From 4c611583267c26ee207d2ac5c39ef7ddad62843e Mon Sep 17 00:00:00 2001
From: akwizgran <michael@briarproject.org>
Date: Wed, 31 Jan 2018 11:50:00 +0000
Subject: [PATCH] Migrate database schema if a migration is available.

---
 .../bramble/db/DatabaseConstants.java         |  6 ----
 .../briarproject/bramble/db/JdbcDatabase.java | 35 +++++++++++++------
 .../briarproject/bramble/db/Migration.java    | 18 ++++++++++
 3 files changed, 43 insertions(+), 16 deletions(-)
 create mode 100644 bramble-core/src/main/java/org/briarproject/bramble/db/Migration.java

diff --git a/bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseConstants.java b/bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseConstants.java
index 080a8ce8e..707234b1f 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseConstants.java
+++ b/bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseConstants.java
@@ -23,10 +23,4 @@ interface DatabaseConstants {
 	 */
 	String SCHEMA_VERSION_KEY = "schemaVersion";
 
-	/**
-	 * The {@link Settings} key under which the minimum supported database
-	 * schema version is stored.
-	 */
-	String MIN_SCHEMA_VERSION_KEY = "minSchemaVersion";
-
 }
diff --git a/bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java b/bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java
index 8b8c3562a..9cbc48e1a 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java
+++ b/bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java
@@ -47,6 +47,7 @@ import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 
+import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.api.db.Metadata.REMOVE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
@@ -57,7 +58,6 @@ import static org.briarproject.bramble.api.sync.ValidationManager.State.INVALID;
 import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
 import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
 import static org.briarproject.bramble.db.DatabaseConstants.DB_SETTINGS_NAMESPACE;
-import static org.briarproject.bramble.db.DatabaseConstants.MIN_SCHEMA_VERSION_KEY;
 import static org.briarproject.bramble.db.DatabaseConstants.SCHEMA_VERSION_KEY;
 import static org.briarproject.bramble.db.ExponentialBackoff.calculateExpiry;
 
@@ -68,8 +68,7 @@ import static org.briarproject.bramble.db.ExponentialBackoff.calculateExpiry;
 @NotNullByDefault
 abstract class JdbcDatabase implements Database<Connection> {
 
-	private static final int SCHEMA_VERSION = 30;
-	private static final int MIN_SCHEMA_VERSION = 30;
+	private static final int CODE_SCHEMA_VERSION = 30;
 
 	private static final String CREATE_SETTINGS =
 			"CREATE TABLE settings"
@@ -310,17 +309,33 @@ abstract class JdbcDatabase implements Database<Connection> {
 
 	private boolean checkSchemaVersion(Connection txn) throws DbException {
 		Settings s = getSettings(txn, DB_SETTINGS_NAMESPACE);
-		int schemaVersion = s.getInt(SCHEMA_VERSION_KEY, -1);
-		if (schemaVersion == SCHEMA_VERSION) return true;
-		if (schemaVersion < MIN_SCHEMA_VERSION) return false;
-		int minSchemaVersion = s.getInt(MIN_SCHEMA_VERSION_KEY, -1);
-		return SCHEMA_VERSION >= minSchemaVersion;
+		int dataSchemaVersion = s.getInt(SCHEMA_VERSION_KEY, -1);
+		if (dataSchemaVersion == CODE_SCHEMA_VERSION) return true;
+		if (CODE_SCHEMA_VERSION < dataSchemaVersion) return false;
+		// Do we have a suitable migration?
+		for (Migration<Connection> m : getMigrations()) {
+			int start = m.getStartVersion(), end = m.getEndVersion();
+			if (start == dataSchemaVersion && end == CODE_SCHEMA_VERSION) {
+				if (LOG.isLoggable(INFO))
+					LOG.info("Migrating from schema " + start + " to " + end);
+				// Apply the migration
+				m.migrate(txn);
+				// Store the new schema version
+				storeSchemaVersion(txn);
+				return true;
+			}
+		}
+		// No suitable migration
+		return false;
+	}
+
+	private Collection<Migration<Connection>> getMigrations() {
+		return Collections.emptyList();
 	}
 
 	private void storeSchemaVersion(Connection txn) throws DbException {
 		Settings s = new Settings();
-		s.putInt(SCHEMA_VERSION_KEY, SCHEMA_VERSION);
-		s.putInt(MIN_SCHEMA_VERSION_KEY, MIN_SCHEMA_VERSION);
+		s.putInt(SCHEMA_VERSION_KEY, CODE_SCHEMA_VERSION);
 		mergeSettings(txn, s, DB_SETTINGS_NAMESPACE);
 	}
 
diff --git a/bramble-core/src/main/java/org/briarproject/bramble/db/Migration.java b/bramble-core/src/main/java/org/briarproject/bramble/db/Migration.java
new file mode 100644
index 000000000..56b04effe
--- /dev/null
+++ b/bramble-core/src/main/java/org/briarproject/bramble/db/Migration.java
@@ -0,0 +1,18 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.db.DbException;
+
+interface Migration<T> {
+
+	/**
+	 * Returns the schema version from which this migration starts.
+	 */
+	int getStartVersion();
+
+	/**
+	 * Returns the schema version at which this migration ends.
+	 */
+	int getEndVersion();
+
+	void migrate(T txn) throws DbException;
+}