using System.Security.Cryptography;
using System.Text.Json;
using ClawdDotNet.Core.Security;
using Shouldly;

namespace ClawdDotNet.Core.Tests.Security;

/// <summary>
/// The keyring: one master key, wrapped several times (#190).
///
/// <para><b>What this is about.</b> A master key that is bound to the machine
/// survives no move — a backup on a new machine then contains nothing but
/// values nobody can read any more. One bound to a passphrase
/// survives the move, but demands someone who types at every start. The keyring solves
/// that by not deciding.</para>
/// </summary>
public sealed class SecretKeyRingTests : IDisposable
{
    private readonly string _dir = Path.Combine(
        Path.GetTempPath(), "clawd-tests", "ring-" + Guid.NewGuid().ToString("N")[..8]);

    private string Pfad => Path.Combine(_dir, "secret.key");

    public SecretKeyRingTests() => Directory.CreateDirectory(_dir);

    public void Dispose()
    {
        try { Directory.Delete(_dir, recursive: true); }
        catch { /* A leftover test folder does not turn a run red. */ }
    }

    private static SecretKeyRing Bund(params ISecretProvider[] anbieter) => new(anbieter);

    /// <summary>
    /// The heart of the matter: two slots, one key.
    ///
    /// <para>If they led to different keys, the whole setup would be worthless — the
    /// recovery path would then open something, but not the existing values.</para>
    /// </summary>
    [Fact]
    public void Zwei_Faecher_fuehren_zu_demselben_Schluessel()
    {
        var maschine = new PlainFileSecretProvider();
        var bund = Bund(maschine, PassphraseSecretProvider.With("geheim"));

        var schluessel = bund.Load(Pfad);
        bund.SetRecoveryPassphrase(Pfad, schluessel, "geheim");

        // Only with the passphrase, without the machine slot - the move.
        var nachUmzug = Bund(PassphraseSecretProvider.With("geheim")).Load(Pfad);

        nachUmzug.ShouldBe(schluessel);
    }

    /// <summary>
    /// The case #190 is about: the machine changes.
    ///
    /// <para>The machine slot no longer opens. Without a recovery slot
    /// all credentials would be lost here.</para>
    /// </summary>
    [Fact]
    public void Nach_einem_Maschinenwechsel_oeffnet_die_Passphrase()
    {
        var bund = Bund(new NieOeffnendesFach(), PassphraseSecretProvider.With("umzug"));
        var schluessel = bund.Load(Pfad);

        bund.SetRecoveryPassphrase(Pfad, schluessel, "umzug");

        var neueMaschine = Bund(new NieOeffnendesFach(), PassphraseSecretProvider.With("umzug"));
        neueMaschine.Load(Pfad).ShouldBe(schluessel);
    }

    /// <summary>
    /// And afterwards day-to-day operation runs without a passphrase again: the machine slot is
    /// created anew on the new machine.
    ///
    /// <para>That presupposes that the new machine has a slot to offer at all.
    /// On a system whose only way would be <c>file</c>, it does
    /// <em>not</em> happen — see <see cref="Ein_Umzug_legt_den_Schluessel_nicht_im_Klartext_ab"/>.</para>
    /// </summary>
    [Fact]
    public void Nach_dem_Umzug_entsteht_das_Maschinenfach_neu()
    {
        var bund = Bund(new NieOeffnendesFach(), PassphraseSecretProvider.With("umzug"));
        var schluessel = bund.Load(Pfad);
        bund.SetRecoveryPassphrase(Pfad, schluessel, "umzug");

        // New machine with a working machine slot: it does not open yet,
        // but the passphrase does - and afterwards the slot is created.
        var neueMaschine = Bund(new MaschinenFach(), PassphraseSecretProvider.With("umzug"));
        neueMaschine.Load(Pfad).ShouldBe(schluessel);

        // From now on the machine slot alone suffices, without a passphrase.
        Bund(new MaschinenFach()).Load(Pfad).ShouldBe(schluessel);
    }

    /// <summary>
    /// A move does <b>not</b> store the master key in plain text just so that the
    /// next start is more convenient.
    ///
    /// <para>On a system without a secure machine slot — i.e. Linux before #180 — the
    /// passphrase stays the way. Putting a <c>file</c> slot next to it would destroy exactly the
    /// protection someone has just chosen.</para>
    /// </summary>
    [Fact]
    public void Ein_Umzug_legt_den_Schluessel_nicht_im_Klartext_ab()
    {
        var bund = Bund(new NieOeffnendesFach(), PassphraseSecretProvider.With("umzug"));
        var schluessel = bund.Load(Pfad);
        bund.SetRecoveryPassphrase(Pfad, schluessel, "umzug");

        var ohneMaschinenfach = Bund(
            new PlainFileSecretProvider(), PassphraseSecretProvider.With("umzug"));

        ohneMaschinenfach.Load(Pfad).ShouldBe(schluessel);
        ohneMaschinenfach.Slots.ShouldNotContain(s => s.Provider == "file");
    }

    /// <summary>
    /// A wrong passphrase opens nothing — and above all does not generate a new
    /// key.
    /// </summary>
    [Fact]
    public void Eine_falsche_Passphrase_oeffnet_nichts()
    {
        var bund = Bund(new NieOeffnendesFach(), PassphraseSecretProvider.With("richtig"));
        var schluessel = bund.Load(Pfad);
        bund.SetRecoveryPassphrase(Pfad, schluessel, "richtig");

        var falsch = Bund(new NieOeffnendesFach(), PassphraseSecretProvider.With("falsch"));

        Should.Throw<CryptographicException>(() => falsch.Load(Pfad));
    }

    /// <summary>
    /// <b>The most important promise of all.</b> If no slot opens, it aborts —
    /// rather than silently generating a new key.
    ///
    /// <para>A new master key would make every existing <c>enc:v2</c> value
    /// unreadable, and silently so: the application would keep running and report nothing but broken
    /// credentials without anyone seeing the connection.</para>
    /// </summary>
    [Fact]
    public void Wenn_kein_Fach_aufgeht_wird_abgebrochen_statt_neu_erzeugt()
    {
        Bund(new PlainFileSecretProvider()).Load(Pfad);
        var vorher = File.ReadAllBytes(Pfad);

        Should.Throw<CryptographicException>(() => Bund(new NieOeffnendesFach()).Load(Pfad));

        File.ReadAllBytes(Pfad).ShouldBe(vorher, "Die Datei darf dabei nicht angefasst werden.");
    }

    /// <summary>
    /// The master key must not stand anywhere in plain text in the file — only that makes
    /// it fit for backups.
    /// </summary>
    [Fact]
    public void Mit_Passphrase_steht_der_Schluessel_nirgends_im_Klartext()
    {
        var bund = Bund(new DpapiSecretProvider(), PassphraseSecretProvider.With("geheim"),
            new PlainFileSecretProvider());

        var schluessel = bund.Load(Pfad);
        bund.SetRecoveryPassphrase(Pfad, schluessel, "geheim");

        var inhalt = File.ReadAllText(Pfad);
        var klartext = Convert.ToBase64String(schluessel);

        inhalt.ShouldNotContain(klartext);

        if (OperatingSystem.IsWindows())
        {
            // With a machine slot the unprotected one drops away.
            inhalt.ShouldNotContain("\"file\"");
        }
    }

    /// <summary>
    /// A keyring without a recovery path works flawlessly — and fails completely on that
    /// one day. That's why it is named beforehand.
    /// </summary>
    [Fact]
    public void Ein_Bund_ohne_Wiederherstellung_meldet_das()
    {
        var bund = Bund(new PlainFileSecretProvider());
        bund.Load(Pfad);

        bund.Problems.ShouldNotBeEmpty();
        bund.Problems.ShouldContain(p => p.Contains("Wiederherstellungsfach"));
        bund.Problems.ShouldContain(p => p.Contains("ungeschützt"));
    }

    [Fact]
    public void Mit_Passphrase_ist_der_Bund_in_Ordnung()
    {
        var bund = Bund(new DpapiSecretProvider(), PassphraseSecretProvider.With("geheim"),
            new PlainFileSecretProvider());

        var schluessel = bund.Load(Pfad);
        bund.SetRecoveryPassphrase(Pfad, schluessel, "geheim");

        bund.Problems.ShouldNotContain(p => p.Contains("Wiederherstellungsfach"));
    }

    /// <summary>
    /// Without a passphrase no recovery slot comes about — there is nothing to make it with.
    /// </summary>
    [Fact]
    public void Ohne_Passphrase_gibt_es_kein_Wiederherstellungsfach()
    {
        var bund = Bund(new PlainFileSecretProvider(), new PassphraseSecretProvider(() => null));
        bund.Load(Pfad);

        bund.Slots.ShouldNotContain(s => s.Provider == "passphrase");
        bund.Slots.ShouldContain(s => s.Provider == "file");
    }

    /// <summary>
    /// If a passphrase is available, it is used — even when later opening
    /// a keyring that does not have one yet.
    ///
    /// <para>Whoever sets <c>CLAWD_SECRET_PASSPHRASE</c> did so on purpose. Not creating the
    /// slot would mean ignoring them and then reproaching them that they
    /// should please store a passphrase.</para>
    /// </summary>
    [Fact]
    public void Eine_bereitstehende_Passphrase_wird_nachtraeglich_uebernommen()
    {
        // First without: only the unprotected slot comes about.
        Bund(new PlainFileSecretProvider(), new PassphraseSecretProvider(() => null)).Load(Pfad);

        // Then with: the recovery slot is added, the unprotected one drops away.
        var mit = Bund(new PlainFileSecretProvider(), PassphraseSecretProvider.With("spaeter"));
        var schluessel = mit.Load(Pfad);

        mit.Slots.ShouldContain(s => s.Provider == "passphrase");

        // The unprotected slot stays: the automatic path takes nothing away. Removing
        // it because an environment variable happens to be set would be an
        // irreversible change nobody asked for.
        mit.Slots.ShouldContain(s => s.Provider == "file");
        mit.Problems.ShouldContain(p => p.Contains("ungeschützt"));

        // And it is the same key as before.
        Bund(PassphraseSecretProvider.With("spaeter")).Load(Pfad).ShouldBe(schluessel);
    }

    // ─── Taking over the legacy formats ───

    /// <summary>
    /// The Linux legacy: 32 raw bytes in the file. Whoever updates should notice
    /// nothing — the same key, just wrapped differently.
    /// </summary>
    [Fact]
    public void Ein_roher_Altschluessel_wird_uebernommen()
    {
        var alt = RandomNumberGenerator.GetBytes(32);
        File.WriteAllBytes(Pfad, alt);

        Bund(new PlainFileSecretProvider()).Load(Pfad).ShouldBe(alt);
    }

    /// <summary>
    /// And after the takeover the slot format is in the file — the old raw key
    /// is gone, the value the same.
    /// </summary>
    [Fact]
    public void Nach_der_Uebernahme_steht_das_Faecherformat_in_der_Datei()
    {
        var alt = RandomNumberGenerator.GetBytes(32);
        File.WriteAllBytes(Pfad, alt);

        var bund = Bund(new PlainFileSecretProvider(), PassphraseSecretProvider.With("neu"));
        var schluessel = bund.Load(Pfad);
        bund.SetRecoveryPassphrase(Pfad, schluessel, "neu");

        var datei = JsonSerializer.Deserialize<SecretKeyRingFile>(File.ReadAllText(Pfad))!;
        datei.Version.ShouldBe(3);
        datei.Slots.ShouldContain(s => s.Provider == "passphrase");

        // And the value has not changed - otherwise all enc:v2 values would be lost.
        Bund(PassphraseSecretProvider.With("neu")).Load(Pfad).ShouldBe(alt);
    }

    /// <summary>
    /// A file of the wrong length is broken and is not replaced: that would make all
    /// encrypted values unreadable without anyone finding out why.
    /// </summary>
    [Fact]
    public void Eine_beschaedigte_Datei_wird_nicht_stillschweigend_ersetzt()
    {
        File.WriteAllBytes(Pfad, RandomNumberGenerator.GetBytes(17));

        Should.Throw<CryptographicException>(() => Bund(new PlainFileSecretProvider()).Load(Pfad));
    }

    /// <summary>A machine slot that works here — the substitute for DPAPI in the test.</summary>
    private sealed class MaschinenFach : ISecretProvider
    {
        public string Name => "dpapi";
        public string Description => "Maschinenfach (Test)";
        public bool IsAvailable => true;
        public bool SurvivesMachineChange => false;

        public SecretSlot? Wrap(byte[] masterKey)
            => new(Name, Convert.ToBase64String(masterKey), DateTimeOffset.UtcNow);

        public byte[]? TryUnwrap(SecretSlot slot)
            => slot.Provider == Name ? Convert.FromBase64String(slot.Payload) : null;
    }

    /// <summary>A slot that never opens — the new machine, the foreign user account.</summary>
    private sealed class NieOeffnendesFach : ISecretProvider
    {
        public string Name => "dpapi";
        public string Description => "Maschinenfach (Test: geht nie auf)";
        public bool IsAvailable => true;
        public bool SurvivesMachineChange => false;

        public SecretSlot? Wrap(byte[] masterKey)
            => new(Name, Convert.ToBase64String(masterKey), DateTimeOffset.UtcNow);

        public byte[]? TryUnwrap(SecretSlot slot) => null;
    }
}