backend barebone done, big chunk of work done

server/internal/api/respond.go

@@ -0,0 +1,33 @@
+// Package api implements the HTTP handlers for the messenger REST API.
+package api
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"messenger/internal/store"
+)
+
+func writeJSON(w http.ResponseWriter, status int, body any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	if err := json.NewEncoder(w).Encode(body); err != nil {
+		http.Error(w, `{"error":"failed to encode response"}`, http.StatusInternalServerError)
+	}
+}
+
+func writeError(w http.ResponseWriter, status int, message string) {
+	writeJSON(w, status, map[string]string{"error": message})
+}
+
+func writeStoreError(w http.ResponseWriter, err error) {
+	switch {
+	case errors.Is(err, store.ErrNotFound):
+		writeError(w, http.StatusNotFound, "not found")
+	case errors.Is(err, store.ErrDuplicate):
+		writeError(w, http.StatusConflict, "already exists")
+	default:
+		writeError(w, http.StatusInternalServerError, "internal server error")
+	}
+}