using Microsoft.Extensions.Options;

namespace ScadaLink.AuditLog.Configuration;

/// <summary>
/// Validates <see cref="AuditLogOptions"/> on startup. The caps drive payload
/// truncation in the M2+ writers, so an unset/zero cap would let arbitrarily
/// large blobs into the central <c>AuditLog</c> table. <see cref="AuditLogOptions.ErrorCapBytes"/>
/// must be at least as large as <see cref="AuditLogOptions.DefaultCapBytes"/>
/// because the error cap is meant to capture <em>more</em> detail than the
/// happy-path summary, not less. <see cref="AuditLogOptions.RetentionDays"/> is
/// bounded to <c>[30, 3650]</c> to keep purge windows sane: too short would
/// drop in-flight investigations, too long would defeat the partition-switch
/// purge's purpose.
/// </summary>
public sealed class AuditLogOptionsValidator : IValidateOptions<AuditLogOptions>
{
    /// <summary>Inclusive lower bound for <see cref="AuditLogOptions.RetentionDays"/>.</summary>
    public const int MinRetentionDays = 30;

    /// <summary>Inclusive upper bound for <see cref="AuditLogOptions.RetentionDays"/>.</summary>
    public const int MaxRetentionDays = 3650;

    /// <inheritdoc />
    public ValidateOptionsResult Validate(string? name, AuditLogOptions options)
    {
        ArgumentNullException.ThrowIfNull(options);

        var failures = new List<string>();

        if (options.DefaultCapBytes <= 0)
        {
            failures.Add(
                $"AuditLog:{nameof(AuditLogOptions.DefaultCapBytes)} ({options.DefaultCapBytes}) " +
                "must be > 0; it drives payload-summary truncation in audit writers.");
        }

        if (options.ErrorCapBytes < options.DefaultCapBytes)
        {
            failures.Add(
                $"AuditLog:{nameof(AuditLogOptions.ErrorCapBytes)} ({options.ErrorCapBytes}) " +
                $"must be >= {nameof(AuditLogOptions.DefaultCapBytes)} ({options.DefaultCapBytes}); " +
                "the error-row cap is intended to capture more detail than the happy-path summary.");
        }

        if (options.RetentionDays < MinRetentionDays || options.RetentionDays > MaxRetentionDays)
        {
            failures.Add(
                $"AuditLog:{nameof(AuditLogOptions.RetentionDays)} ({options.RetentionDays}) " +
                $"must be in [{MinRetentionDays}, {MaxRetentionDays}] days.");
        }

        return failures.Count == 0
            ? ValidateOptionsResult.Success
            : ValidateOptionsResult.Fail(failures);
    }
}