duoqi-api/src/services/progress/streak-service.ts

import { db } from '../../db/client.js';
import { users } from '../../db/schema.js';
import { eq, sql } from 'drizzle-orm';

export interface StreakInfo {
  days: number;
  lastDate: string | null;
  frozen: boolean;
}

/** Minimum correct answers per day to count toward streak */
const STREAK_THRESHOLD = 3;

/**
 * Normalize a date value (Date or string from mysql2) to 'YYYY-MM-DD' string.
 */
function toDateString(value: Date | string | null): string | null {
  if (!value) return null;
  if (typeof value === 'string') return value.slice(0, 10);
  return value.toISOString().slice(0, 10);
}

/**
 * Get the user's current streak info.
 * All date comparisons use UTC date strings (YYYY-MM-DD).
 */
export async function calculateStreak(userId: string): Promise<StreakInfo> {
  const [user] = await db
    .select({
      streakDays: users.streakDays,
      streakLastDate: users.streakLastDate,
    })
    .from(users)
    .where(eq(users.id, userId))
    .limit(1);

  if (!user || !user.streakLastDate) {
    return { days: 0, lastDate: null, frozen: false };
  }

  const today = todayUtc();
  const yesterday = yesterdayUtc();
  const lastDate = toDateString(user.streakLastDate);

  if (lastDate === today) {
    return { days: user.streakDays ?? 0, lastDate, frozen: false };
  }

  if (lastDate === yesterday) {
    return { days: user.streakDays ?? 0, lastDate, frozen: false };
  }

  // Streak is broken
  return { days: 0, lastDate, frozen: false };
}

/**
 * Update the user's streak after answering questions.
 */
export async function updateStreak(userId: string, correctAnswersToday: number): Promise<StreakInfo> {
  const today = todayUtc();

  const [user] = await db
    .select({
      streakDays: users.streakDays,
      streakLastDate: users.streakLastDate,
    })
    .from(users)
    .where(eq(users.id, userId))
    .limit(1);

  if (!user) {
    return { days: 0, lastDate: null, frozen: false };
  }

  const lastDate = toDateString(user.streakLastDate);

  // Already updated streak today
  if (lastDate === today) {
    return { days: user.streakDays ?? 0, lastDate: today, frozen: false };
  }

  // Check if threshold is met
  if (correctAnswersToday < STREAK_THRESHOLD) {
    return {
      days: user.streakDays ?? 0,
      lastDate,
      frozen: false,
    };
  }

  const yesterday = yesterdayUtc();
  const isConsecutive = lastDate === yesterday;
  const newDays = isConsecutive ? (user.streakDays ?? 0) + 1 : 1;

  await db
    .update(users)
    .set({ streakDays: newDays, streakLastDate: sql`CAST(${today} AS DATE)` })
    .where(eq(users.id, userId));

  return { days: newDays, lastDate: today, frozen: false };
}

/**
 * Freeze the streak (set last date to today without incrementing).
 */
export async function freezeStreak(userId: string): Promise<StreakInfo> {
  const today = todayUtc();

  await db
    .update(users)
    .set({ streakLastDate: sql`CAST(${today} AS DATE)` })
    .where(eq(users.id, userId));

  const [user] = await db
    .select({ streakDays: users.streakDays })
    .from(users)
    .where(eq(users.id, userId))
    .limit(1);

  return { days: user?.streakDays ?? 0, lastDate: today, frozen: true };
}

function todayUtc(): string {
  return new Date().toISOString().slice(0, 10);
}

function yesterdayUtc(): string {
  const d = new Date();
  d.setDate(d.getDate() - 1);
  return d.toISOString().slice(0, 10);
}

export { STREAK_THRESHOLD };