using System.Diagnostics;
using System.Text;

namespace DisplayCommands;

public sealed class Cp437Grid(ushort width, ushort height) : IEquatable<Cp437Grid>
{
    private readonly ByteGrid _byteGrid = new(width, height);
    private readonly Encoding _encoding = Encoding.GetEncoding(437);

    public ushort Height { get; } = height;

    public ushort Width { get; } = width;

    internal Memory<byte> Data => _byteGrid.Data;

    public char this[ushort x, ushort y]
    {
        get => ByteToChar(_byteGrid[x, y]);
        set => _byteGrid[x, y] = CharToByte(value);
    }

    public string this[ushort row]
    {
        get
        {
            var rowStart = row * Width;
            return _encoding.GetString(_byteGrid.Data[rowStart..(rowStart + Width)].Span);
        }
        set
        {
            ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual(row, Height, nameof(row));
            ArgumentOutOfRangeException.ThrowIfGreaterThan(value.Length, Width, nameof(value));
            ushort x = 0;
            for (; x < value.Length; x++)
                _byteGrid[x, row] = CharToByte(value[x]);
            for (; x < Width; x++)
                _byteGrid[x, row] = CharToByte(' ');
        }
    }

    private byte CharToByte(char c)
    {
        ReadOnlySpan<char> valuesStr = stackalloc char[] { c };
        Span<byte> convertedStr = stackalloc byte[1];
        var consumed = _encoding.GetBytes(valuesStr, convertedStr);
        Debug.Assert(consumed == 1);
        return convertedStr[0];
    }

    private char ByteToChar(byte b)
    {
        ReadOnlySpan<byte> valueBytes = stackalloc byte[] { b };
        Span<char> resultStr = stackalloc char[1];
        var consumed = _encoding.GetChars(valueBytes, resultStr);
        Debug.Assert(consumed == 1);
        return resultStr[0];
    }

    public bool Equals(Cp437Grid? other)
    {
        if (ReferenceEquals(null, other)) return false;
        if (ReferenceEquals(this, other)) return true;
        return Height == other.Height && Width == other.Width && _byteGrid.Equals(other._byteGrid);
    }

    public override bool Equals(object? obj) => ReferenceEquals(this, obj) || (obj is Cp437Grid other && Equals(other));
    public override int GetHashCode() => HashCode.Combine(_byteGrid, Height, Width);
    public static bool operator ==(Cp437Grid? left, Cp437Grid? right) => Equals(left, right);
    public static bool operator !=(Cp437Grid? left, Cp437Grid? right) => !Equals(left, right);
}