hrynco-notification-service/HrynCo.NotificationService.DAL.Abstract/Templates/EmailTemplateValidation.cs

using System.Text.Json;

namespace HrynCo.NotificationService.DAL.Abstract.Templates;

public static class EmailTemplateValidation
{
    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
    {
        PropertyNameCaseInsensitive = false,
        UnmappedMemberHandling = System.Text.Json.Serialization.JsonUnmappedMemberHandling.Disallow
    };

    public static IReadOnlyList<EmailTemplateVariable> ParseVariables(string json)
    {
        using var document = JsonDocument.Parse(json);
        if (document.RootElement.ValueKind == JsonValueKind.Null)
            throw new EmailTemplateWriteException("Variables must be a JSON array.", false);
        if (document.RootElement.ValueKind != JsonValueKind.Array)
            throw new JsonException("Variables must be an array.");
        foreach (var item in document.RootElement.EnumerateArray())
            ValidateVariableShape(item);
        var variables = JsonSerializer.Deserialize<List<EmailTemplateVariable>>(json, JsonOptions);
        ValidateVariables(variables);
        return variables!;
    }

    private static void ValidateVariableShape(JsonElement item)
    {
        if (item.ValueKind != JsonValueKind.Object)
            throw new JsonException("Each variable must be an object.");
        if (!item.TryGetProperty("name", out var name) || name.ValueKind != JsonValueKind.String)
            throw new JsonException("Every variable needs a name string.");
        if (!item.TryGetProperty("required", out var required) || required.ValueKind is not (JsonValueKind.True or JsonValueKind.False))
            throw new JsonException("Every variable needs a required boolean.");
    }

    public static void ValidateVariables(IReadOnlyList<EmailTemplateVariable>? variables)
    {
        if (variables is null)
            throw new EmailTemplateWriteException("Variables must be a JSON array.", false);
        if (variables.Any(v => v is null || string.IsNullOrWhiteSpace(v.Name)))
            throw new EmailTemplateWriteException("Every variable needs a non-empty name.", false);
        if (variables.Select(v => v.Name).Distinct(StringComparer.Ordinal).Count() != variables.Count)
            throw new EmailTemplateWriteException("Variable names must be unique.", false);
    }

    public static bool ContractsEqual(IReadOnlyList<EmailTemplateVariable> left, IReadOnlyList<EmailTemplateVariable> right) =>
        left.OrderBy(v => v.Name, StringComparer.Ordinal).SequenceEqual(right.OrderBy(v => v.Name, StringComparer.Ordinal));

    public static void ValidateIdentity(string serviceName, string key)
    {
        if (string.IsNullOrWhiteSpace(serviceName) || serviceName.Length > 100)
            throw new EmailTemplateWriteException("Service name is required and must be at most 100 characters.", false);
        if (string.IsNullOrWhiteSpace(key) || key.Length > 100)
            throw new EmailTemplateWriteException("Key is required and must be at most 100 characters.", false);
    }

    public static void ValidateLanguage(EmailTemplate template)
    {
        if (string.IsNullOrWhiteSpace(template.LanguageCode) || template.LanguageCode.Length > 10)
            throw new EmailTemplateWriteException("Language code is required and must be at most 10 characters.", false);
        if (string.IsNullOrWhiteSpace(template.Subject) || string.IsNullOrWhiteSpace(template.HtmlBody) || string.IsNullOrWhiteSpace(template.TextBody))
            throw new EmailTemplateWriteException("Every language needs a subject, HTML body, and text body.", false);
    }

    public static void ValidateDefinition(EmailTemplateDefinition definition)
    {
        ValidateIdentity(definition.ServiceName, definition.Key);
        ValidateVariables(definition.Variables);
        foreach (var language in definition.Languages)
            ValidateLanguage(language);
        var codes = definition.Languages.Select(t => t.LanguageCode);
        if (codes.Distinct(StringComparer.Ordinal).Count() != definition.Languages.Count)
            throw new EmailTemplateWriteException("Language codes must be unique within a template.", false);
    }
}