/*
 * Copyright (c) 2010-2011, The MiCode Open Source Community (www.micode.net)
 *
 * 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.
 */

/**
 * 文件: NotesDatabaseHelper.java
 * 描述: 便签应用的数据库帮助类，负责创建和管理SQLite数据库
 * 作用: 提供数据库的创建、升级和表结构管理，是应用数据持久化的核心组件
 */
package net.micode.notes.data;

import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

import net.micode.notes.data.Notes.DataColumns;
import net.micode.notes.data.Notes.DataConstants;
import net.micode.notes.data.Notes.NoteColumns;

/**
 * 便签数据库帮助类
 * 
 * 继承自SQLiteOpenHelper，负责便签应用数据库的创建、升级和管理
 * 提供了便签表和数据表的创建与管理，以及各种数据库触发器的定义
 * 使用单例模式确保全局只有一个数据库连接实例
 */
public class NotesDatabaseHelper extends SQLiteOpenHelper {
    /** 数据库名称 */
    private static final String DB_NAME = "note.db";

    /** 数据库版本号 */
    private static final int DB_VERSION = 4;

    /**
     * 表名常量接口
     * 定义了数据库中的表名
     */
    public interface TABLE {
        /** 便签表名 */
        public static final String NOTE = "note";

        /** 数据表名 */
        public static final String DATA = "data";
    }

    /** 日志标签 */
    private static final String TAG = "NotesDatabaseHelper";

    /** 单例实例 */
    private static NotesDatabaseHelper mInstance;

    /**
     * 创建便签表的SQL语句
     * 定义了便签表的结构，包括各列名和默认值
     */
    private static final String CREATE_NOTE_TABLE_SQL =
        "CREATE TABLE " + TABLE.NOTE + "(" +
            NoteColumns.ID + " INTEGER PRIMARY KEY," +
            NoteColumns.PARENT_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.ALERTED_DATE + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.BG_COLOR_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.CREATED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +
            NoteColumns.HAS_ATTACHMENT + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.MODIFIED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +
            NoteColumns.NOTES_COUNT + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.SNIPPET + " TEXT NOT NULL DEFAULT ''," +
            NoteColumns.TYPE + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.WIDGET_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.WIDGET_TYPE + " INTEGER NOT NULL DEFAULT -1," +
            NoteColumns.SYNC_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.LOCAL_MODIFIED + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.ORIGIN_PARENT_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.GTASK_ID + " TEXT NOT NULL DEFAULT ''," +
            NoteColumns.VERSION + " INTEGER NOT NULL DEFAULT 0" +
        ")";

    /**
     * 创建数据表的SQL语句
     * 定义了数据表的结构，用于存储便签的具体内容
     */
    private static final String CREATE_DATA_TABLE_SQL =
        "CREATE TABLE " + TABLE.DATA + "(" +
            DataColumns.ID + " INTEGER PRIMARY KEY," +
            DataColumns.MIME_TYPE + " TEXT NOT NULL," +
            DataColumns.NOTE_ID + " INTEGER NOT NULL DEFAULT 0," +
            NoteColumns.CREATED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +
            NoteColumns.MODIFIED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +
            DataColumns.CONTENT + " TEXT NOT NULL DEFAULT ''," +
            DataColumns.DATA1 + " INTEGER," +
            DataColumns.DATA2 + " INTEGER," +
            DataColumns.DATA3 + " TEXT NOT NULL DEFAULT ''," +
            DataColumns.DATA4 + " TEXT NOT NULL DEFAULT ''," +
            DataColumns.DATA5 + " TEXT NOT NULL DEFAULT ''" +
        ")";

    /**
     * 创建数据表NOTE_ID索引的SQL语句
     * 用于优化按便签ID查询数据的性能
     */
    private static final String CREATE_DATA_NOTE_ID_INDEX_SQL =
        "CREATE INDEX IF NOT EXISTS note_id_index ON " +
        TABLE.DATA + "(" + DataColumns.NOTE_ID + ");";

    /**
     * 增加文件夹便签计数的触发器
     * 当便签移动到某个文件夹时，自动增加该文件夹的便签计数
     */
    private static final String NOTE_INCREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER increase_folder_count_on_update "+
        " AFTER UPDATE OF " + NoteColumns.PARENT_ID + " ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + " + 1" +
        "  WHERE " + NoteColumns.ID + "=new." + NoteColumns.PARENT_ID + ";" +
        " END";

    /**
     * 减少文件夹便签计数的触发器
     * 当便签从某个文件夹移出时，自动减少该文件夹的便签计数
     */
    private static final String NOTE_DECREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER decrease_folder_count_on_update " +
        " AFTER UPDATE OF " + NoteColumns.PARENT_ID + " ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + "-1" +
        "  WHERE " + NoteColumns.ID + "=old." + NoteColumns.PARENT_ID +
        "  AND " + NoteColumns.NOTES_COUNT + ">0" + ";" +
        " END";

    /**
     * 增加文件夹便签计数的触发器
     * 当在某个文件夹中插入新便签时，自动增加该文件夹的便签计数
     */
    private static final String NOTE_INCREASE_FOLDER_COUNT_ON_INSERT_TRIGGER =
        "CREATE TRIGGER increase_folder_count_on_insert " +
        " AFTER INSERT ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + " + 1" +
        "  WHERE " + NoteColumns.ID + "=new." + NoteColumns.PARENT_ID + ";" +
        " END";

    /**
     * 减少文件夹便签计数的触发器
     * 当从某个文件夹中删除便签时，自动减少该文件夹的便签计数
     */
    private static final String NOTE_DECREASE_FOLDER_COUNT_ON_DELETE_TRIGGER =
        "CREATE TRIGGER decrease_folder_count_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + "-1" +
        "  WHERE " + NoteColumns.ID + "=old." + NoteColumns.PARENT_ID +
        "  AND " + NoteColumns.NOTES_COUNT + ">0;" +
        " END";

    /**
     * 更新便签内容的触发器
     * 当插入类型为NOTE的数据时，自动更新对应便签的摘要内容
     */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_INSERT_TRIGGER =
        "CREATE TRIGGER update_note_content_on_insert " +
        " AFTER INSERT ON " + TABLE.DATA +
        " WHEN new." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=new." + DataColumns.CONTENT +
        "  WHERE " + NoteColumns.ID + "=new." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * 更新便签内容的触发器
     * 当更新类型为NOTE的数据时，自动更新对应便签的摘要内容
     */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER update_note_content_on_update " +
        " AFTER UPDATE ON " + TABLE.DATA +
        " WHEN old." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=new." + DataColumns.CONTENT +
        "  WHERE " + NoteColumns.ID + "=new." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * 更新便签内容的触发器
     * 当删除类型为NOTE的数据时，自动清空对应便签的摘要内容
     */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_DELETE_TRIGGER =
        "CREATE TRIGGER update_note_content_on_delete " +
        " AFTER delete ON " + TABLE.DATA +
        " WHEN old." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=''" +
        "  WHERE " + NoteColumns.ID + "=old." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * 删除便签相关数据的触发器
     * 当删除便签时，自动删除与该便签关联的所有数据
     */
    private static final String NOTE_DELETE_DATA_ON_DELETE_TRIGGER =
        "CREATE TRIGGER delete_data_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN" +
        "  DELETE FROM " + TABLE.DATA +
        "   WHERE " + DataColumns.NOTE_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    /**
     * 删除文件夹内便签的触发器
     * 当删除文件夹时，自动删除该文件夹内的所有便签
     */
    private static final String FOLDER_DELETE_NOTES_ON_DELETE_TRIGGER =
        "CREATE TRIGGER folder_delete_notes_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN" +
        "  DELETE FROM " + TABLE.NOTE +
        "   WHERE " + NoteColumns.PARENT_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    /**
     * 移动文件夹内便签到回收站的触发器
     * 当文件夹被移动到回收站时，自动将该文件夹内的所有便签也移动到回收站
     */
    private static final String FOLDER_MOVE_NOTES_ON_TRASH_TRIGGER =
        "CREATE TRIGGER folder_move_notes_on_trash " +
        " AFTER UPDATE ON " + TABLE.NOTE +
        " WHEN new." + NoteColumns.PARENT_ID + "=" + Notes.ID_TRASH_FOLER +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.PARENT_ID + "=" + Notes.ID_TRASH_FOLER +
        "  WHERE " + NoteColumns.PARENT_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    /**
     * 构造函数
     * 
     * @param context 上下文环境
     */
    public NotesDatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    /**
     * 创建便签表
     * 
     * @param db 数据库对象
     */
    public void createNoteTable(SQLiteDatabase db) {
        // 执行创建便签表的SQL语句
        db.execSQL(CREATE_NOTE_TABLE_SQL);
        // 重新创建便签表的触发器
        reCreateNoteTableTriggers(db);
        // 创建系统文件夹
        createSystemFolder(db);
        Log.d(TAG, "note table has been created");
    }

    /**
     * 重新创建便签表的触发器
     * 先删除已存在的触发器，然后重新创建
     * 
     * @param db 数据库对象
     */
    private void reCreateNoteTableTriggers(SQLiteDatabase db) {
        // 删除已存在的触发器
        db.execSQL("DROP TRIGGER IF EXISTS increase_folder_count_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS decrease_folder_count_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS decrease_folder_count_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS delete_data_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS increase_folder_count_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS folder_delete_notes_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS folder_move_notes_on_trash");

        // 创建新的触发器
        db.execSQL(NOTE_INCREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER);
        db.execSQL(NOTE_DECREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER);
        db.execSQL(NOTE_DECREASE_FOLDER_COUNT_ON_DELETE_TRIGGER);
        db.execSQL(NOTE_DELETE_DATA_ON_DELETE_TRIGGER);
        db.execSQL(NOTE_INCREASE_FOLDER_COUNT_ON_INSERT_TRIGGER);
        db.execSQL(FOLDER_DELETE_NOTES_ON_DELETE_TRIGGER);
        db.execSQL(FOLDER_MOVE_NOTES_ON_TRASH_TRIGGER);
    }

    /**
     * 创建系统文件夹
     * 包括通话记录文件夹、根文件夹、临时文件夹和回收站文件夹
     * 
     * @param db 数据库对象
     */
    private void createSystemFolder(SQLiteDatabase db) {
        ContentValues values = new ContentValues();

        /**
         * call record foler for call notes
         */
        // 创建通话记录文件夹
        values.put(NoteColumns.ID, Notes.ID_CALL_RECORD_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * root folder which is default folder
         */
        // 创建根文件夹（默认文件夹）
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_ROOT_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * temporary folder which is used for moving note
         */
        // 创建临时文件夹（用于移动便签）
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_TEMPARAY_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * create trash folder
         */
        // 创建回收站文件夹
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_TRASH_FOLER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);
    }

    /**
     * 创建数据表
     * 
     * @param db 数据库对象
     */
    public void createDataTable(SQLiteDatabase db) {
        // 执行创建数据表的SQL语句
        db.execSQL(CREATE_DATA_TABLE_SQL);
        // 重新创建数据表的触发器
        reCreateDataTableTriggers(db);
        // 创建数据表的索引
        db.execSQL(CREATE_DATA_NOTE_ID_INDEX_SQL);
        Log.d(TAG, "data table has been created");
    }

    /**
     * 重新创建数据表的触发器
     * 先删除已存在的触发器，然后重新创建
     * 
     * @param db 数据库对象
     */
    private void reCreateDataTableTriggers(SQLiteDatabase db) {
        // 删除已存在的触发器
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_delete");

        // 创建新的触发器
        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_INSERT_TRIGGER);
        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_UPDATE_TRIGGER);
        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_DELETE_TRIGGER);
    }

    /**
     * 获取NotesDatabaseHelper的单例实例
     * 
     * @param context 上下文环境
     * @return NotesDatabaseHelper的单例实例
     */
    static synchronized NotesDatabaseHelper getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new NotesDatabaseHelper(context);
        }
        return mInstance;
    }

    /**
     * 数据库创建回调方法
     * 当数据库首次创建时调用
     * 
     * @param db 数据库对象
     */
    @Override
    public void onCreate(SQLiteDatabase db) {
        createNoteTable(db);
        createDataTable(db);
    }

    /**
     * 数据库升级回调方法
     * 当数据库版本升级时调用
     * 
     * @param db 数据库对象
     * @param oldVersion 旧版本号
     * @param newVersion 新版本号
     */
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        boolean reCreateTriggers = false;
        boolean skipV2 = false;

        // 从版本1升级到版本2
        if (oldVersion == 1) {
            upgradeToV2(db);
            skipV2 = true; // 这个升级包含了从v2到v3的升级
            oldVersion++;
        }

        // 从版本2升级到版本3
        if (oldVersion == 2 && !skipV2) {
            upgradeToV3(db);
            reCreateTriggers = true;
            oldVersion++;
        }

        // 从版本3升级到版本4
        if (oldVersion == 3) {
            upgradeToV4(db);
            oldVersion++;
        }

        // 如果需要，重新创建触发器
        if (reCreateTriggers) {
            reCreateNoteTableTriggers(db);
            reCreateDataTableTriggers(db);
        }

        // 验证升级是否成功
        if (oldVersion != newVersion) {
            throw new IllegalStateException("Upgrade notes database to version " + newVersion
                    + "fails");
        }
    }

    /**
     * 升级到版本2
     * 完全重建数据库表
     * 
     * @param db 数据库对象
     */
    private void upgradeToV2(SQLiteDatabase db) {
        // 删除旧表
        db.execSQL("DROP TABLE IF EXISTS " + TABLE.NOTE);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE.DATA);
        // 创建新表
        createNoteTable(db);
        createDataTable(db);
    }

    /**
     * 升级到版本3
     * 添加Google Tasks ID列和回收站文件夹
     * 
     * @param db 数据库对象
     */
    private void upgradeToV3(SQLiteDatabase db) {
        // 删除未使用的触发器
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_update");
        // 添加Google Tasks ID列
        db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.GTASK_ID
                + " TEXT NOT NULL DEFAULT ''");
        // 添加回收站系统文件夹
        ContentValues values = new ContentValues();
        values.put(NoteColumns.ID, Notes.ID_TRASH_FOLER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);
    }

    /**
     * 升级到版本4
     * 添加版本列
     * 
     * @param db 数据库对象
     */
    private void upgradeToV4(SQLiteDatabase db) {
        // 添加版本列
        db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.VERSION
                + " INTEGER NOT NULL DEFAULT 0");
    }
}