Follow up from https://github.com/garronej/github_actions_toolkit

src/tools/octokit-addons/getCommonOrigin.ts

@@ -0,0 +1,90 @@
+
+import { getCommitAsyncIterableFactory } from "./getCommitAsyncIterable";
+import type { Octokit } from "@octokit/rest";
+
+/** Return the sha of the first common commit between two branches */
+export function getCommonOriginFactory(params: { octokit: Octokit; }) {
+
+    const { octokit } = params;
+
+    const { getCommitAsyncIterable } = getCommitAsyncIterableFactory({ octokit });
+
+    async function getCommonOrigin(
+        params: {
+            owner: string;
+            repo: string;
+            branch1: string;
+            branch2: string;
+        }
+    ): Promise<{ sha: string; }> {
+
+        const { owner, repo, branch1, branch2 } = params;
+
+        const [
+            commitAsyncIterable1,
+            commitAsyncIterable2
+        ] = ([branch1, branch2] as const)
+            .map(branch => getCommitAsyncIterable({ owner, repo, branch }))
+            ;
+
+
+        let shas1: string[] = [];
+        let shas2: string[] = [];
+
+        while (true) {
+
+            const [
+                itRes1,
+                itRes2
+            ] =
+                await Promise.all(
+                    ([commitAsyncIterable1, commitAsyncIterable2] as const)
+                        .map(
+                            commitAsyncIterable => commitAsyncIterable[Symbol.asyncIterator]()
+                                .next()
+                        )
+                )
+                ;
+
+            let sha1: string | undefined = undefined;
+
+            if (!itRes1.done) {
+
+                sha1 = itRes1.value.sha;
+
+                shas1.push(sha1);
+
+            }
+
+            let sha2: string | undefined = undefined;
+
+            if (!itRes2.done) {
+
+                sha2 = itRes2.value.sha;
+
+                shas2.push(sha2);
+
+            }
+
+            if (!!sha1 && shas2.includes(sha1)) {
+                return { "sha": sha1 };
+            }
+
+            if (!!sha2 && shas1.includes(sha2)) {
+                return { "sha": sha2 };
+            }
+
+            if (itRes1.done && itRes2.done) {
+                throw new Error("No common origin");
+            }
+
+
+        }
+
+
+    }
+
+    return { getCommonOrigin };
+
+
+}