using System.Collections.ObjectModel;
using CommunityToolkit.Mvvm.ComponentModel;
using DodoSSH.Client.Domain;
using DodoSSH.Client.Session;
using DodoSSH.Client.Ssh;

namespace DodoSSH.Client.Shell.ViewModels;

/// <summary>
/// Reaching a host through Spelunk: the editor's half, the connect path's half, and a link from Spelunk.
/// </summary>
/// <remarks>
/// A file of its own because it is one feature and this class is long enough without it. Everything here
/// follows the relay, which is the other route a host can take: a tick box in the editor, a route opened by
/// the connect that will use it, no falling back to a direct dial, and a stated failure when the route
/// cannot be opened. See <see cref="HostSecret.Spelunk"/> and <see cref="SpelunkRoute"/>.
/// </remarks>
internal sealed partial class VaultViewModel
{
    /// <summary>The tag every host made from a Spelunk link wears, and what a link looks for.</summary>
    /// <remarks>
    /// Matched without regard to case, as the editor matches every tag name — see <c>AddEditorTagAsync</c>.
    /// </remarks>
    internal const string SpelunkTag = "spelunk";

    /// <summary>What the status bar and the log name as the identity of a Spelunk sign-in.</summary>
    private const string SpelunkSignInIdentity = "Spelunk sign-in";

    /// <summary>What opens a tunnel when no caller supplied something else.</summary>
    /// <remarks>
    /// Static and shared for the reason <see cref="DefaultReachability"/> is: it holds nothing but a
    /// transport, and every tunnel is a fresh ticket and a fresh socket. Optional in the constructor so both
    /// heads and every existing test go on meaning what they did, and a test that wants to see what was
    /// opened passes a substitute.
    /// </remarks>
    private static readonly ISpelunkTunnel DefaultSpelunk = new SpelunkTunnel();

    /// <summary>Whether the host being edited is reached through Spelunk.</summary>
    /// <remarks>
    /// Ticking it unticks the relay and the other way round, rather than letting both be ticked and refusing
    /// the save: a host has one route, and <see cref="HostSecret.TryValidate"/> would only catch after the
    /// fact what these two boxes can simply not express.
    /// </remarks>
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(EditorAsksForLogin))]
    private bool editorThroughSpelunk;

    /// <summary>Whether Spelunk signs the user in to the host being edited, so it needs no login of its own.</summary>
    /// <remarks>
    /// Inside the Spelunk card, and meaningful only while that is ticked. See
    /// <see cref="SpelunkRoute.SignInThroughSpelunk"/>.
    /// </remarks>
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(EditorAsksForLogin))]
    private bool editorSpelunkSignIn;

    /// <summary>The Spelunk API address in the editor, as typed.</summary>
    [ObservableProperty]
    private string editorSpelunkApi = string.Empty;

    /// <summary>The Spelunk server id in the editor, as typed.</summary>
    [ObservableProperty]
    private string editorSpelunkServerId = string.Empty;

    /// <summary>The credentials the editor offers as the Spelunk API key.</summary>
    /// <remarks>
    /// Credentials only, and no "none" entry: a route with no key cannot be opened, and nothing selected is
    /// how a host made from a link says it has not been chosen yet. A key the host names that has since been
    /// deleted keeps a placeholder, for the reason <see cref="BuildAuthenticationChoices"/> keeps one.
    /// </remarks>
    internal ObservableCollection<AuthenticationChoice> EditorSpelunkKeyChoices { get; } = [];

    /// <summary>The credential chosen to hold the Spelunk API key.</summary>
    [ObservableProperty]
    private AuthenticationChoice? editorSelectedSpelunkKey;

    /// <summary>
    /// Whether the editor's username and login choice mean anything — false for a host Spelunk signs in to.
    /// </summary>
    /// <remarks>
    /// The two controls are disabled rather than hidden while it is false, with a sentence saying why, so a
    /// login somebody had chosen is still there to see — and comes back as it was if the box is unticked
    /// before saving.
    /// </remarks>
    internal bool EditorAsksForLogin => !(EditorThroughSpelunk && EditorSpelunkSignIn);

    /// <inheritdoc cref="DefaultSpelunk" />
    private ISpelunkTunnel Spelunk => spelunk ?? DefaultSpelunk;

    partial void OnEditorThroughSpelunkChanged(bool value)
    {
        if (value)
        {
            EditorRelayEnabled = false;
        }
    }

    partial void OnEditorRelayEnabledChanged(bool value)
    {
        if (value)
        {
            EditorThroughSpelunk = false;
        }
    }

    /// <summary>
    /// Opens the route a host is reached by, or null for a host that is dialled.
    /// </summary>
    /// <remarks>
    /// <para>
    /// The one place that decides, for both transports: a shell comes through here from
    /// <see cref="OpenThroughAsync"/>, and file transfer opens its own connection and comes through here from
    /// the transfers screen — or that screen would fail for exactly the hosts a route exists for.
    /// </para>
    /// <para>
    /// A host naming a route that cannot be opened is a refusal, never a quiet direct dial. See
    /// <see cref="OpenRelayAsync"/> for the relay's half of that argument; Spelunk's is stronger still,
    /// because a Spelunk host's address may be nothing that answers at all.
    /// </para>
    /// <para>
    /// The request a route is used for is made with <see cref="Through"/>, which is where a Spelunk sign-in's
    /// key and account replace the ones the host resolved to.
    /// </para>
    /// </remarks>
    internal async Task<IConnectionRoute?> OpenRouteAsync(HostRowViewModel row, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(row);

        if (row.Host.Spelunk is { } route)
        {
            return await OpenSpelunkTunnelAsync(row, route, cancellationToken).ConfigureAwait(true);
        }

        return row.Host.RelayEnabled
            ? await OpenRelayAsync(row.Label, row.EntityId, cancellationToken).ConfigureAwait(true)
            : null;
    }

    /// <summary>
    /// The request to connect with once a route is open: through its proxy, and for a Spelunk sign-in, with
    /// the key the tunnel was opened with and the account Spelunk named.
    /// </summary>
    /// <remarks>
    /// <para>
    /// Both transports make their request through this, so a sign-in cannot reach one of them with the
    /// stand-in credential <see cref="TryBuildAuthentication"/> gives it — which the SSH layer would refuse
    /// before dialling anyway. See <see cref="SpelunkSignInPending"/>.
    /// </para>
    /// <para>
    /// The host and port are left alone. The host key is pinned under them as for every host, and Spelunk's
    /// SSH server presents the server's real host key, so a sign-in and a plain tunnel to one server are
    /// checked against the same pin.
    /// </para>
    /// </remarks>
    internal static SshConnectionRequest Through(SshConnectionRequest request, IConnectionRoute? route)
    {
        ArgumentNullException.ThrowIfNull(request);

        return route switch
        {
            null => request,
            SpelunkTunnelRoute { SignIn: { } signIn, User: { } user } => request with
            {
                Proxy = route.Proxy,
                Username = user,
                Credential = signIn.Credential,
            },
            _ => request with { Proxy = route.Proxy },
        };
    }

    /// <summary>
    /// Opens a Spelunk tunnel to a host, with the key its credential holds.
    /// </summary>
    /// <remarks>
    /// <para>
    /// The key is read from the keychain at the moment of connecting, like every other secret the connect
    /// path uses, and goes only to the API address the host names. A credential that has gone is refused in
    /// words, exactly as a missing SSH credential is — see <see cref="TryBuildAuthentication"/>.
    /// </para>
    /// <para>
    /// The port is the host's resolved one, group and all: it is the port the agent connects to on the
    /// server's own loopback, which is where the SSH server listens whatever address the world sees.
    /// </para>
    /// <para>
    /// <b>A host Spelunk signs in to gets a new key pair here, every time.</b> It is made in memory for this
    /// one tunnel, its public half goes with the ticket request, and the route carries it to the connection —
    /// see <see cref="SpelunkSignIn"/>. A retry after a host key question, or a reconnect, comes back through
    /// here and makes another.
    /// </para>
    /// </remarks>
    private async Task<IConnectionRoute> OpenSpelunkTunnelAsync(
        HostRowViewModel row,
        SpelunkRoute route,
        CancellationToken cancellationToken)
    {
        if (Credentials.FirstOrDefault(credential => credential.EntityId == route.ApiKeyCredentialId) is not { } key)
        {
            throw new SpelunkTunnelException(
                $"'{row.Label}' is reached through Spelunk with an API key credential that is not in this "
                + "keychain any more. Edit the host to choose another one.");
        }

        return await Spelunk
            .OpenAsync(
                route.ApiBase,
                route.ServerId,
                key.Credential.Password,
                row.Resolved.Port.Value,
                route.SignInThroughSpelunk ? SpelunkSignIn.Create() : null,
                cancellationToken)
            .ConfigureAwait(true);
    }

    /// <summary>
    /// Does what a <c>dodossh://spelunk/connect</c> link asks, as far as it is allowed to.
    /// </summary>
    /// <returns>
    /// The work the link started, connection attempt included, so a caller that wants to can wait for it.
    /// </returns>
    /// <remarks>
    /// <para>
    /// <b>A host for that server in the personal vault, tagged <see cref="SpelunkTag"/>, is connected to</b>,
    /// exactly as a tap on its row would. Those are the hosts links make, and the only ones a link looks for:
    /// a host somebody set up by hand, or one in a team's vault, is theirs to connect to and not the link's.
    /// </para>
    /// <para>
    /// <b>Otherwise, when that Spelunk already gets an API key, the host is made and connected to.</b> In the
    /// personal vault, tagged, named as the link names it, and signing in through Spelunk — so it needs no
    /// SSH key or password — with the key credential a saved host already sends to that same Spelunk. It is
    /// saved the ordinary way and syncs like any host. Nothing leaks by this: the key goes where it already
    /// goes, and the server is one that key's own organisation holds or Spelunk refuses it.
    /// </para>
    /// <para>
    /// <b>The first link from a Spelunk opens the editor instead, and nothing more.</b> Anything on this
    /// machine can make a link, so it must never be able to send an API key to an address no saved host
    /// already sends it to. The host is pre-filled — signing in through Spelunk, tagged, in the personal
    /// vault — and the user chooses the credential holding the key and saves; every later link from that
    /// Spelunk connects straight away.
    /// </para>
    /// </remarks>
    internal async Task OpenSpelunkLinkAsync(SpelunkLink link)
    {
        ArgumentNullException.ThrowIfNull(link);

        var personal = PersonalVaultId();

        if (personal is { } vaultId
            && Hosts.FirstOrDefault(row =>
                row.VaultId == vaultId
                && row.Host.Spelunk?.IsFor(link.ApiBase, link.ServerId) is true
                && WearsSpelunkTag(row.Host)) is { } saved)
        {
            await ConnectToRowCommand.ExecuteAsync(saved).ConfigureAwait(true);
            return;
        }

        var knownKey = KnownSpelunkKey(link.ApiBase, personal);

        if (personal is { } into && knownKey is { } key)
        {
            await AddFromLinkAndConnectAsync(link, into, key).ConfigureAwait(true);
            return;
        }

        await OpenLinkInEditorAsync(link, personal, knownKey).ConfigureAwait(true);
    }

    /// <summary>The personal vault, when this session can read and write it.</summary>
    private Guid? PersonalVaultId() =>
        session.ReadableVaults.FirstOrDefault(vault => vault.IsPersonal && vault.CanWrite)?.VaultId;

    /// <summary>Whether a host wears a tag called <see cref="SpelunkTag"/>, from whichever vault.</summary>
    private bool WearsSpelunkTag(HostSecret host) =>
        host.TagIds.Any(id => tagsById.TryGetValue(id, out var tag) && IsSpelunkTag(tag));

    private static bool IsSpelunkTag(TagSecret tag) =>
        string.Equals(tag.Label.Trim(), SpelunkTag, StringComparison.OrdinalIgnoreCase);

    /// <summary>
    /// The credential a saved host already sends to this Spelunk as its API key, or null when none does.
    /// </summary>
    /// <remarks>
    /// The personal vault's hosts first, so the answer does not depend on the order vaults happen to load in;
    /// and only a credential still in the keychain, because a dangling one would make a host that cannot
    /// connect.
    /// </remarks>
    private Guid? KnownSpelunkKey(string apiBase, Guid? personal) =>
        Hosts
            .OrderByDescending(row => row.VaultId == personal)
            .Select(row => row.Host.Spelunk)
            .Where(route => route is not null && string.Equals(route.ApiBase, apiBase, StringComparison.Ordinal))
            .Select(route => (Guid?)route!.ApiKeyCredentialId)
            .FirstOrDefault(id => Credentials.Any(credential => credential.EntityId == id));

    /// <summary>The host a link makes: what the link says, signing in through Spelunk with a known key.</summary>
    private static HostSecret HostFromLink(SpelunkLink link, Guid apiKeyCredentialId, TagSet tags) => new()
    {
        Label = link.Name,
        Hostname = link.Hostname,
        Port = HostSecret.DefaultPort,
        TagIds = tags,
        Spelunk = new SpelunkRoute
        {
            ApiBase = link.ApiBase,
            ServerId = link.ServerId,
            ApiKeyCredentialId = apiKeyCredentialId,
            SignInThroughSpelunk = true,
        },
    };

    /// <summary>Saves the host a link describes into the personal vault, tagged, and connects to it.</summary>
    private async Task AddFromLinkAndConnectAsync(SpelunkLink link, Guid vaultId, Guid apiKeyCredentialId)
    {
        if (IsBusy)
        {
            // RunAsync would drop it without a word, and the user pressed a button somewhere else to get here.
            Status = $"Busy — open {link.Name} from Spelunk again in a moment.";
            return;
        }

        Guid? hostId = null;

        await RunAsync(
            $"Adding {link.Name} from Spelunk…",
            async () =>
            {
                var tagId = await EnsureSpelunkTagAsync(vaultId, CancellationToken.None).ConfigureAwait(true);

                hostId = await session.Hosts
                    .CreateAsync(
                        vaultId,
                        HostFromLink(link, apiKeyCredentialId, TagSet.Create([tagId])),
                        CancellationToken.None)
                    .ConfigureAwait(true);

                await ReloadAsync(CancellationToken.None).ConfigureAwait(true);
            }).ConfigureAwait(true);

        // A failure has said so on the status line already.
        if (hostId is not { } id || Hosts.FirstOrDefault(row => row.EntityId == id) is not { } row)
        {
            return;
        }

        Status = $"Added {link.Name} from Spelunk at {link.ApiBase}.";

        await ConnectToRowCommand.ExecuteAsync(row).ConfigureAwait(true);

        // After the connect rather than before it: the host is saved either way, and the terminal is what the
        // user is waiting for. As SaveHostAsync does, it goes to the server now rather than at the next tick.
        await AutoSyncAsync(CancellationToken.None).ConfigureAwait(true);
    }

    /// <summary>
    /// Opens the editor on a new host from a link, for the first link from a Spelunk no host sends a key to.
    /// </summary>
    /// <remarks>
    /// Opened before anything is awaited, so the editor is up in the same turn the link arrived in. The tag is
    /// made or found afterwards and added to the host being edited; a tag made for a host that is then
    /// cancelled stays, as the editor's own new-tag box leaves it.
    /// </remarks>
    private async Task OpenLinkInEditorAsync(SpelunkLink link, Guid? personal, Guid? knownKey)
    {
        // Refused while another host is half-edited, as NewHost refuses it, and said the same way: the link
        // is not worth somebody's unsaved host.
        if (AHostEditorIsInTheWay())
        {
            return;
        }

        NewHost();

        if (personal is { } vaultId
            && EditorVaultChoices.FirstOrDefault(choice => choice.VaultId == vaultId) is { } choice)
        {
            EditorSelectedVault = choice;
        }

        EditorLabel = link.Name;
        EditorHostname = link.Hostname;
        EditorPort = HostSecret.DefaultPort;
        EditorThroughSpelunk = true;
        EditorSpelunkSignIn = true;
        EditorSpelunkApi = link.ApiBase;
        EditorSpelunkServerId = link.ServerId.ToString();

        BuildSpelunkKeyChoices(knownKey);

        IsHostPaneOpen = true;

        var said = EditorSelectedSpelunkKey is null
            ? $"Adding {link.Name}, the first server from Spelunk at {link.ApiBase}. Choose the credential "
                + "holding your Spelunk API key and save — Spelunk signs you in, so no SSH key is needed, and "
                + "later links from this Spelunk connect straight away."
            : $"Adding {link.Name} from Spelunk at {link.ApiBase}. Check it and save.";

        Status = said;

        if (personal is { } into)
        {
            await TagHostFromLinkAsync(into, said).ConfigureAwait(true);
        }
    }

    /// <summary>Adds the <see cref="SpelunkTag"/> tag to the host a link opened the editor on.</summary>
    /// <param name="vaultId">The personal vault, where the host is to be saved and the tag is.</param>
    /// <param name="said">What the status line says about the link, put back after the reload.</param>
    private async Task TagHostFromLinkAsync(Guid vaultId, string said)
    {
        try
        {
            var tagId = await EnsureSpelunkTagAsync(vaultId, CancellationToken.None).ConfigureAwait(true);

            // Only onto the host this link opened: the user may have cancelled it, or moved on to another, in
            // the moment the tag took.
            if (!IsEditing || editingEntityId is not null || editingHostVaultId != vaultId)
            {
                return;
            }

            editorTagIds = TagSet.Create([.. editorTagIds, tagId]);

            if (!tagsById.ContainsKey(tagId))
            {
                await ReloadAsync(CancellationToken.None).ConfigureAwait(true);
            }

            BuildTagChoices();
            Status = said;
        }
        catch (Exception exception) when (exception is not OutOfMemoryException)
        {
            // The host can still be saved; it is the tag that could not be made, and a later link would then
            // not find it. Said, rather than failing the whole link over it.
            Status = $"{said} (The '{SpelunkTag}' tag could not be added: {exception.Message})";
        }
    }

    /// <summary>The <see cref="SpelunkTag"/> tag in a vault, made there if it has none.</summary>
    private async Task<Guid> EnsureSpelunkTagAsync(Guid vaultId, CancellationToken cancellationToken)
    {
        var listing = await session.Tags.ListAsync(vaultId, cancellationToken).ConfigureAwait(true);

        if (listing.Items
            .Where(tag => IsSpelunkTag(tag.Secret))
            .OrderBy(tag => tag.EntityId)
            .FirstOrDefault() is { } existing)
        {
            return existing.EntityId;
        }

        return await session.Tags
            .CreateAsync(vaultId, new TagSecret { Label = SpelunkTag }, cancellationToken)
            .ConfigureAwait(true);
    }

    /// <summary>
    /// Whether a host needs this key or credential to connect: as its resolved binding, or as the credential
    /// holding its Spelunk API key.
    /// </summary>
    /// <remarks>
    /// The one question the deletion warning, the table's USED BY column and the detail pane's list all ask,
    /// so a credential that is only somebody's Spelunk key is not deleted as though nothing used it. Spelunk
    /// keys are named by the host itself and never inherited, so the stored route is the whole answer there.
    /// A host Spelunk signs in to uses no binding at all, whatever its group lends.
    /// </remarks>
    private static bool Uses(HostRowViewModel row, ResolvedBindingKind kind, Guid entityId) =>
        (!row.Host.SignsInThroughSpelunk
            && row.Resolved.Binding is { } binding
            && binding.Kind == kind
            && binding.EntityId == entityId)
        || (kind is ResolvedBindingKind.Credential && row.Host.Spelunk?.ApiKeyCredentialId == entityId);

    /// <summary>Puts a host's route into the editor, or clears it for a host that has none.</summary>
    private void LoadEditorSpelunk(SpelunkRoute? route)
    {
        EditorThroughSpelunk = route is not null;
        EditorSpelunkSignIn = route?.SignInThroughSpelunk ?? false;
        EditorSpelunkApi = route?.ApiBase ?? string.Empty;
        EditorSpelunkServerId = route?.ServerId.ToString() ?? string.Empty;

        BuildSpelunkKeyChoices(route?.ApiKeyCredentialId);
    }

    /// <summary>Fills the API key picker, keeping whatever the host names selectable.</summary>
    private void BuildSpelunkKeyChoices(Guid? selectedId)
    {
        EditorSpelunkKeyChoices.Clear();

        foreach (var credential in Credentials)
        {
            EditorSpelunkKeyChoices.Add(AuthenticationChoice.ForCredential(credential.EntityId, credential.Label));
        }

        if (selectedId is { } missing && EditorSpelunkKeyChoices.All(choice => choice.EntityId != missing))
        {
            EditorSpelunkKeyChoices.Add(AuthenticationChoice.Missing(AuthenticationKind.Credential, missing));
        }

        EditorSelectedSpelunkKey = EditorSpelunkKeyChoices.FirstOrDefault(choice => choice.EntityId == selectedId);
    }

    /// <summary>The editor's route, or null when the box is not ticked.</summary>
    /// <remarks>
    /// What cannot be read is written as empty rather than left out, so that
    /// <see cref="HostSecret.TryValidate"/> says what is wrong with it — "needs the id of its Spelunk server"
    /// — instead of the save quietly producing a host that is dialled directly. The address is normalised
    /// here when it can be, so <c>https://api.example.com/</c> saves as the same Spelunk as the link's.
    /// </remarks>
    private SpelunkRoute? BuildSpelunkRoute()
    {
        if (!EditorThroughSpelunk)
        {
            return null;
        }

        return new SpelunkRoute
        {
            ApiBase = SpelunkRoute.TryNormalizeApiBase(EditorSpelunkApi, out var normalized, out _)
                ? normalized
                : EditorSpelunkApi.Trim(),
            ServerId = Guid.TryParse(EditorSpelunkServerId.Trim(), out var serverId) ? serverId : Guid.Empty,
            ApiKeyCredentialId = EditorSelectedSpelunkKey?.EntityId ?? Guid.Empty,
            SignInThroughSpelunk = EditorSpelunkSignIn,
        };
    }
}