Refactor persistent logging to bramble-core.

bramble-api/src/main/java/org/briarproject/bramble/api/logging/PersistentLogManager.java

@@ -0,0 +1,40 @@
+package org.briarproject.bramble.api.logging;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.settings.Settings;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+import java.util.logging.Handler;
+
+@NotNullByDefault
+public interface PersistentLogManager {
+
+	/**
+	 * The namespace of the (@link Settings) where the log key is stored.
+	 */
+	String LOG_SETTINGS_NAMESPACE = "log";
+
+	/**
+	 * The {@link Settings} key under which the log key is stored.
+	 */
+	String LOG_KEY_KEY = "logKey";
+
+	/**
+	 * Creates and returns a persistent log handler that stores its logs in
+	 * the given directory.
+	 * <p>
+	 * This method should only be called once.
+	 */
+	Handler createLogHandler(File dir) throws IOException;
+
+	/**
+	 * Loads and returns the persistent log entries stored in the given
+	 * directory, or an empty list if no log entries are found.
+	 *
+	 * @param old True if the previous session's log should be loaded, or false
+	 * if the current session's log should be loaded
+	 */
+	List<String> getPersistedLog(File dir, boolean old) throws IOException;
+}