// 1. Import the namespace.
using Dunet;

// 2. Add the `Union` attribute to a partial record.
[Union]
partial record Shape
{
    // 3. Define the union variants as inner partial records.
    partial record Circle(double Radius);
    partial record Rectangle(double Length, double Width);
    partial record Triangle(double Base, double Height);
}

// 4. Use the union variants.
var shape = new Shape.Rectangle(3, 4);
var area = shape.Match(
    circle => 3.14 * circle.Radius * circle.Radius,
    rectangle => rectangle.Length * rectangle.Width,
    triangle => triangle.Base * triangle.Height / 2
);
Console.WriteLine(area); // "12"

// 1. Import the namespace.
using Dunet;
// Optional: use static import for more terse code.
using static Option<int>;

// 2. Add the `Union` attribute to a partial record.
// 3. Add one or more type arguments to the union record.
[Union]
partial record Option<T>
{
    partial record Some(T Value);
    partial record None();
}

// 4. Use the union variants.
Option<int> ParseInt(string? value) =>
    int.TryParse(value, out var number)
        ? new Some(number)
        : new None();

string GetOutput(Option<int> number) =>
    number.Match(
        some => some.Value.ToString(),
        none => "Invalid input!"
    );

var input = Console.ReadLine(); // User inputs "not a number".
var result = ParseInt(input);
var output = GetOutput(result);
Console.WriteLine(output); // "Invalid input!"

input = Console.ReadLine(); // User inputs "12345".
result = ParseInt(input);
output = GetOutput(result);
Console.WriteLine(output); // "12345".

// 1. Import the namespace.
using Dunet;

// 2. Define a union type with a single unique variant property:
[Union]
partial record Result
{
    partial record Success(double Value);
    partial record Failure(Exception Error);
}

// 3. Return union variants directly.
Result Divide(double numerator, double denominator)
{
    if (denominator is 0d)
    {
        // No need for `new Result.Failure(new InvalidOperationException("..."));`
        return new InvalidOperationException("Cannot divide by zero!");
    }

    // No need for `new Result.Success(...);`
    return numerator / denominator;
}

var result = Divide(42, 0);
var output = result.Match(
    success => success.Value.ToString(),
    failure => failure.Error.Message
);

Console.WriteLine(output); // "Cannot divide by zero!"

// Choice.cs

using Dunet;

namespace Core;

// 1. Define a union type within a namespace.
[Union]
partial record Choice
{
    partial record Yes;
    partial record No(string Reason);
}

// Program.cs

using Core;
using static Core.Choice;

// 2. Define async methods like you would for any other type.
static async Task<Choice> AskAsync()
{
    // Simulating network call.
    await Task.Delay(1000);

    // 3. Return unions from async methods like any other type.
    return new No("because I don't wanna!");
}

// 4. Asynchronously match any union `Task` or `ValueTask`.
var response = await AskAsync()
    .MatchAsync(
        yes => "Yes!!!",
        no => $"No, {no.Reason}"
    );

// Prints "No, because I don't wanna!" after 1 second.
Console.WriteLine(response);

[Union]
partial record Shape
{
    partial record Point(int X, int Y);
    partial record Line(double Length);
    partial record Rectangle(double Length, double Width);
    partial record Sphere(double Radius);
}

public static bool IsZeroDimensional(this Shape shape) =>
    shape.MatchPoint(
        point => true,
        () => false
    );

public static bool IsOneDimensional(this Shape shape) =>
    shape.MatchLine(
        line => true,
        () => false
    );

public static bool IsTwoDimensional(this Shape shape) =>
    shape.MatchRectangle(
        rectangle => true,
        () => false
    );

public static bool IsThreeDimensional(this Shape shape) =>
    shape.MatchSphere(
        sphere => true,
        () => false
    );

[Union]
public partial record QueryResult<T>
{
    public partial record Ok(T Value);
    public partial record NotFound;
    public partial record Unauthorized;

    public sealed override string ToString() =>
        Match(
            ok => ok.Value.ToString(),
            notFound => "Not found.",
            unauthorized => "Unauthorized access."
        );
}

[Union]
public partial record HttpResponse
{
    public partial record Success;
    public partial record Error(string Message);

    // 1. All variants shall have a status code.
    public required int StatusCode { get; init; }
}

using var client = new HttpClient();
var response = await CreateUserAsync(client, "John", "Smith");

// 2. The `StatusCode` property is available at the union level.
var statusCode = response.StatusCode;

public static async Task<HttpResponse> CreateUserAsync(
    HttpClient client, string firstName, string lastName
)
{
    using var response = await client.PostJsonAsync(
        "/users",
        new { firstName, lastName }
    );

    var content = await response.Content.ReadAsStringAsync();

    if (!response.IsSuccessStatusCode)
    {
        return new HttpResponse.Error(content)
        {
            StatusCode = (int)response.StatusCode,
        };
    }

    return new HttpResponse.Success()
    {
        StatusCode = (int)response.StatusCode,
    };
}

// This type declaration must be partial.
public partial class Parent1
{
    // So must this one.
    public partial class Parent2
    {
        // Unions must always be partial.
        [Union]
        public partial record Nested
        {
            public partial record Variant1;
            public partial record Variant2;
        }
    }
}

// Access variants like any other nested type.
var variant1 = new Parent1.Parent2.Nested.Variant1();