1 files changed, 36 insertions, 1 deletions

diff --git a/src/document/signatures.rs b/src/document/signatures.rs
index e92cf9c..c8af89a 100644
--- a/src/document/signatures.rs
+++ b/src/document/signatures.rs
@@ -154,13 +154,42 @@ impl<'de> serde::Deserialize<'de> for SignEvery {
 #[derive(Debug, Default)]
 pub(crate) struct Signatures {
     by_change: HashMap<ChangeHash, [u8; 64]>,
+    /// The changes signed, in the order their signatures came: the document file
+    /// appends those after the ones it wrote (`since`).
+    order: Vec<ChangeHash>,
     /// This node's latest change, if no signature vouches for it yet (`SignEvery`).
     unsigned: Option<ChangeHash>,
 }
 
 impl Signatures {
+    /// Signatures kept before, as `since` gave them (the document file).
+    pub(crate) fn from_kept(kept: Vec<(ChangeHash, [u8; 64])>) -> Self {
+        let mut signatures = Self::default();
+        for (hash, signature) in kept {
+            signatures.insert(hash, signature);
+        }
+        signatures
+    }
+
     pub(crate) fn insert(&mut self, hash: ChangeHash, signature: [u8; 64]) {
-        self.by_change.insert(hash, signature);
+        if self.by_change.insert(hash, signature).is_none() {
+            self.order.push(hash);
+        }
+    }
+
+    /// How many signatures there are.
+    pub(crate) fn count(&self) -> usize {
+        self.order.len()
+    }
+
+    /// The signatures after the first `count` (`count`), in the order they came.
+    pub(crate) fn since(&self, count: usize) -> Vec<(ChangeHash, [u8; 64])> {
+        self.order
+            .get(count..)
+            .unwrap_or_default()
+            .iter()
+            .map(|hash| (*hash, self.by_change[hash]))
+            .collect()
     }
 
     /// Signs `hash`, this node's latest change, with `key` and keeps the signature: it
@@ -286,6 +315,12 @@ mod tests {
         signatures.left_unsigned(a);
         signatures.sign(b, &key);
         assert!(!signatures.sign_latest(&key));
+        // Kept in the order they came, each once.
+        assert_eq!(signatures.count(), 2);
+        assert_eq!(signatures.since(1)[0].0, b);
+        assert!(signatures.since(5).is_empty());
+        let again = Signatures::from_kept(signatures.since(0));
+        assert_eq!(again.since(0), signatures.since(0));
     }
 
     /// Protocol data, listed paths (within or above them) and asked-for writes are