shahdlala66
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package de.nowchess.chess.monad
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import de.nowchess.api.board.{Board, Color, Piece, Square}
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import de.nowchess.chess.logic.{GameHistory, GameRules, MoveValidator}
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import de.nowchess.chess.monad.Validated
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/** Example usage of the Validated monad for chess move validation.
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*
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* Instead of returning early on the first error (like current code),
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* this accumulates ALL validation errors and reports them together.
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*
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* Benefits:
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* - Better user feedback: "The square is empty AND it's not your turn"
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* - Composable validations
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* - Type-safe error handling
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*/
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object MoveValidationExample:
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/** Validation error types for chess moves. */
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enum ValidationError:
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case EmptySquare(square: Square)
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case WrongColor(piece: Piece, expectedColor: Color)
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case IllegalMove(from: Square, to: Square, piece: Piece)
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case MoveLeavesKingInCheck(color: Color)
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case InvalidSquare(input: String)
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def message: String = this match
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case EmptySquare(sq) => s"No piece on square $sq"
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case WrongColor(piece, expected) => s"Wrong color: $piece belongs to ${piece.color}, but it's ${expected}'s turn"
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case IllegalMove(from, to, piece) => s"Illegal move: ${piece.pieceType} cannot move from $from to $to"
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case MoveLeavesKingInCheck(color) => s"This move would leave ${color}'s king in check"
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case InvalidSquare(input) => s"Invalid square notation: $input"
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import ValidationError.*
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/** Validate that a piece exists at the given square. */
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def validatePieceExists(board: Board, square: Square): Validated[ValidationError, Piece] =
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Validated.fromOption(
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board.pieceAt(square),
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EmptySquare(square)
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)
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/** Validate that the piece belongs to the current player. */
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def validatePieceColor(piece: Piece, expectedColor: Color): Validated[ValidationError, Piece] =
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Validated.cond(
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piece.color == expectedColor,
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piece,
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WrongColor(piece, expectedColor)
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)
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/** Validate that the move is geometrically legal. */
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def validateMoveLegality(board: Board, from: Square, to: Square, piece: Piece): Validated[ValidationError, Unit] =
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Validated.cond(
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MoveValidator.isLegal(board, from, to),
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(),
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IllegalMove(from, to, piece)
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)
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/** Validate that the move doesn't leave the king in check. */
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def validateNoCheck(board: Board, history: GameHistory, from: Square, to: Square, color: Color): Validated[ValidationError, Unit] =
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val (newBoard, _) = board.withMove(from, to)
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Validated.cond(
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!GameRules.isInCheck(newBoard, color),
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(),
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MoveLeavesKingInCheck(color)
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)
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/** EXAMPLE 1: Chain validations sequentially (monadic - stops on first error). */
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def validateMoveSequential(
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board: Board,
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history: GameHistory,
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from: Square,
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to: Square,
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turn: Color
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): Validated[ValidationError, Unit] =
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for
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piece <- validatePieceExists(board, from)
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_ <- validatePieceColor(piece, turn)
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_ <- validateMoveLegality(board, from, to, piece)
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_ <- validateNoCheck(board, history, from, to, turn)
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yield ()
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/** EXAMPLE 2: Accumulate ALL errors at once (applicative). */
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def validateMoveParallel(
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board: Board,
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history: GameHistory,
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from: Square,
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to: Square,
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turn: Color
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): Validated[ValidationError, Unit] =
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val pieceCheck = validatePieceExists(board, from)
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val colorCheck = pieceCheck.flatMap(p => validatePieceColor(p, turn))
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val legalCheck = pieceCheck.flatMap(p => validateMoveLegality(board, from, to, p))
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val checkCheck = validateNoCheck(board, history, from, to, turn)
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// Combine all validations - this will accumulate ALL errors
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Validated.validateAll(colorCheck, legalCheck, checkCheck).map(_ => ())
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/** EXAMPLE 3: Use the validation in practice. */
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def exampleUsage(board: Board, history: GameHistory, from: Square, to: Square, turn: Color): String =
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validateMoveParallel(board, history, from, to, turn) match
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case Validated.Valid(_) =>
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"Move is valid!"
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case Validated.Invalid(errors) =>
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val errorMessages = errors.map(_.message).mkString("\n- ")
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s"Move is invalid for the following reasons:\n- $errorMessages"
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/** EXAMPLE 4: Validate multiple moves at once. */
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def validateMultipleMoves(
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board: Board,
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history: GameHistory,
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moves: List[(Square, Square)],
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turn: Color
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): Validated[ValidationError, List[Unit]] =
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val validations = moves.map { case (from, to) =>
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validateMoveSequential(board, history, from, to, turn)
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}
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Validated.validateAll(validations*)
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