using PerfectNumbers.Core.Gpu.Accelerators;

namespace PerfectNumbers.Core;

internal static partial class PrimeOrderCalculator
{
	public static ulong CalculateHybrid(
		PrimeOrderCalculatorAccelerator gpu,
		ulong prime,
		ulong? previousOrder,
		in MontgomeryDivisorData divisorData,
		in PrimeOrderSearchConfig config)
	{
		// TODO: Is this condition ever met on EvenPerfectBitScanner's execution path? If not, we can add a clarification comment and comment out the entire block. We want to support p candidates at least greater or equal to 31.
		if (prime <= 3UL)
		{
			return prime == 3UL ? 2UL : 1UL;
		}

		ulong phi = prime - 1UL;

		PartialFactorResult phiFactors = PartialFactorHybrid(gpu, phi, config);

		ulong result;
		if (phiFactors.Factors is null)
		{
			result = CalculateByFactorizationCpu(prime, divisorData);

			phiFactors.Dispose();
			return result;
		}

		result = RunHeuristicPipelineHybrid(gpu, prime, previousOrder, config, divisorData, phi, phiFactors);

		phiFactors.Dispose();
		return result;
	}

	public static UInt128 CalculateHybrid(
			PrimeOrderCalculatorAccelerator gpu,
			in UInt128 prime,
			in UInt128? previousOrder,
			in PrimeOrderSearchConfig config)
	{
		MontgomeryDivisorData divisorData;
		UInt128 result;
		if (prime <= ulong.MaxValue)
		{
			ulong? previous = null;
			if (previousOrder.HasValue)
			{
				UInt128 previousValue = previousOrder.Value;
				if (previousValue <= ulong.MaxValue)
				{
					previous = (ulong)previousValue;
				}
				else
				{
					previous = ulong.MaxValue;
				}
			}

			ulong prime64 = (ulong)prime;
			Queue<MontgomeryDivisorData> divisorPool = MontgomeryDivisorDataPool.Shared;
			divisorData = divisorPool.FromModulus(prime64);
			ulong order64 = CalculateHybrid(gpu, prime64, previous, divisorData, config);
			divisorPool.Return(divisorData);
			result = order64 == 0UL ? UInt128.Zero : (UInt128)order64;
		}
		else
		{
			divisorData = MontgomeryDivisorData.Empty;
			result = CalculateWideInternalCpu(prime, previousOrder, divisorData, config);
		}

		return result;
	}
}