ImageChartsQrCodeProvider.cs

using System;
using System.Net.Security;

namespace TwoFactorAuthNet.Providers.Qr;

/// <summary>
/// Provides QR codes generated by image-charts.com.
/// </summary>
/// <seealso href="https://documentation.image-charts.com/gallery/"/>.
public class ImageChartsQrCodeProvider : BaseHttpQrCodeProvider, IQrCodeProvider
{
    /// <summary>
    /// Gets the <see cref="ErrorCorrectionLevel"/> for the QR code.
    /// </summary>
    public ErrorCorrectionLevel ErrorCorrectionLevel { get; private set; }

    /// <summary>
    /// Gets the width of the white border around the data portion of the code.
    /// </summary>
    /// <remarks>
    /// This is in rows, not in pixels.
    /// </remarks>
    public int MarginRows { get; private set; }

    /// <summary>
    /// <see cref="BaseHttpQrCodeProvider.BaseUri"/> for this QR code provider.
    /// </summary>
    private static readonly Uri _baseuri = new("https://image-charts.com/chart");

    /// <summary>
    /// Initializes a new instance of a <see cref="ImageChartsQrCodeProvider"/> with the specified
    /// <see cref="ErrorCorrectionLevel"/>, <see cref="MarginRows"/> and 
    /// <see cref="RemoteCertificateValidationCallback"/>.
    /// </summary>
    /// <param name="errorCorrectionLevel">The <see cref="ErrorCorrectionLevel"/> to use when generating QR codes.</param>
    /// <param name="marginRows">The width of the white border around the data portion of the code.</param>
    /// <param name="remoteCertificateValidationCallback">
    /// The <see cref="RemoteCertificateValidationCallback"/> to use when generating QR codes.
    /// </param>
    /// <exception cref="ArgumentOutOfRangeException">
    /// Thrown when an invalid <see cref="ErrorCorrectionLevel"/> is specified or marginRows is less than 0.
    /// </exception>
    public ImageChartsQrCodeProvider(
        ErrorCorrectionLevel errorCorrectionLevel = ErrorCorrectionLevel.Low,
        int marginRows = 1,
        RemoteCertificateValidationCallback? remoteCertificateValidationCallback = null
    )
        : base(_baseuri, remoteCertificateValidationCallback)
    {
        if (!Enum.IsDefined(typeof(ErrorCorrectionLevel), errorCorrectionLevel))
        {
            throw new ArgumentOutOfRangeException(nameof(errorCorrectionLevel));
        }

        ErrorCorrectionLevel = errorCorrectionLevel;

        if (marginRows < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(marginRows));
        }

        MarginRows = marginRows;
    }

    /// <summary>
    /// Downloads / retrieves / generates a QR code as image.
    /// </summary>
    /// <param name="text">The text to encode in the QR code.</param>
    /// <param name="size">The desired size (width and height equal) for the image.</param>
    /// <returns>Returns the binary representation of the image.</returns>
    /// <seealso cref="IQrCodeProvider"/>
    public byte[] GetQrCodeImage(string text, int size) => DownloadData(GetUri(text, size));

    /// <summary>
    /// Builds an <see cref="Uri"/> based on the instance's <see cref="BaseHttpQrCodeProvider.BaseUri"/>.
    /// </summary>
    /// <param name="qrText">The text to encode in the QR code.</param>
    /// <param name="size">The desired size of the QR code.</param>
    /// <returns>A <see cref="Uri"/> to the QR code.</returns>
    private Uri GetUri(string qrText, int size) => new(BaseUri,
            "?cht=qr"
            + "&chs=" + (size / 2) + "x" + (size / 2)   // Size isn't really reliable; 100 gives an image of 172, 200 gives an image of 387 and 300 gives an image of 602...
            + "&chld=" + (char)ErrorCorrectionLevel + "|" + MarginRows
            + "&chl=" + Uri.EscapeDataString(qrText)
        );

    /// <summary>
    /// Gets the MIME type of the image.
    /// </summary>
    /// <returns>Returns the MIME type of the image.</returns>
    /// <seealso cref="IQrCodeProvider"/>
    public string GetMimeType() => "image/png";
}