Rework sorting to account for parents and date (#12)

Author: cjbarth

CHANGELOG.md

@@ -95,11 +95,11 @@
 - [Update package.json](https://github.com/cjbarth/github-release-notes/commit/f2fea79abb3300381744faed0d11ef539ddf676c) - @cjbarth
 - [Add release-it](https://github.com/cjbarth/github-release-notes/commit/5f4b37dcf1c3bb7a02f5a69b29f989cae803757c) - @cjbarth
 - [Fix tests](https://github.com/cjbarth/github-release-notes/commit/ecceb7ca1d1e80a5ba88b4fbf9863dd673b05bde) - @cjbarth
-- [Track PRs, commits by branch, not date](https://github.com/cjbarth/github-release-notes/commit/acef232efa2f0e66bf5bdd8f28310584fc3b1e7f) - @cjbarth
 - [Fix tests](https://github.com/cjbarth/github-release-notes/commit/718b9aea68980bcdb49a3436414de58ae9832230) - @cjbarth
+- [Correctly compare dates for PR retrieval; fix tests](https://github.com/cjbarth/github-release-notes/commit/0b306da3c19adeef4781a3042488f9b53462fe3a) - @cjbarth
+- [Track PRs, commits by branch, not date](https://github.com/cjbarth/github-release-notes/commit/acef232efa2f0e66bf5bdd8f28310584fc3b1e7f) - @cjbarth
 - [Use commit date as tag date](https://github.com/cjbarth/github-release-notes/commit/ed9fc746a3e7256c8cadb02571e606d0645cb7d9) - @cjbarth
 - [Correctly compare dates for PR retrieval](https://github.com/cjbarth/github-release-notes/commit/e53f9e7f6aff4b32dc3f7e6ccdca1f9d767eaf1a) - @cjbarth
-- [Correctly compare dates for PR retrieval; fix tests](https://github.com/cjbarth/github-release-notes/commit/0b306da3c19adeef4781a3042488f9b53462fe3a) - @cjbarth
 - [Update supported NodeJS versions to current (#291)](https://github.com/cjbarth/github-release-notes/commit/ff0ddae3938db3cfcca5ef317d74eee034c32cc5) - @cjbarth
 - [docs: add viatrix as a contributor (#297)](https://github.com/cjbarth/github-release-notes/commit/8beb6f013cdfe410a0c20cd48291efe4c92a8ace) - @allcontributors[bot]
 - [Return exit code 1 on error for gren changelog (#294)](https://github.com/cjbarth/github-release-notes/commit/69b77665dddb1135a81ce856a7c8edb1003dbc45) - @viatrix

lib/src/Gren.js

@@ -1288,63 +1288,71 @@ class Gren {
         }));
       }
 
-      commits = commits.filter((commit) => branchCommitShas.includes(commit.sha));
-      commits = this._sortCommitsByParent(commits);
-      releaseRange.push(commits);
+      const filteredCommits = commits.filter((commit) => branchCommitShas.includes(commit.sha));
+      const sortedCommits = this._sortCommitsByParent(filteredCommits);
+      releaseRange.push(sortedCommits);
     }
     loadedCommits("Commits acquired");
 
     return dataSource[this.options.dataSource](releaseRanges);
   }
 
   _sortCommitsByParent(commits, dateOrder = "desc") {
-    // 1) Map SHAs -> commit object for O(1) lookups
+    // 1) Map sha -> commit
     const commitMap = new Map(commits.map((c) => [c.sha, c]));
 
-    // 2) Build parent -> [children] adjacency
-    const childrenMap = new Map();
-    for (const commit of commits) {
-      // find the first parent in our set (if any)
-      const parentSha = (commit.parents || []).map((p) => p.sha).find((sha) => commitMap.has(sha));
-      if (parentSha) {
-        if (!childrenMap.has(parentSha)) childrenMap.set(parentSha, []);
-        childrenMap.get(parentSha).push(commit);
+    // 2) Compute parents for each commit
+    const parentMap = new Map();
+    for (const c of commits) {
+      const parentList = (c.parents || []).map((p) => p.sha).filter((sha) => commitMap.has(sha));
+      parentMap.set(c.sha, parentList);
+    }
+
+    // 3) Compute which SHAs appear as a parent -> those that have children
+    const hasChild = new Set();
+    for (const parents of parentMap.values()) {
+      for (const p of parents) {
+        hasChild.add(p);
       }
     }
 
-    // 3) Identify "roots": commits whose first parent is not in our list
-    const roots = commits.filter(
-      (c) => !(c.parents || []).map((p) => p.sha).some((sha) => commitMap.has(sha)),
-    );
+    // 4) Heads = commits that never appear as anyone's parent
+    const heads = commits.filter((c) => !hasChild.has(c.sha)).map((c) => c.sha);
 
-    // 4) Date-based comparator
-    const cmpDate = (a, b) => {
-      const da = new Date(a.committer.date);
-      const db = new Date(b.committer.date);
-      return dateOrder === "asc" ? da - db : db - da;
+    // 5) A helper to compare by newest date
+    const compareDateDesc = (shaA, shaB) => {
+      const da = new Date(
+        commitMap.get(shaA).commit.committer.date || commitMap.get(shaA).commit.author.date,
+      );
+      const db = new Date(
+        commitMap.get(shaB).commit.committer.date || commitMap.get(shaB).commit.author.date,
+      );
+      return db - da;
     };
 
-    // 5) Sort roots by date
-    roots.sort(cmpDate);
-
-    // 6) DFS-like traversal to produce the final list
+    // 6) Candidate pool & result
     const result = [];
-    const visit = (commit) => {
-      result.push(commit);
-      const kids = childrenMap.get(commit.sha) || [];
-      // within the same parent, sort by date too
-      kids.sort(cmpDate);
-      for (const child of kids) {
-        visit(child);
-      }
-    };
+    const seen = new Set();
+    const pool = [...heads];
+
+    while (pool.length) {
+      // pick the newest SHA
+      pool.sort((a, b) => compareDateDesc(a, b));
+      const sha = pool.shift();
 
-    for (const root of roots) {
-      visit(root);
+      if (seen.has(sha)) continue;
+      seen.add(sha);
+
+      // emit that commit
+      result.push(commitMap.get(sha));
+
+      // add its parents to the pool
+      for (const p of parentMap.get(sha) || []) {
+        if (!seen.has(p)) pool.push(p);
+      }
     }
 
-    // This was done parent first, we want the child at the top
-    return result.reverse();
+    return result;
   }
 
   _transformTagsIntoReleaseObjects(tags) {