DuelistLP

A Yu-Gi-Oh!–themed Life Point tracker for Android and iOS, built as a Kotlin Multiplatform app with Compose Multiplatform UI. Two players, one device — track LP, settle who goes first with rock-paper-scissors, and let the soundtrack escalate as the duel tightens.

The app is fully offline. No accounts, no network, no analytics, no permissions beyond what audio playback needs.

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Features

• Dual-sided LP tracker. Two PlayerHalf panels — the second is rotated 180° so opponents seated across from each other both read their own side right-side-up.
• Fast LP adjustments. ±100, ±500, ±1000 quick buttons plus a custom-amount dialog. Long-press accelerates: ticks start at ~180 ms and ramp down to ~35 ms, so swinging from 8000 → 0 takes a couple of seconds.
• Target toggle. Each side can either modify its own LP or push damage onto the opponent — useful when one player is doing the math for both.
• Rock-paper-scissors first-player picker. Animated reveal, automatic re-rounds on ties. The result is recorded as a FirstPlayerDecided event in the match log.
• Adaptive soundtrack. Six looping OST tracks. The active track is chosen by DuelOstPicker against an LP threshold (half of starting LP):
  • both players above threshold → standard duel theme
  • one player below → losing theme
  • both below → tournament theme
  • LP recovery crossing back up → winning theme
• LP-change SFX. A looping tick plays while LP is moving; a settle chord resolves once the value stabilizes.
• Match history. Up to 200 matches persisted locally. Each match stores the full event timeline (every LP delta, the RPS rounds, the victory event) so you can replay it from the detail screen.
• Configurable starting LP. Presets for 2000 / 4000 / 8000 / 16000 plus custom input (minimum 100).
• No light theme. It's a Yu-Gi-Oh! app — purple/gold dark arena only.

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Tech stack

Layer	Choice
Language	Kotlin 2.3.21
UI	Compose Multiplatform 1.11.0-beta03 (Material3 1.11.0-alpha07)
Build	Gradle + AGP 9.1.1, JDK 21 (with desugar_jdk_libs 2.1.5 for older Android APIs)
Persistence	AndroidX DataStore Preferences 1.3.0-alpha08
Serialization	kotlinx-serialization-json 1.11.0
Concurrency	kotlinx-coroutines 1.10.2
Time	kotlinx-datetime 0.7.1
Audio (Android)	Media3 ExoPlayer 1.10.0
Audio (iOS)	AVFoundation (AVPlayer)
Android targets	compileSdk 36, minSdk 26, targetSdk 36
iOS targets	iosArm64 + iosSimulatorArm64, dynamic framework

Project metadata (appName, versionName, bundleIdBase, javaVersion) is owned by the io.github.yuroyami.kmpssot Gradle plugin in the root build.gradle.kts — change it there, not in per-platform configs.

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Repository layout

.
├── shared/                          Kotlin Multiplatform module (UI + logic)
│   └── src/
│       ├── commonMain/              Compose UI, models, audio controllers, store
│       │   ├── kotlin/              ~2.7k LOC — App, screens, components, audio
│       │   └── composeResources/    fonts, OST mp3s, SFX mp3s, background webp
│       ├── androidMain/             AudioEngine.android.kt (ExoPlayer),
│       │                            DuelStore.android.kt (DataStore on filesDir)
│       └── iosMain/                 AudioEngine.ios.kt (AVPlayer),
│                                    DuelStore.ios.kt (DataStore in Documents),
│                                    MainViewController.kt (UIViewController bridge)
├── androidApp/                      Single-Activity wrapper
│   └── src/main/                    AppActivity.kt, AndroidManifest.xml, theme/icons
├── iosApp/                          SwiftUI wrapper hosting Compose
│   └── iosApp/                      iOSApp.swift, KmpScreen.swift, Assets
├── build.gradle.kts                 Root — kmp-ssot config (appName, bundleId, version)
├── settings.gradle.kts              Modules: :androidApp, :shared
├── gradle/libs.versions.toml        Central version catalog
└── local.properties                 SDK paths (gitignored)

Launcher icons are generated on every Gradle sync from the SSOT logo and are gitignored — see .gitignore for the regeneration entrypoint (./gradlew :shared:generateAppIcons).

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Architecture

Navigation is intentionally minimal: App.kt holds a single mutableStateOf(Screen) and switches between Setup, Rps, Duel, History, and MatchDetail. There's no nav library.

State flow:

1. SetupScreen collects player names + starting LP and persists them via DuelStore.saveSettings(...).
2. RpsScreen runs the picking → revealing → result state machine and emits the first-player decision.
3. DuelScreen constructs an in-memory DuelState and mutates it as MatchEvents arrive (LpChange, Victory). When a player hits 0 LP it writes a finalized Match to DuelStore.
4. HistoryScreen and MatchDetailScreen read the persisted match list as a reactive Flow.

Models (commonMain):

sealed class MatchEvent {
    data class LpChange(timestamp, target: PlayerSlot, delta, before, after)
    data class FirstPlayerDecided(timestamp, firstPlayer, p1Pick, p2Pick, rounds)
    data class Victory(timestamp, winner: PlayerSlot)
}
data class DuelState(matchId, startedAt, player1, player2, startingLp,
                     firstPlayer, p1Lp, p2Lp, events, winner)
data class Match(/* same fields as DuelState plus endedAt + final LPs */)

Match is @Serializable and stored as a JSON string in DataStore under matches_json. The store keeps the most recent 200; older matches are dropped.

Audio is driven by two controllers exposed through CompositionLocal:

• LocalOst → OstController — swaps the looping background track. Track changes are mutex-guarded so rapid LP swings don't race the player.
• LocalLpSfx → LpSfxController — runs the LP-change tick loop and fires the settle chord once the LP value has been stable for the debounce window.

Both sit on top of an expect class AudioEngine with two implementations:

• Android writes resource bytes into cacheDir/audio/ and feeds the file:// URI to a Media3 ExoPlayer. Initialized via AudioEngineContext.init(context) in AppActivity.onCreate.
• iOS writes bytes into ~/Library/Caches/audio/ via NSFileManager and plays them through AVPlayer, looping by observing AVPlayerItemDidPlayToEndTime. Sets AVAudioSessionCategoryPlayback so audio survives mixing/backgrounding.

Persistence mirrors the audio split: DuelStoreFactory is expect/actual. Android initializes against context.filesDir; iOS resolves the Documents directory through NSFileManager. Both produce a DataStore at duelistlp.preferences_pb storing starting_lp, player1, player2, and matches_json.

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Running it

Prerequisites

• JDK 21
• Android SDK with compileSdk = 36 available (Android Studio Ladybug+ recommended)
• For iOS: macOS with Xcode 15+, an iOS 14+ simulator or device

Android

./gradlew :androidApp:installDebug

Or open the project in Android Studio and run the androidApp configuration. Debug builds get the .debug application-id suffix so they install alongside release.

iOS

The shared module produces a dynamic framework consumed by the Xcode project.

1. Build the framework once so Xcode can link it:

   ./gradlew :shared:linkDebugFrameworkIosSimulatorArm64

2. Open iosApp/iosApp.xcodeproj in Xcode.
3. Pick a simulator (or your device) and run.

iOSApp.swift disables the idle timer (UIApplication.shared.isIdleTimerDisabled = true) so the screen doesn't sleep mid-duel.

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Theme

Defined in DuelColors.kt:

Token	Hex	Used for
DuelGold	#E8B852	primary accents, buttons
DuelGoldGlow	#FFE07C	highlights
LpYellow	#FFE34C	LP digits
LpStroke	#1B1206	LP digit outline
DuelPurple	#2A1F62	mid-stop background
DuelPurpleDeep	#120A33	bottom-stop background
Crimson	#D7263D	damage / negative deltas
EmeraldHeal	#14C38E	recovery / positive deltas

Typography is the Heuristica family (Regular, Italic, Bold) bundled in composeResources/font/. LP digits use the italic cut with StrokedText for the inked-card-game look.

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Status

Single-developer project at versionName = 0.1.0. Core feature set is complete and exercised end-to-end on both platforms. There are no automated tests yet and no TODOs left in source.