EffectiveTask/DeliveryWebApi/Program.cs

using DeliveryWebApi.Model;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Internal;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

// storage setup
// either use in-memory storage or postgres depending on cfg
builder.Services.AddDbContext<DeliveryDbContext>(options =>
{
    if (builder.Configuration.GetValue<bool>("UseInMemoryDatabase"))
        options.UseInMemoryDatabase("Delivery");
    else
    {
        var connectionString = builder.Configuration.GetConnectionString("DatabaseConnection");
        options.UseNpgsql(connectionString);
    }
});

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    // swagger setup
    app.UseSwagger();
    app.UseSwaggerUI();
    
    // migrate model to seed random test values for developers
    app.Services.CreateScope().ServiceProvider.GetRequiredService<DeliveryDbContext>().Database.EnsureCreated();
}

app.UseHttpsRedirection();

app.MapPut("/addDistrict", (DeliveryDbContext context, string name) =>
{
    if (context.Districts.Any(d => d.Name == name))
        return Results.BadRequest(new { Error = "District with the same name already exists" });
    var district = new District{ Name = name };
    context.Districts.Add(district);
    var updated = context.SaveChanges();
    if (updated <= 0)
        return Results.Json(new { Error = "Something went wrong while adding a new district" }, statusCode: 500);
    return Results.Ok(new { district.Id });
});

app.MapGet("/getDistrict/{id:long}", (DeliveryDbContext context, long id) =>
{
    var district = context.Districts.FirstOrDefault(d => d.Id == id);
    if (district == null)
        return Results.NotFound(new { Error = "District with the given id does not exist" });
    return Results.Ok(new { district.Id, district.Name });
});

app.MapPut("/addOrder", (DeliveryDbContext context, long districtId, float weight, DateTime deliveryDate) =>
{
    var order = new Order{ DistrictId = districtId, Weight = weight, DeliveryDate = deliveryDate };
    context.Orders.Add(order);
    var updated = context.SaveChanges();
    if (updated <= 0)
        return Results.Json(new { Error = "Something went wrong while adding a new order" }, statusCode: 500);
    return Results.Ok(new { order.Id });
});

app.MapGet("/getOrder/{id:long}", (DeliveryDbContext context, long id) =>
{
    var order = context.Orders.FirstOrDefault(o => o.Id == id);
    if (order == null)
        return Results.NotFound(new { Error = "Order with the given id does not exist" });
    return Results.Ok(new { order.Id, order.DistrictId, order.Weight, order.DeliveryDate });
});

app.MapGet("/getOrders", (DeliveryDbContext context, string? districtName, DateTime? firstDeliveryDate) =>
{
    var orders = context.Districts
        .Where(d => districtName == null || d.Name == districtName)
        .SelectMany(d => d.Orders)
        .Where(o => firstDeliveryDate == null || o.DeliveryDate >= firstDeliveryDate)
        .OrderBy(o => o.DeliveryDate)
        .Select(o => new { o.Id, o.District.Name, o.DeliveryDate, o.Weight });
    return Results.Ok(orders);
});

app.Run();