settings: continue refactoring internal constants

Settling on naming 'options' for enumerations (...possibly, everything
else in the future, would that make sense to store for 'setting' object)

Update terminal commands that were reporting status to also report a
full list of 'indexed' settings for the specific entity
Also updates the WebUI outputs which are (hopefuly) are already handled
as-is through the .js processing pipeline and the .html properties
receiving certain special string values

More namespacing and save ~2KiB of RAM by reducing the amount of loaded keys strings
However, ROM side of things may suffer b/c of template specializations for the
generic conversion functions when there are many different types involved.

code/espurna/migrate.cpp

@@ -1,8 +1,9 @@
 /*
 
-MIGRATE MODULE
+Part of the SETTINGS MODULE
 
 Copyright (C) 2016-2019 by Xose Pérez <xose dot perez at gmail dot com>
+Copyright (C) 2020-2021 by Maxim Prokhorov <prokhorov dot max at outlook dot com>
 
 */
 
@@ -12,73 +13,84 @@ Copyright (C) 2016-2019 by Xose Pérez <xose dot perez at gmail dot com>
 #include <vector>
 #include <utility>
 
-void delSettingPrefix(const std::initializer_list<const char*>& prefixes) {
+namespace espurna {
+namespace settings {
+namespace schema {
+namespace {
+
+// Configuration version for the internal key-value storage
+// Represented as a 32bit int, updates every time things change
+constexpr static int Version PROGMEM { CFG_VERSION };
+alignas(4) static constexpr char Key[] PROGMEM = "cfg";
+
+int version() {
+    return getSetting(Key, Version);
+}
+
+} // namespace
+} // namespace schema
+
+namespace migrate {
+namespace {
+
+void deletePrefixes(::settings::query::StringViewIterator prefixes) {
     std::vector<String> to_purge;
 
-    settings::internal::foreach([&](settings::kvs_type::KeyValueResult&& kv) {
-        auto key = kv.key.read();
-        for (const auto* prefix : prefixes) {
-            if (key.startsWith(prefix)) {
+    ::settings::internal::foreach([&](::settings::kvs_type::KeyValueResult&& kv) {
+        const auto key = kv.key.read();
+        for (auto it = prefixes.begin(); it != prefixes.end(); ++it) {
+            if (::settings::query::samePrefix(::settings::StringView{key}, (*it))) {
                 to_purge.push_back(std::move(key));
                 return;
             }
         }
     });
 
-    for (auto& key : to_purge) {
+    for (const auto& key : to_purge) {
         delSetting(key);
     }
 }
 
-void delSettingPrefix(const char* prefix) {
-    delSettingPrefix({prefix});
-}
-
-void delSettingPrefix(const String& prefix) {
-    delSettingPrefix(prefix.c_str());
-}
-
-// Configuration versions
-//
-// 1: based on Embedis, no board definitions
-// 2: based on Embedis, with board definitions 1-based
-// 3: based on Embedis, with board definitions 0-based
-// 4: based on Embedis, no board definitions
-// 5: based on Embedis, updated rfb codes format
-
-int migrateVersion() {
-    const static auto version = getSetting("cfg", CFG_VERSION);
-    if (version != CFG_VERSION) {
-        return version;
+int currentVersion() {
+    const static auto current = schema::version();
+    if (current != schema::Version) {
+        return current;
     }
 
     return 0;
 }
 
+} // namespace
+} // namespace migrate
+} // namespace settings
+} // namespace espurna
+
+void delSettingPrefix(::settings::query::StringViewIterator prefixes) {
+    espurna::settings::migrate::deletePrefixes(std::move(prefixes));
+}
+
+int migrateVersion() {
+    return espurna::settings::migrate::currentVersion();
+}
+
 void migrateVersion(MigrateVersionCallback callback) {
-    int version = migrateVersion();
-    if (version) {
-        callback(version);
+    static const auto current = espurna::settings::migrate::currentVersion();
+    if (current) {
+        callback(current);
     }
 }
 
 void migrate() {
-    // We either get 0, when version did not change
-    // Or, the version we migrate from
-    const auto version = migrateVersion();
-    setSetting("cfg", CFG_VERSION);
-
-    // get rid of old keys that were never used until now
-    // and some very old keys that were forced via migrate.ino
-    if (version) {
-        switch (version) {
-        case 2:
-        case 3:
-        case 4:
-            delSetting("board");
-            break;
-        }
+    using namespace espurna::settings::schema;
+    setSetting(FPSTR(Key), Version);
 
+    using namespace espurna::settings::migrate;
+    switch (currentVersion()) {
+    case 2:
+    case 3:
+    case 4:
+        delSetting(F("board"));
         saveSettings();
+        break;
     }
 }