feat: Add support for NIP-55 (#18)

Reviewed-on: https://git.reya.su/reya/coop-mobile/pulls/18

shared/src/commonMain/kotlin/su/reya/coop/ExternalSignerProxy.kt

@@ -0,0 +1,40 @@
+package su.reya.coop
+
+import rust.nostr.sdk.AsyncNostrSigner
+import rust.nostr.sdk.Event
+import rust.nostr.sdk.PublicKey
+import rust.nostr.sdk.UnsignedEvent
+
+class ExternalSignerProxy(
+    private val handler: ExternalSignerHandler,
+    private val currentUser: PublicKey,
+) : AsyncNostrSigner {
+    override suspend fun getPublicKeyAsync(): PublicKey {
+        return currentUser
+    }
+
+    override suspend fun signEventAsync(unsignedEvent: UnsignedEvent): Event? {
+        val signedJson = handler.signEvent(unsignedEvent, currentUser) ?: return null
+        return Event.fromJson(signedJson)
+    }
+
+    override suspend fun nip04EncryptAsync(publicKey: PublicKey, content: String): String {
+        return handler.nip04Encrypt(content, publicKey)
+            ?: throw Exception("NIP-04 encrypt rejected")
+    }
+
+    override suspend fun nip04DecryptAsync(publicKey: PublicKey, encryptedContent: String): String {
+        return handler.nip04Decrypt(encryptedContent, publicKey)
+            ?: throw Exception("NIP-04 decrypt rejected")
+    }
+
+    override suspend fun nip44EncryptAsync(publicKey: PublicKey, content: String): String {
+        return handler.nip44Encrypt(content, publicKey, currentUser)
+            ?: throw Exception("NIP-44 encrypt rejected")
+    }
+
+    override suspend fun nip44DecryptAsync(publicKey: PublicKey, payload: String): String {
+        return handler.nip44Decrypt(payload, publicKey, currentUser)
+            ?: throw Exception("NIP-44 decrypt rejected")
+    }
+}