/*
 * ConnectBot: simple, powerful, open-source SSH client for Android
 * Copyright 2007 Kenny Root, Jeffrey Sharkey
 *
 * 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 com.five_ten_sg.connectbot.util;

import java.util.LinkedList;
import java.util.List;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * @author Kenny Root
 *
 */
public abstract class RobustSQLiteOpenHelper extends SQLiteOpenHelper {
    private static List<String> mTableNames = new LinkedList<String>();
    private static List<String> mIndexNames = new LinkedList<String>();

    public RobustSQLiteOpenHelper(Context context, String name,
                                  CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    protected static void addTableName(String tableName) {
        mTableNames.add(tableName);
    }

    protected static void addIndexName(String indexName) {
        mIndexNames.add(indexName);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        dropAllTables(db);
    }

    @Override
    public final void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        try {
            onRobustUpgrade(db, oldVersion, newVersion);
        }
        catch (SQLiteException e) {
            // The database has entered an unknown state. Try to recover.
            try {
                regenerateTables(db);
            }
            catch (SQLiteException e2) {
                dropAndCreateTables(db);
            }
        }
    }

    public abstract void onRobustUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) throws SQLiteException;

    private void regenerateTables(SQLiteDatabase db) {
        dropAllTablesWithPrefix(db, "OLD_");

        for (String tableName : mTableNames)
            db.execSQL("ALTER TABLE " + tableName + " RENAME TO OLD_"
                       + tableName);

        onCreate(db);

        for (String tableName : mTableNames)
            repopulateTable(db, tableName);

        dropAllTablesWithPrefix(db, "OLD_");
    }

    private void repopulateTable(SQLiteDatabase db, String tableName) {
        String columns = getTableColumnNames(db, tableName);
        StringBuilder sb = new StringBuilder();
        sb.append("INSERT INTO ")
        .append(tableName)
        .append(" (")
        .append(columns)
        .append(") SELECT ")
        .append(columns)
        .append(" FROM OLD_")
        .append(tableName);
        String sql = sb.toString();
        db.execSQL(sql);
    }

    private String getTableColumnNames(SQLiteDatabase db, String tableName) {
        StringBuilder sb = new StringBuilder();
        Cursor fields = db.rawQuery("PRAGMA table_info(" + tableName + ")", null);

        while (fields.moveToNext()) {
            if (!fields.isFirst())
                sb.append(", ");

            sb.append(fields.getString(1));
        }

        fields.close();
        return sb.toString();
    }

    private void dropAndCreateTables(SQLiteDatabase db) {
        dropAllTables(db);
        onCreate(db);
    }

    private void dropAllTablesWithPrefix(SQLiteDatabase db, String prefix) {
        for (String indexName : mIndexNames)
            db.execSQL("DROP INDEX IF EXISTS " + prefix + indexName);

        for (String tableName : mTableNames)
            db.execSQL("DROP TABLE IF EXISTS " + prefix + tableName);
    }

    private void dropAllTables(SQLiteDatabase db) {
        dropAllTablesWithPrefix(db, "");
    }
}