namespace SQLInsight.Contracts;

/// <summary>
/// Aggregated experience across SQLInsight Hub customers, sent back to agents. Contains no customer, instance or
/// server names: only counts, and only when at least <see cref="MinCustomers"/> different customers are behind them.
/// </summary>
public sealed record HubInsights(DateTimeOffset GeneratedAt, int MinCustomers, IReadOnlyList<UpgradeInsight> Upgrades);

/// <summary>
/// After instances of SQL Server major version <see cref="Major"/> were updated to <see cref="ToBuild"/> or newer, findings
/// of <see cref="RuleId"/> they had went away within a few days on <see cref="Resolved"/> instances and stayed on
/// <see cref="Persisted"/>. Correlation, not proof of cause.
/// </summary>
public sealed record UpgradeInsight(string RuleId, int Major, string ToBuild, string? ToLevel, int Customers, int Resolved, int Persisted)
{
    public double ResolvedShare => Resolved + Persisted == 0 ? 0 : (double)Resolved / (Resolved + Persisted);
}

public static class HubInsightMatcher
{
    /// <summary>
    /// Insights relevant to a finding: the same rule, the same major version, and a build newer than the instance's.
    /// The one backed by most customers first.
    /// </summary>
    public static IReadOnlyList<UpgradeInsight> For(HubInsights? insights, string ruleId, string? productVersion)
    {
        if (insights is null || productVersion is null || !Version.TryParse(productVersion, out var current))
        {
            return [];
        }

        return insights.Upgrades
            .Where(i => i.RuleId == ruleId && i.Major == current.Major && Version.TryParse(i.ToBuild, out var build) && build > current)
            .OrderByDescending(i => i.Customers).ThenBy(i => Version.Parse(i.ToBuild))
            .ToList();
    }
}