResolution<T extends CouchDBDocument>(
    dbName: string,
    doc: T,
    mergeFn?: (latest: T, incoming: T) => T
  ): Promise<T> {
    try {
      return await this.putDoc<T>(dbName, doc);
    } catch (error) {
      if (error instanceof CouchDBError && error.status === 409) {
        console.warn(
          `Conflict detected for doc ${doc._id}. Attempting to resolve.`
        );
        const latestDoc = await this.getDoc<T>(dbName, doc._id);
        if (latestDoc) {
          // Default merge: incoming changes overwrite latest
          const defaultMerge = { ...latestDoc, ...doc, _rev: latestDoc._rev };
          const mergedDoc = mergeFn ? mergeFn(latestDoc, doc) : defaultMerge;
          // Retry the update with the latest revision and merged data
          return this.putDoc<T>(dbName, mergedDoc);
        }
      }
      // Re-throw if it's not a resolvable conflict or fetching the latest doc fails
      throw error;
    }
  }

  // --- User Management ---
  async findUserByUsername(username: string): Promise<User | null> {
    const users = await this.query<User>(
      'users',
      u => u.username.toLowerCase() === username.toLowerCase()
    );
    return users[0] || null;
  }

  async findUserByEmail(email: string): Promise<User | null> {
    const users = await this.query<User>(
      'users',
      u => u.email?.toLowerCase() === email.toLowerCase()
    );
    return users[0] || null;
  }

  async createUser(username: string): Promise<User> {
    if (await this.findUserByUsername(username)) {
      throw new CouchDBError('User already exists', 409);
    }
    const newUser: Omit<User, '_rev'> = { _id: uuidv4(), username };
    return this.putDoc<User>('users', newUser);
  }

  async createUserWithPassword(
    email: string,
    password: string,
    username?: string
  ): Promise<User> {
    // Check if user already exists by email
    const existingUser = await this.findUserByEmail(email);
    if (existingUser) {
      throw new CouchDBError('User already exists', 409);
    }

    const newUser: Omit<User, '_rev'> = {
      _id: uuidv4(),
      username: username || email.split('@')[0], // Default username from email
      email,
      password, // In production, this should be hashed with bcrypt
      emailVerified: false, // Require email verification for password accounts
      status: AccountStatus.PENDING,
      role: UserRole.USER, // Default role is USER
      createdAt: new Date(),
      lastLoginAt: new Date(),
    };
    return this.putDoc<User>('users', newUser);
  }

  async createUserFromOAuth(userData: {
    email: string;
    username: string;
    avatar?: string;
  }): Promise<User> {
    // Check if user already exists by email
    const existingUser = await this.findUserByEmail(userData.email);
    if (existingUser) {
      throw new CouchDBError('User already exists', 409);
    }

    const newUser: Omit<User, '_rev'> = {
      _id: uuidv4(),
      username: userData.username,
      email: userData.email,
      avatar: userData.avatar,
      emailVerified: true, // OAuth users have verified emails
      status: AccountStatus.ACTIVE,
      role: UserRole.USER, // Default role is USER
      createdAt: new Date(),
      lastLoginAt: new Date(),
    };
    return this.putDoc<User>('users', newUser);
  }

  async updateUser(user: User): Promise<User> {
    return this.updateDocWithConflictResolution<User>('users', user);
  }

  // --- Admin User Management ---
  async getAllUsers(): Promise<User[]> {
    return this.getDb<User>('users');
  }

  async getUserById(userId: string): Promise<User | null> {
    return this.getDoc<User>('users', userId);
  }

  async suspendUser(userId: string): Promise<User> {
    const user = await this.getUserById(userId);
    if (!user) {
      throw new CouchDBError('User not found', 404);
    }

    const updatedUser = { ...user, status: AccountStatus.SUSPENDED };
    return this.updateUser(updatedUser);
  }

  async activateUser(userId: string): Promise<User> {
    const user = await this.getUserById(userId);
    if (!user) {
      throw new CouchDBError('User not found', 404);
    }

    const updatedUser = { ...user, status: AccountStatus.ACTIVE };
    return this.updateUser(updatedUser);
  }

  async deleteUser(userId: string): Promise<void> {
    const user = await this.getUserById(userId);
    if (!user) {
      throw new CouchDBError('User not found', 404);
    }

    // Delete user data
    await this.deleteDoc<User>('users', user);

    // Delete user's associated data
    const userMeds = this.getUserDbName('meds', userId);
    const userSettings = this.getUserDbName('settings', userId);
    const userTaken = this.getUserDbName('taken', userId);
    const userReminders = this.getUserDbName('reminders', userId);

    localStorage.removeItem(userMeds);
    localStorage.removeItem(userSettings);
    localStorage.removeItem(userTaken);
    localStorage.removeItem(userReminders);
  }

  async changeUserPassword(userId: string, newPassword: string): Promise<User> {
    const user = await this.getUserById(userId);
    if (!user) {
      throw new CouchDBError('User not found', 404);
    }

    // In production, hash the password with bcrypt
    const updatedUser = { ...user, password: newPassword };
    return this.updateUser(updatedUser);
  }

  // --- User Data Management ---
  private getUserDbName = (
    type: 'meds' | 'settings' | 'taken' | 'reminders',
    userId: string
  ) => `${type}_${userId}`;

  async getMedications(userId: string): Promise<Medication[]> {
    return this.getDb<Medication>(this.getUserDbName('meds', userId));
  }

  async addMedication(
    userId: string,
    med: Omit<Medication, '_id' | '_rev'>
  ): Promise<Medication> {
    const newMed = { ...med, _id: uuidv4() };
    return this.putDoc<Medication>(this.getUserDbName('meds', userId), newMed);
  }

  async updateMedication(userId: string, med: Medication): Promise<Medication> {
    return this.updateDocWithConflictResolution<Medication>(
      this.getUserDbName('meds', userId),
      med
    );
  }

  async deleteMedication(userId: string, med: Medication): Promise<void> {
    return this.deleteDoc<Medication>(this.getUserDbName('meds', userId), med);
  }

  async getCustomReminders(userId: string): Promise<CustomReminder[]> {
    return this.getDb<CustomReminder>(this.getUserDbName('reminders', userId));
  }

  async addCustomReminder(
    userId: string,
    reminder: Omit<CustomReminder, '_id' | '_rev'>
  ): Promise<CustomReminder> {
    const newReminder = { ...reminder, _id: uuidv4() };
    return this.putDoc<CustomReminder>(
      this.getUserDbName('reminders', userId),
      newReminder
    );
  }

  async updateCustomReminder(
    userId: string,
    reminder: CustomReminder
  ): Promise<CustomReminder> {
    return this.updateDocWithConflictResolution<CustomReminder>(
      this.getUserDbName('reminders', userId),
      reminder
    );
  }

  async deleteCustomReminder(
    userId: string,
    reminder: CustomReminder
  ): Promise<void> {
    return this.deleteDoc<CustomReminder>(
      this.getUserDbName('reminders', userId),
      reminder
    );
  }

  async getSettings(userId: string): Promise<UserSettings> {
    const dbName = this.getUserDbName('settings', userId);
    let settings = await this.getDoc<UserSettings>(dbName, userId);
    if (!settings) {
      settings = await this.putDoc<UserSettings>(dbName, {
        _id: userId,
        notificationsEnabled: true,
        hasCompletedOnboarding: false,
      });
    }
    return settings;
  }

  async updateSettings(
    userId: string,
    settings: UserSettings
  ): Promise<UserSettings> {
    return this.updateDocWithConflictResolution<UserSettings>(
      this.getUserDbName('settings', userId),
      settings
    );
  }

  async getTakenDoses(userId: string): Promise<TakenDoses> {
    const dbName = this.getUserDbName('taken', userId);
    let takenDoses = await this.getDoc<TakenDoses>(dbName, userId);
    if (!takenDoses) {
      takenDoses = await this.putDoc<TakenDoses>(dbName, {
        _id: userId,
        doses: {},
      });
    }
    return takenDoses;
  }

  async updateTakenDoses(
    userId: string,
    takenDoses: TakenDoses
  ): Promise<TakenDoses> {
    // Custom merge logic for taken doses to avoid overwriting recent updates
    const mergeFn = (latest: TakenDoses, incoming: TakenDoses): TakenDoses => {
      return {
        ...latest, // Use latest doc as the base
        ...incoming, // Apply incoming changes
        doses: { ...latest.doses, ...incoming.doses }, // Specifically merge the doses object
        _rev: latest._rev, // IMPORTANT: Use the latest revision for the update attempt
      };
    };
    return this.updateDocWithConflictResolution<TakenDoses>(
      this.getUserDbName('taken', userId),
      takenDoses,
      mergeFn
    );
  }

  async deleteAllUserData(userId: string): Promise<void> {
    await latency();
    localStorage.removeItem(this.getUserDbName('meds', userId));
    localStorage.removeItem(this.getUserDbName('settings', userId));
    localStorage.removeItem(this.getUserDbName('taken', userId));
    localStorage.removeItem(this.getUserDbName('reminders', userId));
  }
}

export { CouchDBService };
export const dbService = new CouchDBService();