Migrate SDK to Kotlin Multiplatform (KMP) for use in KMP/CMP projects

[michelutke]

Summary

The Updraft SDK is currently an Android-only library (com.android.library module using Retrofit/RxJava2, ViewBinding, Fragments/Activities). More and more of our projects are built with Kotlin Multiplatform (KMP) and Compose Multiplatform (CMP), where a single shared codebase targets Android and iOS. Today, these projects cannot use the Updraft SDK from shared code — Android apps must wire it up in androidMain platform code, and iOS targets have no Kotlin-consumable SDK at all (the separate updraft-sdk-ios exists, but must be integrated natively via Swift).

This issue requests migrating the SDK to KMP so it can be consumed as a single dependency from a KMP/CMP project's commonMain, with feature parity on Android and iOS.

Motivation

• KMP/CMP is the default stack for new mobile projects at many agencies (including ours) — an Android-only SDK forces per-platform integration glue or dropping Updraft features on iOS.
• Auto-update and feedback logic (version comparison, API calls, settings) is platform-agnostic business logic — a natural fit for commonMain.
• One SDK codebase instead of two (updraft-sdk-android + updraft-sdk-ios) reduces maintenance and feature drift between platforms.

Proposed scope

Phase 1 — KMP core (shared business logic)

Extract non-UI logic into a commonMain module:

• Networking: replace Retrofit/OkHttp with Ktor Client; keep kotlinx.serialization (already in use).
• Concurrency: replace RxJava2 with Kotlin Coroutines/Flow.
• Domain logic: CheckUpdateInteractor, CheckFeedbackEnabledInteractor, version comparison, Settings, API request/response models.
• Storage/prefs: expect/actual or multiplatform-settings.
• Public API entry point (Updraft.initialize(...)) callable from commonMain.

Phase 2 — Platform integrations (expect/actual)

• Screenshot capture, shake detection, install/update flow (APK install vs. TestFlight/itms link), current-activity/lifecycle tracking.
• Android actual reuses existing implementations; iOS actual implemented in Kotlin/Native or bridged to existing iOS SDK internals.

Phase 3 — CMP UI (optional, follow-up)

• Rebuild feedback form + drawing/annotation UI (currently ViewBinding Fragments + custom FreeDrawView) in Compose Multiplatform so the whole feedback flow is shared.
• Until then, platform-native UI can remain behind an interface.

Non-goals (for now)

• Desktop/web targets — Android + iOS first.
• Breaking the existing Android-only artifact: com.appswithlove.updraft:updraft-sdk should keep working, e.g. by publishing the KMP artifact alongside or making the Android artifact a thin wrapper.

Acceptance criteria

• SDK consumable from commonMain of a KMP project targeting Android + iOS
• Auto-update check works on both platforms from shared code
• Feedback flow (screenshot + annotate + submit) works on both platforms
• Existing Android integration path keeps working (no breaking change without a major version bump)
• Sample CMP app added to the repo demonstrating integration
• README documents KMP setup

Open questions

• Relationship to updraft-sdk-ios: replace it, or keep it and share only the core?
• Minimum supported Kotlin/AGP versions for consumers?
• Keep Loco-based string localization, or move to a multiplatform resource solution (e.g. compose-resources / moko-resources)?
• Is CMP UI (Phase 3) required for a first release, or is shared core + native UI enough?

References

• Current Android SDK stack: Retrofit 2 + RxJava2 adapter, kotlinx.serialization, ViewBinding, Fragments, androidx.startup, custom FreeDrawView for annotations
• updraft-sdk-ios
• Kotlin Multiplatform library authoring docs

[michelutke]

Shipped to main via #14 (merged into the M1 branch) + #15: the SDK is now Kotlin Multiplatform with Android + iOS targets, a shared Compose Multiplatform feedback UI, and an XCFramework for pure-Swift consumers. Release checklist for 2.0.0 lives in docs/kmp-migration-m1-status.md; toolchain follow-up in #16.