namespace SQLInsight.Core.Configuration;

/// <summary>
/// Which databases on an instance are monitored, as chosen in SQLInsight Web (Opsætning → Overvågede servere). The
/// system databases (master, model, msdb, tempdb) are always monitored: backups of master and msdb and the state of
/// tempdb concern the whole instance. A database nobody has decided on yet (new since the last discovery) follows
/// <see cref="MonitorNew"/>.
/// </summary>
public sealed class DatabaseSelection
{
    private static readonly HashSet<string> SystemDatabases = new(["master", "model", "msdb", "tempdb"], StringComparer.OrdinalIgnoreCase);

    private readonly HashSet<string> _monitored;
    private readonly HashSet<string> _notMonitored;
    private readonly HashSet<string> _dynamicsAxToHub;

    /// <summary>Every database, and no Dynamics AX findings to the hub: what 1.2 and earlier did.</summary>
    public static readonly DatabaseSelection All = new(true, [], [], []);

    public DatabaseSelection(bool monitorNew, IEnumerable<string> monitored, IEnumerable<string> notMonitored, IEnumerable<string> dynamicsAxToHub)
    {
        ArgumentNullException.ThrowIfNull(monitored);
        ArgumentNullException.ThrowIfNull(notMonitored);
        ArgumentNullException.ThrowIfNull(dynamicsAxToHub);
        MonitorNew = monitorNew;
        _monitored = new HashSet<string>(monitored, StringComparer.OrdinalIgnoreCase);
        _notMonitored = new HashSet<string>(notMonitored, StringComparer.OrdinalIgnoreCase);
        _notMonitored.ExceptWith(_monitored);
        _dynamicsAxToHub = new HashSet<string>(dynamicsAxToHub, StringComparer.OrdinalIgnoreCase);
    }

    /// <summary>Databases not yet decided on (new on the instance) are monitored.</summary>
    public bool MonitorNew { get; }

    /// <summary>Nothing is left out: every database is monitored.</summary>
    public bool IsEverything => MonitorNew && _notMonitored.Count == 0;

    public static bool IsSystemDatabase(string database) => SystemDatabases.Contains(database);

    /// <summary>Whether the database-specific checks run in <paramref name="database"/>.</summary>
    public bool Includes(string database)
    {
        ArgumentNullException.ThrowIfNull(database);
        if (IsSystemDatabase(database) || _monitored.Contains(database))
        {
            return true;
        }

        return !_notMonitored.Contains(database) && MonitorNew;
    }

    /// <summary>
    /// Whether findings about Dynamics AX in <paramref name="database"/> may be sent to SQLInsight Hub. Off unless the
    /// customer turned it on for that database.
    /// </summary>
    public bool SendsDynamicsAxToHub(string? database) => database is not null && _dynamicsAxToHub.Contains(database) && Includes(database);

    /// <summary>At least one database sends Dynamics AX findings to the hub.</summary>
    public bool AnyDynamicsAxToHub => _dynamicsAxToHub.Any(Includes);

    /// <summary>Keeps the databases in <paramref name="names"/> that are monitored.</summary>
    public List<string> Filter(IEnumerable<string> names) => names.Where(Includes).ToList();
}

/// <summary>
/// Dynamics AX findings and SQLInsight Hub: they stay in the customer's network unless sending is turned on for the
/// database (default off).
/// </summary>
public static class DynamicsAxFindings
{
    /// <summary>The community AX rules (rules/community/dynamics-ax.json).</summary>
    public const string RulePrefix = "COM-AX-";

    /// <summary>The built-in AX rules (1.4: batch jobs, number sequences, RecId, AX users behind blocking).</summary>
    public const string BuiltInRulePrefix = "SQLI-AX-";

    private const string DatabaseSubject = "database: ";

    /// <summary>Separates the database from the rest of an AX finding's subject: <c>database: AX30 · batch: 4711</c>.</summary>
    public const string SubjectSeparator = " · ";

    public static bool IsDynamicsAxRule(string ruleId) =>
        ruleId?.StartsWith(RulePrefix, StringComparison.OrdinalIgnoreCase) == true || ruleId?.StartsWith(BuiltInRulePrefix, StringComparison.OrdinalIgnoreCase) == true;

    /// <summary>The subject of an AX finding about <paramref name="detail"/> in <paramref name="database"/>.</summary>
    public static string Subject(string database, string? detail = null) =>
        detail is null ? DatabaseSubject + database : DatabaseSubject + database + SubjectSeparator + detail;

    /// <summary>The database a finding is about, from its subject (<c>database: AX30</c> or <c>database: AX30 · …</c>), or null.</summary>
    public static string? DatabaseOf(string? subject)
    {
        if (subject is null || !subject.StartsWith(DatabaseSubject, StringComparison.OrdinalIgnoreCase) || subject.Length <= DatabaseSubject.Length)
        {
            return null;
        }

        var rest = subject[DatabaseSubject.Length..];
        var separator = rest.IndexOf(SubjectSeparator, StringComparison.Ordinal);
        return separator > 0 ? rest[..separator] : rest;
    }
}