Initial commit

internal/web/pagination.go

@@ -0,0 +1,81 @@
+package web
+
+import (
+	"net/http"
+	"net/url"
+	"strconv"
+)
+
+const defaultCollectionPageSize = 20
+
+type paginationData struct {
+	Page        int
+	TotalPages  int
+	PreviousURL string
+	NextURL     string
+}
+
+func paginateCollection[T any](r *http.Request, values []T) ([]T, *paginationData) {
+	pageSize := collectionPageSize(r)
+	totalPages := (len(values) + pageSize - 1) / pageSize
+	if totalPages <= 1 {
+		return values, nil
+	}
+
+	page, _ := strconv.Atoi(r.URL.Query().Get("page"))
+	if page < 1 {
+		page = 1
+	}
+	if page > totalPages {
+		page = totalPages
+	}
+	start := (page - 1) * pageSize
+	end := min(start+pageSize, len(values))
+	pagination := &paginationData{Page: page, TotalPages: totalPages}
+	if page > 1 {
+		pagination.PreviousURL = collectionPageURL(r.URL, page-1)
+	}
+	if page < totalPages {
+		pagination.NextURL = collectionPageURL(r.URL, page+1)
+	}
+	return values[start:end], pagination
+}
+
+func collectionPageSize(r *http.Request) int {
+	userSuffix := ""
+	if user, ok := userFromContext(r.Context()); ok {
+		userSuffix = "." + strconv.Itoa(user.ID)
+	}
+	for _, cookieName := range []string{"gardomatic.entries-per-page" + userSuffix, "gardomatic.tasks-per-page" + userSuffix} {
+		cookie, err := r.Cookie(cookieName)
+		if err != nil {
+			continue
+		}
+		pageSize, err := strconv.Atoi(cookie.Value)
+		if err == nil && validCollectionPageSize(pageSize) {
+			return pageSize
+		}
+	}
+	return defaultCollectionPageSize
+}
+
+func validCollectionPageSize(pageSize int) bool {
+	switch pageSize {
+	case 10, 20, 50, 100:
+		return true
+	default:
+		return false
+	}
+}
+
+func collectionPageURL(current *url.URL, page int) string {
+	query := current.Query()
+	query.Set("page", strconv.Itoa(page))
+	path := current.Path
+	if path == "" {
+		path = "?"
+	} else {
+		path += "?"
+	}
+	return path + query.Encode()
+}