sqlinsight-pro/src/SQLInsight.Rules/Servers/ScopedRules.cs

using SQLInsight.Core.Collection;
using SQLInsight.Core.Findings;
using SQLInsight.Rules.Engine;

namespace SQLInsight.Rules.Servers;

/// <summary>
/// A rule about something that is not a SQL Server instance (a Windows server, a synthetic check). It produces the
/// same findings, explanations and outcomes as the instance rules, against its own kind of context.
/// </summary>
public interface IScopedRule<in TContext>
{
    /// <summary>Stable identifier, e.g. <c>SQLI-WIN-001</c>. Never reused for a different check.</summary>
    string Id { get; }

    string Title { get; }

    RuleEvaluation Evaluate(TContext context);
}

public abstract class ScopedRule<TContext> : IScopedRule<TContext>
{
    public abstract string Id { get; }
    public abstract string Title { get; }

    public abstract RuleEvaluation Evaluate(TContext context);

    protected Finding CreateFinding(Severity severity, string title, string explanation, string recommendation, IEnumerable<Evidence>? evidence = null,
        string? subject = null, params Reference[] references) => new()
        {
            RuleId = Id,
            Severity = severity,
            Title = title,
            Subject = subject,
            Explanation = explanation,
            Recommendation = recommendation,
            Evidence = evidence?.ToList() ?? [],
            References = references,
        };

    protected static RuleEvaluation Result(IEnumerable<Finding> findings)
    {
        var list = findings.ToArray();
        return list.Length == 0 ? RuleEvaluation.Passed() : RuleEvaluation.Found(list);
    }
}

/// <summary>Runs scoped rules. Like <see cref="RuleEngine"/>: a rule that cannot run is not measurable (with the reason) or an error, never silently passed.</summary>
public static class ScopedRuleEngine
{
    public static IReadOnlyList<RuleResult> Evaluate<TContext>(IEnumerable<IScopedRule<TContext>> rules, TContext context)
    {
        ArgumentNullException.ThrowIfNull(rules);
        return rules.Select(rule => Evaluate(rule, context)).ToList();
    }

    private static RuleResult Evaluate<TContext>(IScopedRule<TContext> rule, TContext context)
    {
        try
        {
            var evaluation = rule.Evaluate(context);
            return new RuleResult { RuleId = rule.Id, RuleTitle = rule.Title, Outcome = evaluation.Outcome, Findings = evaluation.Findings, Reason = evaluation.Reason };
        }
        catch (DataUnavailableException ex)
        {
            return new RuleResult
            {
                RuleId = rule.Id,
                RuleTitle = rule.Title,
                Outcome = ex.NotApplicable ? RuleOutcome.NotApplicable : RuleOutcome.NotMeasurable,
                Reason = ex.Message,
            };
        }
#pragma warning disable CA1031 // One faulty rule must not stop the others; the failure is reported, not hidden.
        catch (Exception ex)
#pragma warning restore CA1031
        {
            return new RuleResult { RuleId = rule.Id, RuleTitle = rule.Title, Outcome = RuleOutcome.Error, Reason = $"{ex.GetType().Name}: {ex.Message}" };
        }
    }
}

/// <summary>Every rule about Windows servers and synthetic checks, for rule listings.</summary>
public static class ServerRuleCatalog
{
    public static IReadOnlyList<(string Id, string Title)> All =>
        WindowsServerRules.Create().Select(r => (r.Id, r.Title))
            .Concat(SyntheticCheckRules.Create().Select(r => (r.Id, r.Title)))
            .ToList();
}