From 619532cd74be787cd9974c28d910db59a7dddadb Mon Sep 17 00:00:00 2001
From: Joseph Goulden <joegoulden@protonmail.com>
Date: Fri, 13 May 2022 15:40:31 +0100
Subject: [PATCH 1/2] feat: Add function to calculate checksum and last word of
 a manually generated mnemonic

---
 src/lib.rs | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index 05963e3..e93b4b6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -529,6 +529,28 @@ impl Mnemonic {
 		let (arr, len) = self.to_entropy_array();
 		arr[0..len].to_vec()
 	}
+
+	/// Calculates the final word (based on the checksum) of a manually generated mnemonic.
+	/// There are multiple valid checksums, the first one (alphabetically) is picked.
+	#[cfg(feature = "std")]
+	pub fn finalize_mnemonic<'a, S: Into<Cow<'a, str>>>(s: S) -> Result<Mnemonic, Error> {
+		let mut words = s.into();
+		Mnemonic::normalize_utf8_cow(&mut words);
+		let language = Mnemonic::language_of(&words)?;
+
+		for word in language.word_list() {
+			let potential_mnemonic = format!("{} {}", words, word);
+			match Mnemonic::parse_in_normalized(language, &potential_mnemonic) {
+				Ok(mnemonic) => return Ok(mnemonic),
+				Err(e) => match e {
+					Error::InvalidChecksum => {}, // Keep searching.
+					_ => return Err(e)
+				}
+			}
+		}
+		Err(Error::InvalidChecksum)
+	}
+
 }
 
 impl fmt::Display for Mnemonic {
@@ -1023,4 +1045,30 @@ mod tests {
 			assert_eq!(seed, &mnemonic.to_seed(passphrase)[..], "failed vector: {}", mnemonic_str);
 		}
 	}
+
+        #[test]
+	fn test_finalize_mnemonic() {
+		let vectors = [
+			(
+				"ozone drill grab fiber curtain grace pudding thank cruise elder eight",
+				"about"
+			),
+			(
+				"light rule cinnamon wrap drastic word pride squirrel upgrade then income fatal apart sustain crack supply proud",
+				"access"
+			),
+			(
+				"hamster diagram private dutch cause delay private meat slide toddler razor book happy fancy gospel tennis maple dilemma loan word shrug inflict delay",
+				"balance"
+			),
+                        (
+				"あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん",
+                                "あおぞら"
+                        )
+		];
+
+		for vector in &vectors {
+			assert_eq!(Mnemonic::parse(format!("{} {}", vector.0, vector.1)), Mnemonic::finalize_mnemonic(vector.0));
+		}
+	}
 }

From c0b9d39786c7390a9cedb885a5c739525581df95 Mon Sep 17 00:00:00 2001
From: Joseph Goulden <joegoulden@protonmail.com>
Date: Mon, 16 May 2022 11:05:54 +0100
Subject: [PATCH 2/2] fix: simplify match clause in finalize_mnemonic

---
 src/lib.rs | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index e93b4b6..3fd61f3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -542,10 +542,8 @@ impl Mnemonic {
 			let potential_mnemonic = format!("{} {}", words, word);
 			match Mnemonic::parse_in_normalized(language, &potential_mnemonic) {
 				Ok(mnemonic) => return Ok(mnemonic),
-				Err(e) => match e {
-					Error::InvalidChecksum => {}, // Keep searching.
-					_ => return Err(e)
-				}
+				Err(Error::InvalidChecksum) => {}, // Keep searching.
+				Err(e) => return Err(e)
 			}
 		}
 		Err(Error::InvalidChecksum)
@@ -1061,10 +1059,10 @@ mod tests {
 				"hamster diagram private dutch cause delay private meat slide toddler razor book happy fancy gospel tennis maple dilemma loan word shrug inflict delay",
 				"balance"
 			),
-                        (
+			(
 				"あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん　あいこくしん",
-                                "あおぞら"
-                        )
+				"あおぞら"
+			)
 		];
 
 		for vector in &vectors {