From e1357392b20ae02ac1748508cae667c09bdf09ab Mon Sep 17 00:00:00 2001
From: Anirudh Oppiliappan <x@icyphox.sh>
Date: Wed, 16 Apr 2025 14:48:38 +0300
Subject: [PATCH] knotserver: git: format-patch for ref comparisons

---
 knotserver/git/diff.go | 31 +++++++++++++++++++++++++++++++
 knotserver/routes.go   |  9 +++++++--
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/knotserver/git/diff.go b/knotserver/git/diff.go
index 3ee87b9..dffa54c 100644
--- a/knotserver/git/diff.go
+++ b/knotserver/git/diff.go
@@ -1,13 +1,17 @@
 package git
 
 import (
+	"bytes"
 	"fmt"
 	"log"
+	"os"
+	"os/exec"
 	"strings"
 
 	"github.com/bluekeyes/go-gitdiff/gitdiff"
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/object"
+	"tangled.sh/tangled.sh/core/patchutil"
 	"tangled.sh/tangled.sh/core/types"
 )
 
@@ -120,6 +124,33 @@ func (g *GitRepo) DiffTree(commit1, commit2 *object.Commit) (*types.DiffTree, er
 	}, nil
 }
 
+// FormatPatch generates a git-format-patch output between two commits,
+// and returns the raw format-patch series, a parsed FormatPatch and an error.
+func (g *GitRepo) FormatPatch(base, commit2 *object.Commit) (string, []patchutil.FormatPatch, error) {
+	var stdout bytes.Buffer
+	cmd := exec.Command(
+		"git",
+		"-C",
+		g.path,
+		"format-patch",
+		fmt.Sprintf("%s..%s", base.Hash.String(), commit2.Hash.String()),
+		"--stdout",
+	)
+	cmd.Stdout = &stdout
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	if err != nil {
+		return "", nil, err
+	}
+
+	formatPatch, err := patchutil.ExtractPatches(stdout.String())
+	if err != nil {
+		return "", nil, err
+	}
+
+	return stdout.String(), formatPatch, nil
+}
+
 func (g *GitRepo) MergeBase(commit1, commit2 *object.Commit) (*object.Commit, error) {
 	isAncestor, err := commit1.IsAncestor(commit2)
 	if err != nil {
diff --git a/knotserver/routes.go b/knotserver/routes.go
index 33408b0..9b6cd47 100644
--- a/knotserver/routes.go
+++ b/knotserver/routes.go
@@ -808,14 +808,19 @@ func (h *Handle) Compare(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	difftree, err := gr.DiffTree(mergeBase, commit2)
+	rawPatch, formatPatch, err := gr.FormatPatch(mergeBase, commit2)
 	if err != nil {
 		l.Error("error comparing revisions", "msg", err.Error())
 		writeError(w, "error comparing revisions", http.StatusBadRequest)
 		return
 	}
 
-	writeJSON(w, types.RepoDiffTreeResponse{difftree})
+	writeJSON(w, types.RepoFormatPatchResponse{
+		Rev1:        commit1.Hash.String(),
+		Rev2:        commit2.Hash.String(),
+		FormatPatch: formatPatch,
+		Patch:       rawPatch,
+	})
 	return
 }
 
-- 
2.54.0