[APP-2160] Add parseDidFromAtUri util for PublicationEmbed

src/components/Post/Embed/ExternalEmbed/PublicationEmbed/__tests__/util.test.ts

@@ -0,0 +1,32 @@
+import {parseDidFromAtUri} from '#/components/Post/Embed/ExternalEmbed/PublicationEmbed/util'
+
+describe('parseDidFromAtUri', () => {
+  it('extracts a plc DID from a publication at-uri', () => {
+    expect(
+      parseDidFromAtUri('at://did:plc:abc123/site.standard.publication/3jx'),
+    ).toBe('did:plc:abc123')
+  })
+
+  it('extracts a web DID', () => {
+    expect(
+      parseDidFromAtUri(
+        'at://did:web:example.com/site.standard.publication/3jx',
+      ),
+    ).toBe('did:web:example.com')
+  })
+
+  it('returns undefined for non-at-uri strings', () => {
+    expect(parseDidFromAtUri('https://example.com')).toBeUndefined()
+  })
+
+  it('returns undefined for empty / nullish input', () => {
+    expect(parseDidFromAtUri('')).toBeUndefined()
+    expect(parseDidFromAtUri(undefined)).toBeUndefined()
+  })
+
+  it('returns undefined when the authority is not a DID', () => {
+    expect(
+      parseDidFromAtUri('at://alice.bsky.social/site.standard.publication/3jx'),
+    ).toBeUndefined()
+  })
+})

src/components/Post/Embed/ExternalEmbed/PublicationEmbed/util.ts

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+/**
+ * Extract the DID from an at-uri of the form `at://did:<method>:<id>/<nsid>/<rkey>`.
+ * Returns undefined if the input is falsy, not an at-uri, or the authority is not a DID.
+ */
+export function parseDidFromAtUri(uri: string | undefined): string | undefined {
+  if (!uri || !uri.startsWith('at://')) return undefined
+  const authority = uri.slice('at://'.length).split('/')[0]
+  if (!authority || !authority.startsWith('did:')) return undefined
+  return authority
+}