import { Document } from 'app/gen-server/entity/Document';
import { Workspace } from 'app/gen-server/entity/Workspace';
import { HomeDBManager, Scope } from 'app/gen-server/lib/HomeDBManager';
import { fromNow } from 'app/gen-server/sqlUtils';
import { GristServer } from 'app/server/lib/GristServer';
import { IElectionStore } from 'app/server/lib/IElectionStore';
import * as log from 'app/server/lib/log';
import { IPermitStore } from 'app/server/lib/Permit';
import fetch from 'node-fetch';

const HOUSEKEEPER_PERIOD_MS = 1 * 60 * 60 * 1000;   // operate every 1 hour
const AGE_THRESHOLD_OFFSET = '-30 days';            // should be an interval known by postgres + sqlite

/**
 * Take care of periodic tasks:
 *
 *  - deleting old soft-deleted documents
 *  - deleting old soft-deleted workspaces
 *
 * Call start(), keep the object around, and call stop() when shutting down.
 *
 * Some care is taken to elect a single server to do the housekeeping, so if there are
 * multiple home servers, there will be no competition or duplication of effort.
 */
export class Housekeeper {
  private _interval?: NodeJS.Timeout;
  private _electionKey?: string;

  public constructor(private _dbManager: HomeDBManager, private _server: GristServer,
                     private _permitStore: IPermitStore, private _electionStore: IElectionStore) {
  }

  /**
   * Start a ticker to launch housekeeping tasks from time to time.
   */
  public async start() {
    await this.stop();
    this._interval = setInterval(() => this.deleteTrashExclusively().catch(log.warn.bind(log)), HOUSEKEEPER_PERIOD_MS);
  }

  /**
   * Stop scheduling housekeeping tasks.  Note: doesn't wait for any housekeeping task in progress.
   */
  public async stop() {
    if (this._interval) {
      clearInterval(this._interval);
      this._interval = undefined;
    }
  }

  /**
   * Deletes old trash if no other server is working on it or worked on it recently.
   */
  public async deleteTrashExclusively(): Promise<boolean> {
    const electionKey = await this._electionStore.getElection('trash', HOUSEKEEPER_PERIOD_MS / 2.0);
    if (!electionKey) {
      log.info('Skipping deleteTrash since another server is working on it or worked on it recently');
      return false;
    }
    this._electionKey = electionKey;
    await this.deleteTrash();
    return true;
  }

  /**
   * Deletes old trash regardless of what other servers may be doing.
   */
  public async deleteTrash() {
    // Delete old soft-deleted docs
    const docs = await this._getDocsToDelete();
    for (const doc of docs) {
      // Last minute check - is the doc really soft-deleted?
      if (doc.removedAt === null && doc.workspace.removedAt === null) {
        throw new Error(`attempted to hard-delete a document that was not soft-deleted: ${doc.id}`);
      }
      // In general, documents can only be manipulated with the coordination of the
      // document worker to which they are assigned.  For an old soft-deleted doc,
      // we could probably get away with ensuring the document is closed/unloaded
      // and then deleting it without ceremony.  But, for consistency, and because
      // it will be useful for other purposes, we work through the api using special
      // temporary permits.
      const permitKey = await this._permitStore.setPermit({docId: doc.id});
      try {
        const result = await fetch(await this._server.getHomeUrlByDocId(doc.id, `/api/docs/${doc.id}`), {
          method: 'DELETE',
          headers: {
            Permit: permitKey
          }
        });
        if (result.status !== 200) {
          log.error(`failed to delete document ${doc.id}: error status ${result.status}`);
        }
      } finally {
        await this._permitStore.removePermit(permitKey);
      }
    }

    // Delete old soft-deleted workspaces
    const workspaces = await this._getWorkspacesToDelete();
    // Note: there's a small chance a workspace could be undeleted right under the wire,
    // and a document added, in which case the method we call here would not yet clean
    // up the docs in s3.  TODO: deal with this.
    for (const workspace of workspaces) {
      // Last minute check - is the workspace really soft-deleted?
      if (workspace.removedAt === null) {
        throw new Error(`attempted to hard-delete a workspace that was not soft-deleted: ${workspace.id}`);
      }
      const scope: Scope = {
        userId: this._dbManager.getPreviewerUserId(),
        specialPermit: {
          workspaceId: workspace.id
        }
      };
      await this._dbManager.deleteWorkspace(scope, workspace.id);
    }
  }

  /**
   * For test purposes, removes any exclusive lock on housekeeping.
   */
  public async testClearExclusivity(): Promise<void> {
    if (this._electionKey) {
      await this._electionStore.removeElection('trash', this._electionKey);
      this._electionKey = undefined;
    }
  }

  private async _getDocsToDelete() {
    const docs = await this._dbManager.connection.createQueryBuilder()
      .select('docs')
      .from(Document, 'docs')
      .leftJoinAndSelect('docs.workspace', 'workspaces')
      .where(`COALESCE(docs.removed_at, workspaces.removed_at) <= ${this._getThreshold()}`)
      // the following has no effect (since null <= date is false) but added for clarity
      .andWhere('COALESCE(docs.removed_at, workspaces.removed_at) IS NOT NULL')
      .getMany();
    return docs;
  }

  private async _getWorkspacesToDelete() {
    const docs = await this._dbManager.connection.createQueryBuilder()
      .select('workspaces')
      .from(Workspace, 'workspaces')
      .leftJoin('workspaces.docs', 'docs')
      .where(`workspaces.removed_at <= ${this._getThreshold()}`)
      // the following has no effect (since null <= date is false) but added for clarity
      .andWhere('workspaces.removed_at IS NOT NULL')
      // wait for workspace to be empty
      .andWhere('docs.id IS NULL')
      .getMany();
    return docs;
  }

  /**
   * TypeORM isn't very adept at handling date representation for
   * comparisons, so we construct the threshold date in SQL so that we
   * don't have to deal with its caprices.
   */
  private _getThreshold() {
    return fromNow(this._dbManager.connection.driver.options.type, AGE_THRESHOLD_OFFSET);
  }
}