MeWeb/src/MeWeb.Core/Checks/Verdicts.cs

using System.Globalization;

using MeWeb.Core.History;
using MeWeb.Core.Knowledge;
using MeWeb.Core.Net;
using MeWeb.Core.Router;
using MeWeb.Shared;

namespace MeWeb.Core.Checks;

public static class Verdicts
{
  public static Finding Online(OnlineReport report, LocalSnapshot local)
  {
    var finding = new Finding { Id = CheckId.Online };
    switch (report.State)
    {
      case OnlineState.Online:
        finding.Outcome = Outcome.Good;
        finding.Summary = "OnlineGood";
        break;
      case OnlineState.Rewritten:
        finding.Outcome = Outcome.Caution;
        finding.Summary = "OnlineRewritten";
        finding.With("FactRedirectedTo", report.Portal);
        break;
      case OnlineState.Captive:
        finding.Outcome = Outcome.Caution;
        finding.Summary = "OnlineCaptive";
        finding.With("FactRedirectedTo", report.Portal);
        break;
      case OnlineState.NoNames when local.Active is not null:
        finding.Outcome = Outcome.Bad;
        finding.Summary = "OnlineNoNames";
        break;
      default:
        finding.Outcome = Outcome.Bad;
        finding.Summary = local.Active is null ? "OnlineNoNetwork" : "OnlineOffline";
        break;
    }
    return finding;
  }

  public static Finding Connection(LocalSnapshot local, CellularReport cellular, KnowledgeBase knowledge)
  {
    var active = local.Active;
    if (active is null) return new Finding { Id = CheckId.Connection, Outcome = Outcome.Bad, Summary = "ConnectionNone" };
    var finding = new Finding
    {
      Id = CheckId.Connection,
      Outcome = Outcome.Info,
      Summary = active.Kind switch
      {
        LinkKind.Wifi => "ConnectionWifi",
        LinkKind.Cable => "ConnectionCable",
        LinkKind.Mobile => "ConnectionMobile",
        _ => "ConnectionOther",
      },
    };
    finding.With("FactAdapter", active.Name);
    if (active.SpeedMbps > 0) finding.WithKey("FactLinkSpeed", "ValueMbps", active.SpeedMbps.ToString(CultureInfo.InvariantCulture));
    finding.With("FactLocalAddress", local.LocalV4);
    var v6 = local.GlobalV6;
    if (v6.Count > 0) finding.With("FactLocalIpv6", string.Join("\n", v6));
    finding.With("FactGateway", local.GatewayV4 ?? active.Gateways.FirstOrDefault());
    if (local.Dns.Count > 0) finding.With("FactDns", string.Join(", ", local.Dns.Take(3)));
    if (cellular is null) return finding;
    var name = !string.IsNullOrWhiteSpace(cellular.Operator) ? cellular.Operator.Trim() : knowledge.CarrierFor(cellular.NetworkCode) ?? cellular.Carrier;
    var code = cellular.NetworkCode is { Length: >= 5 } network ? $"{network[..3]} {network[3..]}" : null;
    finding.With("FactOperator", code is null ? name : name is null ? code : $"{name} ({code})");
    finding.With("FactRadio", cellular.Radio);
    if (cellular.Roaming is not null) finding.WithKey("FactRoaming", cellular.Roaming == true ? "ValueYes" : "ValueNo");
    return finding;
  }

  public static Finding Addresses(string v4, string v6, LocalSnapshot local)
  {
    var finding = new Finding { Id = CheckId.Addresses };
    (finding.Outcome, finding.Summary) = (v4, v6) switch
    {
      (not null, not null) => (Outcome.Good, "AddressesBoth"),
      (not null, null) => (Outcome.Caution, "AddressesV4Only"),
      (null, not null) => (Outcome.Caution, "AddressesV6Only"),
      _ => (Outcome.Unknown, "AddressesNone"),
    };
    if (v4 is not null)
    {
      finding.With("FactPublicV4", v4);
      var own = local.Active?.Addresses.Any(a => Net.Addresses.SameAddress(a, v4)) == true;
      var shared = local.Active?.Kind == LinkKind.Mobile || Net.Addresses.Parse(local.LocalV4) is { } address && Net.Addresses.Classify(address) == AddressKind.Shared;
      finding.WithKey("FactWhoHasIt", own ? "ValueOnThisDevice" : shared ? "ValueSharedProvider" : "ValueSharedAtHome");
    }
    if (v6 is not null)
    {
      finding.With("FactPublicV6", v6);
      var own = local.Active?.Addresses.Any(a => Net.Addresses.SameAddress(a, v6)) == true;
      finding.WithKey("FactWhoHasIpv6", own ? "ValueOnThisDevice" : "ValueIpv6NotThisDevice");
    }
    return finding;
  }

  public static Finding Provider(KnowledgeBase knowledge, AsnEntry v4, AsnEntry v6, bool anyAddress, bool mobile)
  {
    var finding = new Finding { Id = CheckId.Provider };
    if (!anyAddress)
    {
      finding.Outcome = Outcome.Unknown;
      finding.Summary = "ProviderNoAddress";
      return finding;
    }
    if (!knowledge.HasAsnTable)
    {
      finding.Outcome = Outcome.Unknown;
      finding.Summary = "ProviderNoMap";
      return finding;
    }
    var main = v4 ?? v6;
    if (main is null)
    {
      finding.Outcome = Outcome.Unknown;
      finding.Summary = "ProviderNotFound";
      return finding;
    }
    var profile = knowledge.ProviderFor(main.Number);
    finding.Outcome = Outcome.Info;
    finding.Summary = profile is null ? "ProviderUnlisted" : mobile ? "ProviderListedMobile" : "ProviderListed";
    finding.Args = [profile?.Name ?? Display(main)];
    finding.With("FactNetwork", Describe(main));
    if (v6 is not null && v4 is not null && v6.Number != v4.Number) finding.With("FactNetworkIpv6", Describe(v6));
    var upstreams = knowledge.NetworkFor(main.Number)?.Upstreams ?? [];
    if (upstreams.Count > 0) finding.With("FactUpstreams", string.Join("\n", upstreams.Select(u => $"{knowledge.NameOf(u) ?? "AS" + u} (AS{u})")));
    if (profile is null) return finding;
    AddFact(finding, "FactProviderIpv4", "ProviderIpv4", profile.Ipv4);
    AddFact(finding, "FactProviderPublic", "ProviderPublic", profile.PublicAddress);
    AddFact(finding, "FactProviderIpv6", "ProviderIpv6", profile.Ipv6);
    AddFact(finding, "FactProviderPort25", "ProviderPort25", profile.Port25);
    if (profile.Sheet is not null) finding.Facts.Add(new Fact { Label = "FactProviderSheet", Key = "ValueOpenSheet", Link = profile.Sheet });
    return finding;
  }

  public static Finding Router(RouterReport router, LocalSnapshot local)
  {
    var finding = new Finding { Id = CheckId.Router };
    if (router.Gateway is null)
    {
      finding.Outcome = Outcome.Info;
      finding.Summary = local.Active?.Kind == LinkKind.Mobile ? "RouterMobile" : "RouterNone";
      return finding;
    }
    (finding.Outcome, finding.Summary) = router switch
    {
      { AnyMapping: true } => (Outcome.Good, "RouterOpens"),
      { AnyAnswer: true } => (Outcome.Caution, "RouterRefuses"),
      _ => (Outcome.Caution, "RouterSilent"),
    };
    finding.With("FactRouter", Join(router.Make, router.Label));
    finding.With("FactGateway", router.Gateway);
    finding.WithKey("FactUpnp", AnswerKey(router.Upnp), router.Upnp == Answer.Refused ? router.UpnpError.ToString(CultureInfo.InvariantCulture) : router.UpnpVersion.ToString(CultureInfo.InvariantCulture));
    finding.WithKey("FactNatPmp", AnswerKey(router.NatPmp), router.NatPmpResult.ToString(CultureInfo.InvariantCulture));
    finding.WithKey("FactPcp", AnswerKey(router.Pcp), router.PcpResult.ToString(CultureInfo.InvariantCulture));
    finding.With("FactRouterWan", router.WanAddress);
    return finding;
  }

  public static (Finding Finding, NatKind Kind) Nat(LocalSnapshot local, RouterReport router, string v4, string v6, List<Hop> hops)
  {
    var kind = NatOf(local, router, v4);
    var finding = new Finding { Id = CheckId.Nat };
    (finding.Outcome, finding.Summary) = kind switch
    {
      NatKind.Direct => (Outcome.Good, "NatDirect"),
      NatKind.HomeRouter => (Outcome.Good, "NatHomeRouter"),
      NatKind.DoubleNat => (Outcome.Caution, "NatDouble"),
      NatKind.Shared => (Outcome.Bad, "NatShared"),
      NatKind.Translated => (Outcome.Bad, "NatTranslated"),
      NatKind.NoIpv4 => (Outcome.Info, "NatNoIpv4"),
      _ => (Outcome.Unknown, "NatUnknown"),
    };
    finding.With("FactRouterWan", router?.WanAddress);
    finding.With("FactPublicV4", v4);
    var before = Route.BeforeInternet(hops);
    if (hops.Count > 0) finding.With("FactRoute", string.Join(" → ", before.Select(h => h.Address ?? "*").Append(hops.FirstOrDefault(h => h.Kind == AddressKind.Public)?.Address ?? "…")));
    if (kind == NatKind.Unknown && before.Any(h => h.Kind == AddressKind.Shared)) finding.WithKey("FactHint", "HintSharedHop");

    var v6Direct = v6 is not null && local.Active?.Addresses.Any(a => Net.Addresses.SameAddress(a, v6)) == true;
    if (v6 is not null) finding.WithKey("FactIpv6", v6Direct ? "ValueIpv6Direct" : "ValueIpv6Translated");
    if (v6Direct && finding.Outcome is Outcome.Bad or Outcome.Unknown && kind != NatKind.NoIpv4)
    {
      finding.Outcome = Outcome.Caution;
      finding.WithKey("FactWayOut", "ValueIpv6Way");
    }
    return (finding, kind);
  }

  public static NatKind NatOf(LocalSnapshot local, RouterReport router, string v4)
  {
    if (v4 is null) return NatKind.NoIpv4;
    if (local.Active?.Addresses.Any(a => Net.Addresses.SameAddress(a, v4)) == true) return NatKind.Direct;
    var localV4 = Net.Addresses.Parse(local.LocalV4);
    if (router?.Gateway is null && localV4 is not null && Net.Addresses.Classify(localV4) is AddressKind.Shared or AddressKind.Private && local.Active?.Kind == LinkKind.Mobile)
      return NatKind.Shared;
    var wan = Net.Addresses.Parse(router?.WanAddress);
    if (wan is null && localV4 is not null && Net.Addresses.Classify(localV4) == AddressKind.Shared) return NatKind.Shared;
    if (wan is null) return NatKind.Unknown;
    if (Net.Addresses.SameAddress(router.WanAddress, v4)) return NatKind.HomeRouter;
    return Net.Addresses.Classify(wan) switch
    {
      AddressKind.Shared => NatKind.Shared,
      AddressKind.Private => NatKind.DoubleNat,
      AddressKind.Public => NatKind.Translated,
      _ => NatKind.Unknown,
    };
  }

  public static Finding Behaviour(StunReport stun, NatKind nat)
  {
    var finding = new Finding { Id = CheckId.Behaviour };
    (finding.Outcome, finding.Summary) = stun.Behaviour switch
    {
      NatBehaviour.None => (Outcome.Good, "BehaviourNone"),
      NatBehaviour.Easy => (Outcome.Good, "BehaviourEasy"),
      NatBehaviour.Hard => (Outcome.Caution, "BehaviourHard"),
      _ => (Outcome.Unknown, "BehaviourUnknown"),
    };
    finding.With("FactStunFirst", stun.FirstMapped is null ? null : $"{stun.FirstServer} → {stun.FirstMapped}");
    finding.With("FactStunSecond", stun.SecondMapped is null ? null : $"{stun.SecondServer} → {stun.SecondMapped}");
    finding.With("FactLocalPort", stun.LocalPort > 0 ? stun.LocalPort.ToString(CultureInfo.InvariantCulture) : null);
    var ports = stun.Ports;
    if (ports is null) return finding;
    if (ports.Pattern != PortPattern.Unknown)
    {
      var low = ports.Low.ToString(CultureInfo.InvariantCulture);
      var high = ports.High.ToString(CultureInfo.InvariantCulture);
      finding.WithKey("FactPortSlice", ports.Pattern switch
      {
        PortPattern.Kept => "ValuePortsKept",
        PortPattern.InOrder => "ValuePortsInOrder",
        PortPattern.Block => "ValuePortsBlock",
        _ => "ValuePortsScattered",
      }, low, high);
      if (nat == NatKind.Shared && ports.BlockSize >= 64)
        finding.WithKey("FactSharers", "ValueUpTo", (64512 / ports.BlockSize).ToString(CultureInfo.InvariantCulture));
    }
    if (ports.Hairpin is not null) finding.WithKey("FactHairpinExit", ports.Hairpin == true ? "ValueYes" : "ValueNo");
    if (!ports.LifetimeDone) finding.WithKey("FactMappingLife", "ValueMeasuring");
    else if (ports.KeptAtLeast > 0 && ports.LostBefore > ports.KeptAtLeast)
      finding.WithKey("FactMappingLife", "ValueBetweenSeconds", ports.KeptAtLeast.ToString(CultureInfo.InvariantCulture), ports.LostBefore.ToString(CultureInfo.InvariantCulture));
    else if (ports.KeptAtLeast > 0) finding.WithKey("FactMappingLife", "ValueAtLeastSeconds", ports.KeptAtLeast.ToString(CultureInfo.InvariantCulture));
    else if (ports.LostBefore > 0) finding.WithKey("FactMappingLife", "ValueUnderSeconds", ports.LostBefore.ToString(CultureInfo.InvariantCulture));
    if (ports.LifetimeDone && ports.LostBefore is > 0 and <= 30 && finding.Outcome == Outcome.Good) finding.Outcome = Outcome.Caution;
    return finding;
  }

  public static Finding Reach(ReachReport reach, RunReport run)
  {
    var finding = new Finding { Id = CheckId.Reach };
    if (reach is null || reach.Choice == ReachChoice.Skip)
    {
      finding.Outcome = Outcome.Unknown;
      finding.Summary = "ReachSkipped";
      return finding;
    }
    var refusal = reach.V4Refusal ?? reach.V6Refusal;
    if (reach.V4 is null && reach.V6 is null)
    {
      finding.Outcome = Outcome.Unknown;
      finding.Summary = refusal switch
      {
        "own-network" => "ReachOwnNetwork",
        "too-many" => "ReachTooMany",
        "no-listener" => "ReachNoListener",
        _ => "ReachUnavailable",
      };
      if (refusal == "too-many") finding.Args = [Math.Max(1, (int)Math.Ceiling(reach.RetryAfterSeconds / 60.0)).ToString(CultureInfo.InvariantCulture)];
      return finding;
    }

    var reached4 = reach.V4?.Ports.Any(p => p.Outcome == ProbeOutcome.Reached) == true;
    var reached6 = reach.V6?.Ports.Any(p => p.Outcome == ProbeOutcome.Reached) == true;
    var mapped = reach.Mappings.Any(m => m.Done);
    (finding.Outcome, finding.Summary) = (reached4, reached6) switch
    {
      (true, true) => (Outcome.Good, "ReachBoth"),
      (true, false) => (Outcome.Good, "ReachV4"),
      (false, true) => (Outcome.Caution, "ReachV6Only"),
      _ when reach.Choice == ReachChoice.OpenPorts && mapped => (Outcome.Bad, "ReachBlockedAfterMapping"),
      _ when reach.Choice == ReachChoice.OpenPorts => (Outcome.Bad, "ReachNoMapping"),
      _ => (Outcome.Caution, "ReachNothingAsIs"),
    };
    foreach (var attempt in reach.Mappings)
      finding.WithKey("FactMapping", attempt.Done ? "ValueMapped" : "ValueNotMapped", attempt.ExternalPort.ToString(CultureInfo.InvariantCulture), attempt.Via.ToString(), attempt.Error.ToString(CultureInfo.InvariantCulture));
    foreach (var port in reach.V4?.Ports ?? [])
      finding.WithKey("FactReachV4", "Probe" + port.Outcome, port.Port.ToString(CultureInfo.InvariantCulture));
    foreach (var port in reach.V6?.Ports ?? [])
      finding.WithKey("FactReachV6", "Probe" + port.Outcome, port.Port.ToString(CultureInfo.InvariantCulture));
    if (reach.V4 is null && reach.V4Refusal is not null) finding.WithKey("FactReachV4", "Refusal" + Pascal(reach.V4Refusal));
    if (reach.V6 is null && reach.V6Refusal is not null) finding.WithKey("FactReachV6", "Refusal" + Pascal(reach.V6Refusal));
    if (reach.Hairpin is not null) finding.WithKey("FactHairpin", reach.Hairpin == true ? "ValueHairpinYes" : "ValueHairpinNo");
    var route = reach.V4?.Route ?? reach.V6?.Route ?? [];
    if (route.Count > 0) finding.With("FactRouteBack", string.Join(" → ", route.Select(h => h.Name ?? h.Address ?? "*")));
    if (reach.V4?.Ports.Any(p => p.Outcome == ProbeOutcome.OpenNotYou && p.Port is 80 or 443) == true && !mapped)
      finding.WithKey("FactHint", "HintSomethingAnswers");
    return finding;
  }

  public static Finding Mail(Mail.MailReport mail, bool hasV4)
  {
    var finding = new Finding { Id = CheckId.Mail };
    if (!hasV4)
    {
      finding.Outcome = Outcome.Unknown;
      finding.Summary = "MailNoIpv4";
      return finding;
    }
    var listed = mail.Listings.Where(l => l.State == Core.Mail.ListingState.Listed && !l.Residential && !l.Wide).ToList();
    var wide = mail.Listings.Where(l => l.State == Core.Mail.ListingState.Listed && l.Wide).ToList();
    (finding.Outcome, finding.Summary) = mail switch
    {
      { Port25: Core.Mail.PortState.Blocked } => (Outcome.Bad, "MailBlocked"),
      _ when listed.Count > 0 => (Outcome.Bad, "MailListed"),
      _ when mail.Listings.Any(l => l.Residential) => (Outcome.Caution, "MailResidential"),
      _ when wide.Count > 0 => (Outcome.Caution, "MailNetworkListed"),
      { ReverseName: null } => (Outcome.Caution, "MailNoName"),
      { ReverseLooksDynamic: true } => (Outcome.Caution, "MailDynamicName"),
      { Port25: Core.Mail.PortState.Open } => (Outcome.Good, "MailClean"),
      _ => (Outcome.Unknown, "MailUnknown"),
    };
    if (listed.Count > 0) finding.Args = [string.Join(", ", listed.Select(l => l.List))];
    else if (wide.Count > 0) finding.Args = [string.Join(", ", wide.Select(l => l.List))];
    finding.WithKey("FactPort25", mail.Port25 switch
    {
      Core.Mail.PortState.Open => "ValuePort25Open",
      Core.Mail.PortState.Blocked => "ValuePort25Blocked",
      _ => "ValueCantTell",
    }, mail.Banner ?? "");
    if (mail.ReverseName is null) finding.WithKey("FactReverseName", "ValueNoReverse");
    else
    {
      finding.With("FactReverseName", mail.ReverseName);
      finding.WithKey("FactReverseLooks", mail.ReverseLooksDynamic ? "ValueLooksHome" : "ValueLooksServer");
      finding.WithKey("FactReverseConfirmed", mail.ReverseConfirmed ? "ValueYes" : "ValueNo");
    }
    foreach (var listing in mail.Listings)
      finding.Facts.Add(new Fact
      {
        Label = "FactList",
        Key = listing.State switch
        {
          Core.Mail.ListingState.Listed when listing.Residential => "ValueListedHome",
          Core.Mail.ListingState.Listed when listing.Wide => "ValueListedNetwork",
          Core.Mail.ListingState.Listed => "ValueListed",
          Core.Mail.ListingState.Clean => "ValueNotListed",
          _ => "ValueCantTellResolver",
        },
        Args = [listing.List, listing.Code ?? ""],
      });
    return finding;
  }

  public static Finding Dns(DnsReport dns)
  {
    var finding = new Finding { Id = CheckId.Dns };
    (finding.Outcome, finding.Summary) = dns switch
    {
      { Hijacks: true } => (Outcome.Bad, "DnsHijack"),
      { Validates: false } => (Outcome.Caution, "DnsNoValidation"),
      { Validates: true, Hijacks: false } => (Outcome.Good, "DnsGood"),
      _ => (Outcome.Unknown, "DnsUnknown"),
    };
    if (dns.Resolvers.Count > 0) finding.With("FactDns", string.Join(", ", dns.Resolvers.Take(3)));
    if (dns.Validates is not null) finding.WithKey("FactDnssec", dns.Validates == true ? "ValueDnssecYes" : "ValueDnssecNo");
    if (dns.Hijacks is not null) finding.WithKey("FactMissingNames", dns.Hijacks == true ? "ValueHijacked" : "ValueAnsweredMissing");
    if (dns.Ipv6Names is not null) finding.WithKey("FactIpv6Names", dns.Ipv6Names == true ? "ValueYes" : "ValueNo");
    return finding;
  }

  public static Finding Speed(SpeedReport speed)
  {
    var finding = new Finding { Id = CheckId.Speed };
    if (speed.Limited)
    {
      finding.Outcome = Outcome.Unknown;
      finding.Summary = "SpeedLimited";
      return finding;
    }
    if (speed.DownMbps <= 0)
    {
      finding.Outcome = Outcome.Unknown;
      finding.Summary = "SpeedFailed";
      return finding;
    }
    finding.Outcome = Outcome.Info;
    finding.Summary = "SpeedResult";
    finding.Args = [speed.DownMbps.ToString("0.#", CultureInfo.InvariantCulture), speed.UpMbps.ToString("0.#", CultureInfo.InvariantCulture)];
    finding.WithKey("FactDownload", "ValueMbpsDecimal", speed.DownMbps.ToString("0.#", CultureInfo.InvariantCulture));
    finding.WithKey("FactUpload", "ValueMbpsDecimal", speed.UpMbps.ToString("0.#", CultureInfo.InvariantCulture));
    finding.WithKey("FactSample", "ValueSample", (speed.DownBytes / 1048576).ToString(CultureInfo.InvariantCulture), (speed.UpBytes / 1048576).ToString(CultureInfo.InvariantCulture));
    if (speed.RoundTripMs > 0) finding.WithKey("FactRoundTrip", "ValueMilliseconds", speed.RoundTripMs.ToString(CultureInfo.InvariantCulture));
    return finding;
  }

  public static Finding Device(DeviceReport device)
  {
    var finding = new Finding { Id = CheckId.Device };
    var small = device.Cores < 2 || device.MemoryMb < 1800 || device.FreeDiskGb is > 0 and < 20;
    (finding.Outcome, finding.Summary) = device switch
    {
      { Kind: DeviceKind.Phone } => (Outcome.Caution, "DevicePhone"),
      _ when small => (Outcome.Caution, "DeviceSmall"),
      { OnBattery: true } => (Outcome.Info, "DeviceLaptop"),
      _ => (Outcome.Good, "DeviceGood"),
    };
    finding.With("FactSystem", device.System);
    finding.WithKey("FactCores", "ValueCount", device.Cores.ToString(CultureInfo.InvariantCulture));
    finding.WithKey("FactMemory", "ValueGb", Math.Round(device.MemoryMb / 1024.0, 1).ToString("0.#", CultureInfo.InvariantCulture));
    if (device.FreeDiskGb > 0) finding.WithKey("FactDisk", "ValueGbFree", device.FreeDiskGb.ToString(CultureInfo.InvariantCulture));
    if (device.OnBattery is not null) finding.WithKey("FactBattery", device.OnBattery == true ? "ValueYes" : "ValueNo");
    return finding;
  }

  public static Finding History(HistorySummary summary)
  {
    var finding = new Finding { Id = CheckId.History, Outcome = Outcome.Info };
    var since = summary.Since.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture);
    if (summary.Checks <= 1)
    {
      finding.Summary = "HistoryFirst";
      return finding;
    }
    finding.Summary = summary.Changes == 0 ? "HistoryStable" : "HistoryChanged";
    finding.Args = [summary.Checks.ToString(CultureInfo.InvariantCulture), since, summary.Changes.ToString(CultureInfo.InvariantCulture)];
    finding.WithKey("FactChecks", "ValueCount", summary.Checks.ToString(CultureInfo.InvariantCulture));
    finding.Facts.Add(new Fact { Label = "FactSince", Date = since });
    finding.WithKey("FactAddressesSeen", "ValueCount", summary.AddressesSeen.ToString(CultureInfo.InvariantCulture));
    return finding;
  }

  static void AddFact(Finding finding, string label, string prefix, ProviderFact fact)
  {
    if (fact?.Value is null) return;
    finding.Facts.Add(new Fact
    {
      Label = label,
      Key = prefix + Pascal(fact.Value),
      Amount = fact.Price,
      Currency = fact.Currency,
      Link = fact.Source,
      Basis = fact.Basis is null ? null : "Basis" + Pascal(fact.Basis),
      Date = fact.Date,
    });
  }

  static string AnswerKey(Answer answer) => answer switch
  {
    Answer.Answered => "ValueAnswered",
    Answer.Refused => "ValueRefused",
    _ => "ValueSilent",
  };

  static string Display(AsnEntry entry) => string.IsNullOrWhiteSpace(entry.Name) ? $"AS{entry.Number}" : entry.Name;

  static string Describe(AsnEntry entry) => $"{Display(entry)} (AS{entry.Number})";

  static string Join(string make, string label)
  {
    if (string.IsNullOrWhiteSpace(make)) return label;
    if (string.IsNullOrWhiteSpace(label) || label.Contains(make.Split(' ')[0], StringComparison.OrdinalIgnoreCase)) return label ?? make;
    return $"{make} {label}";
  }

  static string Pascal(string value) => string.Concat(value.Split('-').Select(p => p.Length == 0 ? p : char.ToUpperInvariant(p[0]) + p[1..]));
}