using System.Text.Json;
using System.Text.Json.Serialization;

namespace NucleicProtocol.Interop;

public sealed record ProtocolClientConfiguration
{
    [JsonPropertyName("identityDir")]
    public required string IdentityDirectory { get; init; }

    [JsonPropertyName("hostKeyPins")]
    public IReadOnlyDictionary<string, string>? HostKeyPins { get; init; }

    [JsonPropertyName("deviceID")]
    public string? DeviceId { get; init; }

    [JsonPropertyName("deviceLabel")]
    public string DeviceLabel { get; init; } = "Nucleic for Windows";

    [JsonPropertyName("scopeClaim")]
    public string ScopeClaim { get; init; } = "control";

    [JsonPropertyName("channel")]
    public string? Channel { get; init; }
}

/// The owner-only `run/hostd.json` written by nucleic-hostd.
public sealed record HostdRendezvous
{
    [JsonPropertyName("pid")]
    public required int ProcessId { get; init; }

    [JsonPropertyName("host")]
    public string Host { get; init; } = "127.0.0.1";

    [JsonPropertyName("port")]
    public required int Port { get; init; }

    [JsonPropertyName("localPSK")]
    public required string LocalPsk { get; init; }

    /// Selects the DLL's persisted pin on renderer relaunch. A fresh identity has no matching
    /// pin and falls back to the one-time local PSK.
    [JsonPropertyName("hostID")]
    public required string HostId { get; init; }

    public void Validate()
    {
        if (ProcessId <= 0) throw new JsonException("rendezvous pid must be positive");
        if (Host is not ("127.0.0.1" or "::1" or "localhost"))
            throw new JsonException("renderer rendezvous must be loopback-only");
        if (Port is <= 0 or > 65_535) throw new JsonException("rendezvous port is invalid");
        if (string.IsNullOrWhiteSpace(HostId)) throw new JsonException("rendezvous hostID is missing");
        byte[] secret;
        try { secret = Convert.FromBase64String(LocalPsk); }
        catch (FormatException error) { throw new JsonException("rendezvous localPSK is invalid", error); }
        if (secret.Length != 32) throw new JsonException("rendezvous localPSK must be 32 bytes");
    }
}

/// A forward-compatible HostMsg view. The tagged enum remains owned by Swift; C# reads the
/// discriminator and keeps the complete JSON value so a newer field or message never gets lost.
public sealed record ProtocolMessage(string Tag, JsonElement Root, string Json)
{
    public static ProtocolMessage Parse(string json)
    {
        using var document = JsonDocument.Parse(json);
        if (document.RootElement.ValueKind != JsonValueKind.Object ||
            !document.RootElement.TryGetProperty("t", out var tagValue) ||
            tagValue.ValueKind != JsonValueKind.String)
        {
            throw new JsonException("protocol message has no string 't' discriminator");
        }
        return new ProtocolMessage(tagValue.GetString()!, document.RootElement.Clone(), json);
    }
}

public sealed record ProtocolState(
    string State, string? Message, string? Transport, string? Peer,
    string? HostId, JsonElement? Welcome, string Json)
{
    public static ProtocolState Parse(string json)
    {
        using var document = JsonDocument.Parse(json);
        var root = document.RootElement;
        if (!root.TryGetProperty("state", out var state) || state.ValueKind != JsonValueKind.String)
            throw new JsonException("protocol state callback has no state");
        return new ProtocolState(
            state.GetString()!, OptionalString(root, "message"),
            OptionalString(root, "transport"), OptionalString(root, "peer"),
            OptionalString(root, "hostID"),
            root.TryGetProperty("welcome", out var welcome) ? welcome.Clone() : null,
            json);
    }

    private static string? OptionalString(JsonElement root, string name) =>
        root.TryGetProperty(name, out var value) && value.ValueKind == JsonValueKind.String
            ? value.GetString() : null;
}

public sealed record ProjectionDiff(JsonElement Root, string Json)
{
    public static ProjectionDiff Parse(string json)
    {
        using var document = JsonDocument.Parse(json);
        var root = document.RootElement;
        if (root.ValueKind != JsonValueKind.Object ||
            !root.TryGetProperty("version", out var version) || version.GetInt32() != 1 ||
            !root.TryGetProperty("splices", out var splices) ||
            splices.ValueKind != JsonValueKind.Array)
        {
            throw new JsonException("invalid transcript projection result");
        }
        return new ProjectionDiff(root.Clone(), json);
    }
}

internal sealed record TagOnlyIntent([property: JsonPropertyName("t")] string Tag);

[JsonSourceGenerationOptions(
    PropertyNamingPolicy = JsonKnownNamingPolicy.CamelCase,
    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull)]
[JsonSerializable(typeof(ProtocolClientConfiguration))]
[JsonSerializable(typeof(HostdRendezvous))]
[JsonSerializable(typeof(TagOnlyIntent))]
internal partial class ProtocolJsonContext : JsonSerializerContext;

public static class ProtocolJson
{
    public static HostdRendezvous DeserializeRendezvous(string json)
    {
        var value = JsonSerializer.Deserialize(json, ProtocolJsonContext.Default.HostdRendezvous)
            ?? throw new JsonException("empty hostd rendezvous");
        value.Validate();
        return value;
    }
}