From 8c8ed4ea8d5695b2417539fbeab81c8cf8b10032 Mon Sep 17 00:00:00 2001
From: Seongmin Lee <git@boltless.me>
Date: Mon, 6 Jul 2026 01:25:06 +0900
Subject: [PATCH] knotmirror/xrpc: `git.getMergeBase`

Signed-off-by: Seongmin Lee <git@boltless.me>
---
 knotmirror/xrpc/git_get_merge_base.go | 57 +++++++++++++++++++++++++++
 knotmirror/xrpc/xrpc.go               |  1 +
 2 files changed, 58 insertions(+)
 create mode 100644 knotmirror/xrpc/git_get_merge_base.go

diff --git a/knotmirror/xrpc/git_get_merge_base.go b/knotmirror/xrpc/git_get_merge_base.go
new file mode 100644
index 00000000..f59722fa
--- /dev/null
+++ b/knotmirror/xrpc/git_get_merge_base.go
@@ -0,0 +1,57 @@
+package xrpc
+
+import (
+	"fmt"
+	"net/http"
+	"os/exec"
+	"strings"
+
+	"github.com/bluesky-social/indigo/atproto/atclient"
+	"github.com/bluesky-social/indigo/atproto/syntax"
+	"tangled.org/core/api/tangled"
+)
+
+func (x *Xrpc) GetMergeBase(w http.ResponseWriter, r *http.Request) {
+	var (
+		repoQuery = r.URL.Query().Get("repo")
+		base      = r.URL.Query().Get("base")
+		head      = r.URL.Query().Get("head")
+	)
+
+	repo, err := syntax.ParseDID(repoQuery)
+	if err != nil {
+		writeJson(w, http.StatusBadRequest, atclient.ErrorBody{Name: "BadRequest", Message: fmt.Sprintf("repo parameter invalid: %s", repoQuery)})
+		return
+	}
+
+	if base == "" {
+		writeJson(w, http.StatusBadRequest, atclient.ErrorBody{Name: "BadRequest", Message: "missing base parameter"})
+		return
+	}
+	if head == "" {
+		writeJson(w, http.StatusBadRequest, atclient.ErrorBody{Name: "BadRequest", Message: "missing head parameter"})
+		return
+	}
+
+	l := x.logger.With("method", "git.getMergeBase", "repo", repo, "base", base, "head", head)
+	l.Debug("request")
+
+	ctx := r.Context()
+
+	repoPath, err := x.makeRepoPath(ctx, repo)
+	if err != nil {
+		writeJson(w, http.StatusNotFound, atclient.ErrorBody{Name: "RepoNotFound", Message: fmt.Sprintf("unknown repository: %q", repo)})
+		return
+	}
+
+	cmd := exec.Command("git", "-C", repoPath, "merge-base", head, base)
+	out, err := cmd.Output()
+	if err != nil {
+		writeJson(w, http.StatusInternalServerError, atclient.ErrorBody{Name: "InternalError", Message: "failed to compute merge-base"})
+		return
+	}
+
+	writeJson(w, http.StatusOK, tangled.GitTempGetMergeBase_Output{
+		Commit: strings.TrimSpace(string(out)),
+	})
+}
diff --git a/knotmirror/xrpc/xrpc.go b/knotmirror/xrpc/xrpc.go
index f6d308bd..aa2ebc6c 100644
--- a/knotmirror/xrpc/xrpc.go
+++ b/knotmirror/xrpc/xrpc.go
@@ -67,6 +67,7 @@ func (x *Xrpc) Router() http.Handler {
 		// r.Get("/"+tangled.GitTempGetDiffNSID, x.GetDiff) // todo
 		r.Get("/"+tangled.GitTempGetEntryNSID, x.GetEntry) // todo
 		// r.Get("/"+tangled.GitTempGetHeadNSID, x.GetHead) // todo
+		r.Get("/"+tangled.GitTempGetMergeBaseNSID, x.GetMergeBase)
 		r.Get("/"+tangled.GitTempGetTagNSID, x.GetTag) // using types.Response
 		r.Get("/"+tangled.GitTempGetTreeNSID, x.GetTree)
 		r.Get("/"+tangled.GitTempListBranchesNSID, x.ListBranches) // wip, unknown output
-- 
2.51.2