Implement Todo Save Functionality with Room Database

.gitignore

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+# Android Studio
+*.iml
+.gradle
+/local.properties
+/.idea/
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+
+# Gradle files
+gradle/
+gradlew
+gradlew.bat
+
+# Dependency directories
+/node_modules/
+
+# Compiled class files
+*.class
+
+# Log files
+*.log
+
+# Package Files
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# Virtual machine crash logs
+hs_err_pid*
+
+# Android build output
+bin/
+out/

build.gradle.kts

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+plugins {
+    id("com.android.application")
+    id("kotlin-android")
+    id("kotlin-kapt")
+    id("dagger.hilt.android.plugin")
+}
+
+dependencies {
+    // Room Database
+    implementation("androidx.room:room-runtime:2.5.1")
+    implementation("androidx.room:room-ktx:2.5.1")
+    kapt("androidx.room:room-compiler:2.5.1")
+
+    // Coroutines
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.6.4")
+
+    // Testing
+    testImplementation("junit:junit:4.13.2")
+    testImplementation("io.mockk:mockk:1.13.5")
+    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.6.4")
+    androidTestImplementation("androidx.test.ext:junit:1.1.5")
+    androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")
+}

src/main/java/com/example/todoapp/data/dao/TodoDao.kt

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+package com.example.todoapp.data.dao
+
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.OnConflictStrategy
+import androidx.room.Query
+import com.example.todoapp.data.model.Todo
+import kotlinx.coroutines.flow.Flow
+
+@Dao
+interface TodoDao {
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun insertTodo(todo: Todo): Long
+
+    @Query("SELECT * FROM todos WHERE id = :todoId")
+    fun getTodoById(todoId: Long): Flow<Todo?>
+}

src/main/java/com/example/todoapp/data/model/Todo.kt

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+package com.example.todoapp.data.model
+
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+import java.time.LocalDateTime
+
+@Entity(tableName = "todos")
+data class Todo(
+    @PrimaryKey(autoGenerate = true)
+    val id: Long = 0,
+    val title: String,
+    val description: String? = null,
+    val isCompleted: Boolean = false,
+    val createdAt: LocalDateTime = LocalDateTime.now(),
+    val updatedAt: LocalDateTime = LocalDateTime.now()
+) {
+    // Validate todo item input
+    init {
+        require(title.isNotBlank()) { "Todo title cannot be blank" }
+        require(title.length <= 100) { "Todo title cannot exceed 100 characters" }
+        description?.let {
+            require(it.length <= 500) { "Todo description cannot exceed 500 characters" }
+        }
+    }
+}

src/main/java/com/example/todoapp/data/repository/TodoRepository.kt

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+package com.example.todoapp.data.repository
+
+import com.example.todoapp.data.dao.TodoDao
+import com.example.todoapp.data.model.Todo
+import kotlinx.coroutines.flow.Flow
+import javax.inject.Inject
+
+class TodoRepository @Inject constructor(
+    private val todoDao: TodoDao
+) {
+    suspend fun addTodo(todo: Todo): Long {
+        return todoDao.insertTodo(todo)
+    }
+
+    fun getTodoById(todoId: Long): Flow<Todo?> {
+        return todoDao.getTodoById(todoId)
+    }
+}

src/test/java/com/example/todoapp/data/repository/TodoRepositoryTest.kt

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+package com.example.todoapp.data.repository
+
+import com.example.todoapp.data.dao.TodoDao
+import com.example.todoapp.data.model.Todo
+import io.mockk.coEvery
+import io.mockk.mockk
+import kotlinx.coroutines.runBlocking
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class TodoRepositoryTest {
+    private val todoDao = mockk<TodoDao>()
+    private val todoRepository = TodoRepository(todoDao)
+
+    @Test
+    fun `addTodo should save todo item successfully`() = runBlocking {
+        // Arrange
+        val todo = Todo(title = "Test Todo")
+        coEvery { todoDao.insertTodo(todo) } returns 1L
+
+        // Act
+        val result = todoRepository.addTodo(todo)
+
+        // Assert
+        assertEquals(1L, result)
+    }
+
+    @Test(expected = IllegalArgumentException::class)
+    fun `addTodo should throw exception for blank title`() = runBlocking {
+        // Arrange
+        val todo = Todo(title = "")
+
+        // Act & Assert
+        todoRepository.addTodo(todo)
+    }
+
+    @Test(expected = IllegalArgumentException::class)
+    fun `addTodo should throw exception for title exceeding max length`() = runBlocking {
+        // Arrange
+        val longTitle = "a".repeat(101)
+        val todo = Todo(title = longTitle)
+
+        // Act & Assert
+        todoRepository.addTodo(todo)
+    }
+}