From f611f54cadfebc80da34a8c735c7464a69cfbfc9 Mon Sep 17 00:00:00 2001
From: Paul Schaub <vanitasvitae@fsfe.org>
Date: Wed, 24 Jan 2024 11:27:35 +0100
Subject: [PATCH] Add SignatureSubpacketCallback.then()

---
 .../subpackets/SignatureSubpacketCallback.kt  | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/pgpainless-core/src/main/kotlin/org/pgpainless/signature/subpackets/SignatureSubpacketCallback.kt b/pgpainless-core/src/main/kotlin/org/pgpainless/signature/subpackets/SignatureSubpacketCallback.kt
index fbc56035..53760d92 100644
--- a/pgpainless-core/src/main/kotlin/org/pgpainless/signature/subpackets/SignatureSubpacketCallback.kt
+++ b/pgpainless-core/src/main/kotlin/org/pgpainless/signature/subpackets/SignatureSubpacketCallback.kt
@@ -23,4 +23,24 @@ interface SignatureSubpacketCallback<S : BaseSignatureSubpackets> {
     fun modifyUnhashedSubpackets(unhashedSubpackets: S) {
         // Empty default implementation to allow for cleaner overriding
     }
+
+    /**
+     * Return a new [SignatureSubpacketCallback] which first applies the current callback instance,
+     * followed by the passed in [nextCallback].
+     * This is useful to composite different [SignatureSubpacketCallback] instances.
+     */
+    fun then(nextCallback: SignatureSubpacketCallback<S>): SignatureSubpacketCallback<S> {
+        val currCallback = this
+        return object : SignatureSubpacketCallback<S> {
+            override fun modifyHashedSubpackets(hashedSubpackets: S) {
+                currCallback.modifyHashedSubpackets(hashedSubpackets)
+                nextCallback.modifyHashedSubpackets(hashedSubpackets)
+            }
+
+            override fun modifyUnhashedSubpackets(unhashedSubpackets: S) {
+                currCallback.modifyUnhashedSubpackets(unhashedSubpackets)
+                nextCallback.modifyUnhashedSubpackets(unhashedSubpackets)
+            }
+        }
+    }
 }