"use client";

/**
 * Homework results backed by localStorage. Same tiny observable store as the
 * deck library, but deliberately smaller: no folders, no attempts — just the
 * assignment text (so “Make it again” works) and the result.
 *
 * Original photos/documents are never stored; they were reduced to text on the
 * client before this point.
 */

import {
  homeworkRecordSchema,
  type HomeworkGuideRecord,
  type HomeworkMode,
  type HomeworkRecord,
  type HomeworkStep,
} from "./schemas";
import { markSyncDirty } from "./sync-state";
import { uid } from "./utils";

const STORAGE_KEY = "freezmo.homework.v1";
const EMPTY: HomeworkRecord[] = [];
/** Enough to regenerate from, while staying well under the storage quota. */
export const MAX_STORED_SOURCE = 24_000;

type Listener = () => void;

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

function read(): HomeworkRecord[] {
  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: HomeworkRecord[] = [];
    for (const entry of parsed) {
      const result = homeworkRecordSchema.safeParse(entry);
      if (result.success) valid.push(result.data as HomeworkRecord);
      else console.warn("[freezmo] skipping invalid homework record", result.error.issues);
    }
    return valid;
  } catch (error) {
    console.warn("[freezmo] could not read the homework history", error);
    return EMPTY;
  }
}

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

function write(next: HomeworkRecord[]): void {
  records = next;
  cached = next;
  try {
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
  } catch (error) {
    console.warn("[freezmo] could not save the homework history (storage full?)", error);
  }
  /* A homework result with sync on pushes itself (see lib/sync-auto). */
  if (markSyncDirty()) void import("./sync-auto").then((module) => module.scheduleAutoSync());
  listeners.forEach((listener) => listener());
}

/** Used by backup import and sync: wholesale replacement of the history. */
export function replaceHomework(next: HomeworkRecord[]): void {
  const valid: HomeworkRecord[] = [];
  for (const entry of next) {
    const result = homeworkRecordSchema.safeParse(entry);
    if (result.success) valid.push(result.data as HomeworkRecord);
    else console.warn("[freezmo] skipping invalid homework record in import", result.error.issues);
  }
  write(valid);
}

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

export const homeworkStore = {
  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(): HomeworkRecord[] {
    ensureLoaded();
    return cached;
  },
  getServerSnapshot(): HomeworkRecord[] {
    return EMPTY;
  },
};

/** Newest first. */
export function sortHomework(list: HomeworkRecord[]): HomeworkRecord[] {
  return [...list].sort((a, b) => b.updatedAt - a.updatedAt);
}

export function getHomework(id: string): HomeworkRecord | undefined {
  return homeworkStore.getSnapshot().find((record) => record.id === id);
}

/** Everything needed to store a result (the route's payload plus the source). */
export type NewHomeworkResult =
  | { mode: "make"; title: string; language?: string; sourceText: string; answer: string }
  | { mode: "guide"; title: string; language?: string; sourceText: string; steps: HomeworkStep[] }
  | {
      mode: "check";
      title: string;
      language?: string;
      sourceText: string;
      verdict: string;
      correct: string[];
      wrong: Array<{ issue: string; why: string; fix: string }>;
      corrected: string;
      attempt?: string;
    };

function buildRecord(
  base: { id: string; createdAt: number; updatedAt: number },
  input: NewHomeworkResult,
): HomeworkRecord {
  const shared = {
    ...base,
    title: input.title.slice(0, 200),
    language: input.language,
    sourceText: input.sourceText.slice(0, MAX_STORED_SOURCE),
  };
  if (input.mode === "make") return { ...shared, mode: "make", answer: input.answer };
  if (input.mode === "check") {
    return {
      ...shared,
      mode: "check",
      verdict: input.verdict,
      correct: input.correct,
      wrong: input.wrong,
      corrected: input.corrected,
      attempt: input.attempt?.slice(0, 20_000),
    };
  }
  return { ...shared, mode: "guide", steps: input.steps };
}

export function saveHomework(input: NewHomeworkResult): HomeworkRecord {
  ensureLoaded();
  const now = Date.now();
  const record = buildRecord({ id: uid("hw"), createdAt: now, updatedAt: now }, input);
  write([record, ...homeworkStore.getSnapshot()]);
  return record;
}

/** “Make it again” keeps the same history row. */
export function updateHomework(id: string, input: NewHomeworkResult): HomeworkRecord | undefined {
  ensureLoaded();
  const existing = homeworkStore.getSnapshot().find((record) => record.id === id);
  if (!existing) return undefined;
  const updated = buildRecord(
    { id: existing.id, createdAt: existing.createdAt, updatedAt: Date.now() },
    input,
  );
  write(homeworkStore.getSnapshot().map((record) => (record.id === id ? updated : record)));
  return updated;
}

export function deleteHomework(id: string): void {
  ensureLoaded();
  write(homeworkStore.getSnapshot().filter((record) => record.id !== id));
}

/** The final screen's text: the step answers assembled into one solution. */
export function assembleSolution(record: HomeworkGuideRecord): string {
  const parts = record.steps.map((step, index) => `${index + 1}. ${step.title}\n${step.answer}`);
  return [record.title, ...parts].join("\n\n");
}

/** Label for a row in the history list. */
export function homeworkModeLabelKey(mode: HomeworkMode): string {
  if (mode === "make") return "homework.history.made";
  if (mode === "check") return "homework.history.checked";
  return "homework.history.guide";
}

export type { HomeworkGuideRecord };