Implement Room Database Entity for Todo Items

.gitignore

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+# Gradle files
+.gradle/
+build/
+
+# Local configuration file
+local.properties
+
+# Android Studio generated files
+*.iml
+.idea/
+
+# Compiled class files
+*.class
+
+# Log files
+*.log
+
+# Android generated files
+bin/
+gen/
+out/
+
+# Dependency directories
+/captures
+.externalNativeBuild
+.cxx
+
+# macOS system files
+.DS_Store
+
+# Backup files
+*.bak
+*.swp
+
+# Kotlin build artifacts
+*.jar
+*.war
+*.ear
+
+# Virtual machine crash logs
+hs_err_pid*
+
+# Android Profiling
+*.hprof

app/build.gradle.kts

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+plugins {
+    id("com.android.application")
+    id("org.jetbrains.kotlin.android")
+    id("kotlin-kapt")
+}
+
+android {
+    namespace = "com.todoapp"
+    compileSdk = 33
+
+    defaultConfig {
+        applicationId = "com.todoapp"
+        minSdk = 24
+        targetSdk = 33
+        versionCode = 1
+        versionName = "1.0"
+
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_1_8
+        targetCompatibility = JavaVersion.VERSION_1_8
+    }
+    kotlinOptions {
+        jvmTarget = "1.8"
+    }
+}
+
+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")
+
+    // Kotlin standard library
+    implementation("org.jetbrains.kotlin:kotlin-stdlib:1.8.20")
+
+    // Testing
+    testImplementation("junit:junit:4.13.2")
+    testImplementation("org.jetbrains.kotlin:kotlin-test:1.8.20")
+
+    // Android testing
+    androidTestImplementation("androidx.test.ext:junit:1.1.5")
+    androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")
+}

app/src/main/java/com/todoapp/data/entity/Todo.kt

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+package com.todoapp.data.entity
+
+import androidx.room.ColumnInfo
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+import java.time.LocalDateTime
+
+/**
+ * Room database entity representing a Todo item.
+ * 
+ * @property id Unique identifier for the Todo item
+ * @property title Title of the Todo item
+ * @property description Detailed description of the Todo item
+ * @property isCompleted Indicates whether the Todo item is completed
+ * @property createdAt Timestamp of when the Todo item was created
+ * @property dueDate Optional due date for the Todo item
+ */
+@Entity(tableName = "todos")
+data class Todo(
+    @PrimaryKey(autoGenerate = true)
+    val id: Int = 0,
+
+    @ColumnInfo(name = "title")
+    val title: String,
+
+    @ColumnInfo(name = "description")
+    val description: String? = null,
+
+    @ColumnInfo(name = "is_completed")
+    val isCompleted: Boolean = false,
+
+    @ColumnInfo(name = "created_at")
+    val createdAt: LocalDateTime = LocalDateTime.now(),
+
+    @ColumnInfo(name = "due_date")
+    val dueDate: LocalDateTime? = null
+) {
+    /**
+     * Validates the Todo item properties.
+     * 
+     * @throws IllegalArgumentException if validation fails
+     */
+    init {
+        require(title.isNotBlank()) { "Title cannot be blank" }
+        require(title.length <= 100) { "Title cannot exceed 100 characters" }
+        description?.let {
+            require(it.length <= 500) { "Description cannot exceed 500 characters" }
+        }
+    }
+}

app/src/test/java/com/todoapp/data/entity/TodoTest.kt

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+package com.todoapp.data.entity
+
+import org.junit.Test
+import java.time.LocalDateTime
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertNotNull
+
+class TodoTest {
+
+    @Test
+    fun `create todo with valid data`() {
+        val todo = Todo(
+            title = "Test Todo",
+            description = "Test description"
+        )
+
+        assertNotNull(todo)
+        assertEquals("Test Todo", todo.title)
+        assertEquals("Test description", todo.description)
+        assertEquals(false, todo.isCompleted)
+        assertNotNull(todo.createdAt)
+    }
+
+    @Test
+    fun `create todo with all properties`() {
+        val dueDate = LocalDateTime.now().plusDays(1)
+        val todo = Todo(
+            title = "Complete project",
+            description = "Finish the todo app implementation",
+            isCompleted = true,
+            dueDate = dueDate
+        )
+
+        assertEquals("Complete project", todo.title)
+        assertEquals("Finish the todo app implementation", todo.description)
+        assertEquals(true, todo.isCompleted)
+        assertEquals(dueDate, todo.dueDate)
+    }
+
+    @Test
+    fun `fail to create todo with blank title`() {
+        assertFailsWith<IllegalArgumentException> {
+            Todo(title = "")
+        }
+    }
+
+    @Test
+    fun `fail to create todo with title exceeding 100 characters`() {
+        val longTitle = "a".repeat(101)
+        assertFailsWith<IllegalArgumentException> {
+            Todo(title = longTitle)
+        }
+    }
+
+    @Test
+    fun `fail to create todo with description exceeding 500 characters`() {
+        val longDescription = "a".repeat(501)
+        assertFailsWith<IllegalArgumentException> {
+            Todo(
+                title = "Valid Title",
+                description = longDescription
+            )
+        }
+    }
+}