2026-04-28 · architecture 5 min
MVI over MVVM: why StateFlow + SharedFlow is the right shape for Android
read →
# uptime
by the numbers
CASE_01 · 2024–present · TIKTOK_USDS_JV
I lead the architecture and evolution of TikTok USDS JV's custom mobile security SDK across Android, iOS, and macOS — shared C++ core, encrypted JNI bridge, ARM64/x86-64 hardening at the assembly level. The work modernized the cross-platform core and migrated us off commercial obfuscators — technical sovereignty over a security stack running on the TikTok app at an average 1.9B DAU.
scale
average DAU running the SDK
CASE_02 · 2022–2024 · ZETTLE_US
I led the Android Key-In and PayPal Invoicing features for Zettle's US launch, drove early architecture decisions across the Stockholm timezone gap, and built the custom design system library shared between PayPal Here and Zettle modules. Introduced TalkBack and accessibility into both surfaces; wrote the Kotlin microservices that bridge PayPal's payment systems with Zettle's invoicing and manual-card-input flows.
CASE_03 · 2020–2022 · PAYPAL_HERE
I owned the Android application for PayPal Here, the company's hardware-anchored POS — 600K+ merchants globally, 200K+ active on Android across multiple countries. I defined the global standard for POS hardware integration and led the Verifone terminal work — Bluetooth and IP transport, EMVco-spec data exchange, card-type-based POS activation routed back to the back-office service.
scale
merchants on the POS platform
CASE_04 · 2014–2018 · VISA_VTS
I led the Android SDK for the Visa Token Service (VTS), enabling card issuers to ship NFC/HCE mobile payments inside their banking apps. Built the JNI-Bridge — hardened Java↔C with encrypted channels — managed OpenSSL inside the NDK for RSA key generation in C, and shipped ARXAN obfuscation with a custom stack-trace system that kept the SDK supportable with zero symbol exposure.
Open-source pieces of the closed-source work. Edit on GitHub; the site repopulates within a minute, no redeploy.
alex@arguello ~/lab $ ls -lh --sort=time total 1 demos · last fetch 2026-04-27 14:03:11Z superapp ★ 2026-04-28 hybrid Compose + RN super-app — offline-first, OTA-updatable architecture alex@arguello ~/lab $ _