feat: add ktlint configuration and update code style guidelines

.editorconfig

@@ -0,0 +1,18 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 4
+max_line_length = 120
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{kt,kts}]
+ij_kotlin_code_style_defaults = KOTLIN_OFFICIAL
+ktlint_standard_filename = disabled
+ktlint_standard_function-naming = disabled
+ktlint_standard_package-name = disabled
+ktlint_standard_property-naming = disabled
+
+[**/build/generated/**/*.kt]
+ktlint = disabled

README.md

@@ -69,6 +69,22 @@ To build a debug APK for Android from the command line, run:
 Once the build completes successfully, the generated APK will be located at:
 `composeApp/build/outputs/apk/debug/composeApp-debug.apk`
 
+### Code Style
+Kotlin formatting is enforced with the Gradle ktlint plugin. Run the check before submitting Kotlin changes:
+```sh
+./gradlew ktlintCheck
+```
+
+Most formatting issues can be fixed automatically with:
+```sh
+./gradlew ktlintFormat
+```
+
+The ktlint setup lives in the Gradle version catalog, the root and `composeApp` Gradle scripts, and `.editorconfig`.
+Generated Kotlin files under `build/generated` are skipped, and a few existing project conventions are configured there:
+the `smiling_pixel` package segment, Compose-style function names, existing interface file names, and existing preference
+key naming.
+
 ### Running Tests
 To run all multiplatform tests across configured targets:
 ```sh
@@ -78,3 +94,11 @@ Or to run tests for a specific platform (e.g., Desktop/JVM):
 ```sh
 ./gradlew composeApp:jvmTest
 ```
+
+The broader Gradle verification command is:
+```sh
+./gradlew check
+```
+
+At the time ktlint was added, `ktlintCheck` passed, while `check` was intentionally not pursued further because the
+remaining failure was the unrelated Wasm yarn lock actualization task `kotlinWasmStoreYarnLock`.

build.gradle.kts

@@ -7,4 +7,5 @@ plugins {
     alias(libs.plugins.composeMultiplatform) apply false
     alias(libs.plugins.composeCompiler) apply false
     alias(libs.plugins.kotlinMultiplatform) apply false
-}
+    alias(libs.plugins.ktlint) apply false
+}

composeApp/build.gradle.kts

@@ -9,6 +9,7 @@ plugins {
     alias(libs.plugins.composeCompiler)
     alias(libs.plugins.composeHotReload)
     alias(libs.plugins.kotlinSerialization)
+    alias(libs.plugins.ktlint)
     alias(libs.plugins.ksp)
     alias(libs.plugins.room)
 }
@@ -18,33 +19,46 @@ plugins {
 
 val enableIos = project.findProperty("enableIos")?.toString()?.toBoolean() == true
 
+ktlint {
+    filter {
+        exclude("**/ActualResourceCollectors.kt")
+        exclude("**/AppDatabaseConstructor.kt")
+        exclude("**/AppDatabase_Impl.kt")
+        exclude("**/DiaryRoomDao_Impl.kt")
+        exclude("**/Drawable*.kt")
+        exclude("**/ExpectResourceCollectors.kt")
+        exclude("**/FileMetadataRoomDao_Impl.kt")
+        exclude("**/Res.kt")
+    }
+}
+
 kotlin {
     androidTarget {
         compilerOptions {
             jvmTarget.set(JvmTarget.JVM_11)
         }
     }
-    
+
     if (enableIos) {
         listOf(
             iosArm64(),
-            iosSimulatorArm64()
+            iosSimulatorArm64(),
         ).forEach { iosTarget ->
             iosTarget.binaries.framework {
                 baseName = "ComposeApp"
                 isStatic = true
             }
         }
     }
-    
+
     jvm()
-    
+
     @OptIn(ExperimentalWasmDsl::class)
     wasmJs {
         browser()
         binaries.executable()
     }
-    
+
     sourceSets {
         all {
             languageSettings.optIn("kotlin.time.ExperimentalTime")
@@ -71,7 +85,7 @@ kotlin {
             implementation(libs.kotlinx.coroutines.core)
             // Kotlinx serialization (used by typed navigation routes)
             implementation("org.jetbrains.kotlinx:kotlinx-serialization-core:1.9.0")
-            
+
             implementation(libs.ktor.client.core)
             implementation(libs.ktor.client.content.negotiation)
             implementation(libs.ktor.serialization.kotlinx.json)
@@ -81,7 +95,7 @@ kotlin {
             implementation(libs.coil.compose)
             implementation(libs.coil.network.ktor)
         }
-        
+
         val nonWebMain by creating {
             dependsOn(commonMain.get())
             dependencies {
@@ -134,12 +148,21 @@ room {
 
 android {
     namespace = "io.github.smiling_pixel.mark_day"
-    compileSdk = libs.versions.android.compileSdk.get().toInt()
+    compileSdk =
+        libs.versions.android.compileSdk
+            .get()
+            .toInt()
 
     defaultConfig {
         applicationId = "io.github.smiling_pixel.mark_day"
-        minSdk = libs.versions.android.minSdk.get().toInt()
-        targetSdk = libs.versions.android.targetSdk.get().toInt()
+        minSdk =
+            libs.versions.android.minSdk
+                .get()
+                .toInt()
+        targetSdk =
+            libs.versions.android.targetSdk
+                .get()
+                .toInt()
         versionCode = 1
         versionName = "1.0"
     }
@@ -148,18 +171,20 @@ android {
             // Exclude metadata files from Java libraries (like Google API clients)
             // that cause packaging conflicts (duplicate files) when merging into the APK.
             // These files are only used by desktop JVMs and are unnecessary on Android.
-            excludes += setOf(
-                "/META-INF/{AL2.0,LGPL2.1}",
-                "META-INF/INDEX.LIST",
-                "META-INF/DEPENDENCIES"
-            )
+            excludes +=
+                setOf(
+                    "/META-INF/{AL2.0,LGPL2.1}",
+                    "META-INF/INDEX.LIST",
+                    "META-INF/DEPENDENCIES",
+                )
             // Keep a single copy of license/notice files for OSS compliance
-            pickFirsts += setOf(
-                "META-INF/LICENSE",
-                "META-INF/LICENSE.txt",
-                "META-INF/NOTICE",
-                "META-INF/NOTICE.txt"
-            )
+            pickFirsts +=
+                setOf(
+                    "META-INF/LICENSE",
+                    "META-INF/LICENSE.txt",
+                    "META-INF/NOTICE",
+                    "META-INF/NOTICE.txt",
+                )
         }
     }
     buildTypes {

composeApp/src/androidMain/kotlin/io/github/smiling_pixel/MainActivity.kt

@@ -4,21 +4,19 @@ import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
+import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.tooling.preview.Preview
-import io.github.smiling_pixel.database.createDatabase
+import androidx.lifecycle.lifecycleScope
+import io.github.smiling_pixel.client.GoogleSignInHelper
 import io.github.smiling_pixel.database.DiaryRepository
+import io.github.smiling_pixel.database.createDatabase
 import io.github.smiling_pixel.filesystem.FileRepository
 import io.github.smiling_pixel.filesystem.fileManager
 import io.github.smiling_pixel.preference.AndroidContextProvider
-import androidx.lifecycle.lifecycleScope
 import kotlinx.coroutines.launch
 
-import androidx.activity.result.contract.ActivityResultContracts
-import io.github.smiling_pixel.client.GoogleSignInHelper
-
 class MainActivity : ComponentActivity() {
-
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         enableEdgeToEdge()
@@ -30,7 +28,7 @@ class MainActivity : ComponentActivity() {
                 lifecycleScope.launch {
                     GoogleSignInHelper.onActivityResult(result)
                 }
-            }
+            },
         )
 
         // Build Room-backed repository on Android and pass it into App
@@ -53,4 +51,4 @@ class MainActivity : ComponentActivity() {
 @Composable
 fun AppAndroidPreview() {
     App()
-}
+}

composeApp/src/androidMain/kotlin/io/github/smiling_pixel/Platform.android.kt

@@ -6,4 +6,4 @@ class AndroidPlatform : Platform {
     override val name: String = "Android ${Build.VERSION.SDK_INT}"
 }
 
-actual fun getPlatform(): Platform = AndroidPlatform()
+actual fun getPlatform(): Platform = AndroidPlatform()