using System.Reflection;
using System.Text.Json;

namespace NucleicBroker;

/// <summary>
/// The broker's request dispatcher (docs/WINDOWS_PORT.md §3.3): one instance per process,
/// fed NDJSON lines from hostd, answering through an <see cref="OutboundWriter"/>. Requests
/// run concurrently (an image pull must not block a container.list), responses/notifications
/// serialize through the writer's single drain loop. Also the <see cref="IBrokerEvents"/>
/// sink the facade raises async events into.
/// </summary>
public sealed class BrokerService : IBrokerEvents
{
    private readonly IWslc wslc;
    private readonly IAiProvider ai;
    private readonly OutboundWriter outbound;
    private readonly Dictionary<long, IWslcProcess> procs = new();
    private readonly Lock procsLock = new();
    private long nextProcId;

    public BrokerService(IWslc wslc, IAiProvider ai, OutboundWriter outbound)
    {
        this.wslc = wslc;
        this.ai = ai;
        this.outbound = outbound;
        wslc.SetEvents(this);
    }

    /// <summary>Broker protocol revision, bumped with any wire change; hostd degrades from
    /// the `hello` capabilities rather than parsing versions (docs/WINDOWS_PORT.md §2.3).</summary>
    public const int ProtocolVersion = 1;

    /// <summary>Handle one inbound NDJSON line. The returned task completes once the
    /// response has been ENQUEUED (tests await it; the stdin loop fires and forgets).</summary>
    public async Task HandleLineAsync(string line, CancellationToken ct = default)
    {
        JsonElement? id = null;
        string method;
        JsonElement? @params = null;
        try
        {
            using var doc = JsonDocument.Parse(line);
            var root = doc.RootElement;
            // Clone: the id/params outlive this JsonDocument (responses are built after
            // arbitrary awaits).
            if (root.TryGetProperty("id", out var rawId)) id = rawId.Clone();
            if (root.TryGetProperty("params", out var rawParams)) @params = rawParams.Clone();
            method = root.TryGetProperty("method", out var m) && m.ValueKind == JsonValueKind.String
                ? m.GetString()!
                : throw new JsonException("missing method");
        }
        catch (JsonException e)
        {
            outbound.EnqueueJson(Rpc.Error(id, Rpc.ParseError, $"unparseable request: {e.Message}"));
            return;
        }

        try
        {
            var result = await DispatchAsync(method, @params, id, ct).ConfigureAwait(false);
            // A null result means the handler already enqueued its own response because it had to
            // send it before doing something else (proc.exec — see below). Everything else
            // returns a value and is responded to here.
            if (result is not null && id is { } requestId)
                outbound.EnqueueJson(Rpc.Response(requestId, result));
        }
        catch (JsonException e)
        {
            outbound.EnqueueJson(Rpc.Error(id, Rpc.InvalidParams, e.Message));
        }
        catch (WslcError e)
        {
            outbound.EnqueueJson(Rpc.Error(id, Rpc.FacadeError, e.Message, new { kind = e.Kind }));
        }
        catch (NotSupportedException)
        {
            outbound.EnqueueJson(Rpc.Error(id, Rpc.MethodNotFound, $"unknown method: {method}"));
        }
        catch (Exception e)
        {
            outbound.EnqueueJson(Rpc.Error(id, Rpc.InternalError, e.Message));
        }
    }

    /// <summary>Returns the result to respond with, or null when the handler has already
    /// responded (it needed the response on the wire before continuing).</summary>
    private async Task<object?> DispatchAsync(
        string method, JsonElement? p, JsonElement? id, CancellationToken ct)
    {
        switch (method)
        {
            case "hello":
            {
                // Two kinds of capability in one list: the RPC families this broker serves, and
                // what the facade underneath can actually do (docs/WINDOWS_PORT.md D13). hostd
                // needs both — "proc" says the methods exist, "tty" says proc.exec(tty:true)
                // will work rather than failing `unsupported` at the Terminal panel.
                var caps = new List<string> { "components", "session", "image", "container", "proc" };
                caps.AddRange(wslc.Capabilities);
                if (ai.IsAvailable) caps.Add("ai");
                return new
                {
                    protocol = ProtocolVersion,
                    brokerVersion = Assembly.GetExecutingAssembly().GetName().Version?.ToString(3) ?? "0.0.0",
                    wslcVersion = wslc.WslcVersion,
                    capabilities = caps,
                };
            }

            case "components.missing":
                return new { flags = await wslc.MissingComponentsAsync(ct).ConfigureAwait(false) };
            case "components.install":
                await wslc.InstallComponentsAsync(ct).ConfigureAwait(false);
                return new { };

            case "session.ensure":
            {
                var spec = Rpc.Params<SessionSpec>(p);
                var gateway = await wslc.EnsureSessionAsync(spec, ct).ConfigureAwait(false);
                return new { gateway };
            }
            case "session.terminate":
                await wslc.TerminateSessionAsync(ct).ConfigureAwait(false);
                return new { };

            case "image.pull":
            {
                var args = Rpc.Params<ImagePullParams>(p);
                await wslc.PullImageAsync(args.Ref, args.Auth, ct).ConfigureAwait(false);
                return new { };
            }
            case "image.list":
                return new { images = await wslc.ListImagesAsync(ct).ConfigureAwait(false) };
            case "image.delete":
                await wslc.DeleteImageAsync(Rpc.Params<ImageRefParams>(p).Ref, ct).ConfigureAwait(false);
                return new { };
            case "image.inspect":
            {
                var image = await wslc.InspectImageAsync(Rpc.Params<ImageRefParams>(p).Ref, ct)
                    .ConfigureAwait(false);
                return new { image };
            }

            case "container.create":
                await wslc.CreateContainerAsync(Rpc.Params<ContainerCreateSpec>(p), ct).ConfigureAwait(false);
                return new { };
            case "container.start":
                await wslc.StartContainerAsync(Rpc.Params<ContainerNameParams>(p).Name, ct).ConfigureAwait(false);
                return new { };
            case "container.stop":
            {
                var args = Rpc.Params<ContainerStopParams>(p);
                await wslc.StopContainerAsync(args.Name, args.Signal ?? 15, args.GraceMs ?? 5000, ct)
                    .ConfigureAwait(false);
                return new { };
            }
            case "container.delete":
            {
                var args = Rpc.Params<ContainerDeleteParams>(p);
                await wslc.DeleteContainerAsync(args.Name, args.Force ?? false, ct).ConfigureAwait(false);
                return new { };
            }
            case "container.list":
                return new { containers = await wslc.ListContainersAsync(ct).ConfigureAwait(false) };
            case "container.state":
            {
                var state = await wslc.ContainerStateAsync(Rpc.Params<ContainerNameParams>(p).Name, ct)
                    .ConfigureAwait(false);
                return new { state };
            }
            case "container.stats":
            {
                var stats = await wslc.ContainerStatsAsync(Rpc.Params<ContainerNameParams>(p).Name, ct)
                    .ConfigureAwait(false);
                return new { stats };
            }

            case "proc.exec":
            {
                var spec = Rpc.Params<ProcSpec>(p);
                var procId = Interlocked.Increment(ref nextProcId);
                var proc = await wslc.ExecAsync(procId, spec, ct).ConfigureAwait(false);
                lock (procsLock) procs[procId] = proc;
                // Respond BEFORE running it. Output and exit are enqueued on the same ordered
                // outbound queue as this response, so a command that finishes fast (`echo`) would
                // otherwise put `proc.exit` on the wire ahead of the `procId` naming it — and a
                // client that registers interest when it learns the procId then waits forever.
                // Hit on the first live run, hardware-confirmed (docs/WINDOWS_PORT.md §13.3).
                if (id is { } requestId)
                    outbound.EnqueueJson(Rpc.Response(requestId, new { procId }));

                try
                {
                    await proc.StartAsync(ct).ConfigureAwait(false);
                }
                catch (Exception e)
                {
                    // The response is already on the wire, so this failure CANNOT be reported as a
                    // JSON-RPC error — that would put two responses under one id, which is a
                    // protocol violation and left the client waiting for an exit that never came.
                    // Report it the way the process itself would have: the reason on stderr, then
                    // an exit. 126 is the shell's "command found but not executable", which is
                    // what "could not start" means to every caller above.
                    lock (procsLock) procs.Remove(procId);
                    var reason = $"nucleic-brokerd: could not start process: {e.Message}\n";
                    ProcOutput(procId, stderr: true, System.Text.Encoding.UTF8.GetBytes(reason));
                    ProcExited(procId, 126);
                }
                return null;
            }
            case "proc.stdin":
            {
                var args = Rpc.Params<ProcStdinParams>(p);
                await Proc(args.ProcId).WriteStdinAsync(Convert.FromBase64String(args.B64), ct)
                    .ConfigureAwait(false);
                return new { };
            }
            case "proc.closeStdin":
                await Proc(Rpc.Params<ProcIdParams>(p).ProcId).CloseStdinAsync(ct).ConfigureAwait(false);
                return new { };
            case "proc.signal":
            {
                var args = Rpc.Params<ProcSignalParams>(p);
                await Proc(args.ProcId).SignalAsync(args.Sig, ct).ConfigureAwait(false);
                return new { };
            }
            case "proc.resize":
            {
                var args = Rpc.Params<ProcResizeParams>(p);
                await Proc(args.ProcId).ResizeAsync(args.Cols, args.Rows, ct).ConfigureAwait(false);
                return new { };
            }

            case "ai.generate":
            {
                var args = Rpc.Params<AiGenerateParams>(p);
                var text = await ai.GenerateAsync(args.Prompt, args.Schema, ct).ConfigureAwait(false);
                return new { text };
            }

            default:
                throw new NotSupportedException(method);
        }
    }

    private IWslcProcess Proc(long procId)
    {
        lock (procsLock)
        {
            return procs.TryGetValue(procId, out var proc)
                ? proc
                : throw new WslcError(WslcError.NotFound, $"unknown procId {procId}");
        }
    }

    // MARK: IBrokerEvents — facade threads enqueue and return immediately.

    public void ProcOutput(long procId, bool stderr, ReadOnlySpan<byte> chunk) =>
        outbound.EnqueueProcOutput(procId, stderr, chunk);

    public void ProcExited(long procId, int code)
    {
        lock (procsLock) procs.Remove(procId);
        outbound.EnqueueJson(Rpc.Notification("proc.exit", new { procId, code }));
    }

    public void SessionDown(string reason) =>
        outbound.EnqueueJson(Rpc.Notification("session.down", new { reason }));

    public void PullProgress(string reference, string status, long current, long total) =>
        outbound.EnqueueJson(Rpc.Notification(
            "image.pullProgress", new { @ref = reference, status, current, total }));

    public void InstallProgress(string status, double percent) =>
        outbound.EnqueueJson(Rpc.Notification(
            "components.installProgress", new { status, percent }));

    // Param records for methods whose shapes aren't shared DTOs.
    private sealed record ImagePullParams(string Ref, RegistryAuth? Auth);
    private sealed record ImageRefParams(string Ref);
    private sealed record ContainerNameParams(string Name);
    private sealed record ContainerStopParams(string Name, int? Signal, int? GraceMs);
    private sealed record ContainerDeleteParams(string Name, bool? Force);
    private sealed record ProcIdParams(long ProcId);
    private sealed record ProcStdinParams(long ProcId, string B64);
    private sealed record ProcSignalParams(long ProcId, int Sig);
    private sealed record ProcResizeParams(long ProcId, int Cols, int Rows);
    private sealed record AiGenerateParams(string Prompt, JsonElement? Schema);
}