Add HTTP API

Add `-api` mode to start the HTTP API with the following routes:
- /health
- /shops
- /shops/:id
- /products
- /products/:id

Signed-off-by: Julien Riou <julien@riou.xyz>

api.go

@@ -0,0 +1,170 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"strconv"
+	"time"
+
+	"encoding/json"
+
+	"github.com/gorilla/mux"
+	log "github.com/sirupsen/logrus"
+	"gorm.io/gorm"
+)
+
+// StatusWriter to log response status code
+type StatusWriter struct {
+	http.ResponseWriter
+	Status int
+}
+
+// NewStatusResponseWriter to create a new StatusWriter handler for HTTP logging
+func NewStatusResponseWriter(w http.ResponseWriter) *StatusWriter {
+	return &StatusWriter{
+		ResponseWriter: w,
+		Status:         http.StatusOK,
+	}
+}
+
+// WriteHeader to write status code to response
+func (sw *StatusWriter) WriteHeader(code int) {
+	sw.Status = code
+	sw.ResponseWriter.WriteHeader(code)
+}
+
+// LoggingMiddleware to log HTTP requests
+func LoggingMiddleware(r *mux.Router) mux.MiddlewareFunc {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+			start := time.Now()
+			sw := NewStatusResponseWriter(w)
+
+			defer func() {
+				log.Printf("%s %s %v %d %s %s", req.RemoteAddr, req.Method, time.Since(start), sw.Status, req.URL.Path, req.URL.RawQuery)
+			}()
+			next.ServeHTTP(w, req)
+		})
+	}
+}
+
+// handle health checks
+func handleHealth(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "OK")
+}
+
+// shopsHandler to expose shops over HTTP with a database connection
+type shopsHandler struct {
+	db *gorm.DB
+}
+
+// ServeHTTP to implement the handle interface for serving shops
+func (h *shopsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	var shops []Shop
+	trx := h.db.Find(&shops)
+	if trx.Error == nil {
+		w.WriteHeader(http.StatusOK)
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(shops)
+	} else {
+		w.WriteHeader(http.StatusInternalServerError)
+	}
+}
+
+// shopHandler to expose shops over HTTP with a database connection
+type shopHandler struct {
+	db *gorm.DB
+}
+
+// ServeHTTP to implement the handle interface for serving shop
+func (h *shopHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	vars := mux.Vars(r)
+	id := vars["id"]
+
+	var shop Shop
+	trx := h.db.First(&shop, id)
+	if trx.Error == nil {
+		w.WriteHeader(http.StatusOK)
+		json.NewEncoder(w).Encode(shop)
+	} else {
+		w.WriteHeader(http.StatusInternalServerError)
+	}
+}
+
+// productsHandler to expose products over HTTP with a database connection
+type productsHandler struct {
+	db *gorm.DB
+}
+
+// ServeHTTP to implement the handle interface for serving products
+func (h *productsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	var products []Product
+	var trx *gorm.DB
+	availableFilter := r.URL.Query().Get("available")
+
+	if availableFilter != "" {
+		available, err := strconv.ParseBool(availableFilter)
+		if err != nil {
+			log.Warnf("cannot parse available query to boolean: %s", err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		} else {
+			trx = h.db.Preload("Shop").Where(map[string]interface{}{"available": available}).Find(&products)
+		}
+	} else {
+		trx = h.db.Preload("Shop").Find(&products)
+	}
+
+	if trx.Error == nil {
+		w.WriteHeader(http.StatusOK)
+		json.NewEncoder(w).Encode(products)
+	} else {
+		w.WriteHeader(http.StatusInternalServerError)
+	}
+}
+
+// productHandler to expose product over HTTP with a database connection
+type productHandler struct {
+	db *gorm.DB
+}
+
+// ServeHTTP to implement the handle interface for serving product
+func (h *productHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	id := vars["id"]
+
+	var product Product
+	trx := h.db.Preload("Shop").First(&product, id)
+	if trx.Error == nil {
+		w.WriteHeader(http.StatusOK)
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(product)
+	} else {
+		w.WriteHeader(http.StatusInternalServerError)
+	}
+}
+
+// StartAPI to handle HTTP requests
+func StartAPI(db *gorm.DB, config ApiConfig) error {
+	router := mux.NewRouter().StrictSlash(true)
+
+	router.Path("/health").HandlerFunc(handleHealth)
+
+	router.Path("/shops").Handler(&shopsHandler{db: db})
+	router.Path("/shops/{id:[0-9]+}").Handler(&shopHandler{db: db})
+
+	router.Path("/products").Handler(&productsHandler{db: db})
+	router.Path("/products/{id:[0-9]+}").Handler(&productHandler{db: db})
+
+	// register middlewares
+	router.Use(LoggingMiddleware(router))
+
+	log.Printf("starting API on %s", config.Address)
+	if config.Certfile != "" && config.Keyfile != "" {
+		return http.ListenAndServeTLS(config.Address, config.Certfile, config.Keyfile, router)
+	} else {
+		return http.ListenAndServe(config.Address, router)
+	}
+}