"use client";

/**
 * Reported questions. Two copies: one in this browser — the source of truth
 * for skipping, works offline and Undo can take it back — and one appended to
 * the server's `reports.jsonl` (see /api/reports) so the operator can inspect
 * what was flagged.
 *
 * Reports are deliberately not part of the backup/sync payload: the server
 * file is the cross-device record, the local list is just this browser's skip
 * state.
 */

import { z } from "zod";

import type { Activity } from "./schemas";

const STORAGE_KEY = "freezmo.reports.v1";
const LIMIT = 200;
const EMPTY: QuestionReport[] = [];

export const questionReportSchema = z.object({
  deckId: z.string().min(1).max(80),
  deckTitle: z.string().max(200).optional(),
  activityId: z.string().min(1).max(80),
  type: z.string().min(1).max(40),
  question: z.string().min(1).max(600),
  at: z.number(),
});
export type QuestionReport = z.infer<typeof questionReportSchema>;

type Listener = () => void;

let reports: QuestionReport[] | null = null;
let cached: QuestionReport[] = EMPTY;
const listeners = new Set<Listener>();

function read(): QuestionReport[] {
  if (typeof window === "undefined") return EMPTY;
  try {
    const raw = window.localStorage.getItem(STORAGE_KEY);
    if (!raw) return EMPTY;
    const parsed: unknown = JSON.parse(raw);
    if (!Array.isArray(parsed)) return EMPTY;
    const valid: QuestionReport[] = [];
    for (const entry of parsed) {
      const result = questionReportSchema.safeParse(entry);
      if (result.success) valid.push(result.data);
      else console.warn("[freezmo] skipping invalid report", result.error.issues);
    }
    return valid;
  } catch (error) {
    console.warn("[freezmo] could not read reports", error);
    return EMPTY;
  }
}

function ensureLoaded(): void {
  if (reports !== null) return;
  reports = read();
  cached = reports;
}

function write(next: QuestionReport[]): void {
  reports = next;
  cached = next;
  try {
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
  } catch (error) {
    console.warn("[freezmo] could not save reports", error);
  }
  listeners.forEach((listener) => listener());
}

function onStorage(event: StorageEvent): void {
  if (event.key === STORAGE_KEY) {
    reports = null;
    ensureLoaded();
    listeners.forEach((l) => l());
  }
}

export const reportStore = {
  subscribe(listener: Listener): () => void {
    ensureLoaded();
    if (listeners.size === 0) window.addEventListener("storage", onStorage);
    listeners.add(listener);
    return () => {
      listeners.delete(listener);
      if (listeners.size === 0) window.removeEventListener("storage", onStorage);
    };
  },
  getSnapshot(): QuestionReport[] {
    ensureLoaded();
    return cached;
  },
  getServerSnapshot(): QuestionReport[] {
    return EMPTY;
  },
};

/** Short text of an activity, for the report payload. */
export function activityText(activity: Activity): string {
  switch (activity.type) {
    case "flashcard":
      return activity.front;
    case "multiple_choice":
      return activity.question;
    case "true_false":
      return activity.statement;
    case "fill_blank":
      return activity.sentence;
    case "matching":
      return activity.instruction;
    case "ordering":
      return activity.instruction;
    case "short_answer":
      return activity.question;
  }
}

export function isReported(deckId: string, activityId: string): boolean {
  return reportStore.getSnapshot().some((report) => report.deckId === deckId && report.activityId === activityId);
}

/**
 * The deck's activities minus the reported ones. Never returns an empty list:
 * a deck where everything was reported stays studiable (and regenerable).
 */
export function withoutReported(deckId: string, activities: Activity[]): Activity[] {
  const kept = activities.filter((activity) => !isReported(deckId, activity.id));
  return kept.length > 0 ? kept : activities;
}

/** Adds (or refreshes) a report and sends a copy to the server, best effort. */
/**
 * A pseudo-activity so a homework result can use the same report flow as a
 * study card (the report only keeps the flattened question/type/id).
 */
export function homeworkReportActivity(input: { id: string; title: string; answer: string }): Activity {
  const body = input.answer.trim().slice(0, 1200) || input.title;
  return {
    id: input.id,
    xp: 0,
    type: "short_answer",
    question: input.title.slice(0, 600) || "Homework result",
    referenceAnswer: body,
    keyPoints: [body.slice(0, 200) || "Result"],
    explanation: input.title.slice(0, 600) || "Homework result",
  };
}

export function reportQuestion(input: {
  /** A deck id, or the homework record's id for a homework exercise. */
  deckId: string;
  deckTitle?: string;
  activity: Activity;
}): QuestionReport {
  const entry: QuestionReport = {
    deckId: input.deckId,
    deckTitle: input.deckTitle,
    activityId: input.activity.id,
    type: input.activity.type,
    question: activityText(input.activity).slice(0, 600),
    at: Date.now(),
  };
  ensureLoaded();
  const others = reportStore
    .getSnapshot()
    .filter((report) => !(report.deckId === entry.deckId && report.activityId === entry.activityId));
  write([entry, ...others].slice(0, LIMIT));

  // The operator's copy: appended under the shared data dir by /api/reports.
  // Offline or a server hiccup never blocks the skip.
  void fetch("/api/reports", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify(entry),
  }).catch(() => {});

  return entry;
}

/** Undo: forget the report locally (the server file is append-only). */
export function unreportQuestion(deckId: string, activityId: string): void {
  ensureLoaded();
  write(
    reportStore
      .getSnapshot()
      .filter((report) => !(report.deckId === deckId && report.activityId === activityId)),
  );
}