Implement backend for pairing mailbox

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxManager.java

@@ -0,0 +1,30 @@
+package org.briarproject.bramble.api.mailbox;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+
+import javax.annotation.Nullable;
+
+public interface MailboxManager {
+
+	/**
+	 * @return true if a mailbox is already paired.
+	 */
+	boolean isPaired(Transaction txn) throws DbException;
+
+	/**
+	 * Returns the currently running pairing task,
+	 * or null if no pairing task is running.
+	 */
+	@Nullable
+	MailboxPairingTask getCurrentPairingTask();
+
+	/**
+	 * Starts and returns a pairing task. If a pairing task is already running,
+	 * it will be returned and the argument will be ignored.
+	 *
+	 * @param qrCodePayload The ISO-8859-1 encoded bytes of the mailbox QR code.
+	 */
+	MailboxPairingTask startPairingTask(String qrCodePayload);
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxPairingState.java

@@ -0,0 +1,59 @@
+package org.briarproject.bramble.api.mailbox;
+
+import javax.annotation.Nullable;
+
+public abstract class MailboxPairingState {
+
+	/**
+	 * The QR code payload that was scanned by the user.
+	 * This is null if the code should not be re-used anymore in this state.
+	 */
+	@Nullable
+	public final String qrCodePayload;
+
+	MailboxPairingState(@Nullable String qrCodePayload) {
+		this.qrCodePayload = qrCodePayload;
+	}
+
+	public static class QrCodeReceived extends MailboxPairingState {
+		public QrCodeReceived(String qrCodePayload) {
+			super(qrCodePayload);
+		}
+	}
+
+	public static class Pairing extends MailboxPairingState {
+		public Pairing(String qrCodePayload) {
+			super(qrCodePayload);
+		}
+	}
+
+	public static class Paired extends MailboxPairingState {
+		public Paired() {
+			super(null);
+		}
+	}
+
+	public static class InvalidQrCode extends MailboxPairingState {
+		public InvalidQrCode() {
+			super(null);
+		}
+	}
+
+	public static class MailboxAlreadyPaired extends MailboxPairingState {
+		public MailboxAlreadyPaired() {
+			super(null);
+		}
+	}
+
+	public static class ConnectionError extends MailboxPairingState {
+		public ConnectionError(String qrCodePayload) {
+			super(qrCodePayload);
+		}
+	}
+
+	public static class AssertionError extends MailboxPairingState {
+		public AssertionError(String qrCodePayload) {
+			super(qrCodePayload);
+		}
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxPairingTask.java

@@ -0,0 +1,21 @@
+package org.briarproject.bramble.api.mailbox;
+
+import org.briarproject.bramble.api.Consumer;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public interface MailboxPairingTask extends Runnable {
+
+	/**
+	 * Adds an observer to the task. The observer will be notified on the
+	 * event thread of the current state of the task and any subsequent state
+	 * changes.
+	 */
+	void addObserver(Consumer<MailboxPairingState> observer);
+
+	/**
+	 * Removes an observer from the task.
+	 */
+	void removeObserver(Consumer<MailboxPairingState> observer);
+
+}