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/DB/DBCommon.swift

@@ -0,0 +1,88 @@
+import Foundation
+import SQLite3
+
+enum CreateTable {} // used for CREATE TABLE statements
+
+extension SQLiteDatabase {
+	func initCommonScheme() {
+		try? run(sql: CreateTable.cache)
+		try? run(sql: CreateTable.filter)
+	}
+}
+
+
+// MARK: - transit
+
+extension CreateTable {
+	/// `ts`: Timestamp,  `dns`: String,  `opt`: Int
+	static var cache: String {"""
+		CREATE TABLE IF NOT EXISTS cache(
+			ts INTEGER DEFAULT (strftime('%s','now')),
+			dns TEXT NOT NULL,
+			opt INTEGER
+		);
+		"""}
+}
+
+extension SQLiteDatabase {
+	/// `INSERT INTO cache (dns, opt) VALUES (?, ?);`
+	func logWritePrepare() throws -> OpaquePointer {
+		try prepare(sql: "INSERT INTO cache (dns, opt) VALUES (?, ?);")
+	}
+	/// `prep` must exist and be initialized with `logWritePrepare()`
+	func logWrite(_ pStmt: OpaquePointer!, _ domain: String, blocked: Bool = false) throws {
+		guard let prep = pStmt else {
+			return
+		}
+		try prepared(run: prep, bind: [BindText(domain), BindInt32(blocked ? 1 : 0)])
+	}
+}
+
+
+// MARK: - filter
+
+extension CreateTable {
+	/// `domain`: String,  `opt`: Int
+	static var filter: String {"""
+		CREATE TABLE IF NOT EXISTS filter(
+			domain TEXT UNIQUE NOT NULL,
+			opt INTEGER
+		);
+		"""}
+}
+
+struct FilterOptions: OptionSet {
+    let rawValue: Int32
+	static let none    = FilterOptions([])
+    static let blocked = FilterOptions(rawValue: 1 << 0)
+    static let ignored = FilterOptions(rawValue: 1 << 1)
+	static let any     = FilterOptions(rawValue: 0b11)
+}
+
+extension SQLiteDatabase {
+	func loadFilters(where matching: FilterOptions? = nil) -> [String : FilterOptions]? {
+		let rv = matching?.rawValue ?? 0
+		return try? run(sql: "SELECT domain, opt FROM filter \(rv>0 ? "WHERE opt & ?" : "");",
+						bind: rv>0 ? [BindInt32(rv)] : []) {
+			allRowsKeyed($0) {
+				(key: readText($0, 0) ?? "",
+				 value: FilterOptions(rawValue: sqlite3_column_int($0, 1)))
+			}
+		}
+	}
+	func setFilter(_ domain: String, _ value: FilterOptions?) {
+		if let rv = value?.rawValue, rv > 0 {
+			try? run(sql: "INSERT OR REPLACE INTO filter (domain, opt) VALUES (?, ?);",
+					 bind: [BindText(domain), BindInt32(rv)]) { _ = sqlite3_step($0) }
+		} else {
+			try? run(sql: "DELETE FROM filter WHERE domain = ? LIMIT 1;",
+					 bind: [BindText(domain)]) { _ = sqlite3_step($0) }
+		}
+	}
+//	func loadFilterCount() -> (blocked: Int32, ignored: Int32)? {
+//		try? run(sql: "SELECT SUM(opt&1), SUM(opt&2)/2 FROM filter;") {
+//			try ifStep($0, SQLITE_ROW)
+//			return (sqlite3_column_int($0, 0), sqlite3_column_int($0, 1))
+//		}
+//	}
+}