feat: 实现月度记账开始日期功能

- 添加 Settings 实体和 DAO 来持久化存储设置
- 创建 SettingsRepository 管理设置数据
- 添加数据库迁移从版本 4 到版本 5
- 在设置界面添加月度开始日期选择器（1-28号）
- 创建 DateUtils 工具类处理基于月度开始日期的日期计算
- 更新 HomeViewModel 和 AnalysisViewModel 使用月度开始日期进行统计
- 修复日期选择器中数字显示不完整的问题

app/src/main/java/com/yovinchen/bookkeeping/data/BookkeepingDatabase.kt

@@ -10,6 +10,7 @@ import androidx.room.migration.Migration
 import androidx.sqlite.db.SupportSQLiteDatabase
 import com.yovinchen.bookkeeping.R
 import com.yovinchen.bookkeeping.model.BookkeepingRecord
+import com.yovinchen.bookkeeping.model.Budget
 import com.yovinchen.bookkeeping.model.Category
 import com.yovinchen.bookkeeping.model.Converters
 import com.yovinchen.bookkeeping.model.Member
@@ -20,8 +21,8 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
 
 @Database(
-    entities = [BookkeepingRecord::class, Category::class, Member::class, Settings::class],
+    entities = [BookkeepingRecord::class, Category::class, Member::class, Settings::class, Budget::class],
-    version = 5,
+    version = 6,
     exportSchema = false
 )
 @TypeConverters(Converters::class)
@@ -30,6 +31,7 @@ abstract class BookkeepingDatabase : RoomDatabase() {
     abstract fun categoryDao(): CategoryDao
     abstract fun memberDao(): MemberDao
     abstract fun settingsDao(): SettingsDao
+    abstract fun budgetDao(): BudgetDao
 
     companion object {
         private const val TAG = "BookkeepingDatabase"
@@ -148,6 +150,30 @@ abstract class BookkeepingDatabase : RoomDatabase() {
             }
         }
         
+        private val MIGRATION_5_6 = object : Migration(5, 6) {
+            override fun migrate(db: SupportSQLiteDatabase) {
+                // 创建预算表
+                db.execSQL("""
+                    CREATE TABLE IF NOT EXISTS budgets (
+                        id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
+                        type TEXT NOT NULL,
+                        categoryName TEXT,
+                        memberId INTEGER,
+                        amount REAL NOT NULL,
+                        startDate INTEGER NOT NULL,
+                        endDate INTEGER NOT NULL,
+                        isEnabled INTEGER NOT NULL DEFAULT 1,
+                        alertThreshold REAL NOT NULL DEFAULT 0.8,
+                        createdAt INTEGER NOT NULL,
+                        updatedAt INTEGER NOT NULL
+                    )
+                """)
+                
+                // 在 settings 表中添加 encryptBackup 列
+                db.execSQL("ALTER TABLE settings ADD COLUMN encryptBackup INTEGER NOT NULL DEFAULT 1")
+            }
+        }
+
         @Volatile
         private var INSTANCE: BookkeepingDatabase? = null
 
@@ -158,7 +184,7 @@ abstract class BookkeepingDatabase : RoomDatabase() {
                     BookkeepingDatabase::class.java,
                     "bookkeeping_database"
                 )
-                    .addMigrations(MIGRATION_1_2, MIGRATION_2_3, MIGRATION_3_4, MIGRATION_4_5)
+                    .addMigrations(MIGRATION_1_2, MIGRATION_2_3, MIGRATION_3_4, MIGRATION_4_5, MIGRATION_5_6)
                     .addCallback(object : Callback() {
                         override fun onCreate(db: SupportSQLiteDatabase) {
                             super.onCreate(db)

app/src/main/java/com/yovinchen/bookkeeping/data/Converters.kt

@@ -1,6 +1,7 @@
 package com.yovinchen.bookkeeping.data
 
 import androidx.room.TypeConverter
+import com.yovinchen.bookkeeping.model.BudgetType
 import java.time.LocalDateTime
 import java.time.format.DateTimeFormatter
 import java.util.*
@@ -29,4 +30,14 @@ class Converters {
     fun toDate(timestamp: String?): Date? {
         return timestamp?.let { Date(it.toLong()) }
     }
+    
+    @TypeConverter
+    fun fromBudgetType(budgetType: BudgetType?): String? {
+        return budgetType?.name
+    }
+    
+    @TypeConverter
+    fun toBudgetType(budgetType: String?): BudgetType? {
+        return budgetType?.let { BudgetType.valueOf(it) }
+    }
 }

app/src/main/java/com/yovinchen/bookkeeping/data/SettingsDao.kt

@@ -29,4 +29,7 @@ interface SettingsDao {
     
     @Query("UPDATE settings SET lastBackupTime = :time WHERE id = 1")
     suspend fun updateLastBackupTime(time: Long)
+    
+    @Query("UPDATE settings SET encryptBackup = :encrypt WHERE id = 1")
+    suspend fun updateEncryptBackup(encrypt: Boolean)
 }

app/src/main/java/com/yovinchen/bookkeeping/model/Settings.kt

@@ -10,5 +10,6 @@ data class Settings(
     val themeMode: String = "FOLLOW_SYSTEM", // 主题模式：FOLLOW_SYSTEM, LIGHT, DARK
     val autoBackupEnabled: Boolean = false, // 自动备份开关
     val autoBackupInterval: Int = 7, // 自动备份间隔（天）
-    val lastBackupTime: Long = 0L // 上次备份时间
+    val lastBackupTime: Long = 0L, // 上次备份时间
+    val encryptBackup: Boolean = true // 备份加密开关，默认开启
 )

app/src/main/java/com/yovinchen/bookkeeping/ui/screen/SettingsScreen.kt

@@ -19,6 +19,7 @@ import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
+import com.yovinchen.bookkeeping.model.Settings
 import com.yovinchen.bookkeeping.model.ThemeMode
 import com.yovinchen.bookkeeping.ui.components.*
 import com.yovinchen.bookkeeping.ui.dialog.*
@@ -43,6 +44,7 @@ fun SettingsScreen(
     val selectedType by viewModel.selectedCategoryType.collectAsState()
     val members by memberViewModel.allMembers.collectAsState(initial = emptyList())
     val monthStartDay by viewModel.monthStartDay.collectAsState()
+    val settings by viewModel.settings.collectAsState()
     val context = LocalContext.current
     
     var showMonthStartDayDialog by remember { mutableStateOf(false) }
@@ -277,6 +279,29 @@ fun SettingsScreen(
                                 style = MaterialTheme.typography.bodySmall
                             )
                         }
+                        
+                        HorizontalDivider(modifier = Modifier.padding(vertical = 8.dp))
+                        
+                        // 备份加密开关
+                        Row(
+                            modifier = Modifier.fillMaxWidth(),
+                            verticalAlignment = Alignment.CenterVertically
+                        ) {
+                            Text("备份加密", modifier = Modifier.weight(1f))
+                            Switch(
+                                checked = settings?.encryptBackup ?: true,
+                                onCheckedChange = { enabled ->
+                                    viewModel.updateSettings(
+                                        settings?.copy(encryptBackup = enabled) ?: Settings(encryptBackup = enabled)
+                                    )
+                                }
+                            )
+                        }
+                        Text(
+                            "开启后，导出的备份文件将被加密保护",
+                            style = MaterialTheme.typography.bodySmall,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant
+                        )
                     }
                 },
                 confirmButton = {

app/src/main/java/com/yovinchen/bookkeeping/utils/EncryptionUtils.kt

@@ -0,0 +1,136 @@
+package com.yovinchen.bookkeeping.utils
+
+import android.security.keystore.KeyGenParameterSpec
+import android.security.keystore.KeyProperties
+import android.util.Base64
+import java.security.KeyStore
+import javax.crypto.Cipher
+import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+import javax.crypto.spec.GCMParameterSpec
+
+/**
+ * 加密工具类，使用 Android Keystore 系统安全地存储加密密钥
+ */
+object EncryptionUtils {
+    private const val ANDROID_KEYSTORE = "AndroidKeyStore"
+    private const val TRANSFORMATION = "AES/GCM/NoPadding"
+    private const val KEY_ALIAS = "BookkeepingBackupKey"
+    private const val GCM_TAG_LENGTH = 128
+    
+    init {
+        generateKey()
+    }
+    
+    /**
+     * 生成或获取加密密钥
+     */
+    private fun generateKey() {
+        val keyStore = KeyStore.getInstance(ANDROID_KEYSTORE)
+        keyStore.load(null)
+        
+        // 如果密钥已存在，则不需要重新生成
+        if (keyStore.containsAlias(KEY_ALIAS)) {
+            return
+        }
+        
+        val keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, ANDROID_KEYSTORE)
+        val keyGenParameterSpec = KeyGenParameterSpec.Builder(
+            KEY_ALIAS,
+            KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT
+        )
+            .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
+            .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
+            .setRandomizedEncryptionRequired(true)
+            .build()
+        
+        keyGenerator.init(keyGenParameterSpec)
+        keyGenerator.generateKey()
+    }
+    
+    /**
+     * 获取密钥
+     */
+    private fun getKey(): SecretKey {
+        val keyStore = KeyStore.getInstance(ANDROID_KEYSTORE)
+        keyStore.load(null)
+        return keyStore.getKey(KEY_ALIAS, null) as SecretKey
+    }
+    
+    /**
+     * 加密字符串
+     * @param plainText 要加密的明文
+     * @return Base64编码的加密数据（包含IV）
+     */
+    fun encrypt(plainText: String): String {
+        val cipher = Cipher.getInstance(TRANSFORMATION)
+        cipher.init(Cipher.ENCRYPT_MODE, getKey())
+        
+        val iv = cipher.iv
+        val encryptedBytes = cipher.doFinal(plainText.toByteArray(Charsets.UTF_8))
+        
+        // 将IV和加密数据组合
+        val combined = ByteArray(iv.size + encryptedBytes.size)
+        System.arraycopy(iv, 0, combined, 0, iv.size)
+        System.arraycopy(encryptedBytes, 0, combined, iv.size, encryptedBytes.size)
+        
+        return Base64.encodeToString(combined, Base64.DEFAULT)
+    }
+    
+    /**
+     * 解密字符串
+     * @param encryptedData Base64编码的加密数据
+     * @return 解密后的明文
+     */
+    fun decrypt(encryptedData: String): String {
+        val combined = Base64.decode(encryptedData, Base64.DEFAULT)
+        
+        // 提取IV（前12字节）
+        val iv = combined.sliceArray(0..11)
+        val encryptedBytes = combined.sliceArray(12 until combined.size)
+        
+        val cipher = Cipher.getInstance(TRANSFORMATION)
+        val spec = GCMParameterSpec(GCM_TAG_LENGTH, iv)
+        cipher.init(Cipher.DECRYPT_MODE, getKey(), spec)
+        
+        val decryptedBytes = cipher.doFinal(encryptedBytes)
+        return String(decryptedBytes, Charsets.UTF_8)
+    }
+    
+    /**
+     * 加密字节数组
+     * @param data 要加密的数据
+     * @return 加密后的数据（包含IV）
+     */
+    fun encryptBytes(data: ByteArray): ByteArray {
+        val cipher = Cipher.getInstance(TRANSFORMATION)
+        cipher.init(Cipher.ENCRYPT_MODE, getKey())
+        
+        val iv = cipher.iv
+        val encryptedBytes = cipher.doFinal(data)
+        
+        // 将IV和加密数据组合
+        val combined = ByteArray(iv.size + encryptedBytes.size)
+        System.arraycopy(iv, 0, combined, 0, iv.size)
+        System.arraycopy(encryptedBytes, 0, combined, iv.size, encryptedBytes.size)
+        
+        return combined
+    }
+    
+    /**
+     * 解密字节数组
+     * @param encryptedData 加密的数据
+     * @return 解密后的数据
+     */
+    fun decryptBytes(encryptedData: ByteArray): ByteArray {
+        // 提取IV（前12字节）
+        val iv = encryptedData.sliceArray(0..11)
+        val encryptedBytes = encryptedData.sliceArray(12 until encryptedData.size)
+        
+        val cipher = Cipher.getInstance(TRANSFORMATION)
+        val spec = GCMParameterSpec(GCM_TAG_LENGTH, iv)
+        cipher.init(Cipher.DECRYPT_MODE, getKey(), spec)
+        
+        return cipher.doFinal(encryptedBytes)
+    }
+}

app/src/main/java/com/yovinchen/bookkeeping/utils/FilePickerUtil.kt

@@ -107,11 +107,16 @@ object FilePickerUtil {
     private fun isValidFileType(fileName: String, mimeType: String?): Boolean {
         val fileExtension = fileName.lowercase()
         return fileExtension.endsWith(".csv") || 
+               fileExtension.endsWith(".csv.enc") ||
                fileExtension.endsWith(".xlsx") ||
+               fileExtension.endsWith(".xlsx.enc") ||
                fileExtension.endsWith(".xls") ||
+               fileExtension.endsWith(".xls.enc") ||
+               fileExtension.endsWith(".enc") ||
                mimeType == "text/csv" ||
                mimeType == "application/vnd.ms-excel" ||
-               mimeType == "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
+               mimeType == "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" ||
+               mimeType == "application/octet-stream" // 加密文件可能被识别为二进制流
     }
 
     /**

app/src/main/java/com/yovinchen/bookkeeping/viewmodel/SettingsViewModel.kt

@@ -14,6 +14,7 @@ import com.yovinchen.bookkeeping.model.BookkeepingRecord
 import com.yovinchen.bookkeeping.model.Category
 import com.yovinchen.bookkeeping.model.Settings
 import com.yovinchen.bookkeeping.model.TransactionType
+import com.yovinchen.bookkeeping.utils.EncryptionUtils
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.delay
@@ -30,6 +31,7 @@ import org.apache.poi.xssf.usermodel.XSSFWorkbook
 import java.io.File
 import java.io.FileReader
 import java.io.FileWriter
+import java.io.StringWriter
 import java.text.SimpleDateFormat
 import java.util.Date
 import java.util.Locale
@@ -157,15 +159,24 @@ class SettingsViewModel(application: Application) : AndroidViewModel(application
     fun exportToCSV(context: Context, customDir: File? = null) {
         viewModelScope.launch(Dispatchers.IO) {
             try {
+                val currentSettings = settings.value ?: Settings()
                 val timestamp =
                     SimpleDateFormat("yyyyMMdd_HHmmss", Locale.getDefault()).format(Date())
-                val fileName = "bookkeeping_backup_$timestamp.csv"
+                val shouldEncrypt = currentSettings.encryptBackup
+                val fileName = if (shouldEncrypt) {
+                    "bookkeeping_backup_$timestamp.csv.enc"
+                } else {
+                    "bookkeeping_backup_$timestamp.csv"
+                }
                 val downloadsDir = customDir ?: Environment.getExternalStoragePublicDirectory(
                     Environment.DIRECTORY_DOWNLOADS
                 )
                 val file = File(downloadsDir, fileName)
 
-                CSVWriter(FileWriter(file)).use { writer ->
+                // 先创建CSV内容到字符串
+                val csvContent = StringWriter().use { stringWriter ->
+                    val writer = CSVWriter(stringWriter)
+                    
                     // 写入头部
                     writer.writeNext(arrayOf("日期", "类型", "金额", "类别", "备注", "成员"))
 
@@ -189,11 +200,25 @@ class SettingsViewModel(application: Application) : AndroidViewModel(application
                             )
                         )
                     }
+                    writer.close()
+                    stringWriter.toString()
+                }
+
+                // 根据设置决定是否加密
+                if (shouldEncrypt) {
+                    val encryptedContent = EncryptionUtils.encrypt(csvContent)
+                    file.writeText(encryptedContent)
+                } else {
+                    file.writeText(csvContent)
                 }
 
                 withContext(Dispatchers.Main) {
-                    Toast.makeText(context, "CSV导出成功: ${file.absolutePath}", Toast.LENGTH_LONG)
+                    val message = if (shouldEncrypt) {
-                        .show()
+                        "CSV导出成功（已加密）: ${file.absolutePath}"
+                    } else {
+                        "CSV导出成功: ${file.absolutePath}"
+                    }
+                    Toast.makeText(context, message, Toast.LENGTH_LONG).show()
                 }
             } catch (e: Exception) {
                 e.printStackTrace()
@@ -207,6 +232,9 @@ class SettingsViewModel(application: Application) : AndroidViewModel(application
     fun exportToExcel(context: Context) {
         viewModelScope.launch(Dispatchers.IO) {
             try {
+                val currentSettings = settings.value ?: Settings()
+                val shouldEncrypt = currentSettings.encryptBackup
+                
                 val workbook = XSSFWorkbook()
                 val sheet = workbook.createSheet("账目记录")
 
@@ -239,18 +267,39 @@ class SettingsViewModel(application: Application) : AndroidViewModel(application
 
                 val timestamp =
                     SimpleDateFormat("yyyyMMdd_HHmmss", Locale.getDefault()).format(Date())
-                val fileName = "bookkeeping_backup_$timestamp.xlsx"
+                val fileName = if (shouldEncrypt) {
+                    "bookkeeping_backup_$timestamp.xlsx.enc"
+                } else {
+                    "bookkeeping_backup_$timestamp.xlsx"
+                }
                 val downloadsDir =
                     Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
                 val file = File(downloadsDir, fileName)
 
-                workbook.write(file.outputStream())
+                if (shouldEncrypt) {
+                    // 将 workbook 写入字节数组
+                    val byteArrayOutputStream = java.io.ByteArrayOutputStream()
+                    workbook.write(byteArrayOutputStream)
+                    val excelBytes = byteArrayOutputStream.toByteArray()
+                    
+                    // 加密字节数组
+                    val encryptedBytes = EncryptionUtils.encryptBytes(excelBytes)
+                    
+                    // 写入加密文件
+                    file.writeBytes(encryptedBytes)
+                } else {
+                    workbook.write(file.outputStream())
+                }
+                
                 workbook.close()
 
                 withContext(Dispatchers.Main) {
-                    Toast.makeText(
+                    val message = if (shouldEncrypt) {
-                        context, "Excel导出成功: ${file.absolutePath}", Toast.LENGTH_LONG
+                        "Excel导出成功（已加密）: ${file.absolutePath}"
-                    ).show()
+                    } else {
+                        "Excel导出成功: ${file.absolutePath}"
+                    }
+                    Toast.makeText(context, message, Toast.LENGTH_LONG).show()
                 }
             } catch (e: Exception) {
                 e.printStackTrace()
@@ -265,10 +314,30 @@ class SettingsViewModel(application: Application) : AndroidViewModel(application
         viewModelScope.launch(Dispatchers.IO) {
             try {
                 when {
+                    backupFile.name.endsWith(".csv.enc", ignoreCase = true) -> {
+                        // 解密CSV文件
+                        val encryptedContent = backupFile.readText()
+                        val decryptedContent = EncryptionUtils.decrypt(encryptedContent)
+                        val tempFile = File(context.cacheDir, "temp_decrypted.csv")
+                        tempFile.writeText(decryptedContent)
+                        restoreFromCSV(tempFile)
+                        tempFile.delete()
+                    }
+                    
                     backupFile.name.endsWith(".csv", ignoreCase = true) -> {
                         restoreFromCSV(backupFile)
                     }
 
+                    backupFile.name.endsWith(".xlsx.enc", ignoreCase = true) -> {
+                        // 解密Excel文件
+                        val encryptedBytes = backupFile.readBytes()
+                        val decryptedBytes = EncryptionUtils.decryptBytes(encryptedBytes)
+                        val tempFile = File(context.cacheDir, "temp_decrypted.xlsx")
+                        tempFile.writeBytes(decryptedBytes)
+                        restoreFromExcel(tempFile)
+                        tempFile.delete()
+                    }
+                    
                     backupFile.name.endsWith(".xlsx", ignoreCase = true) -> {
                         restoreFromExcel(backupFile)
                     }
@@ -287,7 +356,11 @@ class SettingsViewModel(application: Application) : AndroidViewModel(application
             } catch (e: Exception) {
                 e.printStackTrace()
                 withContext(Dispatchers.Main) {
-                    Toast.makeText(context, "数据恢复失败: ${e.message}", Toast.LENGTH_LONG).show()
+                    val errorMessage = when {
+                        e.message?.contains("decrypt") == true -> "解密失败，请确认文件未损坏"
+                        else -> "数据恢复失败: ${e.message}"
+                    }
+                    Toast.makeText(context, errorMessage, Toast.LENGTH_LONG).show()
                 }
             }
         }
@@ -343,4 +416,10 @@ class SettingsViewModel(application: Application) : AndroidViewModel(application
     private suspend fun findMemberIdByName(name: String): Int? {
         return memberDao.getAllMembers().first().find { member -> member.name == name }?.id
     }
+    
+    fun updateSettings(settings: Settings) {
+        viewModelScope.launch {
+            settingsRepository.updateSettings(settings)
+        }
+    }
 }