refactor(storage): new storage file structure

- new directory structure containing manifest.json and one json file per provider, by default.
- the manifest.json file can specify a filepath for each vpn provider
- each vpn provider json data file can contain the `"preferred": true` field to enforce it is used even if outdated, unless there is a version mismatch
- `STORAGE_SERVERS_DIRECTORY_PATH` replaces `STORAGE_FILEPATH` (which is now a migration source only). It sets the directory where server manifest and per-provider JSON files are stored (default: `/gluetun/servers/`).
- First-run migration: On startup, gluetun checks for the old /gluetun/servers.json file; if found and no new manifest exists, it automatically migrates all data to /gluetun/servers/ directory structure
- Silent fallback: If legacy file isn't found, uses the new directory path normally
- Legacy cleanup: After successful migration, attempts to remove the old fat JSON file (logs warning only if removal fails, e.g., read-only bind mounts)

gluetun-servers/pkg/updaters/providers/purevpn/parse.go

@@ -0,0 +1,65 @@
+package purevpn
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/qdm12/gluetun-servers/pkg/constants"
+)
+
+var countryCodeToName = constants.CountryCodes() //nolint:gochecknoglobals
+
+//nolint:gochecknoglobals
+var countryCityCodeToCityName = map[string]string{
+	"aume":  "Melbourne",
+	"aupe":  "Perth",
+	"ausd":  "Sydney",
+	"ukl":   "London",
+	"ukm":   "Manchester",
+	"usca":  "Los Angeles",
+	"usfl":  "Miami",
+	"usga":  "Atlanta",
+	"usil":  "Chicago",
+	"usnj":  "Newark",
+	"usny":  "New York",
+	"uspe":  "Perth",
+	"usphx": "Phoenix",
+	"ussa":  "Seattle",
+	"ussf":  "San Francisco",
+	"ustx":  "Houston",
+	"usut":  "Salt Lake City",
+	"usva":  "Ashburn",
+	"uswdc": "Washington DC",
+}
+
+func parseHostname(hostname string) (country, city string, warnings []string) {
+	const minHostnameLength = 2 + 3 + 2 // 2 country code + 3 city code + "2-"
+	if len(hostname) < minHostnameLength {
+		warnings = append(warnings,
+			fmt.Sprintf("hostname %q is too short to parse country and city codes", hostname))
+	}
+	countryCode := strings.ToLower(hostname[0:2])
+	country, ok := countryCodeToName[countryCode]
+	if !ok {
+		warnings = append(warnings, fmt.Sprintf("unknown country code %q in hostname %q",
+			countryCode, hostname))
+	}
+
+	twoMinusIndex := strings.Index(hostname, "2-")
+	switch twoMinusIndex {
+	case -1:
+		warnings = append(warnings,
+			fmt.Sprintf("hostname %q does not contain '2-'", hostname))
+		return country, city, warnings
+	case 2: //nolint:mnd
+		// no city code
+		return country, "", warnings
+	}
+	countryCityCode := strings.ToLower(hostname[:twoMinusIndex])
+	city, ok = countryCityCodeToCityName[countryCityCode]
+	if !ok {
+		warnings = append(warnings, fmt.Sprintf("unknown country-city code %q in hostname %q",
+			countryCityCode, hostname))
+	}
+	return country, city, warnings
+}