platform: modularize api/gui, add docs-tests-web foundation, and refresh root config

selective-vpn-api/app/resolver/dns_upstreams.go

@@ -0,0 +1,57 @@
+package resolver
+
+import "strings"
+
+func BuildResolverFallbackPool(raw string, fallbackDefaults []string, normalize func(string) string) []string {
+	switch strings.ToLower(strings.TrimSpace(raw)) {
+	case "off", "none", "0":
+		return nil
+	}
+
+	candidates := fallbackDefaults
+	if strings.TrimSpace(raw) != "" {
+		candidates = nil
+		fields := strings.FieldsFunc(raw, func(r rune) bool {
+			return r == ',' || r == ';' || r == ' ' || r == '\n' || r == '\t'
+		})
+		for _, f := range fields {
+			if normalize == nil {
+				continue
+			}
+			if n := normalize(f); n != "" {
+				candidates = append(candidates, n)
+			}
+		}
+	}
+	return UniqueStrings(candidates)
+}
+
+func MergeDNSUpstreamPools(primary, fallback []string, maxUpstreams int, normalize func(string) string) []string {
+	if maxUpstreams < 1 {
+		maxUpstreams = 1
+	}
+	out := make([]string, 0, len(primary)+len(fallback))
+	seen := map[string]struct{}{}
+	add := func(items []string) {
+		for _, item := range items {
+			if len(out) >= maxUpstreams {
+				return
+			}
+			if normalize == nil {
+				continue
+			}
+			n := normalize(item)
+			if n == "" {
+				continue
+			}
+			if _, ok := seen[n]; ok {
+				continue
+			}
+			seen[n] = struct{}{}
+			out = append(out, n)
+		}
+	}
+	add(primary)
+	add(fallback)
+	return out
+}