Shogi/Shogi.UI/Pages/Play/GameBoard/SeatedGameBoard.razor

@using Shogi.Contracts.Api.Commands
@using Shogi.Contracts.Types;
@using System.Text.RegularExpressions;
@using System.Net;
@inject ShogiApi ShogiApi;

<div style="position: relative;">
	<GameBoardPresentation Session="Session"
												 Perspective="Perspective"
												 OnClickHand="OnClickHand"
												 OnClickTile="OnClickTile"
												 SelectedPosition="@selectedBoardPosition"
												 SelectedPieceFromHand="@selectedPieceFromHand" />

	@if (showPromotePrompt)
	{
		<!-- Promote prompt -->
		<!-- TODO: Add a background div which prevents mouse inputs to the board while this decision is being made. -->
		<section class="promote-prompt">
			<p>Do you wish to promote?</p>
			<div>
				<button type="button" @onclick="() => OnClickPromotionChoice(true)">Yes</button>
				<button type="button" @onclick="() => OnClickPromotionChoice(false)">No</button>
				<button type="button" @onclick="() => showPromotePrompt = false">Cancel</button>
			</div>
		</section>
	}
</div>

@code {
	[Parameter, EditorRequired]
	public WhichPlayer Perspective { get; set; }
	[Parameter, EditorRequired]
	public Session Session { get; set; } = default!;
	private string? selectedBoardPosition;
	private WhichPiece? selectedPieceFromHand;
	private bool showPromotePrompt;
	private string? moveTo;

	protected override void OnParametersSet()
	{
		base.OnParametersSet();
		selectedBoardPosition = null;
		selectedPieceFromHand = null;
		if (Session == null)
		{
			throw new ArgumentException($"{nameof(Session)} cannot be null.", nameof(Session));
		}
	}

	bool IsWithinPromoteArea(string position)
	{
		if (Perspective == WhichPlayer.Player1 && Regex.IsMatch(position, ".[7-9]"))
		{
			return true;
		}
		if (Perspective == WhichPlayer.Player2 && Regex.IsMatch(position, ".[1-3]"))
		{
			return true;
		}
		return false;
	}

	async Task OnClickTile(string position)
	{
		if (showPromotePrompt) return;

		var pieceAtPosition = Session.BoardState.Board[position];
		if (selectedBoardPosition == position)
		{
			// Deselect the selected position.
			selectedBoardPosition = null;
			StateHasChanged();
			return;
		}

		if (selectedBoardPosition == null && pieceAtPosition?.Owner == Perspective)
		{
			// Select an owned piece.
			selectedBoardPosition = position;
			// Prevent selecting pieces from the hand and board at the same time.
			selectedPieceFromHand = null;
			StateHasChanged();
			return;
		}

		if (selectedPieceFromHand is not null)
		{
			if (pieceAtPosition is null)
			{
				// Placing a piece from the hand to an empty space.
				var success = await ShogiApi.Move(
						Session.SessionId,
						new MovePieceCommand(selectedPieceFromHand.Value, position));
				if (!success)
				{
					selectedPieceFromHand = null;
				}
			}
			StateHasChanged();
			return;
		}

		if (selectedBoardPosition != null)
		{
			if (pieceAtPosition == null || pieceAtPosition?.Owner != Perspective)
			{
				var pieceBeingMoved = Session.BoardState.Board[selectedBoardPosition];
				var isPromotedAlready = pieceBeingMoved != null && pieceBeingMoved.IsPromoted;
				Console.WriteLine("Is promoted? {0}", isPromotedAlready);
				// Moving to an empty space or capturing an opponent's piece.
				if (!isPromotedAlready && (IsWithinPromoteArea(position) || IsWithinPromoteArea(selectedBoardPosition)))
				{
					Console.WriteLine("Prompt!");
					moveTo = position;
					showPromotePrompt = true;
				}
				else
				{
					var success = await ShogiApi.Move(Session.SessionId, new MovePieceCommand(selectedBoardPosition, position, false));
					if (!success)
					{
						selectedBoardPosition = null;
					}
				}
				StateHasChanged();
				return;
			}
		}
	}

	void OnClickHand(Piece piece)
	{
		if (showPromotePrompt) return;

		// Prevent selecting from both the hand and the board.
		selectedBoardPosition = null;

		selectedPieceFromHand = piece.WhichPiece == selectedPieceFromHand
				// Deselecting the already-selected piece
				? selectedPieceFromHand = null
				: selectedPieceFromHand = piece.WhichPiece;

		StateHasChanged();
	}

	private async Task OnClickPromotionChoice(bool shouldPromote)
	{
		if (selectedBoardPosition != null && moveTo != null)
		{
			await ShogiApi.Move(Session.SessionId, new MovePieceCommand(selectedBoardPosition, moveTo, shouldPromote));
			showPromotePrompt = false;
			return;
		}

		throw new InvalidOperationException("Unexpected scenario during OnClickPromotionChoice.");
	}
}