namespace StellaOps.Policy.Licensing;

public sealed record LicenseCompatibilityResult(bool IsCompatible, string? Reason);

public sealed class LicenseCompatibilityChecker
{
    public LicenseCompatibilityResult Check(
        LicenseDescriptor first,
        LicenseDescriptor second,
        ProjectContext context)
    {
        if (first is null)
        {
            throw new ArgumentNullException(nameof(first));
        }

        if (second is null)
        {
            throw new ArgumentNullException(nameof(second));
        }

        if (IsApacheGpl2Conflict(first.Id, second.Id))
        {
            return new LicenseCompatibilityResult(
                false,
                "Apache-2.0 is incompatible with GPL-2.0-only due to patent clauses.");
        }

        if (first.Category == LicenseCategory.Proprietary
            && second.Category == LicenseCategory.StrongCopyleft)
        {
            return new LicenseCompatibilityResult(
                false,
                "Strong copyleft is incompatible with proprietary licensing.");
        }

        if (second.Category == LicenseCategory.Proprietary
            && first.Category == LicenseCategory.StrongCopyleft)
        {
            return new LicenseCompatibilityResult(
                false,
                "Strong copyleft is incompatible with proprietary licensing.");
        }

        if (context.DistributionModel == DistributionModel.Commercial
            && first.Category == LicenseCategory.StrongCopyleft
            && second.Category == LicenseCategory.StrongCopyleft)
        {
            return new LicenseCompatibilityResult(
                true,
                "Strong copyleft pairing detected; ensure redistribution obligations are met.");
        }

        return new LicenseCompatibilityResult(true, null);
    }

    private static bool IsApacheGpl2Conflict(string first, string second)
    {
        return (IsApache(first) && IsGpl2Only(second))
            || (IsApache(second) && IsGpl2Only(first));
    }

    private static bool IsApache(string licenseId)
        => licenseId.Equals("Apache-2.0", StringComparison.OrdinalIgnoreCase);

    private static bool IsGpl2Only(string licenseId)
        => licenseId.Equals("GPL-2.0-only", StringComparison.OrdinalIgnoreCase)
           || licenseId.Equals("GPL-2.0+", StringComparison.OrdinalIgnoreCase);
}