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

selective-vpn-api/app/vpn_locations_cache.go

@@ -0,0 +1,51 @@
+package app
+
+import (
+	"sync"
+	"time"
+)
+
+const (
+	vpnLocationsCommandTimeout = 7 * time.Second
+	vpnLocationsFreshTTL       = 10 * time.Minute
+	vpnLocationsBackoffMin     = 2 * time.Second
+	vpnLocationsBackoffMax     = 60 * time.Second
+	vpnLocationsCachePath      = stateDir + "/vpn-locations-cache.json"
+)
+
+type vpnLocationItem struct {
+	Label  string `json:"label"`
+	ISO    string `json:"iso"`
+	Target string `json:"target,omitempty"`
+}
+
+type vpnLocationsSnapshot struct {
+	Locations         []vpnLocationItem `json:"locations"`
+	UpdatedAt         string            `json:"updated_at,omitempty"`
+	Stale             bool              `json:"stale"`
+	RefreshInProgress bool              `json:"refresh_in_progress"`
+	LastError         string            `json:"last_error,omitempty"`
+	NextRetryAt       string            `json:"next_retry_at,omitempty"`
+}
+
+type vpnLocationsCacheDisk struct {
+	Locations []vpnLocationItem `json:"locations"`
+	UpdatedAt string            `json:"updated_at,omitempty"`
+}
+
+type vpnLocationsStore struct {
+	mu sync.Mutex
+
+	loaded bool
+
+	locations []vpnLocationItem
+	swr       refreshCoordinator
+}
+
+var vpnLocationCache = &vpnLocationsStore{
+	swr: newRefreshCoordinator(
+		vpnLocationsFreshTTL,
+		vpnLocationsBackoffMin,
+		vpnLocationsBackoffMax,
+	),
+}