/**
 * useErrorReporter.ts — Gap 2.2: Cattura errori JS non gestiti e li invia a /api/logs/frontend.
 *
 * Auto-registra window.onerror e window.onunhandledrejection al primo import (side effect).
 * Esporta anche un hook React per garantire mount nell'albero dei componenti.
 *
 * Features:
 * - Batching: accumula errori in un buffer da svuotare ogni 5s (max 10 per batch)
 * - Dedup: skip errori identici entro 10s (stesso msg+stack prefix)
 * - Rate limiting: max 20 errori per sessione → previene spam su loop di errori
 * - Fire-and-forget: fetch con keepalive:true, nessun await, zero impact UX
 * - Zero crash: try/catch ovunque, mai propaga eccezioni
 *
 * Compatibilità: Safari iOS 14+ (unhandledrejection disponibile da iOS 14.5).
 * Su versioni precedenti il handler viene skippato silenziosamente.
 */

import { useEffect } from "react";

const _BACKEND_URL = (import.meta.env.VITE_BACKEND_URL ?? "").replace(/\/$/, "");
const _ENDPOINT    = _BACKEND_URL ? `${_BACKEND_URL}/api/logs/frontend` : null;

// ── State modulo ──────────────────────────────────────────────────────────────
let _sessionCount  = 0;
const _MAX_SESSION = 20;
const _dedup       = new Map<string, number>(); // key → last_sent_ms
const _DEDUP_TTL   = 10_000;
let   _flushTimer: ReturnType<typeof setTimeout> | null = null;
const _buf: Array<{
  level: string; msg: string; source: string;
  url?: string; stack?: string; ts_ms: number;
}> = [];

function _dedupKey(msg: string, stack?: string): string {
  return `${msg.slice(0, 80)}|${(stack ?? "").slice(0, 80)}`;
}

function _isDuplicate(msg: string, stack?: string): boolean {
  const key  = _dedupKey(msg, stack);
  const last = _dedup.get(key);
  const now  = Date.now();
  if (last && now - last < _DEDUP_TTL) return true;
  _dedup.set(key, now);
  // Prune vecchi entry per tenere la mappa piccola
  if (_dedup.size > 50) {
    for (const [k, t] of _dedup) {
      if (now - t > _DEDUP_TTL) _dedup.delete(k);
      if (_dedup.size <= 50) break;
    }
  }
  return false;
}

function _scheduleFlush(): void {
  if (_flushTimer !== null) return;
  _flushTimer = setTimeout(_flush, 5_000);
}

function _flush(): void {
  _flushTimer = null;
  if (!_ENDPOINT || _buf.length === 0) { _buf.length = 0; return; }
  const batch = _buf.splice(0, 10);
  try {
    for (const entry of batch) {
      // keepalive:true → funziona anche se la tab viene chiusa (iOS safe)
      fetch(_ENDPOINT, {
        method:    "POST",
        headers:   { "Content-Type": "application/json" },
        body:      JSON.stringify(entry),
        keepalive: true,
      }).catch(() => { /* silent */ });
    }
  } catch {
    // silent
  }
}

function _report(
  level: "error" | "warn" | "info",
  msg:   string,
  opts?: { source?: string; url?: string; stack?: string }
): void {
  try {
    if (!_ENDPOINT) return;
    if (_sessionCount >= _MAX_SESSION) return;
    if (_isDuplicate(msg, opts?.stack)) return;

    _sessionCount++;
    _buf.push({
      level,
      msg:    msg.slice(0, 500),
      source: opts?.source ?? "window",
      url:    opts?.url ?? (typeof location !== "undefined" ? location.href : undefined),
      stack:  opts?.stack?.slice(0, 800),
      ts_ms:  Date.now(),
    });
    _scheduleFlush();
  } catch {
    // silent — mai impattare l'app
  }
}

// ── Auto-registrazione side effect ────────────────────────────────────────────
let _registered = false;

function _registerGlobalHandlers(): void {
  if (_registered || typeof window === "undefined") return;
  _registered = true;

  const _prevOnError = window.onerror;
  window.onerror = (msg, source, _line, _col, error) => {
    _report("error", String(msg), {
      source: "window.onerror",
      url:    String(source ?? ""),
      stack:  error?.stack,
    });
    if (typeof _prevOnError === "function") {
      return (_prevOnError as (...a: unknown[]) => unknown)(msg, source, _line, _col, error) as boolean;
    }
    return false;
  };

  // unhandledrejection — Safari iOS 14.5+
  try {
    window.addEventListener("unhandledrejection", (e) => {
      const reason = e.reason;
      const msg    = reason instanceof Error
        ? reason.message
        : String(reason ?? "Unhandled promise rejection");
      const stack  = reason instanceof Error ? reason.stack : undefined;
      _report("error", msg, { source: "unhandledrejection", stack });
    }, { passive: true });
  } catch {
    // WKWebView fallback — silent
  }
}

// Registra immediatamente all'import (side effect di modulo)
_registerGlobalHandlers();

// ── React hook ────────────────────────────────────────────────────────────────

/**
 * Hook React per montare il reporter nell'albero dei componenti.
 * La registrazione avviene già come side effect di import, questo hook
 * garantisce il re-mount su HMR in sviluppo.
 */
export function useErrorReporter(): void {
  useEffect(() => {
    _registerGlobalHandlers();
  }, []);
}

/**
 * Report manuale di un errore (es. catch block, errore di business logic).
 *
 * @example
 *   try { ... } catch(e) { reportError(e, { source: "agentLoop" }); }
 */
export function reportError(
  error:  Error | string,
  opts?:  { source?: string; level?: "error" | "warn" | "info" }
): void {
  const msg   = error instanceof Error ? error.message : String(error);
  const stack = error instanceof Error ? error.stack   : undefined;
  _report(opts?.level ?? "error", msg, { source: opts?.source, stack });
}