/*
 * Copyright (C) 2007 The Android Open Source Project
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package org.odk.collect.android.database;

import java.io.File;

import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteException;
import android.os.Environment;
import android.util.Log;
import org.odk.collect.android.R;
import org.odk.collect.android.application.Collect;


/**
 * We've taken this from Android's SQLiteOpenHelper. However, we can't appropriately lock the
 * database so there may be issues if a thread opens the database read-only and another thread tries
 * to open the database read/write. I don't think this will ever happen in ODK, though. (fingers
 * crossed).
 */

/**
 * A helper class to manage database creation and version management. You create a subclass
 * implementing {@link #onCreate}, {@link #onUpgrade} and optionally {@link #onOpen}, and this class
 * takes care of opening the database if it exists, creating it if it does not, and upgrading it as
 * necessary. Transactions are used to make sure the database is always in a sensible state.
 * <p>
 * For an example, see the NotePadProvider class in the NotePad sample application, in the
 * <em>samples/</em> directory of the SDK.
 * </p>
 */
public abstract class ODKSQLiteOpenHelper {
    private static final String t = ODKSQLiteOpenHelper.class.getSimpleName();

    private final String mPath;
    private final String mName;
    private final CursorFactory mFactory;
    private final int mNewVersion;

    private SQLiteDatabase mDatabase = null;
    private boolean mIsInitializing = false;


    /**
     * Create a helper object to create, open, and/or manage a database. The database is not
     * actually created or opened until one of {@link #getWritableDatabase} or
     * {@link #getReadableDatabase} is called.
     * 
     * @param path to the file
     * @param name of the database file, or null for an in-memory database
     * @param factory to use for creating cursor objects, or null for the default
     * @param version number of the database (starting at 1); if the database is older,
     *            {@link #onUpgrade} will be used to upgrade the database
     */
    public ODKSQLiteOpenHelper(String path, String name, CursorFactory factory, int version) {
        if (version < 1)
            throw new IllegalArgumentException("Version must be >= 1, was " + version);

        mPath = path;
        mName = name;
        mFactory = factory;
        mNewVersion = version;
    }


    /**
     * Create and/or open a database that will be used for reading and writing. Once opened
     * successfully, the database is cached, so you can call this method every time you need to
     * write to the database. Make sure to call {@link #close} when you no longer need it.
     * <p>
     * Errors such as bad permissions or a full disk may cause this operation to fail, but future
     * attempts may succeed if the problem is fixed.
     * </p>
     * 
     * @throws SQLiteException if the database cannot be opened for writing
     * @return a read/write database object valid until {@link #close} is called
     */
    public synchronized SQLiteDatabase getWritableDatabase() {
        if (mDatabase != null && mDatabase.isOpen() && !mDatabase.isReadOnly()) {
            return mDatabase; // The database is already open for business
        }

        if (mIsInitializing) {
            throw new IllegalStateException("getWritableDatabase called recursively");
        }

        // If we have a read-only database open, someone could be using it
        // (though they shouldn't), which would cause a lock to be held on
        // the file, and our attempts to open the database read-write would
        // fail waiting for the file lock. To prevent that, we acquire the
        // lock on the read-only database, which shuts out other users.

        boolean success = false;
        SQLiteDatabase db = null;
        // if (mDatabase != null) mDatabase.lock();
        try {
            mIsInitializing = true;
            if (mName == null) {
                db = SQLiteDatabase.create(null);
            } else {
                db = SQLiteDatabase.openOrCreateDatabase(mPath + File.separator + mName, mFactory);
                // db = mContext.openOrCreateDatabase(mName, 0, mFactory);
            }

            int version = db.getVersion();
            if (version != mNewVersion) {
                db.beginTransaction();
                try {
                    if (version == 0) {
                        onCreate(db);
                    } else {
                        onUpgrade(db, version, mNewVersion);
                    }
                    db.setVersion(mNewVersion);
                    db.setTransactionSuccessful();
                } finally {
                    db.endTransaction();
                }
            }

            onOpen(db);
            success = true;
            return db;
        } finally {
            mIsInitializing = false;
            if (success) {
                if (mDatabase != null) {
                    try {
                        mDatabase.close();
                    } catch (Exception e) {
                    }
                    // mDatabase.unlock();
                }
                mDatabase = db;
            } else {
                // if (mDatabase != null) mDatabase.unlock();
                if (db != null)
                    db.close();
            }
        }
    }


    /**
     * Create and/or open a database. This will be the same object returned by
     * {@link #getWritableDatabase} unless some problem, such as a full disk, requires the database
     * to be opened read-only. In that case, a read-only database object will be returned. If the
     * problem is fixed, a future call to {@link #getWritableDatabase} may succeed, in which case
     * the read-only database object will be closed and the read/write object will be returned in
     * the future.
     * 
     * @throws SQLiteException if the database cannot be opened
     * @return a database object valid until {@link #getWritableDatabase} or {@link #close} is
     *         called.
     */
    public synchronized SQLiteDatabase getReadableDatabase() {
        if (mDatabase != null && mDatabase.isOpen()) {
            return mDatabase; // The database is already open for business
        }

        if (mIsInitializing) {
            throw new IllegalStateException("getReadableDatabase called recursively");
        }

        try {
            return getWritableDatabase();
        } catch (SQLiteException e) {
            if (mName == null)
                throw e; // Can't open a temp database read-only!
            Log.e(t, "Couldn't open " + mName + " for writing (will try read-only):", e);
        }

        SQLiteDatabase db = null;
        try {
            mIsInitializing = true;
            String path = mPath + File.separator + mName;
            // mContext.getDatabasePath(mName).getPath();
            try {
                db = SQLiteDatabase.openDatabase(path, mFactory, SQLiteDatabase.OPEN_READONLY);
            } catch (RuntimeException e) {
                Log.e(t, e.getMessage(), e);
                String cardstatus = Environment.getExternalStorageState();
                if (!cardstatus.equals(Environment.MEDIA_MOUNTED)) {
                    throw new RuntimeException(Collect.getInstance().getString(R.string.sdcard_unmounted, cardstatus));
                } else {
                    throw e;
                }
            }

            if (db.getVersion() != mNewVersion) {
                throw new SQLiteException("Can't upgrade read-only database from version "
                        + db.getVersion() + " to " + mNewVersion + ": " + path);
            }

            onOpen(db);
            Log.w(t, "Opened " + mName + " in read-only mode");
            mDatabase = db;
            return mDatabase;
        } finally {
            mIsInitializing = false;
            if (db != null && db != mDatabase)
                db.close();
        }
    }


    /**
     * Close any open database object.
     */
    public synchronized void close() {
        if (mIsInitializing)
            throw new IllegalStateException("Closed during initialization");

        if (mDatabase != null && mDatabase.isOpen()) {
            mDatabase.close();
            mDatabase = null;
        }
    }


    /**
     * Called when the database is created for the first time. This is where the creation of tables
     * and the initial population of the tables should happen.
     * 
     * @param db The database.
     */
    public abstract void onCreate(SQLiteDatabase db);


    /**
     * Called when the database needs to be upgraded. The implementation should use this method to
     * drop tables, add tables, or do anything else it needs to upgrade to the new schema version.
     * <p>
     * The SQLite ALTER TABLE documentation can be found <a
     * href="http://sqlite.org/lang_altertable.html">here</a>. If you add new columns you can use
     * ALTER TABLE to insert them into a live table. If you rename or remove columns you can use
     * ALTER TABLE to rename the old table, then create the new table and then populate the new
     * table with the contents of the old table.
     * 
     * @param db The database.
     * @param oldVersion The old database version.
     * @param newVersion The new database version.
     */
    public abstract void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion);


    /**
     * Called when the database has been opened. Override method should check
     * {@link SQLiteDatabase#isReadOnly} before updating the database.
     * 
     * @param db The database.
     */
    public void onOpen(SQLiteDatabase db) {
    }
}
