import { getSessions, runLargeOperation } from '../core';
import { captureCurrentSession } from './session-snapshot';

// Debounce window for autosave. A full-tab snapshot + storage write runs on
// every tab open/close/move; a longer window coalesces rapid bursts (e.g.
// opening or closing many tabs at once) into a single snapshot.
const AUTOSAVE_DEBOUNCE_MS = 3000;

export class AutoSaveManager {
  private autoSaveTimer: ReturnType<typeof setTimeout> | null = null;
  private autoSaveInFlight = false;
  private autoSavePending = false;

  // Bound handler references — stored so add/removeListener share identity
  // (removeListener must use the SAME reference that was added).
  readonly autoSaveHandler = async (): Promise<void> => {
    await this.scheduleAutoSave();
  };
  readonly autoSaveUpdatedHandler = async (_tabId: number, changeInfo: chrome.tabs.OnUpdatedInfo = {}): Promise<void> => {
    // Ignore noisy media/title/favicon/loading updates. Sessions only store URL and group/window structure.
    if (!("url" in changeInfo)) return;
    await this.scheduleAutoSave();
  };

  async setEnabled(enabled: boolean) {
    await chrome.storage.local.set({ autoSave: enabled });
    chrome.tabs.onCreated.removeListener(this.autoSaveHandler);
    chrome.tabs.onRemoved.removeListener(this.autoSaveHandler);
    chrome.tabs.onMoved.removeListener(this.autoSaveHandler);
    chrome.tabs.onAttached.removeListener(this.autoSaveHandler);
    chrome.tabs.onDetached.removeListener(this.autoSaveHandler);
    chrome.tabs.onUpdated.removeListener(this.autoSaveUpdatedHandler);
    if (chrome.tabGroups?.onUpdated) chrome.tabGroups.onUpdated.removeListener(this.autoSaveHandler);
    if (this.autoSaveTimer) clearTimeout(this.autoSaveTimer);
    this.autoSaveTimer = null;
    this.autoSavePending = false;
    if (enabled) {
      chrome.tabs.onCreated.addListener(this.autoSaveHandler);
      chrome.tabs.onRemoved.addListener(this.autoSaveHandler);
      chrome.tabs.onMoved.addListener(this.autoSaveHandler);
      chrome.tabs.onAttached.addListener(this.autoSaveHandler);
      chrome.tabs.onDetached.addListener(this.autoSaveHandler);
      chrome.tabs.onUpdated.addListener(this.autoSaveUpdatedHandler);
      if (chrome.tabGroups?.onUpdated) chrome.tabGroups.onUpdated.addListener(this.autoSaveHandler);
    }
    return { enabled };
  }

  private async saveAutoSessionIfChanged() {
    const { session, signature, tabCount } = await captureCurrentSession();
    const { autoSaveSignature } = await chrome.storage.local.get("autoSaveSignature");
    if (autoSaveSignature === signature) return { skipped: true, tabs: tabCount };

    const sessions = await getSessions();
    sessions.__auto__ = session;
    await chrome.storage.local.set({ sessions, autoSaveSignature: signature });
    return { skipped: false, tabs: tabCount };
  }

  private async runAutoSave() {
    if (this.autoSaveInFlight) {
      this.autoSavePending = true;
      return;
    }
    this.autoSaveInFlight = true;
    try {
      const { autoSave } = await chrome.storage.local.get("autoSave");
      if (autoSave) await runLargeOperation("session.auto_save", () => this.saveAutoSessionIfChanged());
    } finally {
      this.autoSaveInFlight = false;
      if (this.autoSavePending) {
        this.autoSavePending = false;
        this.autoSaveTimer = setTimeout(() => this.runAutoSave(), AUTOSAVE_DEBOUNCE_MS);
      }
    }
  }

  private async scheduleAutoSave(delayMs = AUTOSAVE_DEBOUNCE_MS) {
    const { autoSave } = await chrome.storage.local.get("autoSave");
    if (!autoSave) return;
    if (this.autoSaveTimer) clearTimeout(this.autoSaveTimer);
    this.autoSaveTimer = setTimeout(() => this.runAutoSave(), delayMs);
  }
}