WalkLog App

A Health Connect-powered Android walking companion that turns daily steps into missions, reports, recaps, and widgets.

WalkLog App

WalkLog reads today's step count through Google Health Connect and turns walking activity into missions, weekly reports, monthly recaps, home insights, and app widgets.

Deep Dive Docs

Deep Dive Docs are currently maintained in Korean. English versions will be added later.

Document	Topic
Baseline Profile	ART JIT vs AOT, profile generation, cold-start improvements, and setup
R8 Obfuscation	Shrinking, obfuscation, optimization, APK size reduction, and ProGuard rules
Security Design	Network Security Config, MitM defense, backup protection, and OWASP mapping
Architecture Decision Records	Reasons and tradeoffs behind modularization, architecture, UDF, convention plugins, XML+Compose, and more
NDK/JNI Engine	C++ Walking Insights Engine design, JNI data flow, CMake setup, and algorithms
LiteRT Activity Classifier	On-device HAR model, sensor collection pipeline, tensor layout, and battery optimization
User Flow & Data Flow	End-to-end data flow from Health Connect collection to each screen

Features

Area	Key Features
Onboarding	Four-step `HorizontalPager` flow for nickname input, Health Connect permissions, goal setup, and notification permissions
Home	Real-time step count, goal progress, streak, weather-based walking card, and weekly report summary
Mission	Daily and recovery missions, peak-time-based recommended walking windows, and achievement point rewards
Weekly Report	Recent 12-week archive, detailed charts, and `FileProvider`-based image sharing
Monthly Recap	Eight story-style slides for monthly step data with auto-play and pause support
Step History	Calendar-based daily steps plus detailed activity data such as calories and distance
Settings	Profile, target steps, recovery steps, notifications, and light/dark/system theme settings
Reward	Locked teaser screen for future point redemption features
App Widget	Jetpack Glance widget with WorkManager-based automatic updates every 15 minutes

Screenshots

Architecture

This project follows the structure of Now in Android (NiA).

Layer Principles

Layer	Role	NiA Equivalent
`core:model`	Data classes	`core:model`
`core:data`	Repository	`core:data`
`core:domain`	Use cases	`core:domain`
`core:datastore`	DataSource	`core:datastore`
`core:database`	Room DB, DAO, Entity	`core:database`

core:model contains only pure Kotlin data classes and has no Android dependency.
core:database and core:datastore expose model types upward through api(core:model).
core:domain explicitly declares both api(core:data) and api(core:model).
Each ViewModel exposes a single StateFlow<UiState>, and UI state flows in one direction: Intent -> ViewModel -> State -> UI.

Module Graph

Generate the full dependency graph:

./gradlew projectDependencyGraph

Dependency Injection

Hilt is applied consistently across all layers.

Location	Approach
`@HiltAndroidApp`	`WalkLogApplication`, the root of the DI graph
`@AndroidEntryPoint`	All Fragments
`@HiltViewModel`	All ViewModels
`@Singleton`	`StepRepositoryImpl`, `HealthConnectStepDataSource`, and more
`@InstallIn(SingletonComponent)`	`DatabaseModule`, `DataModule`, `AnalyticsModule`, and more
Hilt WorkManager	`TodayMissionWidgetWorker`

// Interface binding example (core:analytics)
@Module
@InstallIn(SingletonComponent::class)
abstract class AnalyticsModule {
    @Binds
    abstract fun bindCrashReporter(impl: CrashlyticsReporter): CrashReporter
}

Step Data Pipeline

WalkLog uses Google Health Connect as its data source.

The datasource reads aggregated step counts from Health Connect. On app startup, the repository seeds the latest value into the database, then observes state through Room Flow. Use cases transform the data for each screen, and ViewModels expose it to feature screens through StateFlow<UiState>.

Design decisions:

Decision	Reason
Health Connect READ-ONLY	Health Connect handles deduplication, noise filtering, and multi-app aggregation
10-second polling (`observeCurrentSteps`)	Health Connect does not provide a real-time stream API
`onStart` Health Connect seed + Room Flow	Write the latest Health Connect value to DB, then reactively update through Room Flow
Keep `DailyStepEntity` local cache	Shows the latest cached value even when Health Connect is offline or permission is missing
`fallbackToDestructiveMigration()`	Health Connect migration (v2)
Missing date -> `DailyStepCount(steps = 0)`	Weekly, monthly, and calendar UIs can render complete date ranges

Points & Reward System

WalkLog grants points when missions are completed and prevents duplicate rewards through date-based payment history.

When the ViewModel detects mission completion from the real-time step count, the use case checks whether points have already been granted for today's mission type. If not, the Repository stores the points and last rewarded date in DataStore.

Crash Reporting

core:analytics abstracts Firebase Crashlytics so feature modules do not depend on Firebase directly.

feature:* -> CrashReporter (interface, core:analytics)
                  ^
         CrashlyticsReporter (impl, bound in app via Hilt)

interface CrashReporter {
    fun recordException(throwable: Throwable)
    fun log(message: String)
    fun setKey(key: String, value: String)
}

Centralized CrashKeys:

object CrashKeys {
    const val SCREEN = "screen"
    const val SENSOR_STATUS = "sensor_status"
    const val CURRENT_STEPS = "current_steps"
    const val TARGET_STEPS = "target_steps"
    const val WIDGET_INSTANCE_COUNT = "widget_instance_count"
    const val WORKER_RUN_ATTEMPT = "worker_run_attempt"

    object Screens {
        const val HOME = "home"
        const val WEEKLY_REPORT = "weekly_report"
        const val MISSION_DETAIL = "mission_detail"
        const val RECAP = "recap"
        const val FORECAST = "forecast"
        const val ONBOARDING = "onboarding"
        const val SETTINGS = "settings"
        const val HISTORY = "history"
    }
}

Performance

Baseline Profile

The :benchmark module follows the Now in Android pattern and separates Baseline Profile generation and performance measurement by screen-level subpackages.

# Generate Baseline Profile
./gradlew :app:generateBaselineProfile

# Measure startup time (None / Partial(Disable) / Partial(Require) / Full, 4 CompilationModes)
./gradlew :benchmark:connectedBenchmarkAndroidTest \
  -Pandroid.testInstrumentationRunnerArguments.class=com.river.walklog.benchmark.startup.StartupBenchmark

# Measure home scroll frame performance (None / Partial(Require) / Full, 3 CompilationModes)
./gradlew :benchmark:connectedBenchmarkAndroidTest \
  -Pandroid.testInstrumentationRunnerArguments.class=com.river.walklog.benchmark.home.ScrollHomeFeedBenchmark

Covered user flows:

StartupBaselineProfile: cold start -> enter Home screen (includeInStartupProfile = true)
HomeBaselineProfile: scroll Home, open Weekly Report, open Mission Detail

Measured metrics:

StartupBenchmark: StartupTimingMetric + JIT / ClassInit TraceSectionMetric, 20 iterations, COLD startup
ScrollHomeFeedBenchmark: FrameTimingMetric, 10 iterations, WARM startup

R8 Full Mode

R8 full optimization is enabled for release builds.

getByName("release") {
    isMinifyEnabled = true
    isShrinkResources = true
}

Security

Network Security Config

<network-security-config>
    <base-config cleartextTrafficPermitted="false">
        <trust-anchors>
            <certificates src="system" />
        </trust-anchors>
    </base-config>
    <debug-overrides>
        <trust-anchors>
            <certificates src="system" />
            <certificates src="user" />
        </trust-anchors>
    </debug-overrides>
</network-security-config>

Backup / Data Protection

<cloud-backup>
    <exclude domain="database" path="." />
    <exclude domain="file" path="datastore" />
</cloud-backup>

Room DB data (step history) and DataStore data (nickname, points, settings) are excluded from cloud backup and device transfer.

Testing

Test Strategy

Location	Runner	Target
`src/test/`	Robolectric JVM	Component units such as ViewModel, UseCase, Repository, and single Composable
`src/androidTest/`	Physical device / emulator	Full screens, tested at Route-level Compose UI

./gradlew test
./gradlew :core:domain:test
./gradlew :core:data:test
./gradlew :feature:home:test
./gradlew connectedAndroidTest

Test Coverage

Model layer - MissionTest (progressRatio boundaries)

Common layer - ResultTest (onSuccess / onError chaining)

Domain / Data layer

WeeklyStepSummaryTest, MonthlyRecapTest - domain model invariants
GetWeeklyStepSummaryUseCaseTest, GetWeeklyReportArchiveUseCaseTest, GetWeeklyBestHourUseCaseTest - aggregation, archive, and best-hour logic
StepRepositoryImplTest - Health Connect delegation, Flow mapping, zero-fill for missing dates

Feature ViewModel layer

HistoryViewModelTest - calendar item structure, month navigation, statistics formatting
OnboardingViewModelTest - four-step page transition state machine and repository call on completion
SettingsViewModelTest - nickname observation, point observation, and Intent-to-repository mapping

Compose UI tests (androidTest)

HomeScreenTest - UI for each sensor status: loading, no permission, unavailable, normal
WeeklyReportScreenTest - archive/detail rendering and share button state
MissionDetailScreenTest - before/after achievement states and back callback
RecapScreenTest - slide transition and pause/play
ForecastDetailBottomSheetTest - BottomSheet show/dismiss

Main Tools

MockK: Coroutine-friendly Kotlin mock library
Turbine: Flow testing library
Robolectric: Android environment emulation on the JVM
createAndroidComposeRule<ComponentActivity>(): NiA-style device test standard

Tech Stack

Area	Technology
Language	Kotlin 2.1.0, C++17
UI	Jetpack Compose, Material 3, XML Layouts + ViewBinding, XML Navigation host
Animation	Lottie
Architecture	MVVM, Google Recommended Architecture
DI	Hilt 2.55, Hilt WorkManager
Async	Kotlin Coroutines, Flow
Persistence	Room 2.7.1, DataStore Preferences
Network	OkHttp (KMA ultra-short-term forecast API), in-memory weather cache
On-device AI	LiteRT 1.0.1 (Activity Classifier), NDK/JNI (Walking Insights Engine)
Widget	Jetpack Glance 1.1.1, WorkManager
Analytics	Firebase Crashlytics, Firebase Analytics
Performance	Baseline Profile, R8 Full Mode
Security	Network Security Config, ProGuard/R8 obfuscation, backup protection
Image	Coil 3
Build	Gradle Kotlin DSL, Version Catalog, Convention Plugins, CMake 3.22.1
Testing	JUnit4, MockK, Turbine, Robolectric, Compose UI Test, Espresso

Convention Plugins

Plugin ID	Applied To	Includes
`river.android.application`	`:app`	compileSdk 36, minSdk 28, Kotlin Android, Hilt
`river.android.library`	Most `core:*` modules	compileSdk 36, minSdk 28, Kotlin Android, Hilt included automatically
`river.android.feature`	`feature:*`	Library base + Hilt + Compose + HiltNavigation
`river.android.compose`	Compose modules	Compose BOM, tooling, compiler plugin
`river.android.test`	Unit test modules	JUnit4, MockK, Turbine, Coroutines Test
`river.android.uitest`	Compose UI tests	Robolectric, Compose UI Test, Mock
`river.kotlin.library`	Pure Kotlin modules such as `core:domain`	JVM target, Kotlin only
`river.kotlin.test`	Pure Kotlin tests	JUnit, Kotlin Test, Coroutines Test

When adding a new feature module, declaring only id("river.android.feature") automatically applies Hilt, Compose, and test settings.

Getting Started

Requirements

Android Studio Hedgehog or later (includes JDK 21)
Android SDK 35
Firebase project + google-services.json

Build

./gradlew build
./gradlew installDebug
./gradlew assembleRelease

Module Specific

./gradlew :core:domain:test
./gradlew :core:data:test
./gradlew :feature:home:connectedAndroidTest
./gradlew :app:generateBaselineProfile
./gradlew projectDependencyGraph

Permissions

Permission	Required Version	Purpose
`android.permission.health.READ_STEPS`	Devices with Health Connect	Read step count
`PERMISSION_READ_HEALTH_DATA_IN_BACKGROUND`	Health Connect	Background widget updates
`INTERNET`	All versions	KMA weather API
`POST_NOTIFICATIONS`	API 33+	Peak-hour notifications
`RECEIVE_BOOT_COMPLETED`	All versions	Re-register AlarmManager after reboot

Health Connect Android 14+ manifest requirements: To show the Health Connect permission dialog correctly, both activity-alias declarations must be present in AndroidManifest.xml.

<activity-alias android:name=".HealthConnectPrivacyRationaleActivity" ...>
    <intent-filter>
        <action android:name="androidx.health.ACTION_SHOW_PERMISSIONS_RATIONALE" />
    </intent-filter>
</activity-alias>

<activity-alias android:name=".HealthConnectPermissionUsageActivity"
    android:permission="android.permission.START_VIEW_PERMISSION_USAGE" ...>
    <intent-filter>
        <action android:name="android.intent.action.VIEW_PERMISSION_USAGE" />
        <category android:name="android.intent.category.HEALTH_PERMISSIONS" />
    </intent-filter>
</activity-alias>

Next expansion points:

Reward store / badge collection / level system (feature:reward)
Place activity_classifier.tflite, then validate HAR classification on a physical device

Name		Name	Last commit message	Last commit date
Latest commit History 51 Commits
.github		.github
app		app
benchmark		benchmark
build-logic		build-logic
core		core
docs		docs
feature		feature
gradle		gradle
.editorconfig		.editorconfig
.gitignore		.gitignore
README.ko.md		README.ko.md
README.md		README.md
build.gradle.kts		build.gradle.kts
codecov.yml		codecov.yml
gradle.properties		gradle.properties
gradlew		gradlew
gradlew.bat		gradlew.bat
project.dot.png		project.dot.png
renovate.json		renovate.json
settings.gradle.kts		settings.gradle.kts

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WalkLog App

Deep Dive Docs

Contents

Features

Screenshots

Architecture

Layer Principles

Module Graph

Dependency Injection

Step Data Pipeline

Points & Reward System

Crash Reporting

Performance

Baseline Profile

R8 Full Mode

Security

Network Security Config

Backup / Data Protection

Testing

Test Strategy

Test Coverage

Main Tools

Tech Stack

Convention Plugins

Getting Started

Requirements

Build

Module Specific

Permissions

Next expansion points:

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