using GeradoresService.Core;

namespace GeradoresService.Generators.Outros;

/// <summary>Códigos de barras EAN-13 / EAN-8 (GS1). Controlo: pesos 3,1,3,1… a partir da direita.</summary>
public sealed class EanGenerator : GeneratorBase
{
    public override string Id => "ean";
    public override string Name => "EAN / Código de barras";
    public override string Category => Categories.Outros;
    public override string Description => "Códigos EAN-13 e EAN-8 com dígito de controlo GS1.";

    public override IReadOnlyList<GeneratorOption> Options =>
    [
        Option("tipo", "Tipo", "ean13", ("ean13", "EAN-13"), ("ean8", "EAN-8")),
        Option("prefixo", "Prefixo GS1", "560", ("560", "560 — Portugal"), ("qualquer", "Qualquer")),
    ];

    public override GeneratedItem Generate(GeneratorContext context)
    {
        var length = context.Option(Options[0]) == "ean8" ? 8 : 13;
        var prefix = context.Option(Options[1]) == "560" ? "560" : context.Digits(3);
        var body = prefix + context.Digits(length - 1 - prefix.Length);
        return new GeneratedItem(body + CheckDigit(body));
    }

    public static int CheckDigit(string payload)
    {
        var sum = 0;
        for (var i = 0; i < payload.Length; i++)
        {
            var weight = (payload.Length - i) % 2 == 1 ? 3 : 1;
            sum += (payload[i] - '0') * weight;
        }
        return (10 - sum % 10) % 10;
    }

    public override ValidationResult Validate(string value)
    {
        var ean = Checksums.Clean(value);
        if (ean.Length is not (8 or 13) || !Checksums.AllDigits(ean))
            return ValidationResult.WrongFormat("Um EAN tem 8 ou 13 dígitos.");

        var expected = CheckDigit(ean[..^1]);
        var details = new List<string> { $"Tipo: EAN-{ean.Length}" };
        if (ean.Length == 13 && ean.StartsWith("560"))
            details.Add("Prefixo 560: Portugal");

        return expected == ean[^1] - '0'
            ? ValidationResult.Valid(ean, $"EAN-{ean.Length} válido.", details)
            : ValidationResult.BadChecksum($"Dígito de controlo inválido: esperado {expected}, encontrado {ean[^1]}.", details);
    }
}