A fuel tracker that never phones home.

01Overview

TankIt is a personal fuel management app for drivers in Austria and France. The core loop is simple: snap a photo of a fuel receipt, let the app read it automatically, and watch your history, efficiency, and spending build up over time.

On top of that, a real-time price finder surfaces the cheapest station near you, and home screen widgets bring key numbers to a glance.

A privacy-first iOS app that turns fuel receipts into spending insights, finds the cheapest nearby station in real time, and stays out of the cloud.

02Privacy

Privacy isn’t a feature, it’s a constraint that shapes every other decision. Concretely:

• All ML inference (OCR, rectangle detection, LLM extraction) runs entirely on-device.
• No analytics SDK, no crash reporter that phones home, no user accounts.
• Receipt images are stored locally on your iPhone, never transmitted.
• The only network calls leave the device for the two government price APIs — and only your GPS coordinate goes with them.
• You can export the entire dataset (CSV + ZIP of receipts) at any time. Nothing to lock in.

03On-device intelligence

OCR — Apple Vision framework

VNRecognizeTextRequest runs at .accurate level, with language correction tuned per use case:

• Receipt text → language correction enabled, languages ["fr-FR", "de-AT", "en-US"].
• Odometer photos → language correction disabled so digit sequences aren’t mangled into words.

Structured extraction — LLM + regex pipeline

After OCR produces raw text, ExtractionService runs a two-stage pipeline:

• LLM path (Foundation Models, when available): Apple’s FoundationModels framework (LanguageModelSession) with a @Generable structured output type — the on-device model returns typed fields directly, no string parsing. @Guide annotations steer each field toward the expected format.
• Regex fallback: A hand-crafted multilingual parser for receipts from French, Austrian, and German stations — covering labelled patterns (Prix/L, Preis/L, GESAMTSUMME, NET À PAYER) and free-form layouts. A derived-value step closes the price triangle: if any one of {total, volume, price/L} is missing but the other two are present, it calculates the third.

Receipt image correction

ReceiptCorrectionView wraps VNDetectRectanglesRequest to find the receipt boundary, then applies a perspective warp. Available both immediately after scanning and retrospectively from the fill history.

04External APIs

The only outbound traffic from TankIt: two official government fuel price registries. No third-party data brokers, no scraping.

Routing — FuelPriceRouter

A shared router abstracts both APIs behind a single fetch(coordinate:countryCode:fuelType:) call. It:

• Auto-detects the relevant country from GPS coordinates.
• Caches results for 10 minutes with a ~1 km grid quantisation key.
• Persists the cheapest station to the App Group UserDefaults so widgets always show fresh data without their own network call.
• Triggers a WidgetCenter.shared.reloadTimelines after each successful fetch.

Apple Maps — navigation deep-link

The price finder uses maps://?daddr=lat,lon&dirflg=d to open turn-by-turn navigation with zero additional SDK dependencies.

05Tech stack

Language & UI

• Swift 6 — strict concurrency throughout (@MainActor, Sendable, structured tasks).
• SwiftUI — 100% declarative UI; the only UIKit view controller is the camera viewfinder.
• WidgetKit — four widget types (small + medium for both price finder and efficiency).

Persistence

• SwiftData — model layer (FuelEntry, Vehicle) with @Model annotations, relationship rules, and reverse-index queries.
• UserDefaults (App Group) — shared container group.com.tankit.app for passing live data between the main app and widgets without a server round-trip.

Intelligence

• Apple Vision — on-device OCR & rectangle detection.
• FoundationModels — on-device LLM for structured field extraction, with a regex fallback when the framework isn’t available.
• StoreKit 2 — modern transaction-listener subscription model.

06Architecture highlights

07Platform & requirements

• iOS 18+, iPhone only. On-device LLM extraction kicks in where Foundation Models is available; a regex parser handles the rest.
• Xcode 16 / Swift 6.
• Location permission for price finder (optional — manual address search available).
• Camera permission for receipt scanning (optional — manual entry available).