MyCardholder

An open source cardholder app to store you cards in one place.

Backup logic

The following terminology is used below:

• Cloud checksum - backup file name.
• Local checksum - sum of all card timestamps.

Backup Download

sequenceDiagram
    participant Client
    participant Cloud

    Note over Client, Cloud: Getting cloud checksum
    Client->>Cloud: Get cloud checksum
    Cloud-->>Client: Cloud checksum
    
    Note over Client: Comparison of checksums
    Client->>Client: Compare Cloud checksum > Local checksum
    alt New backup available
        Note over Client, Cloud: Download backup file
        Client->>Cloud: Get backup file
        Cloud-->>Client: Backup file bytes
        
        Note over Client: Import data from backup file
        Client->>Client: Reading cards from a backup file
        Client->>Client: Import cards into the database

        Client->>Client: Backup downloaded successfully
    else No download required
        Note over Client: Skip Download
        Client->>Client: Backup is up-to-date
    end

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Backup Upload

sequenceDiagram
    participant Client
    participant Cloud

    Note over Client, Cloud: Getting cloud checksum
    Client->>Cloud: Get cloud checksum
    Cloud-->>Client: Cloud checksum
    
    Note over Client: Comparison of checksums
    Client->>Client: Compare Cloud checksum < Local checksum
    alt Cloud upload required
        Note over Client: Writing a new backup file
        Client->>Client: Export cards from the database
        Client->>Client: Writing cards to a backup file

        Note over Client, Cloud: Upload backup file
        Client->>Cloud: Backup file bytes
        Cloud-->>Client: OK        

        Client->>Client: Backup uploaded successfully
    else No upload required
        Note over Client: Skip Upload
        Client->>Client: Backup is up-to-date
    end

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Tech-stack

• Kotlin
  • Android KTX - set of extensions that are included with Android Jetpack and other Android libraries
  • Coroutines - recommended solution for asynchronous programming on Android
  • Kotlin Flow - data flow across all app layers, including views
• Firebase
  • ML Kit's barcode scanning
• Jetpack
  • CameraX - camera capabilities
  • Constraintlayout - position and size widgets in a flexible way with relative positioning
  • Hilt - dependency injection
  • Lifecycle - perform an action when lifecycle state changes
  • Navigation - in-app navigation
  • Room - store offline cache
• Coil - image loading library
• ZXing - barcode encoding/decoding library

UI

• View Binding - retrieve xml view ids
• Material Design 3 - application design system providing UI components
• Dark Theme - dark theme for the app (Android 10+)