namespace Campaign_Tracker.Server.ExtensionData;

/// <summary>
/// Implements <see cref="ILegacyLinkIntegrityCheck"/> by scanning every record supplied
/// by the registered <see cref="ILegacyLinkedRecordProvider"/> implementations and
/// validating each one's legacy link through <see cref="ILegacyLinkValidator"/> (AC #4).
/// When no providers are registered (i.e. no extension records exist yet), the report
/// reflects zero records and 100% consistency.
/// </summary>
public sealed class LegacyLinkIntegrityService : ILegacyLinkIntegrityCheck
{
    private readonly IEnumerable<ILegacyLinkedRecordProvider> _providers;
    private readonly ILegacyLinkValidator _validator;
    private readonly TimeProvider _timeProvider;

    public LegacyLinkIntegrityService(
        IEnumerable<ILegacyLinkedRecordProvider> providers,
        ILegacyLinkValidator validator,
        TimeProvider timeProvider)
    {
        _providers = providers;
        _validator = validator;
        _timeProvider = timeProvider;
    }

    public async Task<LegacyLinkIntegrityReport> CheckAsync(CancellationToken cancellationToken = default)
    {
        var failures = new List<LegacyLinkIntegrityFailure>();
        var seenLinks = new Dictionary<string, ILegacyLinkedRecord>(StringComparer.OrdinalIgnoreCase);
        var providers = _providers.ToArray();
        int total = 0;

        foreach (var provider in providers)
        {
            var records = await provider.GetAllAsync(cancellationToken);
            foreach (var record in records)
            {
                total++;
                var result = await _validator.ValidateAsync(record.LegacyLink, cancellationToken);
                if (!result.IsValid)
                {
                    failures.Add(new LegacyLinkIntegrityFailure(
                        record.RecordType,
                        record.RecordId,
                        record.LegacyLink,
                        result.Error ?? "Unknown validation error"));
                }

                var linkKey = $"{record.LegacyLink.Type}:{record.LegacyLink.Value}";
                if (seenLinks.TryGetValue(linkKey, out var existing) &&
                    (!string.Equals(existing.RecordType, record.RecordType, StringComparison.OrdinalIgnoreCase) ||
                     !string.Equals(existing.RecordId, record.RecordId, StringComparison.OrdinalIgnoreCase)))
                {
                    failures.Add(new LegacyLinkIntegrityFailure(
                        record.RecordType,
                        record.RecordId,
                        record.LegacyLink,
                        $"Legacy reference is also linked by {existing.RecordType} '{existing.RecordId}', creating an ambiguous active-record join."));
                }
                else
                {
                    seenLinks[linkKey] = record;
                }
            }
        }

        int consistent = total - failures.Count;
        double pct = total == 0 ? 100.0 : (consistent / (double)total) * 100.0;

        return new LegacyLinkIntegrityReport(
            CheckedAt: _timeProvider.GetUtcNow(),
            ProviderCount: providers.Length,
            TotalRecords: total,
            ConsistentRecords: consistent,
            FailedRecords: failures.Count,
            ConsistencyPercentage: Math.Round(pct, 4),
            Failures: failures);
    }
}