using System;
using Gma.QrCodeNet.Encoding.Masking;

namespace Gma.QrCodeNet.Encoding.EncodingRegion;

/// <summary>
/// 6.9 Format information
/// The Format Information is a 15 bit sequence containing 5 data bits, with 10 error correction bits calculated using the (15, 5) BCH code.
/// </summary>
/// <remarks>ISO/IEC 18004:2000 Chapter 8.9 Page 53</remarks>
internal static class FormatInformation
{
	/// <summary>
	/// From Appendix C in JISX0510:2004 (p.65).
	/// </summary>
	private const int FormatInfoPoly = 0x537;

	/// <summary>
	/// From Appendix C in JISX0510:2004 (p.65).
	/// </summary>
	private const int FormatInfoMaskPattern = 0x5412;

	/// <summary>
	/// Embed format information to tristatematrix.
	/// Process combination of create info bits, BCH error correction bits calculation, embed towards matrix.
	/// </summary>
	/// <remarks>ISO/IEC 18004:2000 Chapter 8.9 Page 53</remarks>
	internal static void EmbedFormatInformation(this TriStateMatrix triMatrix, ErrorCorrectionLevel errorLevel, Pattern pattern)
	{
		BitList formatInfo = GetFormatInfoBits(errorLevel, pattern);
		int width = triMatrix.Width;
		for (int index = 0; index < 15; index++)
		{
			MatrixPoint point = PointForInfo1(index);
			bool bit = formatInfo[index];
			triMatrix[point.X, point.Y, MatrixStatus.NoMask] = bit;

			if (index < 7)
			{
				triMatrix[8, width - 1 - index, MatrixStatus.NoMask] = bit;
			}
			else
			{
				triMatrix[width - 8 + (index - 7), 8, MatrixStatus.NoMask] = bit;
			}
		}
	}

	private static MatrixPoint PointForInfo1(int bitsIndex)
	{
		if (bitsIndex <= 7)
		{
			return bitsIndex >= 6
				? new MatrixPoint(bitsIndex + 1, 8)
				: new MatrixPoint(bitsIndex, 8);
		}
		else
		{
			return bitsIndex == 8
				? new MatrixPoint(8, 8 - (bitsIndex - 7))
				: new MatrixPoint(8, 8 - (bitsIndex - 7) - 1);
		}
	}

	private static BitList GetFormatInfoBits(ErrorCorrectionLevel errorLevel, Pattern pattern)
	{
		int formatInfo = (int)pattern.MaskPatternType;

		// Pattern bits length = 3
		formatInfo |= GetErrorCorrectionIndicatorBits(errorLevel) << 3;

		int bchCode = BCHCalculator.CalculateBCH(formatInfo, FormatInfoPoly);

		// bchCode length = 10
		formatInfo = (formatInfo << 10) | bchCode;

		// xor maskPattern
		formatInfo ^= FormatInfoMaskPattern;

		BitList resultBits = new()
		{
			{ formatInfo, 15 }
		};

		if (resultBits.Count != 15)
		{
			throw new Exception("FormatInfoBits length is not 15");
		}
		else
		{
			return resultBits;
		}
	}

	/// <summary>
	/// According Table 25 — Error correction level indicators
	/// Using these bits as enum values would destroy their order which currently corresponds to error correction strength.
	/// </summary>
	internal static int GetErrorCorrectionIndicatorBits(ErrorCorrectionLevel errorLevel)
	{
		// L 01
		// M 00
		// Q 11
		// H 10
		return errorLevel switch
		{
			ErrorCorrectionLevel.H => 0x02,
			ErrorCorrectionLevel.L => 0x01,
			ErrorCorrectionLevel.M => 0x00,
			ErrorCorrectionLevel.Q => 0x03,
			_ => throw new ArgumentException($"Unsupported error correction level [{errorLevel}]", nameof(errorLevel))
		};
	}
}