Feature 01 task 1: Go module, fail-fast config and /health (#2)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

internal/server/server.go

@@ -0,0 +1,67 @@
+// Package server builds the MealQuest HTTP router.
+package server
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+)
+
+// NewRouter returns the HTTP handler for the service. version is reported by
+// GET /health.
+func NewRouter(logger *slog.Logger, version string) http.Handler {
+	r := chi.NewRouter()
+	r.Get("/health", health(logger, version))
+	r.MethodNotAllowed(apiErrorHandler(logger, http.StatusMethodNotAllowed, "method_not_allowed", "method not allowed"))
+	r.NotFound(apiErrorHandler(logger, http.StatusNotFound, "not_found", "not found"))
+	return r
+}
+
+type errorBody struct {
+	Error apiError `json:"error"`
+}
+
+type apiError struct {
+	Code      string `json:"code"`
+	Message   string `json:"message"`
+	Retryable bool   `json:"retryable"`
+}
+
+// apiErrorHandler responds with status and a fixed, non-retryable API error.
+func apiErrorHandler(logger *slog.Logger, status int, code, message string) http.HandlerFunc {
+	body, err := json.Marshal(errorBody{Error: apiError{
+		Code:    code,
+		Message: message,
+	}})
+	if err != nil {
+		panic(err) // fixed string and bool fields cannot fail to marshal
+	}
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(status)
+		if _, err := w.Write(body); err != nil {
+			logger.WarnContext(r.Context(), "write error response", "code", code, "error", err)
+		}
+	}
+}
+
+type healthResponse struct {
+	Status  string `json:"status"`
+	Version string `json:"version"`
+}
+
+func health(logger *slog.Logger, version string) http.HandlerFunc {
+	body, err := json.Marshal(healthResponse{Status: "ok", Version: version})
+	if err != nil {
+		panic(err) // two string fields cannot fail to marshal
+	}
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		if _, err := w.Write(body); err != nil {
+			logger.WarnContext(r.Context(), "write health response", "error", err)
+		}
+	}
+}