bitwarden-android/src/App/Pages/Vault/ScanPage.xaml.cs

using System;
using System.Collections.Generic;
using Xamarin.Forms;

namespace Bit.App.Pages
{
    public partial class ScanPage : BaseContentPage
    {
        private readonly Action<string> _callback;

        private DateTime? _timerStarted = null;
        private TimeSpan _timerMaxLength = TimeSpan.FromMinutes(3);

        public ScanPage(Action<string> callback)
        {
            _callback = callback;
            InitializeComponent();
            _zxing.Options = new ZXing.Mobile.MobileBarcodeScanningOptions
            {
                UseNativeScanning = true,
                PossibleFormats = new List<ZXing.BarcodeFormat> { ZXing.BarcodeFormat.QR_CODE },
                AutoRotate = false,
            };
        }

        protected override void OnAppearing()
        {
            base.OnAppearing();
            _zxing.IsScanning = true;
            _timerStarted = DateTime.Now;
            Device.StartTimer(new TimeSpan(0, 0, 2), () =>
            {
                if(_timerStarted == null || (DateTime.Now - _timerStarted) > _timerMaxLength)
                {
                    return false;
                }
                _zxing.AutoFocus();
                return true;
            });
        }

        protected override void OnDisappearing()
        {
            _timerStarted = null;
            _zxing.IsScanning = false;
            base.OnDisappearing();
        }

        private void OnScanResult(ZXing.Result result)
        {
            // Stop analysis until we navigate away so we don't keep reading barcodes
            _zxing.IsAnalyzing = false;
            _zxing.IsScanning = false;
            if(!string.IsNullOrWhiteSpace(result?.Text) &&
                Uri.TryCreate(result.Text, UriKind.Absolute, out Uri uri) &&
                !string.IsNullOrWhiteSpace(uri?.Query))
            {
                var queryParts = uri.Query.Substring(1).ToLowerInvariant().Split('&');
                foreach(var part in queryParts)
                {
                    if(part.StartsWith("secret="))
                    {
                        _callback(part.Substring(7)?.ToUpperInvariant());
                        return;
                    }
                }
            }
            _callback(null);
        }
    }
}