using System;

namespace Gma.QrCodeNet.Encoding.EncodingRegion;

/// <summary>
/// Embed version information for version larger than or equal to 7.
/// </summary>
/// <remarks>ISO/IEC 18004:2000 Chapter 8.10 Page 54</remarks>
internal static class VersionInformation
{
	private const int VIRectangleHeight = 3;
	private const int VIRectangleWidth = 6;

	private const int LengthDataBits = 6;
	private const int LengthECBits = 12;
	private const int VersionBCHPoly = 0x1f25;

	/// <summary>
	/// Embed version information to Matrix
	/// Only for version greater than or equal to 7
	/// </summary>
	internal static void EmbedVersionInformation(this TriStateMatrix tsMatrix, int version)
	{
		if (version < 7)
		{
			return;
		}

		BitList versionInfo = VersionInfoBitList(version);

		int matrixWidth = tsMatrix.Width;

		// 1 cell between version info and position stencil
		int shiftLength = QRCodeConstantVariable.PositionStencilWidth + VIRectangleHeight + 1;

		// Reverse order input
		int viIndex = LengthDataBits + LengthECBits - 1;

		for (int viWidth = 0; viWidth < VIRectangleWidth; viWidth++)
		{
			for (int viHeight = 0; viHeight < VIRectangleHeight; viHeight++)
			{
				bool bit = versionInfo[viIndex];
				viIndex--;

				// Bottom left
				tsMatrix[viWidth, (matrixWidth - shiftLength + viHeight), MatrixStatus.NoMask] = bit;

				// Top right
				tsMatrix[(matrixWidth - shiftLength + viHeight), viWidth, MatrixStatus.NoMask] = bit;
			}
		}
	}

	private static BitList VersionInfoBitList(int version)
	{
		BitList result = new()
		{
			{ version, LengthDataBits },
			{ BCHCalculator.CalculateBCH(version, VersionBCHPoly), LengthECBits }
		};

		if (result.Count != (LengthECBits + LengthDataBits))
		{
			throw new Exception("Version Info creation error. Result is not 18 bits");
		}

		return result;
	}
}