import { and, desc, eq, inArray, sql } from 'drizzle-orm';
import type { Db } from '../db/client.js';
import { attempts, cardProgress, cards, lessons, sessions } from '../db/schema.js';
import { ApiError } from '../lib/errors.js';
import { getDescendantLessonIds } from './lessons.js';

const MIN_ATTEMPTS_FOR_SCORE = 3;

export interface CardStats {
  cardId: number;
  attempts: number;
  correct: number;
  incorrect: number;
  box: { forward: number; backward: number | null };
  lastShownAt: number | null;
  nextDueAt: number;
  history: { shownAt: number; result: 'correct' | 'incorrect'; direction: 'forward' | 'backward' }[];
}

export async function getCardStats(db: Db, cardId: number): Promise<CardStats> {
  const card = db.select().from(cards).where(eq(cards.id, cardId)).get();
  if (!card) throw ApiError.notFound('Card');
  const prog = db.select().from(cardProgress).where(eq(cardProgress.cardId, cardId)).all();
  const history = db.select({
    shownAt: attempts.shownAt, result: attempts.result, direction: attempts.direction,
  }).from(attempts).where(eq(attempts.cardId, cardId)).orderBy(desc(attempts.shownAt)).all();

  const forward = prog.find((p) => p.direction === 'forward');
  const backward = prog.find((p) => p.direction === 'backward');
  const correct = history.filter((h) => h.result === 'correct').length;
  return {
    cardId,
    attempts: history.length,
    correct,
    incorrect: history.length - correct,
    box: { forward: forward?.box ?? 1, backward: backward?.box ?? null },
    lastShownAt: forward?.lastShownAt ?? null,
    nextDueAt: forward?.nextDueAt ?? 0,
    history,
  };
}

export interface LessonStats {
  lessonId: number;
  totalCards: number;
  mastered: number;
  score: number;
  sessions: number;
  totalDurationSeconds: number;
  attempts: number;
  correct: number;
  incorrect: number;
}

export async function getLessonStats(db: Db, lessonId: number): Promise<LessonStats> {
  const lesson = db.select().from(lessons).where(eq(lessons.id, lessonId)).get();
  if (!lesson) throw ApiError.notFound('Lesson');
  const ids = await getDescendantLessonIds(db, lessonId);
  const cardRows = db.select({ id: cards.id }).from(cards).where(inArray(cards.lessonId, ids)).all();
  const cardIds = cardRows.map((c) => c.id);

  const totalCards = cardIds.length;
  let mastered = 0;
  let attemptsTotal = 0;
  let correctTotal = 0;
  let score = 0;
  let countedForScore = 0;

  if (cardIds.length > 0) {
    const prog = db.select().from(cardProgress).where(inArray(cardProgress.cardId, cardIds)).all();
    const att = db.select().from(attempts).where(inArray(attempts.cardId, cardIds)).all();
    attemptsTotal = att.length;
    correctTotal = att.filter((a) => a.result === 'correct').length;
    const byCard = new Map<number, typeof prog[number][]>();
    for (const p of prog) {
      if (!byCard.has(p.cardId)) byCard.set(p.cardId, []);
      byCard.get(p.cardId)!.push(p);
    }
    for (const id of cardIds) {
      const ps = byCard.get(id) ?? [];
      if (ps.some((p) => p.box >= 4)) mastered += 1;
      const total = ps.reduce((s, p) => s + p.correctCount + p.incorrectCount, 0);
      const correct = ps.reduce((s, p) => s + p.correctCount, 0);
      if (total >= MIN_ATTEMPTS_FOR_SCORE) {
        score += correct / total;
        countedForScore += 1;
      }
    }
    score = countedForScore === 0 ? 0 : score / countedForScore;
  }

  const sessRows = db.select({
    id: sessions.id, duration: sessions.durationSeconds,
  }).from(sessions).where(and(inArray(sessions.lessonId, ids), eq(sessions.status, 'completed'))).all();
  const totalDurationSeconds = sessRows.reduce((s, r) => s + (r.duration ?? 0), 0);

  return {
    lessonId, totalCards, mastered, score,
    sessions: sessRows.length, totalDurationSeconds,
    attempts: attemptsTotal, correct: correctTotal, incorrect: attemptsTotal - correctTotal,
  };
}

export interface Overview {
  totalSessions: number;
  totalDurationSeconds: number;
  totalAttempts: number;
  streakDays: number;
  recentSessions: { id: number; lessonId: number; startedAt: number; durationSeconds: number | null; cardsShown: number; cardsCorrect: number }[];
}

function dayKeyUTC(unixSec: number): string {
  const d = new Date(unixSec * 1000);
  return `${d.getUTCFullYear()}-${d.getUTCMonth()}-${d.getUTCDate()}`;
}

export async function getOverview(db: Db): Promise<Overview> {
  const sessRows = db.select().from(sessions).where(eq(sessions.status, 'completed')).all();
  const totalDurationSeconds = sessRows.reduce((s, r) => s + (r.durationSeconds ?? 0), 0);
  const totalAttempts = db.select({ c: sql<number>`count(*)`.as('c') }).from(attempts).get()?.c ?? 0;

  const days = new Set(sessRows.map((s) => dayKeyUTC(s.startedAt)));
  let streak = 0;
  const cursor = new Date();
  for (;;) {
    const k = dayKeyUTC(Math.floor(cursor.getTime() / 1000));
    if (days.has(k)) {
      streak += 1;
      cursor.setUTCDate(cursor.getUTCDate() - 1);
    } else break;
  }

  const recent = db.select({
    id: sessions.id, lessonId: sessions.lessonId, startedAt: sessions.startedAt,
    durationSeconds: sessions.durationSeconds, cardsShown: sessions.cardsShown, cardsCorrect: sessions.cardsCorrect,
  }).from(sessions).where(eq(sessions.status, 'completed')).orderBy(desc(sessions.startedAt)).limit(10).all();

  return {
    totalSessions: sessRows.length,
    totalDurationSeconds,
    totalAttempts: Number(totalAttempts),
    streakDays: streak,
    recentSessions: recent.map((r) => ({ ...r, durationSeconds: r.durationSeconds ?? null })),
  };
}

export interface HeatmapPoint { day: string; sessions: number; attempts: number; }
export async function getHeatmap(db: Db, weeks: number): Promise<HeatmapPoint[]> {
  const since = Math.floor(Date.now() / 1000) - weeks * 7 * 24 * 60 * 60;
  const sessRows = db.select({ startedAt: sessions.startedAt }).from(sessions)
    .where(and(eq(sessions.status, 'completed'), sql`${sessions.startedAt} >= ${since}`)).all();
  const attRows = db.select({ shownAt: attempts.shownAt }).from(attempts)
    .where(sql`${attempts.shownAt} >= ${since}`).all();
  const map = new Map<string, { sessions: number; attempts: number }>();
  for (const s of sessRows) {
    const k = dayKeyUTC(s.startedAt);
    const m = map.get(k) ?? { sessions: 0, attempts: 0 };
    m.sessions += 1; map.set(k, m);
  }
  for (const a of attRows) {
    const k = dayKeyUTC(a.shownAt);
    const m = map.get(k) ?? { sessions: 0, attempts: 0 };
    m.attempts += 1; map.set(k, m);
  }
  return Array.from(map.entries()).map(([day, v]) => ({ day, ...v }));
}