Refactoring I.

- Revamp whole DB to Display flow
- Filter Pipeline, arbitrary filtering and sorting
- Binary tree arrays for faster lookup & manipulation
- DB: introducing custom functions
- DB scheme: split req into heap & cache
- cache written by GlassVPN only
- heap written by Main App only
- Introducing DB separation: DBCore, DBCommon, DBAppOnly
- Introducing DB data sources: TestDataSource, GroupedDomainDataSource, RecordingsDB, DomainFilter
- Background sync: Move entries from cache to heap and notify all observers
- GlassVPN: Binary tree filter lookup
- GlassVPN: Reusing prepared statement

main/Data Source/DomainFilter.swift

@@ -0,0 +1,51 @@
+import Foundation
+
+enum DomainFilter {
+	static private var data: [String: FilterOptions] = {
+		AppDB?.loadFilters() ?? [:]
+	}()
+	
+	/// Get filter with given `domain` name
+	@inline(__always) static subscript(_ domain: String) -> FilterOptions? {
+		data[domain]
+	}
+	
+	/// Update local memory object by loading values from persistent db.
+	/// - Note: Will trigger `NotifyDNSFilterChanged` notification.
+	static func reload() {
+		data = AppDB?.loadFilters() ?? [:]
+		NotifyDNSFilterChanged.post()
+	}
+	
+	/// Get list of domains (sorted by name) which do contain the given filter
+	static func list(where matching: FilterOptions) -> [String] {
+		data.compactMap { $1.contains(matching) ? $0 : nil }.sorted()
+	}
+	
+	/// Get total number of blocked and ignored domains. Shown in settings overview.
+	static func counts() -> (blocked: Int, ignored: Int) {
+		data.reduce(into: (0, 0)) {
+			if $1.1.contains(.blocked) { $0.0 += 1 }
+			if $1.1.contains(.ignored) { $0.1 += 1 } }
+	}
+	
+	/// Union `filter` with set.
+	/// - Note: Will trigger `NotifyDNSFilterChanged` notification.
+	static func update(_ domain: String, add filter: FilterOptions) {
+		update(domain, set: (data[domain] ?? FilterOptions()).union(filter))
+	}
+
+	/// Subtract `filter` from set.
+	/// - Note: Will trigger `NotifyDNSFilterChanged` notification.
+	static func update(_ domain: String, remove filter: FilterOptions) {
+		update(domain, set: data[domain]?.subtracting(filter))
+	}
+
+	/// Update persistent db, local memory object, and post notification to subscribers
+	/// - Parameter set: Remove a filter with `nil` or `.none`
+	static private func update(_ domain: String, set: FilterOptions?) {
+		AppDB?.setFilter(domain, set)
+		data[domain] = (set == FilterOptions.none) ? nil : set
+		NotifyDNSFilterChanged.post(domain)
+	}
+}