import { watch, type FSWatcher } from 'node:fs';
import { readFile, rename, rm } from 'node:fs/promises';
import { join } from 'node:path';

import { Injectable, OnModuleDestroy, OnModuleInit } from '@nestjs/common';
import { PinoLogger } from 'nestjs-pino';

import { ClockService } from '../common/clock.service';
import { AppConfig } from '../config/app-config.service';

import { PluginStorageService } from './plugin-storage.service';
import { PluginPackageError } from './plugin.constants';
import { PluginsService } from './plugins.service';

/** Debounce window: an editor/copy may fire several `rename` events per file. */
const DEBOUNCE_MS = 300;

/**
 * Registers plugin ZIPs a Site Admin drops into `<PLUGINS_DIR>/_dropzone/`
 * (ADR 0008 lifecycle). Each dropped file runs the exact same validation as the
 * GUI upload; a valid package installs and the ZIP is consumed, an invalid one
 * moves to `_quarantine/` with its error logged. The watcher is inert under
 * `NODE_ENV=test` — tests call {@link processDropped} directly for determinism.
 */
@Injectable()
export class PluginWatcherService implements OnModuleInit, OnModuleDestroy {
  private watcher: FSWatcher | undefined;
  private readonly pendingTimers = new Map<string, NodeJS.Timeout>();

  constructor(
    private readonly plugins: PluginsService,
    private readonly storage: PluginStorageService,
    private readonly config: AppConfig,
    private readonly clock: ClockService,
    private readonly logger: PinoLogger,
  ) {
    this.logger.setContext(PluginWatcherService.name);
  }

  async onModuleInit(): Promise<void> {
    if (this.config.env.NODE_ENV === 'test') return;
    // The dropzone is an optional convenience over the GUI upload. If its
    // directory cannot be created or watched (e.g. PLUGINS_DIR is not writable
    // on this deployment), log and carry on — it must never take down the api.
    try {
      await this.storage.ensureServiceDirs();
      this.watcher = watch(this.storage.dropzoneDir, (_event, filename) => {
        if (!filename || !filename.endsWith('.zip')) return;
        this.schedule(filename.toString());
      });
      this.logger.info({ dir: this.storage.dropzoneDir }, 'watching plugin dropzone');
    } catch (error) {
      this.logger.warn(
        { err: error, dir: this.storage.dropzoneDir },
        'plugin dropzone unavailable; drop-to-install disabled (GUI upload still works)',
      );
    }
  }

  onModuleDestroy(): void {
    this.watcher?.close();
    for (const timer of this.pendingTimers.values()) clearTimeout(timer);
    this.pendingTimers.clear();
  }

  private schedule(filename: string): void {
    const existing = this.pendingTimers.get(filename);
    if (existing) clearTimeout(existing);
    this.pendingTimers.set(
      filename,
      setTimeout(() => {
        this.pendingTimers.delete(filename);
        void this.processDropped(join(this.storage.dropzoneDir, filename));
      }, DEBOUNCE_MS),
    );
  }

  /**
   * Installs one dropped ZIP. On success the file is removed from the dropzone;
   * on any validation failure it is quarantined and the error logged. Returns
   * the outcome so tests can assert without relying on filesystem events.
   */
  async processDropped(
    filePath: string,
  ): Promise<{ installed: true; id: string } | { installed: false; code: string }> {
    let zip: Buffer;
    try {
      zip = await readFile(filePath);
    } catch {
      // The file vanished between the event and the read — nothing to do.
      return { installed: false, code: 'plugin_invalid_zip' };
    }

    try {
      const view = await this.plugins.install(zip);
      // The package is now unpacked under PLUGINS_DIR; consume the dropped ZIP.
      await rm(filePath, { force: true });
      this.logger.info({ id: view.id, version: view.version }, 'installed plugin from dropzone');
      return { installed: true, id: view.id };
    } catch (error) {
      const code = error instanceof PluginPackageError ? error.code : 'plugin_bad_structure';
      await this.quarantine(filePath);
      this.logger.warn({ code, file: filePath }, 'quarantined invalid plugin drop');
      return { installed: false, code };
    }
  }

  private async quarantine(filePath: string): Promise<void> {
    const name = filePath.split('/').pop() ?? 'package.zip';
    const stamp = this.clock.now().toISOString().replace(/[:.]/g, '-');
    await this.storage.ensureServiceDirs();
    await rename(filePath, join(this.storage.quarantineDir, `${stamp}-${name}`)).catch(
      () => undefined,
    );
  }
}