phase 3 initial completion

internal/api/handlers/repos.go

@@ -169,6 +169,31 @@ func (h *RepoHandler) Commits(w http.ResponseWriter, r *http.Request) {
 	jsonOK(w, commits)
 }
 
+func (h *RepoHandler) Diff(w http.ResponseWriter, r *http.Request) {
+	repo, ok := h.lookupRepo(w, r)
+	if !ok {
+		return
+	}
+
+	base := r.URL.Query().Get("base")
+	head := r.URL.Query().Get("head")
+	if base == "" || head == "" {
+		jsonError(w, "base and head query params are required", http.StatusBadRequest)
+		return
+	}
+
+	gitdomain.SetRepoRoot(h.cfg.RepoRoot)
+	diffs, err := gitdomain.Diff(repo.DiskPath, base, head)
+	if err != nil {
+		jsonError(w, "could not compute diff", http.StatusInternalServerError)
+		return
+	}
+	if diffs == nil {
+		diffs = []gitdomain.FileDiff{}
+	}
+	jsonOK(w, diffs)
+}
+
 // lookupRepo resolves {owner}/{repo} URL params to a DB row, enforcing access.
 func (h *RepoHandler) lookupRepo(w http.ResponseWriter, r *http.Request) (*models.Repository, bool) {
 	ownerName := chi.URLParam(r, "owner")

internal/api/router.go

@@ -77,6 +77,7 @@ func New(cfg *config.Config, engine *xorm.Engine, store sessions.Store, staticFi
 					r.Get("/tree", repoH.Tree)
 					r.Get("/blob", repoH.Blob)
 					r.Get("/commits", repoH.Commits)
+					r.Get("/diff", repoH.Diff)
 					r.Route("/pulls", func(r chi.Router) {
 						r.Get("/", prH.List)
 						r.With(csrf).Post("/", prH.Create)

internal/domain/git/binary.go

@@ -138,3 +138,67 @@ func TreeLS(repoPath, ref, subPath string) ([]TreeEntry, error) {
 func BlobCat(repoPath, ref, filePath string) ([]byte, error) {
 	return run(repoPath, "show", ref+":"+filePath)
 }
+
+// FileDiff represents a single changed file in a diff.
+type FileDiff struct {
+	Path      string `json:"path"`
+	OldPath   string `json:"oldPath,omitempty"` // set on renames
+	Additions int    `json:"additions"`
+	Deletions int    `json:"deletions"`
+	Patch     string `json:"patch"` // unified diff hunk(s) for this file
+}
+
+// Diff returns per-file diffs between two refs.
+func Diff(repoPath, base, head string) ([]FileDiff, error) {
+	out, err := run(repoPath,
+		"diff", "--unified=5", "--no-color",
+		"--diff-filter=ACDMRT", // exclude untracked
+		base+".."+head,
+	)
+	if err != nil {
+		return nil, err
+	}
+	return parseUnifiedDiff(string(out)), nil
+}
+
+// parseUnifiedDiff splits a multi-file unified diff into per-file FileDiff entries.
+func parseUnifiedDiff(raw string) []FileDiff {
+	var files []FileDiff
+	var cur *FileDiff
+	var patchLines []string
+
+	commit := func() {
+		if cur != nil {
+			cur.Patch = strings.Join(patchLines, "\n")
+			files = append(files, *cur)
+		}
+	}
+
+	for _, line := range strings.Split(raw, "\n") {
+		if strings.HasPrefix(line, "diff --git ") {
+			commit()
+			cur = &FileDiff{}
+			patchLines = nil
+			continue
+		}
+		if cur == nil {
+			continue
+		}
+		switch {
+		case strings.HasPrefix(line, "--- a/"):
+			cur.OldPath = strings.TrimPrefix(line, "--- a/")
+		case strings.HasPrefix(line, "+++ b/"):
+			cur.Path = strings.TrimPrefix(line, "+++ b/")
+		case strings.HasPrefix(line, "+") && !strings.HasPrefix(line, "+++"):
+			cur.Additions++
+			patchLines = append(patchLines, line)
+		case strings.HasPrefix(line, "-") && !strings.HasPrefix(line, "---"):
+			cur.Deletions++
+			patchLines = append(patchLines, line)
+		default:
+			patchLines = append(patchLines, line)
+		}
+	}
+	commit()
+	return files
+}