feat: introduce index.d.ts for typescript support

File taken directly from what I made for @types/kesha-antonov__react-native-background-downloader. Verified working by installing locally in a typescript project that consumes it, and verifying via --traceResolution that the index.d.ts file is successfully found and that types resolve.

index.d.ts

@@ -0,0 +1,118 @@
+// Type definitions for @kesha-antonov/react-native-background-downloader 2.6
+// Project: https://github.com/kesha-antonov/react-native-background-downloader
+// Definitions by: Philip Su <https://github.com/fivecar>,
+//                 Adam Hunter <https://github.com/adamrhunter>,
+//                 Junseong Park <https://github.com/Kweiza>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+
+export interface DownloadHeaders {
+  [key: string]: string | null;
+}
+
+type SetHeaders = (h: DownloadHeaders) => void;
+
+export interface TaskInfoObject {
+  id: string;
+  percent: number;
+  bytesWritten: number;
+  totalBytes: number;
+}
+export type TaskInfo = string | TaskInfoObject;
+
+export interface BeginHandlerObject {
+  expectedBytes: number;
+  headers: { [key: string]: string };
+}
+
+export type BeginHandler = ({
+  expectedBytes,
+  headers,
+}: BeginHandlerObject) => any;
+export type ProgressHandler = (
+  percent: number,
+  bytesWritten: number,
+  totalBytes: number
+) => any;
+export type DoneHandler = () => any;
+export type ErrorHandler = (error: any, errorCode: any) => any;
+export type DownloadTaskState =
+  | "DOWNLOADING"
+  | "PAUSED"
+  | "DONE"
+  | "FAILED"
+  | "STOPPED";
+
+export interface DownloadTask {
+  constructor: (taskInfo: TaskInfo) => DownloadTask;
+
+  id: string;
+  state: DownloadTaskState;
+  percent: number;
+  bytesWritten: number;
+  totalBytes: number;
+
+  begin: (handler: BeginHandler) => DownloadTask;
+  progress: (handler: ProgressHandler) => DownloadTask;
+  done: (handler: DoneHandler) => DownloadTask;
+  error: (handler: ErrorHandler) => DownloadTask;
+
+  _beginHandler: BeginHandler;
+  _progressHandler: ProgressHandler;
+  _doneHandler: DoneHandler;
+  _errorHandler: ErrorHandler;
+
+  pause: () => any;
+  resume: () => any;
+  stop: () => any;
+}
+
+export type CheckForExistingDownloads = () => Promise<DownloadTask[]>;
+export type EnsureDownloadsAreRunning = () => Promise<void>;
+
+export interface DownloadOption {
+  id: string;
+  url: string;
+  destination: string;
+  headers?: DownloadHeaders | undefined;
+}
+
+export type Download = (options: DownloadOption) => DownloadTask;
+export type CompleteHandler = (id: string) => void;
+
+export interface Directories {
+  documents: string;
+}
+
+export interface Network {
+  WIFI_ONLY: string;
+  ALL: string;
+}
+
+export interface Priority {
+  HIGH: string;
+  MEDIUM: string;
+  LOW: string;
+}
+
+export const setHeaders: SetHeaders;
+export const checkForExistingDownloads: CheckForExistingDownloads;
+export const ensureDownloadsAreRunning: EnsureDownloadsAreRunning;
+export const download: Download;
+export const completeHandler: CompleteHandler;
+export const directories: Directories;
+export const Network: Network;
+export const Priority: Priority;
+
+export interface RNBackgroundDownloader {
+  setHeaders: SetHeaders;
+  checkForExistingDownloads: CheckForExistingDownloads;
+  ensureDownloadsAreRunning: EnsureDownloadsAreRunning;
+  download: Download;
+  completeHandler: CompleteHandler;
+  directories: Directories;
+  Network: Network;
+  Priority: Priority;
+}
+
+declare const RNBackgroundDownloader: RNBackgroundDownloader;
+export default RNBackgroundDownloader;

package.json

@@ -25,11 +25,13 @@
     }
   ],
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
     "README.md",
     "LICENSE",
     "react-native-background-downloader.podspec",
     "package.json",
+    "index.d.ts",
     "index.js",
     "lib/",
     "ios/",