using GeradoresService.Core;

namespace GeradoresService.Generators.Financeiro;

/// <summary>
/// Números de cartão de pagamento válidos pelo algoritmo de Luhn (apenas para testes).
/// </summary>
public sealed class CartaoCreditoGenerator : GeneratorBase
{
    private sealed record Brand(string Key, string Name, int Length, Func<Random, string> Prefix, Func<string, bool> Matches);

    private static readonly Brand[] Brands =
    [
        new("visa", "Visa", 16, _ => "4", n => n.StartsWith('4') && n.Length is 13 or 16 or 19),
        new("mastercard", "Mastercard", 16,
            r => r.Next(2) == 0 ? (51 + r.Next(5)).ToString() : (2221 + r.Next(500)).ToString(),
            n => n.Length == 16 && (InRange(n, 2, 51, 55) || InRange(n, 4, 2221, 2720))),
        new("amex", "American Express", 15, r => r.Next(2) == 0 ? "34" : "37",
            n => n.Length == 15 && (n.StartsWith("34") || n.StartsWith("37"))),
    ];

    public override string Id => "cartao-credito";
    public override string Name => "Cartão de crédito";
    public override string Category => Categories.Financeiro;
    public override string Description => "Número de cartão válido pelo algoritmo de Luhn, com validade e CVV. Apenas para testes.";

    public override IReadOnlyList<GeneratorOption> Options =>
    [
        Option("rede", "Rede", "visa", [.. Brands.Select(b => (b.Key, b.Name)), ("qualquer", "Qualquer")]),
        Option("formato", "Formato", "espacos", ("espacos", "4111 1111 1111 1111"), ("compacto", "4111111111111111")),
    ];

    public override GeneratedItem Generate(GeneratorContext context)
    {
        var key = context.Option(Options[0]);
        var brand = key == "qualquer" ? context.Pick(Brands) : Brands.Single(b => b.Key == key);

        var body = brand.Prefix(context.Random);
        body += context.Digits(brand.Length - 1 - body.Length);
        var number = body + Checksums.LuhnCheckDigit(body);

        var expiry = DateTime.UtcNow.AddMonths(context.Random.Next(6, 60));
        var cvv = context.Digits(brand.Key == "amex" ? 4 : 3);
        var display = context.Option(Options[1]) == "compacto" ? number : Format(number);

        return new GeneratedItem(display, new Dictionary<string, string>
        {
            ["Número"] = display,
            ["Rede"] = brand.Name,
            ["Validade"] = expiry.ToString("MM/yy"),
            ["CVV"] = cvv,
        });
    }

    private static string Format(string number) => number.Length == 15
        ? $"{number[..4]} {number[4..10]} {number[10..]}"
        : string.Join(' ', number.Chunk(4).Select(c => new string(c)));

    private static bool InRange(string n, int digits, int min, int max) =>
        int.TryParse(n.AsSpan(0, digits), out var p) && p >= min && p <= max;

    public override ValidationResult Validate(string value)
    {
        var number = Checksums.Clean(value);
        if (number.Length is < 12 or > 19 || !Checksums.AllDigits(number))
            return ValidationResult.WrongFormat("Um número de cartão tem entre 12 e 19 dígitos.");

        var brand = Brands.FirstOrDefault(b => b.Matches(number));
        var details = new List<string>
        {
            $"Rede: {brand?.Name ?? "desconhecida"}",
            "Controlo: algoritmo de Luhn",
        };

        if (!Checksums.LuhnValid(number))
        {
            var expected = Checksums.LuhnCheckDigit(number[..^1]);
            return ValidationResult.BadChecksum($"Falha no algoritmo de Luhn: último dígito devia ser {expected}.", details);
        }
        return ValidationResult.Valid(Format(number), $"Número de cartão válido{(brand is null ? "" : $" ({brand.Name})")}.", details);
    }
}