feat(did): Add DID URL utilities

- isDidUrl(): checks if given URL is a DID URL.
- decodeFromDidUrl(): decode information of the DID URL.

See also: https://w3c-ccg.github.io/did-spec/#fragment

packages/did/README.md

@@ -34,6 +34,10 @@ Used to describe which Tangle network interacts.
 
     * [~decodeFromDid(tangleid)](#module_did..decodeFromDid)
 
+    * [~isDidUrl(url)](#module_did..isDidUrl)
+
+    * [~decodeFromDidUrl(url)](#module_did..decodeFromDidUrl)
+
     * [~createMetaPublicKeys(controller, publicKeyPems)](#module_did..createMetaPublicKeys)
 
 
@@ -62,6 +66,28 @@ Encode TangleID DID with specific network and address.
 Decode infromation of network and address from TangleID.
 
 **Returns**: <code>Object</code> - } The infromation of network and address.  
+<a name="module_did..isDidUrl"></a>
+
+### *did*~isDidUrl(url)
+
+| Param | Type | Description |
+| --- | --- | --- |
+| url | <code>string</code> | the URL to be checked. |
+
+Checks if given URL is a DID URL.
+
+**Returns**: <code>boolean</code> - The boolean that represent the url whether DID URL.  
+<a name="module_did..decodeFromDidUrl"></a>
+
+### *did*~decodeFromDidUrl(url)
+
+| Param | Type | Description |
+| --- | --- | --- |
+| url | <code>string</code> | the DID URL that will be decoded. |
+
+Decode information of the DID URL.
+
+**Returns**: <code>Object</code> - The information of the DID URL. [https://w3c-ccg.github.io/did-spec/#generic-did-syntax](https://w3c-ccg.github.io/did-spec/#generic-did-syntax)  
 <a name="module_did..createMetaPublicKeys"></a>
 
 ### *did*~createMetaPublicKeys(controller, publicKeyPems)

packages/did/src/did.ts

@@ -3,6 +3,9 @@ import { encodeToMnid, decodeFromMnid } from '@tangleid/mnid';
 // @ts-ignore
 import { parse } from 'did-resolver';
 import { Did, MnidModel, PublicKeyPem, PublicKeyMeta } from '../../types';
+
+const DID_URL_REGEX = /^did:(?<method>[a-z0-9]+):(?<idstring>[A-Za-z0-9\.\-_]+)(?:#(?<fragment>.*))?$/;
+
 /**
  * Encode TangleID DID with specific network and address.
  * @function encodeToDid
@@ -36,6 +39,39 @@ export const decodeFromDid = (tangleid: Did): MnidModel => {
   return mamParsed;
 };
 
+/**
+ * Checks if given URL is a DID URL.
+ * @function isDidUrl
+ * @param {string} url - the URL to be checked.
+ * @return {boolean} The boolean that represent the url whether DID URL.
+ */
+export const isDidUrl = (url: string): boolean => {
+  return DID_URL_REGEX.test(url);
+};
+
+/**
+ * Decode information of the DID URL.
+ * @function decodeFromDidUrl
+ * @param {string} url - the DID URL that will be decoded.
+ * @return {{did: string, method: string, idstring: string, fragment: string | null}}
+ *   The information of the DID URL. {@link https://w3c-ccg.github.io/did-spec/#generic-did-syntax}
+ */
+export const decodeFromDidUrl = (url: string) => {
+  const matches = DID_URL_REGEX.exec(url);
+  if (matches === null) {
+    throw new Error('Invalid DID URL');
+  }
+
+  const [, method, idstring, fragment] = matches;
+
+  return {
+    did: `did:${method}:${idstring}`,
+    method,
+    idstring,
+    fragment: fragment || null,
+  };
+};
+
 /**
  * Create metadata of public keys from PEM-formatted public Keys.
  * @function createMetaPublicKeys