// « Prochaine meilleure activité » : recommandation justifiée, fondée sur
// cartes dues, faiblesses, erreurs à revoir, plan actif et récence d'activité.

import { all, get } from "../db/index.ts";
import { masteryForCourse } from "./mastery.ts";

export type Recommendation = {
  kind: "flashcards" | "quiz" | "error-review" | "exam" | "concept" | "plan" | "chat";
  label: string;
  reason: string;
  href: string;
  courseCode: string;
  priority: number;
};

export function recommendations(userId: number, courseCode: string, max = 4): Recommendation[] {
  const recs: Recommendation[] = [];

  const due = get<{ n: number }>(
    `SELECT COUNT(*) as n FROM card_states cs JOIN flashcards f ON f.id = cs.card_id
     WHERE cs.user_id = ? AND f.course_code = ? AND cs.suspended = 0 AND cs.due_at <= datetime('now')`,
    userId, courseCode
  );
  if ((due?.n ?? 0) > 0) {
    recs.push({
      kind: "flashcards",
      label: `Réviser ${due!.n} carte${due!.n > 1 ? "s" : ""} due${due!.n > 1 ? "s" : ""}`,
      reason: "La répétition espacée ne fonctionne que si les cartes sont revues à temps — ces cartes arrivent à échéance aujourd'hui.",
      href: `/apprendre/${courseCode.toLowerCase()}/flashcards`,
      courseCode,
      priority: 90 + Math.min(9, due!.n),
    });
  }

  const errors = get<{ n: number }>(
    "SELECT COUNT(*) as n FROM error_notebook WHERE user_id = ? AND course_code = ? AND status = 'a-revoir'",
    userId, courseCode
  );
  if ((errors?.n ?? 0) >= 3) {
    recs.push({
      kind: "error-review",
      label: `Revoir ${errors!.n} erreurs du cahier`,
      reason: "Retravailler ses propres erreurs est l'une des formes de pratique les plus rentables.",
      href: `/apprendre/${courseCode.toLowerCase()}/erreurs`,
      courseCode,
      priority: 75,
    });
  }

  const mastery = masteryForCourse(userId, courseCode);
  const weakest = mastery.filter((c) => c.observations > 0 && c.score < 0.5).sort((a, b) => a.score - b.score)[0];
  if (weakest) {
    recs.push({
      kind: "quiz",
      label: `Quiz ciblé : ${weakest.name}`,
      reason: `Votre maîtrise estimée de « ${weakest.name} » est de ${(weakest.score * 100).toFixed(0)} % — quelques questions ciblées la feront progresser.`,
      href: `/apprendre/${courseCode.toLowerCase()}/quiz?concept=${weakest.slug}`,
      courseCode,
      priority: 70,
    });
  }
  const fresh = mastery.filter((c) => c.observations === 0 && c.importance >= 2).sort((a, b) => (a.week ?? 0) - (b.week ?? 0))[0];
  if (fresh) {
    recs.push({
      kind: "concept",
      label: `Découvrir : ${fresh.name}`,
      reason: `Notion importante de la semaine ${fresh.week ?? "?"} encore jamais pratiquée — mieux vaut la rencontrer avant qu'elle s'accumule.`,
      href: `/apprendre/${courseCode.toLowerCase()}/concepts?focus=${fresh.slug}`,
      courseCode,
      priority: 50,
    });
  }

  const plan = get<{ id: number; plan: string }>(
    "SELECT id, plan FROM study_plans WHERE user_id = ? AND course_code = ? AND active = 1 ORDER BY id DESC LIMIT 1",
    userId, courseCode
  );
  if (plan) {
    try {
      const daysArr = JSON.parse(plan.plan) as { date: string; items: { label: string; done?: boolean }[] }[];
      const today = new Date().toISOString().slice(0, 10);
      const todayPlan = daysArr.find((d) => d.date === today);
      const pending = todayPlan?.items.filter((i) => !i.done) ?? [];
      if (pending.length) {
        recs.push({
          kind: "plan",
          label: `Plan du jour : ${pending[0].label}`,
          reason: `Votre plan d'étude prévoit ${pending.length} activité${pending.length > 1 ? "s" : ""} aujourd'hui.`,
          href: `/apprendre/${courseCode.toLowerCase()}/plan`,
          courseCode,
          priority: 85,
        });
      }
    } catch { /* plan illisible — ignoré */ }
  }

  const examTried = get<{ n: number }>(
    `SELECT COUNT(*) as n FROM exam_attempts ea JOIN mock_exams me ON me.id = ea.exam_id
     WHERE ea.user_id = ? AND me.course_code = ?`,
    userId, courseCode
  );
  const avgScore = mastery.filter((m) => m.observations > 0);
  const avg = avgScore.length ? avgScore.reduce((s, m) => s + m.score, 0) / avgScore.length : 0;
  if ((examTried?.n ?? 0) === 0 && avg >= 0.5) {
    recs.push({
      kind: "exam",
      label: "Premier examen blanc (mode pratique)",
      reason: "Votre maîtrise moyenne dépasse 50 % — un examen blanc révélera où concentrer la suite.",
      href: `/apprendre/${courseCode.toLowerCase()}/examens`,
      courseCode,
      priority: 60,
    });
  }

  const recentChat = all(
    "SELECT id FROM activity_log WHERE user_id = ? AND course_code = ? AND created_at >= datetime('now','-7 days') LIMIT 1",
    userId, courseCode
  );
  if (!recentChat.length) {
    recs.push({
      kind: "chat",
      label: "Poser une question au cours",
      reason: "Aucune activité cette semaine — reprendre par une question sur la dernière séance est un bon réamorçage.",
      href: `/chat?course=${courseCode}`,
      courseCode,
      priority: 40,
    });
  }

  return recs.sort((a, b) => b.priority - a.priority).slice(0, max);
}