using System.Reflection;
using BulkArchiveMailer.Core;
using Xunit;

namespace BulkArchiveMailer.Core.Tests
{
    /// <summary>
    /// Covers the one AppSettingsData behavior that's easy to silently
    /// break when adding a field: loading a config.json written before
    /// FromAccountSmtpAddress existed must not throw, and a non-empty
    /// value must round-trip once the operator picks a "from" account in
    /// SettingsForm.
    ///
    /// Note the old-JSON case asserts null, not "": DataContractJsonSerializer
    /// builds the target via FormatterServices.GetUninitializedObject,
    /// which skips this property's "" initializer entirely for any member
    /// absent from the source JSON, leaving the CLR default (null) - see
    /// the long comment on AppSettingsData.FromAccountSmtpAddress. Every
    /// call site (MailSender, SettingsForm) already treats null the same
    /// as "" for this reason.
    ///
    /// Goes through AppSettings' private Serialize/Deserialize via
    /// reflection rather than Load()/Save(), so this test never touches
    /// the real %APPDATA%\BulkArchiveMailer\config.json on the machine
    /// running it.
    /// </summary>
    public class AppSettingsTests
    {
        [Fact]
        public void Deserialize_OldJsonWithoutFromAccountField_DoesNotThrowAndTreatsAsUnset()
        {
            const string oldJson = @"{
                ""archiveFolder"": ""C:\\archives"",
                ""emailDomain"": ""redlab.lo"",
                ""testModeDefault"": true,
                ""signatureHtmlPath"": """"
            }";

            var settings = InvokeDeserialize(oldJson);

            Assert.True(string.IsNullOrEmpty(settings.FromAccountSmtpAddress));
            Assert.Equal("redlab.lo", settings.EmailDomain);
        }

        [Fact]
        public void SerializeThenDeserialize_RoundTripsFromAccountSmtpAddress()
        {
            var data = new AppSettingsData
            {
                ArchiveFolder = "C:\\archives",
                EmailDomain = "redlab.lo",
                FromAccountSmtpAddress = "svc-mailer@redlab.lo",
            };

            var json = InvokeSerialize(data);
            var roundTripped = InvokeDeserialize(json);

            Assert.Equal("svc-mailer@redlab.lo", roundTripped.FromAccountSmtpAddress);
        }

        private static AppSettingsData InvokeDeserialize(string json)
        {
            var method = typeof(AppSettings).GetMethod("Deserialize", BindingFlags.NonPublic | BindingFlags.Static);
            return (AppSettingsData)method.Invoke(null, new object[] { json });
        }

        private static string InvokeSerialize(AppSettingsData data)
        {
            var method = typeof(AppSettings).GetMethod("Serialize", BindingFlags.NonPublic | BindingFlags.Static);
            return (string)method.Invoke(null, new object[] { data });
        }
    }
}