swarm-controller: count default-branch merges and lines per repo

swarm-controller/src/forge.rs

@@ -132,6 +132,28 @@ fn merge_base_of(commits: &[forgejo_api::structs::Commit]) -> Option<String> {
     }
 }
 
+/// Lines added and deleted, as [`Client::compare_line_stats`] sums them.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub struct LineStats {
+    pub added: u64,
+    pub deleted: u64,
+}
+
+/// `commits`' per-commit stats summed; a negative or missing figure is zero.
+fn line_stats(commits: &[forgejo_api::structs::Commit]) -> LineStats {
+    let sum = |pick: fn(&forgejo_api::structs::CommitStats) -> Option<i64>| -> u64 {
+        commits
+            .iter()
+            .filter_map(|c| c.stats.as_ref().and_then(pick))
+            .map(|n| u64::try_from(n).unwrap_or(0))
+            .sum()
+    };
+    LineStats {
+        added: sum(|s| s.additions),
+        deleted: sum(|s| s.deletions),
+    }
+}
+
 /// `pulls` as the dropdown's rows, newest (highest number) first. A PR
 /// without a usable number cannot be named, so it is left out.
 fn open_pulls(pulls: Vec<forgejo_api::structs::PullRequest>) -> Vec<OpenPull> {
@@ -1179,6 +1201,28 @@ impl Client {
         Ok(open_pulls(pulls))
     }
 
+    /// Lines added and deleted by the commits `before..after` of
+    /// `owner/repo`, summed over the per-commit stats the forge's compare
+    /// returns. A commit the forge sent no stats for counts as zero.
+    ///
+    /// The sum is over commits, not a net diff of the two endpoints: a line
+    /// one commit adds and a later one removes counts once in each total.
+    pub async fn compare_line_stats(
+        &self,
+        owner: &str,
+        repo: &str,
+        before: &str,
+        after: &str,
+    ) -> Result<LineStats> {
+        let basehead = format!("{before}...{after}");
+        let compare = self
+            .api
+            .call(|api| api.repo_compare_diff(owner, repo, &basehead).into_future())
+            .await
+            .with_context(|| format!("compare {basehead} in {owner}/{repo}"))?;
+        Ok(line_stats(compare.commits.as_deref().unwrap_or_default()))
+    }
+
     /// Every open issue in `owner/repo`, each with its dependency-derived
     /// `blocked` / `depended_on_by_count` pre-resolved server-side — the
     /// whole job behind `GET /api/repos/{org}/{repo}/issue-report`. Doing
@@ -2228,6 +2272,25 @@ impl Client {
 #[cfg(test)]
 mod tests {
     use super::*;
+    /// Commit stats sum per side; a commit with none, or a negative figure,
+    /// adds zero.
+    #[test]
+    fn compare_stats_sum_across_commits() {
+        let commit = |stats: Option<(i64, i64)>| {
+            serde_json::from_value::<forgejo_api::structs::Commit>(serde_json::json!({
+                "stats": stats.map(|(a, d)| serde_json::json!({"additions": a, "deletions": d})),
+            }))
+            .expect("commit parses")
+        };
+        let got = line_stats(&[commit(Some((5, 2))), commit(None), commit(Some((-1, 4)))]);
+        assert_eq!(
+            got,
+            LineStats {
+                added: 5,
+                deleted: 6
+            }
+        );
+    }
 
     /// The event list each swarm hook is registered with, as Forgejo names
     /// the event types (`modules/webhook/type.go`).