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

/** Combo bonus tiers: minimum combo count → bonus XP */
const COMBO_BONUSES: ReadonlyArray<{ minCombo: number; bonus: number }> = [
  { minCombo: 10, bonus: 20 },
  { minCombo: 5, bonus: 10 },
  { minCombo: 3, bonus: 5 },
];

const BASE_XP = 10;
const DEFAULT_DAILY_GOAL = 50;

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);
}

export interface DailyXpStatus {
  earned: number;
  goal: number;
  date: string;
}

/**
 * Calculate total XP for a correct answer, including combo bonus.
 * Combo bonus is cumulative: 3-combo = +5, 5-combo = +10, 10-combo = +20.
 */
export function calculateXp(baseXp: number, comboCount: number): number {
  let bonus = 0;
  for (const tier of COMBO_BONUSES) {
    if (comboCount >= tier.minCombo) {
      bonus = tier.bonus;
      break;
    }
  }
  return baseXp + bonus;
}

/**
 * Add XP to a user. Handles daily XP reset if the date has changed.
 * Uses atomic SQL update to prevent race conditions.
 */
export async function addXp(userId: string, amount: number): Promise<void> {
  const today = new Date().toISOString().slice(0, 10);

  // Atomically update total XP and handle daily reset
  await db
    .update(users)
    .set({
      xpTotal: sql`COALESCE(xp_total, 0) + ${amount}`,
      dailyXpEarned: sql`CASE
        WHEN COALESCE(daily_xp_date, '') = ${today}
        THEN COALESCE(daily_xp_earned, 0) + ${amount}
        ELSE ${amount}
      END`,
      dailyXpDate: sql`CAST(${today} AS DATE)`,
    })
    .where(eq(users.id, userId));
}

/**
 * Get the user's daily XP status.
 */
export async function getDailyXpStatus(userId: string): Promise<DailyXpStatus> {
  const today = new Date().toISOString().slice(0, 10);
  const [user] = await db
    .select({
      dailyXpEarned: users.dailyXpEarned,
      dailyXpDate: users.dailyXpDate,
      dailyXpGoal: users.dailyXpGoal,
    })
    .from(users)
    .where(eq(users.id, userId))
    .limit(1);

  if (!user) {
    return { earned: 0, goal: DEFAULT_DAILY_GOAL, date: today };
  }

  const isToday = toDateString(user.dailyXpDate) === today;
  return {
    earned: isToday ? (user.dailyXpEarned ?? 0) : 0,
    goal: user.dailyXpGoal ?? DEFAULT_DAILY_GOAL,
    date: today,
  };
}

export { BASE_XP };