Generate and send random Secret Santa assignments via email

SecretSanta.cs

void Main()
{
	var santas = new[]
	{
		// TODO: Fill out names and email addresses of all participants
		new Santa("Person 1", "[email protected]"),
		new Santa("Person 2", "[email protected]"),
		new Santa("Person 3", "[email protected]"),
		new Santa("Person 4", "[email protected]"),
	};

	var shuffledIndexes = GenerateShuffledIndexes(santas.Length);
	AssignRecipients(santas, shuffledIndexes);

	SendEmails(santas);
}

int[] GenerateShuffledIndexes(int length)
{
	if (length <= 2)
	{
		throw new Exception("Your Secret Santa isn't very secret, you need more friends!");
	}
	
	int[] indexes;
	
	do
	{
		// OrderBy NewGuid is cheeky but it's good enough for this purpose
		indexes = Enumerable.Range(0, length).OrderBy(x => Guid.NewGuid()).ToArray();
	}
	// If any index maps onto itself, try again - you don't want to buy yourself a gift
	while (indexes.Select((value, index) => value == index).Contains(true));
	
	return indexes;
}

void AssignRecipients(Santa[] santas, int[] recipientIndexes)
{
	for (var i = 0; i < santas.Length; i++)
	{
		santas[i].RecipientName = santas[recipientIndexes[i]].Name;
	}
}

void SendEmails(Santa[] santas)
{
	// TODO: Configure email account to send from.
	// If you're using gmail, you may have to temporarily disable 2FA and enable "Less secure app access"
	const string senderEmailAccount = "[email protected]";
	var client = new System.Net.Mail.SmtpClient("smtp.gmail.com", 587)
	{
		Credentials = new System.Net.NetworkCredential(senderEmailAccount, "password"),
		DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network,
		EnableSsl = true,
	};

	foreach (var santa in santas)
	{
		var subject = "🎅 Your Secret Santa Assignment! 🎄";
		var body = $@"Ho ho ho! Dear {santa.Name},

You have been randomly assigned to buy a Secret Santa gift for....

(🥁 drumroll please....)

{santa.RecipientName}!

⛄🎁 Merrrrrry Christmas! 🦌🥕
";
		client.Send(senderEmailAccount, santa.EmailAddress, subject, body);
	}
}

class Santa
{
	internal Santa(string name, string emailAddress)
	{
		this.Name = name;
		this.EmailAddress = emailAddress;
	}

	internal string Name { get; }
	internal string EmailAddress { get; }

	internal string RecipientName { get; set; }
}