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")