/*
Copyright 2021-2024 New Vector Ltd.

SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
Please see LICENSE in the repository root for full details.
*/

import { merge } from "lodash-es";

import { getUrlParams } from "../UrlParams";
import {
  DEFAULT_CONFIG,
  type ConfigOptions,
  type ResolvedConfigOptions,
} from "./ConfigOptions";
import { isFailure } from "../utils/fetch";

export class Config {
  private static internalInstance: Config | undefined;

  public static get(): ResolvedConfigOptions {
    if (!this.internalInstance?.config)
      throw new Error("Config instance read before config got initialized");
    return this.internalInstance.config;
  }

  public static async init(): Promise<void> {
    if (!Config.internalInstance?.initPromise) {
      const internalInstance = new Config();
      Config.internalInstance = internalInstance;

      let fetchTarget: string;

      if (
        window.location.pathname.endsWith("/room/") ||
        window.location.pathname.endsWith("/room")
      ) {
        // it looks like we are running in standalone mode so use the config at the root
        fetchTarget = new URL("/config.json", window.location.href).href;
      } else {
        // otherwise we are probably running as a widget so use the config in the same directory
        fetchTarget = "config.json";
      }

      Config.internalInstance.initPromise = downloadConfig(fetchTarget).then(
        (config) => {
          internalInstance.config = merge({}, DEFAULT_CONFIG, config);
        },
      );
    }
    return Config.internalInstance.initPromise;
  }

  /**
   * This is a alternative initializer that does not load anything
   * from a hosted config file but instead just initializes the config using the
   * default config.
   *
   * It is supposed to only be used in tests. (It is executed in `vite.setup.js`)
   */
  public static initDefault(): void {
    Config.internalInstance = new Config();
    Config.internalInstance.config = { ...DEFAULT_CONFIG };
  }

  // Convenience accessors
  public static defaultHomeserverUrl(): string | undefined {
    return (
      getUrlParams().homeserver ??
      Config.get().default_server_config?.["m.homeserver"].base_url
    );
  }

  public static defaultServerName(): string | undefined {
    const homeserver = getUrlParams().homeserver;
    if (homeserver) {
      const url = new URL(homeserver);
      return url.hostname;
    }
    return Config.get().default_server_config?.["m.homeserver"].server_name;
  }

  public config?: ResolvedConfigOptions;
  private initPromise?: Promise<void>;
}

async function downloadConfig(fetchTarget: string): Promise<ConfigOptions> {
  const response = await fetch(fetchTarget);

  if (isFailure(response)) {
    // Lack of a config isn't an error, we should just use the defaults.
    // Also treat a blank config as no config, assuming the status code is 0, because we don't get 404s from file:
    // URIs so this is the only way we can not fail if the file doesn't exist when loading from a file:// URI.
    return DEFAULT_CONFIG;
  }

  return response.json();
}