SafelyYouCodingChallenge/dotnet/SafelyYou/Program.cs

using SafelyYou;
using SafelyYou.Api;
using SafelyYou.Data;
using Serilog;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
// Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi

Log.Logger = new LoggerConfiguration()
    .WriteTo.Console()
    .CreateLogger();

builder.Services.AddSerilog();
builder.Services.AddOpenApi();

builder.Services.AddSingleton<KnownDevices>(_ =>
{
    var deviceIds = File.ReadAllLines("./devices.csv").Skip(1).Select(id => new DeviceId(id)).ToHashSet();
    Log.Logger.Information("@deviceIds", deviceIds);
    return new KnownDevices(deviceIds);
});

builder.Services.AddSingleton<HeartBeatHistories>();
builder.Services.AddSingleton<UploadTimes>();

var app = builder.Build();
app.UseSerilogRequestLogging();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
}

//app.UseHttpsRedirection();

// heartbeat history
// upload stats

app.MapPost("api/v1/devices/{deviceId}/heartbeat", (string deviceId, HeartbeatRequest request,
    KnownDevices knownDevices, HeartBeatHistories histories) =>
{
    var device = new DeviceId(deviceId);
    if (!knownDevices.Contains(device))
    {
        return Results.NotFound(new NotFoundResponse($"Device ID {deviceId} not found"));
    }

    var addResult = histories.Add(device, request.SentAt);

    return addResult switch
    {
        DeviceHeartBeatHistory.AddResult.Added => Results.NoContent(),
        DeviceHeartBeatHistory.AddResult.OutOfSequence => Results.InternalServerError(
            new ErrorResponse("Attempted to add a timestamp that was out of sequence or invalid.")),
        _ => throw new ArgumentOutOfRangeException()
    };
});

app.MapPost("api/v1/devices/{deviceId}/stats", (string deviceId, UploadStatsRequest request, KnownDevices knownDevices, UploadTimes uploadTimes) =>
{
    var device = new DeviceId(deviceId);
    if (!knownDevices.Contains(device))
    {
        return Results.NotFound(new NotFoundResponse($"Device ID {deviceId} not found"));
    }
    
    uploadTimes.Add(device, request.UploadTime);

    return Results.NoContent();
    
    // not sure where the 500 would go here beyond doing a try/catch
    // note: sent_at isn't used here since the data is a short-cut of aggregation, so it's dropped.
});

app.MapGet("api/v1/devices/{deviceId}/stats", (string deviceId, KnownDevices knownDevices, HeartBeatHistories histories, UploadTimes uploadTimes) =>
{
    var device = new DeviceId(deviceId);
    if (!knownDevices.Contains(device))
    {
        return Results.NotFound(new NotFoundResponse($"Device ID {deviceId} not found"));
    }

    var averageUploadTimeNanos = uploadTimes.AverageUploadTimeNanoseconds(device);
    var timeSpanText = FormatAsGoDuration(averageUploadTimeNanos);
    var uptime = histories.Uptime(device);
    
    return Results.Ok(new GetDeviceStatsResponse(timeSpanText, uptime));
    
    // no 500 here
});


app.Run();

// Matches Go's time.Duration.String() (e.g. "3m17.331667813s").
static string FormatAsGoDuration(System.Numerics.BigInteger nanos)
{
    if (nanos <= 0) return "0s";

    var u = (ulong)nanos;
    Span<char> buf = stackalloc char[32];
    var w = buf.Length;

    // Fractional seconds from nanoseconds, omitting trailing zeros — same as Go fmtFrac(..., 9).
    var frac = u % 1_000_000_000UL;
    u /= 1_000_000_000UL;

    buf[--w] = 's';
    if (frac != 0)
    {
        var print = false;
        for (var i = 0; i < 9; i++)
        {
            var digit = frac % 10;
            frac /= 10;
            if (digit != 0) print = true;
            if (print) buf[--w] = (char)('0' + digit);
        }
        buf[--w] = '.';
    }

    var secs = u % 60;
    u /= 60;
    do
    {
        buf[--w] = (char)('0' + secs % 10);
        secs /= 10;
    } while (secs > 0);

    if (u > 0)
    {
        buf[--w] = 'm';
        var mins = u % 60;
        u /= 60;
        do
        {
            buf[--w] = (char)('0' + mins % 10);
            mins /= 10;
        } while (mins > 0);

        if (u > 0)
        {
            buf[--w] = 'h';
            do
            {
                buf[--w] = (char)('0' + u % 10);
                u /= 10;
            } while (u > 0);
        }
    }

    return new string(buf[w..]);
}