Multi-Module Deep Dive

Dependency graph

:feature:attachment ──────┐
:feature:compose ─────────┤
:feature:detail ──────────┤
:feature:inbox ───────────┤
:feature:settings ────────┤
:feature:auth ────────────┤
                          ├──> :core:data ──> :core:database ──> :core:model
                          │       │                                   │
                          │       └──> :core:network ─────────────────┤
                          │       └──> :core:pgp ─────────────────────┤
                          │
:app ─────────────────────┴──> :core:designsystem ──> :core:model

Module responsibilities

:core:model — Pure library

• No Android framework dependencies.
• No plugins (no Hilt, no Compose, no KSP).
• Contains: Email, EmailThread, EmailAttachment, EmailEvent, AppConfig, InboxTab, StringUtils, EmailHtmlSafety.
• All other modules depend on this.

:core:designsystem — Theme + components

• Compose-only library (kotlin.compose plugin, no KSP/Hilt).
• Contains: MonoMailTheme, Color, Type, shape, FontFamilies, Animations.
• Shared components: SlideSheet, AvatarCircle, BlurredModalOverlay, EmptyStateView, ShimmerEffect, etc.
• No business logic dependencies.

:core:database — Room + SQLCipher

• KSP for Room annotation processing.
• Hilt for injectable DAOs.
• Contains: AppDatabase (Room + SQLCipher), all entities, DAOs, Converters, migrations.

:core:network — Retrofit + providers

• Retrofit interfaces (GmailApi, OutlookApi).
• Provider implementations (GmailProvider, OutlookProvider, ImapProvider).
• EmailProvider interface, ProviderModels, ProviderExceptions.
• RetrofitClient factory with auth interceptor.

:core:data — Repository layer

• EmailRepository — central data access, bridges providers ↔ Room.
• auth/ — AuthManager, AccountManager, MicrosoftAuthManager, UserProfile, GoogleAuthHelper.
• settings/SettingsDataStore — all app settings.
• push/PushNotificationManager — interface + flavor-specific impls.
• worker/ — EmailSyncWorker, ScheduledSendWorker, NotificationActionReceiver.
• attachment/AttachmentCacheManager — temp file caching.

:core:pgp — Encryption engine

• PGPainless-based: PgpManager (encrypt/decrypt/sign), PgpKeyManager (key lifecycle), PgpKeyStorage (file+prefs persistence).
• SecurityUtil — AES-GCM via Android KeyStore.

:feature:* modules — Feature screens

• Each feature module is an Android library with Compose, KSP, and Hilt.
• Contains screens, ViewModels, and any feature-specific composables.
• Depends on :core:data and :core:designsystem.
• Never depends on another feature module.
• All navigation is owned by :app via NavGraph.kt.

Flavor distribution

Every module has a distribution flavor dimension with github and playstore variants:

• All modules must provide flavor-specific source sets if they differ.
• Module-level buildConfigField can expose flavor-specific values.
• :app consumes the correct variant of each module automatically based on its own flavor.

Flavor-specific code lives in src/{flavor}/java/ within the module:

:core:data/src/
  main/java/.../auth/GoogleAuthHelper.kt       // interface
  github/java/.../auth/GoogleAuthHelperImpl.kt  // no-op
  playstore/java/.../auth/GoogleAuthHelperImpl.kt  // real implementation