modified for request

OthelloBoardModel.cs

using System;

public enum Disk { NONE, DARK, LIGHT }

public class OthelloBoardModel : IOthelloBoardModel {
    public event Action<int, int, Disk> OnRequestDisk = delegate { };
    public event Action<int, int, Disk> OnPlaceDisk = delegate { };
    public event Action<int, int> OnFlipDisk = delegate { };

    private readonly Disk[][] board;

    private Disk currentSide = Disk.DARK;

    public OthelloBoardModel() {
        board = new Disk[ 8 ][];
        for ( int i = 0; i < 8; ++i ) {
            board[ i ] = new Disk[ 8 ];
        }
    }

    public Disk GetCurrentSide() {
        return currentSide;
    }

    public void SetSide( Disk side ) {
        currentSide = side;
    }

    public void RequestDisk( int x, int y ) {
        if ( x < 1 || x > 8 || y < 1 || y > 8 ) {
            return;
        }

        if ( board[ x - 1 ][ y - 1 ] != Disk.NONE ) {
            return;
        }

        OnRequestDisk.Invoke( x, y, currentSide );
    }

    public void PlaceDisk( int x, int y ) {
        if ( x < 1 || x > 8 || y < 1 || y > 8 ) {
            return;
        }

        if ( board[ x - 1 ][ y - 1 ] != Disk.NONE ) {
            return;
        }

        board[ x - 1 ][ y - 1 ] = currentSide;
        OnPlaceDisk.Invoke( x, y, currentSide );
    }

    public Disk GetDisk( int x, int y ) {
        if ( x < 1 || x > 8 || y < 1 || y > 8 ) {
            return Disk.NONE;
        }

        return board[ x - 1 ][ y - 1 ];
    }

    public void FlipDisk( int x, int y ) {
        if ( x < 1 || x > 8 || y < 1 || y > 8 ) {
            return;
        }

        if ( board[ x - 1 ][ y - 1 ] == Disk.NONE ) {
            return;
        }

        if ( board[ x - 1 ][ y - 1 ] == Disk.DARK ) {
            board[ x - 1 ][ y - 1 ] = Disk.LIGHT;
        }
        else if ( board[ x - 1 ][ y - 1 ] == Disk.LIGHT ) {
            board[ x - 1 ][ y - 1 ] = Disk.DARK;
        }
        
        OnFlipDisk.Invoke( x, y );
    }
}