using Explorer.Domain;

namespace Explorer.Application;

public static class BackgroundMaintenancePlanner
{
    public static Source? NextLocalScan(
        IEnumerable<Source> sources,
        DateTimeOffset utc,
        IReadOnlySet<long>? alreadyQueued = null)
    {
        var cutoff = utc - TimeSpan.FromDays(AppConstants.IdleRescanAfterDays);
        return EligibleLocal(sources, alreadyQueued)
            .Where(source => source.Status == SourceStatus.Stale
                             || source.LastIndexedUtc is null
                             || source.LastIndexedUtc < cutoff)
            .OrderBy(source => source.Status == SourceStatus.Stale ? 0 : 1)
            .ThenBy(source => source.LastIndexedUtc ?? DateTimeOffset.MinValue)
            .FirstOrDefault();
    }

    public static Source? NextLocalVerify(
        IEnumerable<Source> sources,
        IReadOnlySet<long>? alreadyQueued = null)
        => EligibleLocal(sources, alreadyQueued)
            .OrderBy(source => source.Status == SourceStatus.Stale ? 0 : 1)
            .ThenBy(source => source.LastIndexedUtc ?? DateTimeOffset.MinValue)
            .FirstOrDefault();

    public static Source? NextHashCollisionSource(
        IEnumerable<Source> sources,
        IReadOnlySet<long>? alreadyEnqueued = null)
        => EligibleLocal(sources, alreadyEnqueued)
            .OrderBy(source => source.LastIndexedUtc ?? DateTimeOffset.MinValue)
            .FirstOrDefault();

    private static IEnumerable<Source> EligibleLocal(IEnumerable<Source> sources, IReadOnlySet<long>? skip)
        => sources.Where(source =>
            source.Kind == SourceKind.NtfsLocal
            && source.IsIndexed
            && source.Status is SourceStatus.Online or SourceStatus.Stale
            && !string.IsNullOrWhiteSpace(source.LastRootPath)
            && (skip is null || !skip.Contains(source.Id)));
}