fix: technical debts left by the Sites, Authors and SEO slices, plus backend support for the new Sites and Authors pagination

api/handlers/site/siteHandler.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"log"
 	"net/http"
+	"net/url"
 	"strconv"
 
 	"github.com/go-chi/chi/v5"
@@ -135,17 +136,60 @@ func writeSiteError(w http.ResponseWriter, err error) {
 	}
 }
 
-func (h *Handler) List(w http.ResponseWriter, _ *http.Request) {
-	sites, err := h.ListUseCase.List()
+const (
+	defaultListPage = 1
+	defaultListSize = 25
+)
+
+type listQuery struct {
+	Page int    `validate:"gte=1"`
+	Size int    `validate:"omitempty,oneof=5 25 50 100"`
+	Q    string `validate:"max=200"`
+}
+
+func intQueryParam(values url.Values, name string, fallback int) (int, error) {
+	if !values.Has(name) {
+		return fallback, nil
+	}
+	return strconv.Atoi(values.Get(name))
+}
+
+func readListQuery(values url.Values) (listQuery, error) {
+	paged := values.Has("page") || values.Has("size")
+	page, err := intQueryParam(values, "page", defaultListPage)
+	if err != nil {
+		return listQuery{}, err
+	}
+	size := 0
+	if paged {
+		size, err = intQueryParam(values, "size", defaultListSize)
+		if err != nil {
+			return listQuery{}, err
+		}
+		if size == 0 {
+			return listQuery{}, errors.New("invalid size")
+		}
+	}
+	return listQuery{Page: page, Size: size, Q: values.Get("q")}, nil
+}
+
+func (h *Handler) List(w http.ResponseWriter, r *http.Request) {
+	query, err := readListQuery(r.URL.Query())
+	if err != nil || validator.Validate.Struct(query) != nil {
+		http.Error(w, apperr.BodyErrorMessage, http.StatusBadRequest)
+		return
+	}
+	page, err := h.ListUseCase.ListPage(useCases.ListSitesCommand{Q: query.Q, Page: query.Page, Size: query.Size})
 	if err != nil {
 		http.Error(w, "Internal server error", http.StatusInternalServerError)
 		return
 	}
-	body, err := json.Marshal(sites)
+	body, err := json.Marshal(page.Items)
 	if err != nil {
 		http.Error(w, "Failed to encode response", http.StatusInternalServerError)
 		return
 	}
+	w.Header().Set("X-Total-Count", strconv.Itoa(page.Total))
 	if _, err := w.Write(body); err != nil {
 		log.Printf("Failed to write response: %v", err)
 	}