using System.Diagnostics.Contracts;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using StitchATon2.Infra.Buffers;

namespace StitchATon2.Domain;

public static class Utils
{
    [Pure]
    public static string GetSBSNotation(int row)
        => row <= 26
            ? new string([(char)(row + 'A' - 1)])
            : new string(['A', (char)(row + 'A' - 27)]);

    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static int DivCeil(int a, int b)
    {
        return (a + b - 1) / b;
    }
    
    [Pure]
    public static (int Column, int Row) GetSBSCoordinate(string coordinate)
    {
        var column = coordinate[^1] - '0';
        if(char.IsDigit(coordinate[^2]))
            column += 10 * (coordinate[^2] - '0');

        var row = char.IsLetter(coordinate[1])
            ? 26 + coordinate[1] - 'A' + 1
            : coordinate[0] - 'A' + 1;

        return (column, row);
    }
    
    /// <summary>
    /// Performs a SIMD-accelerated calculation that generates a buffer of bounded, scaled indices.
    /// </summary>
    /// <param name="scaleFactor">The amount by which to scale the sequence values.</param>
    /// <param name="length">The total number of scalar values to generate.</param>
    /// <param name="max">Upper limit (exclusive) for clamping values.</param>
    /// <param name="offset">The offset to apply before clamping.</param>
    public static IBuffer<int> BoundsMatrix(float scaleFactor, int length, int max, int offset)
    {
        var vectorSize = DivCeil(length, Vector<float>.Count);
        using var buffer = MemoryAllocator.Allocate<Vector<float>>(vectorSize);

        var span = buffer.Span;
        var vectorMin = Vector<int>.Zero;
        var vectorOffset = new Vector<int>(offset - 1);
        var vectorMax = new Vector<int>(max - 1);
        var vectorScale = new Vector<float>(scaleFactor);

        var vectorSequence = Vector.CreateSequence(0f, 1f);

        var seq = 0f;
        for (var i = 0; i < vectorSize; i++, seq += Vector<float>.Count)
        {
            var sequence = new Vector<float>(seq) + vectorSequence;
            span[i] = Vector.FusedMultiplyAdd(sequence, vectorScale, vectorScale);
            span[i] = Vector.Ceiling(span[i]);
        }
        
        var result = MemoryAllocator.Allocate<int>(vectorSize * Vector<int>.Count);
        var resultSpan = MemoryMarshal.Cast<int, Vector<int>>(result.Span);
        for (var i = 0; i < vectorSize; i++)
        {
            resultSpan[i] = Vector.ConvertToInt32(span[i]);
            resultSpan[i] = Vector.Add(resultSpan[i], vectorOffset);
            resultSpan[i] = Vector.ClampNative(resultSpan[i], vectorMin, vectorMax);
        }

        return result;
    }
}