bmc.maui/BuyMeCofee.Maui/Controls/BuyMeACoffeeQrCode.cs

using BuyMeCofee.Maui.Constants;
using BuyMeCofee.Maui.Helpers;
using QRCoder;
using SkiaSharp;
using SkiaSharp.Views.Maui;
using SkiaSharp.Views.Maui.Controls;

namespace BuyMeCofee.Maui.Controls;

/// <summary>
/// Generates and displays a QR code linking to a Buy Me a Coffee profile,
/// with the BMC coffee cup logo overlaid in the center.
/// </summary>
public class BuyMeACoffeeQrCode : ContentView
{
    #region Bindable Properties

    public static readonly BindableProperty UsernameProperty =
        BindableProperty.Create(nameof(Username), typeof(string), typeof(BuyMeACoffeeQrCode),
            string.Empty, propertyChanged: OnQrPropertyChanged);

    public static readonly BindableProperty SizeProperty =
        BindableProperty.Create(nameof(Size), typeof(double), typeof(BuyMeACoffeeQrCode),
            200.0, propertyChanged: OnSizeChanged);

    public static readonly BindableProperty ForegroundColorProperty =
        BindableProperty.Create(nameof(ForegroundColor), typeof(Color), typeof(BuyMeACoffeeQrCode),
            Colors.Black, propertyChanged: OnQrPropertyChanged);

    public static new readonly BindableProperty BackgroundColorProperty =
        BindableProperty.Create(nameof(BackgroundColor), typeof(Color), typeof(BuyMeACoffeeQrCode),
            Colors.White, propertyChanged: OnQrPropertyChanged);

    public static readonly BindableProperty LogoSizeFractionProperty =
        BindableProperty.Create(nameof(LogoSizeFraction), typeof(double), typeof(BuyMeACoffeeQrCode),
            0.25, propertyChanged: OnVisualPropertyChanged);

    #endregion

    #region Properties

    /// <summary>Your Buy Me a Coffee username/slug.</summary>
    public string Username
    {
        get => (string)GetValue(UsernameProperty);
        set => SetValue(UsernameProperty, value);
    }

    /// <summary>Width and height of the QR code control. Default: 200</summary>
    public double Size
    {
        get => (double)GetValue(SizeProperty);
        set => SetValue(SizeProperty, value);
    }

    /// <summary>QR code foreground (module) color. Default: Black</summary>
    public Color ForegroundColor
    {
        get => (Color)GetValue(ForegroundColorProperty);
        set => SetValue(ForegroundColorProperty, value);
    }

    /// <summary>QR code background color. Default: White</summary>
    public new Color BackgroundColor
    {
        get => (Color)GetValue(BackgroundColorProperty);
        set => SetValue(BackgroundColorProperty, value);
    }

    /// <summary>Logo size as fraction of QR code size (0.0 - 0.35). Default: 0.25</summary>
    public double LogoSizeFraction
    {
        get => (double)GetValue(LogoSizeFractionProperty);
        set => SetValue(LogoSizeFractionProperty, value);
    }

    #endregion

    private readonly SKCanvasView _canvas;
    private SKBitmap? _qrBitmap;
    private SKBitmap? _logoBitmap;

    public BuyMeACoffeeQrCode()
    {
        _canvas = new SKCanvasView
        {
            WidthRequest = Size,
            HeightRequest = Size,
        };
        _canvas.PaintSurface += OnPaintSurface;

        Content = _canvas;
        LoadLogo();
        RegenerateQr();
    }

    private void LoadLogo()
    {
        try
        {
            using var stream = BmcBrandAssets.GetCupLogoStream();
            _logoBitmap = SKBitmap.Decode(stream);
        }
        catch
        {
            _logoBitmap = null;
        }
    }

    private void RegenerateQr()
    {
        _qrBitmap?.Dispose();
        _qrBitmap = null;

        if (string.IsNullOrWhiteSpace(Username))
        {
            _canvas.InvalidateSurface();
            return;
        }

        var url = $"{BmcConstants.BaseUrl}{Username}";

        using var generator = new QRCodeGenerator();
        var data = generator.CreateQrCode(url, QRCodeGenerator.ECCLevel.H);
        var renderer = new PngByteQRCode(data);

        var darkRgba = ColorToRgba(ForegroundColor);
        var lightRgba = ColorToRgba(BackgroundColor);
        var pngBytes = renderer.GetGraphic(20, darkRgba, lightRgba);

        using var stream = new MemoryStream(pngBytes);
        _qrBitmap = SKBitmap.Decode(stream);

        _canvas.InvalidateSurface();
    }

    private void OnPaintSurface(object? sender, SKPaintSurfaceEventArgs e)
    {
        var canvas = e.Surface.Canvas;
        canvas.Clear(SKColors.Transparent);

        if (_qrBitmap is null) return;

        var info = e.Info;
        var size = Math.Min(info.Width, info.Height);

        // Draw QR code scaled to fill
        var qrRect = new SKRect(0, 0, size, size);
        using var qrPaint = new SKPaint { IsAntialias = false };
        canvas.DrawBitmap(_qrBitmap, qrRect, qrPaint);

        if (_logoBitmap is null) return;

        // Draw white quiet zone behind logo
        var logoSize = (float)(size * Math.Clamp(LogoSizeFraction, 0.0, 0.35));
        var logoPadding = logoSize * 0.15f;
        var cx = size / 2f;
        var cy = size / 2f;

        var quietRect = new SKRect(
            cx - logoSize / 2 - logoPadding,
            cy - logoSize / 2 - logoPadding,
            cx + logoSize / 2 + logoPadding,
            cy + logoSize / 2 + logoPadding);

        using var quietPaint = new SKPaint
        {
            Color = SKColors.White,
            IsAntialias = true,
            Style = SKPaintStyle.Fill,
        };
        canvas.DrawRoundRect(quietRect, 8, 8, quietPaint);

        // Draw logo centered
        var logoRect = new SKRect(
            cx - logoSize / 2, cy - logoSize / 2,
            cx + logoSize / 2, cy + logoSize / 2);
        using var logoPaint = new SKPaint { IsAntialias = true };
        canvas.DrawBitmap(_logoBitmap, logoRect, logoPaint);
    }

    private static byte[] ColorToRgba(Color color)
    {
        return
        [
            (byte)(color.Red * 255),
            (byte)(color.Green * 255),
            (byte)(color.Blue * 255),
            (byte)(color.Alpha * 255),
        ];
    }

    #region Property Changed Handlers

    private static void OnQrPropertyChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if (bindable is BuyMeACoffeeQrCode qr)
            qr.RegenerateQr();
    }

    private static void OnVisualPropertyChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if (bindable is BuyMeACoffeeQrCode qr)
            qr._canvas.InvalidateSurface();
    }

    private static void OnSizeChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if (bindable is BuyMeACoffeeQrCode qr)
        {
            var size = (double)newValue;
            qr._canvas.WidthRequest = size;
            qr._canvas.HeightRequest = size;
            qr._canvas.InvalidateSurface();
        }
    }

    #endregion
}