Initial pass on adding support for persistence using sqlcipher

To keep the database schema simple we just save the
otpauth:// url and let KeyInfo take care of checking for
validity.

This patch also includes multiple fixes for the KeyInfo
class.

We still need a separate activity to allow the user to
enter their PIN/password. Currently, "test" is used as the
password for the database.

app/src/main/java/me/impy/aegis/db/Database.java

@@ -0,0 +1,91 @@
+package me.impy.aegis.db;
+
+import android.content.Context;
+
+import net.sqlcipher.Cursor;
+import net.sqlcipher.database.SQLiteDatabase;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import me.impy.aegis.KeyProfile;
+import me.impy.aegis.crypto.KeyInfo;
+
+public class Database {
+    private static Database instance;
+    private static Boolean libsLoaded = false;
+    private SQLiteDatabase db;
+
+    private Database(Context context, String filename, char[] password) {
+        DatabaseHelper helper = new DatabaseHelper(context, filename);
+        db = helper.getWritableDatabase(password);
+    }
+
+    public static Database createInstance(Context context, String filename, char[] password) {
+        // load the sqlcipher library, once
+        if (!libsLoaded) {
+            SQLiteDatabase.loadLibs(context);
+            libsLoaded = true;
+        }
+
+        if (instance == null) {
+            instance = new Database(context, filename, password);
+        }
+
+        return instance;
+    }
+
+    // adds a key to the database and returns it's ID
+    public void addKey(KeyProfile profile) throws Exception {
+        db.execSQL("insert into otp (name, url) values (?, ?)",
+                new Object[]{ profile.Name, profile.Info.getURL() });
+        profile.ID = getLastID(db, "otp");
+    }
+
+    public void updateKey(KeyProfile profile) throws Exception {
+        db.execSQL("update otp set name=? url=? where id=?",
+                new Object[]{ profile.Name, profile.Info.getURL(), profile.ID });
+    }
+
+    public void removeKey(KeyProfile profile) {
+        db.execSQL("delete from otp where id=?", new Object[]{ profile.ID });
+    }
+
+    public List<KeyProfile> getKeys() throws Exception {
+        List<KeyProfile> list = new ArrayList<>();
+        Cursor cursor = db.rawQuery("select * from otp", null);
+
+        try {
+            while (cursor.moveToNext()) {
+                KeyProfile profile = new KeyProfile();
+                profile.ID = cursor.getInt(cursor.getColumnIndexOrThrow("id"));
+                profile.Name = cursor.getString(cursor.getColumnIndexOrThrow("name"));
+
+                String url = cursor.getString(cursor.getColumnIndexOrThrow("url"));
+                profile.Info = KeyInfo.FromURL(url);
+
+                list.add(profile);
+            }
+            return list;
+        } finally {
+            cursor.close();
+        }
+    }
+
+    public void close() {
+        db.close();
+    }
+
+    private int getLastID(SQLiteDatabase db, String table) throws Exception {
+        Cursor cursor = db.rawQuery(String.format("select id from %s order by id desc limit 1", table), null);
+        try {
+            if (!cursor.moveToFirst()) {
+                throw new Exception("no items in the table, this should not happen here");
+            }
+
+            return cursor.getInt(cursor.getColumnIndexOrThrow("id"));
+        } finally {
+            cursor.close();
+        }
+    }
+}