using Microsoft.AspNetCore.Hosting.Server;
using Microsoft.AspNetCore.Hosting.Server.Features;
using Microsoft.Data.Sqlite;
var builder = WebApplication.CreateBuilder(args);
var settings = new LabSettings {
    Replica = builder.Configuration["Lab:Replica"] ?? "one",
    Workers = builder.Configuration.GetValue("Lab:Workers", 2),
    Partition = builder.Configuration.GetValue("Lab:Partition", 0),
    QueueCapacity = builder.Configuration.GetValue("Lab:QueueCapacity", 4),
    PoolSize = builder.Configuration.GetValue("Lab:PoolSize", 2),
    WorkMilliseconds = builder.Configuration.GetValue("Lab:WorkMilliseconds", 20),
    LedgerPath = builder.Configuration["Lab:LedgerPath"] ?? Path.Combine(Path.GetTempPath(), "sharprune-local-ledger.db")
};
settings.Validate(); builder.Services.AddSingleton(settings); builder.Services.AddSingleton<LabRuntime>(); builder.Services.AddSingleton<LocalIo>();
builder.Services.AddSingleton<IHostedService>(services => services.GetRequiredService<LabRuntime>());
builder.Services.AddSingleton<LocalLedger>(); var app = builder.Build();
app.Services.GetRequiredService<LocalLedger>().Initialize();
app.MapGet("/instance", (LabRuntime lab) => new { replica = settings.Replica, visits = lab.Visit() });
app.MapGet("/live", () => TypedResults.Text("live"));
app.MapGet("/io-delay", async (CancellationToken token) => { await Task.Delay(20, token); return TypedResults.Text("controlled loopback reply"); });
app.MapGet("/io", async (CancellationToken token, IServer server, LocalIo io) => {
    using var response = await io.Client.GetAsync(LocalAddress(server), token); response.EnsureSuccessStatusCode(); _ = await response.Content.ReadAsByteArrayAsync(token);
    return TypedResults.Ok(new { replica = settings.Replica, kind = "async-loopback-http" });
});
app.MapGet("/sync", (CancellationToken token, IServer server, LocalIo io) => {
    using var response = io.Client.GetAsync(LocalAddress(server), token).GetAwaiter().GetResult(); response.EnsureSuccessStatusCode(); _ = response.Content.ReadAsByteArrayAsync(token).GetAwaiter().GetResult();
    return TypedResults.Ok(new { replica = settings.Replica, kind = "deliberate-blocking-demo" });
});
app.MapGet("/cpu", () => { uint value = 1; for (int i = 0; i < 200000; i++) value = unchecked(value * 1664525 + 1013904223); return TypedResults.Ok(new { replica = settings.Replica, kind = "bounded-cpu", value }); });
app.MapGet("/threadpool", () => new { threads = ThreadPool.ThreadCount, pending = ThreadPool.PendingWorkItemCount, completed = ThreadPool.CompletedWorkItemCount });
app.MapGet("/ready", (LabRuntime lab) => lab.Accepting ? Results.Ok(new { ready = true }) : Results.StatusCode(503));
app.MapGet("/stats", (LabRuntime lab) => new { replica = settings.Replica, accepting = lab.Accepting, main = lab.Main.Snapshot(), batch = lab.Batch.Snapshot(), dependencyCalls = lab.Circuit.DependencyCalls });
app.MapGet("/work", (HttpContext context, LabRuntime lab, int? budgetMs) => Handle(context, lab.Main, lab, budgetMs));
app.MapGet("/batch", (HttpContext context, LabRuntime lab, int? budgetMs) => Handle(context, lab.Batch, lab, budgetMs));
app.MapGet("/unstable", (LabRuntime lab, string? key) => {
    if (key != "demo" && key != "always") return Results.BadRequest();
    int attempt = lab.Attempt(key); return key == "always" || attempt == 1 ? Results.StatusCode(503) : Results.Ok(new { replica = settings.Replica, attempt });
});
app.MapGet("/session/{name}", (LabRuntime lab, string name) => name == "demo" ? Results.Ok(new { replica = settings.Replica, value = lab.Session() }) : Results.BadRequest());
app.MapPost("/once/{key}", (string key, LedgerInput input, LocalLedger ledger) => {
    if (key != "demo" || input.Amount is < 1 or > 100) return Results.BadRequest();
    LedgerDecision result = ledger.Record(key, input.Amount); return result.Conflict ? Results.Conflict(new { error = "key amount conflict" }) : Results.Ok(result);
});
app.MapGet("/ledger", (LocalLedger ledger) => new { receipts = ledger.Count() });
app.MapGet("/guarded", (LabRuntime lab) => lab.Circuit.Invoke(lab.DependencyFailing));
app.MapGet("/partition/{key}", (string key, int? owner) => {
    if (key != "A" && key != "B") return Results.BadRequest();
    int partition = StablePartition.For(key, 2);
    return owner == partition && settings.Partition == partition ? Results.Ok(new { replica = settings.Replica, partition, key }) : Results.Conflict(new { expectedPartition = partition });
});
if (app.Environment.IsDevelopment()) {
    app.MapPost("/lab/gate/{lane}/{action}", (string lane, string action, LabRuntime lab) => {
        WorkLane? target = lane == "main" ? lab.Main : lane == "batch" ? lab.Batch : null;
        if (target is null || action != "open" && action != "close") return Results.BadRequest();
        if (action == "open") target.Gate.Open(); else target.Gate.Close(); return Results.NoContent();
    });
    app.MapPost("/lab/drain", (LabRuntime lab) => { lab.Drain(); return Results.NoContent(); });
    app.MapPost("/lab/dependency/{failing:bool}", (bool failing, LabRuntime lab) => { lab.DependencyFailing = failing; return Results.NoContent(); });
}
app.Run();
static async Task<IResult> Handle(HttpContext context, WorkLane lane, LabRuntime lab, int? budgetMs) {
    if (budgetMs is < 1 or > 1000) return Results.BadRequest();
    using var budget = CancellationTokenSource.CreateLinkedTokenSource(context.RequestAborted);
    if (budgetMs is int milliseconds) budget.CancelAfter(milliseconds);
    var item = new WorkItem(budget.Token);
    AdmissionDecision decision = lab.Admit(lane, item);
    if (decision == AdmissionDecision.Draining) return Results.StatusCode(503);
    if (decision == AdmissionDecision.Full) return Results.StatusCode(429);
    try { await item.Completion.Task.WaitAsync(budget.Token); return Results.Ok(new { replica = lab.Settings.Replica, completed = true }); }
    catch (OperationCanceledException) when (!context.RequestAborted.IsCancellationRequested) { return Results.Problem(statusCode: 504, title: "Classroom work budget expired"); }
}
static Uri LocalAddress(IServer server) {
    string address = server.Features.Get<IServerAddressesFeature>()!.Addresses.Single();
    return new UriBuilder("http", "127.0.0.1", new Uri(address).Port) { Path = "/io-delay" }.Uri;
}
public sealed class LocalIo : IDisposable { public HttpClient Client { get; } = new() { Timeout = TimeSpan.FromSeconds(5) }; public void Dispose() => Client.Dispose(); }
public sealed record LedgerInput(int Amount);
public sealed class LabSettings {
    public string Replica { get; init; } = "one"; public int Partition { get; init; } public int Workers { get; init; } public int QueueCapacity { get; init; }
    public int PoolSize { get; init; } public int WorkMilliseconds { get; init; } public string LedgerPath { get; init; } = "";
    public void Validate() {
        if (Partition is < 0 or > 1 || Replica.Length is < 1 or > 32 || Workers is < 1 or > 8 || QueueCapacity is < 1 or > 16 || PoolSize is < 1 or > 8 || WorkMilliseconds is < 1 or > 250 || string.IsNullOrWhiteSpace(LedgerPath)) throw new InvalidOperationException("Invalid bounded lab settings");
    }
}
public enum AdmissionDecision { Accepted, Full, Draining }
public sealed class LabRuntime : IHostedService, IDisposable {
    private readonly object admissionSync = new();
    private int accepting = 1, visits, sessions, demoAttempts, alwaysAttempts, failing = 1, disposed;
    public LabSettings Settings { get; } public WorkLane Main { get; } public WorkLane Batch { get; }
    public ClassroomCircuit Circuit { get; } = new();
    public LabRuntime(LabSettings settings) { Settings = settings; Main = new(settings.Workers, settings.QueueCapacity, settings.PoolSize, settings.WorkMilliseconds); Batch = new(1, 1, 1, settings.WorkMilliseconds); }
    public bool Accepting => Volatile.Read(ref accepting) == 1;
    public bool DependencyFailing { get => Volatile.Read(ref failing) == 1; set => Volatile.Write(ref failing, value ? 1 : 0); }
    public void Drain() { lock (admissionSync) Volatile.Write(ref accepting, 0); }
    public AdmissionDecision Admit(WorkLane lane, WorkItem item) {
        lock (admissionSync) {
            if (!Accepting) return AdmissionDecision.Draining;
            return lane.TrySubmit(item) ? AdmissionDecision.Accepted : AdmissionDecision.Full;
        }
    }
    public int Visit() => Interlocked.Increment(ref visits); public int Session() => Interlocked.Increment(ref sessions);
    public int Attempt(string key) => key == "demo" ? Interlocked.Increment(ref demoAttempts) : Interlocked.Increment(ref alwaysAttempts);
    public Task StartAsync(CancellationToken token) { Main.Start(); Batch.Start(); return Task.CompletedTask; }
    public Task StopAsync(CancellationToken token) => Task.WhenAll(Main.StopAsync(token), Batch.StopAsync(token));
    public void Dispose() { if (Interlocked.Exchange(ref disposed, 1) != 0) return; Main.Dispose(); Batch.Dispose(); }
}
public static class StablePartition {
    public static int For(string key, int count) { uint hash = 2166136261; foreach (byte b in System.Text.Encoding.UTF8.GetBytes(key)) hash = unchecked((hash ^ b) * 16777619); return (int)(hash % (uint)count); }
}