using System.Text.RegularExpressions;

namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer;

/// <summary>
///     Options for the SQL Server historian backend (the <c>ServerHistorian:SqlServer</c> config block).
/// </summary>
public sealed partial class SqlServerHistorianOptions
{
    /// <summary>Required. ADO.NET connection string for the historian database (never the ConfigDb).</summary>
    public string ConnectionString { get; set; } = "";

    /// <summary>SQL schema holding the historian objects. Spliced into DDL/DML, so it is regex-validated.</summary>
    public string Schema { get; set; } = "hist";

    /// <summary>Per-command timeout. Must be positive.</summary>
    public TimeSpan CommandTimeout { get; set; } = TimeSpan.FromSeconds(30);

    /// <summary>
    ///     <c>true</c> creates the schema and applies missing scripts on first use; <c>false</c> only verifies
    ///     that the required schema version (<c>SqlServerSchemaBootstrapper.RequiredVersion</c>, currently 2) exists and
    ///     fails every historian call with a clear error otherwise.
    /// </summary>
    public bool AutoCreateSchema { get; set; } = true;

    /// <summary>
    ///     Days of history to keep, measured on source time. <c>null</c> (default) keeps everything. When set,
    ///     a driver node deletes older <c>hist.Sample</c>/<c>hist.Event</c> rows every <see cref="PurgeInterval"/>.
    /// </summary>
    public int? RetentionDays { get; set; }

    /// <summary>How often the retention purge runs. Must be positive.</summary>
    public TimeSpan PurgeInterval { get; set; } = TimeSpan.FromHours(1);

    /// <summary>
    ///     Rows per <c>DELETE TOP(n)</c> batch. Default 4000 stays under SQL Server's 5000-lock escalation
    ///     threshold so a purge never escalates to a table lock.
    /// </summary>
    public int PurgeBatchSize { get; set; } = 4000;

    [GeneratedRegex("^[A-Za-z_][A-Za-z0-9_]{0,127}$")]
    private static partial Regex IdentifierRegex();

    /// <summary>True when <paramref name="schema"/> is a safe SQL identifier.</summary>
    /// <param name="schema">Candidate schema name.</param>
    /// <returns>Whether it matches <c>^[A-Za-z_][A-Za-z0-9_]{0,127}$</c>.</returns>
    public static bool IsValidSchemaName(string? schema) => schema is not null && IdentifierRegex().IsMatch(schema);

    /// <summary>Validates the options without touching SQL.</summary>
    /// <returns>One message per problem; empty when valid.</returns>
    public IReadOnlyList<string> Validate()
    {
        var errors = new List<string>();
        if (string.IsNullOrWhiteSpace(ConnectionString))
            errors.Add("ServerHistorian:SqlServer:ConnectionString is required.");
        if (!IsValidSchemaName(Schema))
            errors.Add("ServerHistorian:SqlServer:Schema must be a SQL identifier matching ^[A-Za-z_][A-Za-z0-9_]{0,127}$.");
        if (CommandTimeout <= TimeSpan.Zero)
            errors.Add("ServerHistorian:SqlServer:CommandTimeout must be greater than zero.");
        if (RetentionDays is < 1)
            errors.Add("ServerHistorian:SqlServer:RetentionDays must be at least 1 when set (omit it to keep history forever).");
        if (PurgeInterval <= TimeSpan.Zero)
            errors.Add("ServerHistorian:SqlServer:PurgeInterval must be greater than zero.");
        if (PurgeBatchSize < 1)
            errors.Add("ServerHistorian:SqlServer:PurgeBatchSize must be at least 1.");
        return errors;
    }
}