using System.Text;
using static DodoSSH.Client.Domain.Tests.HostFactory;

namespace DodoSSH.Client.Domain.Tests;

/// <summary>
/// The payload encoding.
/// </summary>
/// <remarks>
/// Two properties carry weight here. Determinism, because the sync engine compares to decide whether
/// to push, and a codec that produced different bytes for the same host would make every pass look
/// like a change. And failing closed on anything malformed, because these bytes are decrypted inside
/// a sync pass where an exception would strand every item queued behind the bad one.
/// </remarks>
public sealed class HostSecretCodecTests
{
    [Fact]
    public void AFullHost_RoundTrips()
    {
        var host = Host(
            label: "prod-db",
            hostname: "db.internal",
            port: 2222,
            username: "deploy",
            notes: "primary replica",
            jumps: [Bastion, Relay],
            options: [("ServerAliveInterval", "30"), ("Compression", "yes")]);

        HostSecretCodec.TryDecode(HostSecretCodec.Encode(host), out var document).ShouldBeTrue();

        document.ShouldNotBeNull();
        document.Host.ShouldBe(host);
        document.SchemaVersion.ShouldBe(HostSecretCodec.CurrentSchemaVersion);
        document.IsReadOnly.ShouldBeFalse();
    }

    [Fact]
    public void AMinimalHost_RoundTrips()
    {
        var host = Host(username: null, notes: null);

        HostSecretCodec.TryDecode(HostSecretCodec.Encode(host), out var document).ShouldBeTrue();

        document!.Host.ShouldBe(host);
        document.Host.Username.ShouldBeNull();
        document.Host.Notes.ShouldBeNull();
    }

    [Fact]
    public void Encoding_IsDeterministic()
    {
        var host = Host(options: [("Compression", "yes"), ("ServerAliveInterval", "30")]);

        HostSecretCodec.Encode(host).ShouldBe(HostSecretCodec.Encode(host));
    }

    [Fact]
    public void DirectiveOrder_DoesNotAffectTheEncoding()
    {
        // Two clients that agree on the content must produce the same bytes regardless of the order
        // the user happened to type the directives in.
        var one = Host(options: [("Compression", "yes"), ("ServerAliveInterval", "30")]);
        var other = Host(options: [("ServerAliveInterval", "30"), ("Compression", "yes")]);

        HostSecretCodec.Encode(one).ShouldBe(HostSecretCodec.Encode(other));
    }

    [Fact]
    public void APayloadFromANewerSchema_IsReadableButReadOnly()
    {
        // The forward-compatibility rule. An old client can show the host but must not re-encode it,
        // because it has no representation for the newer client's extra fields and would drop them.
        var payload = Json("""
            {
              "schemaVersion": 99,
              "label": "prod-db",
              "hostname": "db.internal",
              "port": 22,
              "unknownFutureField": { "nested": true }
            }
            """);

        HostSecretCodec.TryDecode(payload, out var document).ShouldBeTrue();

        document!.Host.Label.ShouldBe("prod-db");
        document.Host.Hostname.ShouldBe("db.internal");
        document.IsReadOnly.ShouldBeTrue();
    }

    [Fact]
    public void AnUnknownFieldAtTheCurrentSchema_IsSkippedRatherThanFatal()
    {
        var payload = Json("""
            {
              "schemaVersion": 1,
              "label": "prod-db",
              "hostname": "db.internal",
              "port": 22,
              "somethingElse": 5
            }
            """);

        HostSecretCodec.TryDecode(payload, out var document).ShouldBeTrue();
        document!.IsReadOnly.ShouldBeFalse();
    }

    [Theory]
    [InlineData("")]
    [InlineData("not json at all")]
    [InlineData("{")]
    [InlineData("[]")]
    [InlineData("null")]
    public void MalformedBytes_ReturnFalseRatherThanThrow(string text)
    {
        HostSecretCodec.TryDecode(Json(text), out var document).ShouldBeFalse();
        document.ShouldBeNull();
    }

    [Theory]
    [InlineData("""{ "schemaVersion": 0, "label": "a", "hostname": "b", "port": 22 }""")]
    [InlineData("""{ "schemaVersion": -1, "label": "a", "hostname": "b", "port": 22 }""")]
    [InlineData("""{ "schemaVersion": 1, "label": "", "hostname": "b", "port": 22 }""")]
    [InlineData("""{ "schemaVersion": 1, "label": "a", "hostname": "", "port": 22 }""")]
    [InlineData("""{ "schemaVersion": 1, "label": "a", "hostname": "b", "port": 0 }""")]
    [InlineData("""{ "schemaVersion": 1, "label": "a", "hostname": "b", "port": 70000 }""")]
    public void AStructurallyInvalidPayload_IsRejected(string json)
    {
        HostSecretCodec.TryDecode(Json(json), out _).ShouldBeFalse();
    }

    [Fact]
    public void DuplicateDirectiveNamesDifferingOnlyInCase_AreRejected()
    {
        // Fails closed. SSH treats keywords case-insensitively, so this payload has no single
        // meaning; guessing which one wins would make two clients disagree about the same bytes.
        var payload = Json("""
            {
              "schemaVersion": 1,
              "label": "prod-db",
              "hostname": "db.internal",
              "port": 22,
              "options": { "Compression": "yes", "compression": "no" }
            }
            """);

        HostSecretCodec.TryDecode(payload, out _).ShouldBeFalse();
    }

    [Fact]
    public void AnEmptyJumpHostId_IsRejected()
    {
        var payload = Json($$"""
            {
              "schemaVersion": 1,
              "label": "prod-db",
              "hostname": "db.internal",
              "port": 22,
              "jumpHostIds": ["{{Guid.Empty}}"]
            }
            """);

        HostSecretCodec.TryDecode(payload, out _).ShouldBeFalse();
    }

    [Fact]
    public void Encode_RefusesAnInvalidHost()
    {
        // Throwing rather than returning false, because unlike decoding, this is a caller bug: the
        // host came from this process and should have been validated before it got here.
        Should.Throw<ArgumentException>(() => HostSecretCodec.Encode(Host(label: "  ")));
        Should.Throw<ArgumentException>(() => HostSecretCodec.Encode(Host(port: 0)));
    }

    [Fact]
    public void TheEncoding_CarriesNoPlaintextOutsideTheEnvelope()
    {
        // A reminder of what this codec is for: every one of these values is inside the ciphertext.
        // There is no plaintext host label anywhere in the system.
        var host = Host(label: "prod-db", notes: "root password in 1Password");

        var text = Encoding.UTF8.GetString(HostSecretCodec.Encode(host));

        text.Contains("prod-db", StringComparison.Ordinal).ShouldBeTrue();
        text.Contains("1Password", StringComparison.Ordinal).ShouldBeTrue();
    }

    private static byte[] Json(string text) => Encoding.UTF8.GetBytes(text);
}