import { eq } from 'drizzle-orm';
import type { NodePgDatabase } from 'drizzle-orm/node-postgres';
import type * as schema from '../../db/schema/index.js';
import { users, userStats } from '../../db/schema/index.js';
import { notFound, conflict, ERROR_CODES } from '../../utils/errors.js';
import type { User } from '../../db/schema/users.js';
import type { SelfLevel } from '../../db/schema/index.js';

type Db = NodePgDatabase<typeof schema>;

export type UserStatItem = {
  stack: string;
  level: string;
  totalQuestions: number;
  correctAnswers: number;
  testsTaken: number;
  lastTestAt: string | null;
};

export type ProfileStats = {
  byStack: UserStatItem[];
  totalTestsTaken: number;
  totalQuestions: number;
  correctAnswers: number;
  accuracy: number | null;
};

export type ProfileUpdateInput = {
  nickname?: string;
  avatarUrl?: string | null;
  country?: string | null;
  city?: string | null;
  selfLevel?: SelfLevel | null;
  isPublic?: boolean;
};

export type PublicProfile = {
  id: string;
  nickname: string;
  avatarUrl: string | null;
  country: string | null;
  city: string | null;
  selfLevel: string | null;
  isPublic: boolean;
  stats: ProfileStats;
};

export type PrivateProfile = PublicProfile & {
  email: string;
  emailVerifiedAt: string | null;
  createdAt: string;
  updatedAt: string;
};

async function getStatsForUser(db: Db, userId: string): Promise<ProfileStats> {
  const rows = await db
    .select()
    .from(userStats)
    .where(eq(userStats.userId, userId));

  const byStack: UserStatItem[] = rows.map((r) => ({
    stack: r.stack,
    level: r.level,
    totalQuestions: r.totalQuestions,
    correctAnswers: r.correctAnswers,
    testsTaken: r.testsTaken,
    lastTestAt: r.lastTestAt?.toISOString() ?? null,
  }));

  const totalTestsTaken = rows.reduce((sum, r) => sum + r.testsTaken, 0);
  const totalQuestions = rows.reduce((sum, r) => sum + r.totalQuestions, 0);
  const correctAnswers = rows.reduce((sum, r) => sum + r.correctAnswers, 0);
  const accuracy = totalQuestions > 0 ? correctAnswers / totalQuestions : null;

  return { byStack, totalTestsTaken, totalQuestions, correctAnswers, accuracy };
}

function toPublicProfile(user: User, stats: ProfileStats): PublicProfile {
  return {
    id: user.id,
    nickname: user.nickname,
    avatarUrl: user.avatarUrl,
    country: user.country,
    city: user.city,
    selfLevel: user.selfLevel,
    isPublic: user.isPublic,
    stats,
  };
}

function toPrivateProfile(user: User, stats: ProfileStats): PrivateProfile {
  return {
    ...toPublicProfile(user, stats),
    email: user.email,
    emailVerifiedAt: user.emailVerifiedAt?.toISOString() ?? null,
    createdAt: user.createdAt.toISOString(),
    updatedAt: user.updatedAt.toISOString(),
  };
}

export class UserService {
  constructor(private readonly db: Db) {}

  async getById(userId: string): Promise<User | null> {
    const [user] = await this.db.select().from(users).where(eq(users.id, userId)).limit(1);
    return user ?? null;
  }

  async getByNickname(nickname: string): Promise<User | null> {
    const [user] = await this.db
      .select()
      .from(users)
      .where(eq(users.nickname, nickname.trim()))
      .limit(1);
    return user ?? null;
  }

  async getPrivateProfile(userId: string): Promise<PrivateProfile> {
    const [user, stats] = await Promise.all([this.getById(userId), getStatsForUser(this.db, userId)]);
    if (!user) {
      throw notFound('User not found');
    }
    return toPrivateProfile(user, stats);
  }

  async getPublicProfile(username: string): Promise<PublicProfile> {
    const user = await this.getByNickname(username);
    if (!user) {
      throw notFound('User not found');
    }
    if (!user.isPublic) {
      throw notFound('User not found');
    }
    const stats = await getStatsForUser(this.db, user.id);
    return toPublicProfile(user, stats);
  }

  async updateProfile(userId: string, input: ProfileUpdateInput): Promise<PrivateProfile> {
    const updateData: Partial<typeof users.$inferInsert> = {
      updatedAt: new Date(),
    };

    if (input.nickname !== undefined) {
      const trimmed = input.nickname.trim();
      const [existing] = await this.db
        .select({ id: users.id })
        .from(users)
        .where(eq(users.nickname, trimmed))
        .limit(1);

      if (existing && existing.id !== userId) {
        throw conflict(ERROR_CODES.NICKNAME_TAKEN, 'Nickname already taken');
      }
      updateData.nickname = trimmed;
    }
    if (input.avatarUrl !== undefined) updateData.avatarUrl = input.avatarUrl;
    if (input.country !== undefined) updateData.country = input.country;
    if (input.city !== undefined) updateData.city = input.city;
    if (input.selfLevel !== undefined) updateData.selfLevel = input.selfLevel;
    if (input.isPublic !== undefined) updateData.isPublic = input.isPublic;

    const [updated] = await this.db
      .update(users)
      .set(updateData)
      .where(eq(users.id, userId))
      .returning();

    if (!updated) {
      throw notFound('User not found');
    }

    const stats = await getStatsForUser(this.db, userId);
    return toPrivateProfile(updated, stats);
  }
}