/*
 This file is part of GNU Taler
 (C) 2024 Taler Systems S.A.

 GNU Taler is free software; you can redistribute it and/or modify it under the
 terms of the GNU General Public License as published by the Free Software
 Foundation; either version 3, or (at your option) any later version.

 GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

 You should have received a copy of the GNU General Public License along with
 GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
 */

import {
  AbsoluteTime,
  CancellationToken,
  ObservabilityEvent,
} from "./index.js";
import {
  HttpRequestLibrary,
  HttpRequestOptions,
  HttpResponse,
} from "./http-common.js";
import { ObservabilityEventType } from "./notifications.js";
import { getErrorDetailFromException } from "./errors.js";

/**
 * Observability sink can be passed into various operations (HTTP requests, DB access)
 * to do structured logging within a particular context (task, request, ...).
 */
export interface ObservabilityContext {
  observe(evt: ObservabilityEvent): void;
}

let seqId = 1000;

export class ObservableHttpClientLibrary implements HttpRequestLibrary {
  private readonly cancelatorById = new Map<string, CancellationToken.Source>();
  constructor(
    private impl: HttpRequestLibrary,
    private oc: ObservabilityContext,
  ) {}

  public cancelRequest(id: string): void {
    const cancelator = this.cancelatorById.get(id);
    if (!cancelator) return;
    cancelator.cancel();
  }

  async fetch(
    url: string,
    opt?: HttpRequestOptions | undefined,
  ): Promise<HttpResponse> {
    const id = `req-${seqId}`;
    seqId = seqId + 1;

    const cancelator = CancellationToken.create();
    if (opt?.cancellationToken) {
      opt.cancellationToken.onCancelled(cancelator.cancel);
    }
    this.cancelatorById.set(id, cancelator);

    this.oc.observe({
      id,
      when: AbsoluteTime.now(),
      type: ObservabilityEventType.HttpFetchStart,
      url: url,
    });

    const optsWithCancel = opt ?? {};
    optsWithCancel.cancellationToken = cancelator.token;
    try {
      const res = await this.impl.fetch(url, optsWithCancel);
      this.oc.observe({
        id,
        when: AbsoluteTime.now(),
        type: ObservabilityEventType.HttpFetchFinishSuccess,
        url,
        status: res.status,
      });
      return res;
    } catch (e) {
      this.oc.observe({
        id,
        when: AbsoluteTime.now(),
        type: ObservabilityEventType.HttpFetchFinishError,
        url,
        error: getErrorDetailFromException(e),
      });
      throw e;
    } finally {
      this.cancelatorById.delete(id);
    }
  }
}