領域層最簡單的說法，就是這個類別只能引用 Kotlin，所以不能在 import 看到 Android 的東西

例如

import android.content.Context

AI 寫扣經過

1. 建立 Note，用來儲存筆記

   data class Note(
       val id: Long = 0,
       val title: String,
       val content: String,
       val categoryId: Long,
       val tags: List<String>,
       val createdAt: Long,
       val updatedAt: Long
   )
   

2. 建立筆記的分類，用來分類筆記

   data class Category(
       val id: Long = 0,
       val name: String,
       val sortOrder: Int
   )
   

3. 建立介面，用來管理筆記操作。介面這種東西，最萬用的說明就是搖控器，你不需要知道按下音量鍵大聲的邏輯和操作，只要知道他會大聲就好

   interface NoteRepository {
   
       fun getAllNotes(): Flow<List<Note>>
   
       fun getAllCategories(): Flow<List<Category>>
   
       suspend fun getNoteById(id: Long): Note?
   
       suspend fun saveNote(note: Note)
   
       suspend fun deleteNote(note: Note)
   
       suspend fun saveCategory(category: Category)
   
       suspend fun deleteCategory(category: Category)
   }
   

4. 建立 CategoryEntity 和 Category 的轉換器

   fun NoteEntity.toDomain(): Note {
       return Note(
           id = this.id,
           title = this.title,
           content = this.content,
           categoryId = this.categoryId,
           tags = this.tags,
           createdAt = this.createdAt,
           updatedAt = this.updatedAt
       )
   }
   
   fun Note.toEntity(): NoteEntity {
       return NoteEntity(
           id = this.id,
           title = this.title,
           content = this.content,
           categoryId = this.categoryId,
           tags = this.tags,
           createdAt = this.createdAt,
           updatedAt = this.updatedAt
       )
   }
   
   fun CategoryEntity.toDomain(): Category {
       return Category(
           id = this.id,
           name = this.name,
           sortOrder = this.sortOrder
       )
   }
   
   fun Category.toEntity(): CategoryEntity {
       return CategoryEntity(
           id = this.id,
           name = this.name,
           sortOrder = this.sortOrder
       )
   }
   

5. 建立 NoteRepositoryImpl，透過 Hilt 注入 NoteDao 和 CategoryDao，實現 NoteRepository 介面

   class NoteRepositoryImpl @Inject constructor(
       private val noteDao: NoteDao,
       private val categoryDao: CategoryDao
   ) : NoteRepository {    
   
       override fun getAllNotes(): Flow<List<Note>> {
           return noteDao.getAllNotes().map { entities ->
               entities.map { it.toDomain() }
           }
       }   
   
       override fun getAllCategories(): Flow<List<Category>> {
           return categoryDao.getAllCategories().map { entities ->
               entities.map { it.toDomain() }
           }
       }   
   
       override suspend fun getNoteById(id: Long): Note? {
           return noteDao.getNoteById(id)?.toDomain()
       }   
   
       override suspend fun saveNote(note: Note) {
           noteDao.insertNote(note.toEntity())
       }   
   
       override suspend fun deleteNote(note: Note) {
           noteDao.deleteNote(note.toEntity())
       }   
   
       override suspend fun saveCategory(category: Category) {
           categoryDao.insertCategory(category.toEntity())
       }   
   
       override suspend fun deleteCategory(category: Category) {
           categoryDao.deleteCategory(category.toEntity())
       }
   }
   

6. 建立 RepositoryModule 處理綁定的問題

   @Module
   @InstallIn(SingletonComponent::class)
   abstract class RepositoryModule {
   
       @Binds
       @Singleton
       abstract fun bindNoteRepository(
           noteRepositoryImpl: NoteRepositoryImpl
       ): NoteRepository
   }