using SQLInsight.Core.Findings;

namespace SQLInsight.Rules.Engine;

/// <summary>
/// What a rule concluded. Created through the static factory methods.
/// </summary>
public sealed record RuleEvaluation
{
    private RuleEvaluation(RuleOutcome outcome, IReadOnlyList<Finding> findings, string? reason)
    {
        Outcome = outcome;
        Findings = findings;
        Reason = reason;
    }

    public RuleOutcome Outcome { get; }
    public IReadOnlyList<Finding> Findings { get; }

    /// <summary>Why the rule could not be measured, if it could not.</summary>
    public string? Reason { get; }

    public static RuleEvaluation Passed() => new(RuleOutcome.Passed, [], null);

    public static RuleEvaluation Found(params Finding[] findings)
    {
        ArgumentNullException.ThrowIfNull(findings);
        if (findings.Length == 0)
        {
            throw new ArgumentException("At least one finding is required. Use Passed() when there is none.", nameof(findings));
        }

        return new(RuleOutcome.Findings, findings, null);
    }

    public static RuleEvaluation NotMeasurable(string reason) => new(RuleOutcome.NotMeasurable, [], reason);

    public static RuleEvaluation NotApplicable(string reason) => new(RuleOutcome.NotApplicable, [], reason);
}

public enum RuleOutcome
{
    /// <summary>The rule ran and found nothing wrong.</summary>
    Passed,

    /// <summary>The rule ran and found one or more problems.</summary>
    Findings,

    /// <summary>The rule could not be evaluated on this instance. This is never the same as <see cref="Passed"/>.</summary>
    NotMeasurable,

    /// <summary>The rule failed while running. This is never the same as <see cref="Passed"/>.</summary>
    Error,

    /// <summary>
    /// The rule does not apply to this kind of instance: its SQL Server version lacks what the rule looks at (Query
    /// Store on 2005 …), or Azure manages it. Not a gap in the monitoring, so not counted as not measurable.
    /// Last in the enum: outcomes are stored as numbers.
    /// </summary>
    NotApplicable,
}