//
//  PGNMove.swift
//  Sage
//
//  Created by Kajetan Dąbrowski on 19/10/2016.
//  Copyright © 2016 Nikolai Vazquez. All rights reserved.
//

import Foundation

/// A PGN move representation in a string.
public struct PGNMove: RawRepresentable, ExpressibleByStringLiteral {


    /// PGN Move parsing error
    ///
    /// - invalidMove: The move is invalid
    public enum ParseError: Error {
        case invalidMove(String)
    }

    public typealias RawValue = String
    public typealias StringLiteralType = String
    public typealias ExtendedGraphemeClusterLiteralType = String
    public typealias UnicodeScalarLiteralType = String
    public let rawValue: String

    static private let pattern = "^(?:([NBRQK]?)([a-h]?)([1-8]?)(x?)([a-h])([1-8])((?:=[NBRQ])?)|(O-O)|(O-O-O))([+#]?)$"
    static private let regex: NSRegularExpression! = try? NSRegularExpression(pattern: pattern, options: [])

    private var match: NSTextCheckingResult?
    private var unwrappedMatch: NSTextCheckingResult {
        guard let unwrappedMatch = match else {
            fatalError("PGNMove not possible. Check move.isPossible before checking other properties")
        }
        return unwrappedMatch
    }

    public init?(rawValue: String) {
        self.rawValue = rawValue
        parse()
        if !isPossible { return nil }
    }

    public init(stringLiteral value: StringLiteralType) {
        rawValue = value
        parse()
    }

    public init(unicodeScalarLiteral value: UnicodeScalarLiteralType) {
        rawValue = value
        parse()
    }

    public init(extendedGraphemeClusterLiteral value: ExtendedGraphemeClusterLiteralType) {
        rawValue = value
        parse()
    }

    mutating private func parse() {
        let matches = PGNMove.regex.matches(in: rawValue, options: [], range: fullRange)
        match = matches.filter { $0.range.length == self.fullRange.length }.first
    }

    private var fullRange: NSRange {
        return NSRange(location: 0, length: rawValue.count)
    }

    /// Indicates whether the move is possible.
    public var isPossible: Bool {
        return match != nil
    }

    /// Indicated whether the pgn represents a capture
    public var isCapture: Bool {
        return unwrappedMatch.range(at: 4).length > 0
    }

    /// Indicates whether the move represents a promotion
    public var isPromotion: Bool {
        return unwrappedMatch.range(at: 7).length > 0
    }

    /// Indicates whether the move is castle
    public var isCastle: Bool {
        return isCastleKingside || isCastleQueenside
    }

    /// Indicates whether the move is castle kingside
    public var isCastleKingside: Bool {
        return unwrappedMatch.range(at: 8).length > 0
    }

    /// Indicates whether the move is castle queenside
    public var isCastleQueenside: Bool {
        return unwrappedMatch.range(at: 9).length > 0
    }

    /// Indicates whether the move represents a check
    public var isCheck: Bool {
        return unwrappedMatch.range(at: 10).length > 0
    }

    /// Indicates whether the move represents a checkmate
    public var isCheckmate: Bool {
        return stringAt(rangeIndex: 10) == "#"
    }

    /// A piece kind that is moved by the move
    public var piece: Piece.Kind {
        let pieceLetter = stringAt(rangeIndex: 1)
        guard let piece = PGNMove.pieceFor(letter: pieceLetter) else {
            fatalError("Invalid piece")
        }
        return piece
    }

    /// The rank to move to
    public var rank: Rank {
        let rankSymbol = stringAt(rangeIndex: 6)
        guard let raw = Int(rankSymbol), let rank = Rank(rawValue: raw) else { fatalError("Could not get rank") }
        return rank
    }

    /// The file to move to
    public var file: File {
        guard let fileSymbol = stringAt(rangeIndex: 5).first,
            let file = File(fileSymbol) else { fatalError("Could not get file") }
        return file
    }

    /// The rank to move from.
    /// For example in the move 'Nf3' there is no source rank, since PGNMove is out of board context.
    /// However, if you specify the move like 'N4d2' the move will represent the knight from the fourth rank.
    public var sourceRank: Rank? {
        let sourceRankSymbol = stringAt(rangeIndex: 3)
        if sourceRankSymbol == "" { return nil }
        guard let sourceRankRaw = Int(sourceRankSymbol),
            let sourceRank = Rank(rawValue: sourceRankRaw) else { fatalError("Could not get source rank") }
        return sourceRank
    }

    /// The file to move from.
    /// For example in the move 'Nf3' there is no source file, since PGNMove is out of board context.
    /// However, if you specify the move like 'Nfd2' the move will represent the knight from the d file.
    public var sourceFile: File? {
        let sourceFileSymbol = stringAt(rangeIndex: 2)
        if sourceFileSymbol == "" { return nil }
        guard let sourceFileRaw = sourceFileSymbol.first,
            let sourceFile = File(sourceFileRaw) else { fatalError("Could not get source file") }
        return sourceFile
    }

    /// Represents a piece that the move wants to promote to
    public var promotionPiece: Piece.Kind? {
        if !isPromotion { return nil }
        guard let pieceLetter = stringAt(rangeIndex: 7).last,
            let piece = PGNMove.pieceFor(letter: String(pieceLetter)) else { fatalError("Could not get promotion piece") }
        return piece
    }

    private static func pieceFor(letter: String) -> Piece.Kind? {
        switch letter {
        case "N":
            return ._knight
        case "B":
            return ._bishop
        case "K":
            return ._king
        case "Q":
            return ._queen
        case "R":
            return ._rook
        case "":
            return ._pawn
        default:
            return nil
        }
    }

    private func stringAt(rangeIndex: Int) -> String {
        guard let match = match else { fatalError() }
        let range = match.range(at: rangeIndex)
        let substring = (rawValue as NSString).substring(with: range)
        return substring
    }
}

public struct PGNParser {


    /// Parses the move in context of the game position
    ///
    /// - parameter move:     Move that needs to be parsed
    /// - parameter position: position to parse in
    ///
    /// - throws: Errors if move is invalid, or if it cannot be executed in this position, or if it's ambiguous.
    ///
    /// - returns: Parsed move that can be applied to a game (containing source and destination squares)
    public static func parse(move: PGNMove, in position: Game.Position) throws -> Move {
        if !move.isPossible { throw PGNMove.ParseError.invalidMove(move.rawValue) }
        let colorToMove = position.playerTurn
        if move.isCastleKingside { return Move(castle: colorToMove, direction: .right) }
        if move.isCastleQueenside { return Move(castle: colorToMove, direction: .left) }

        let piece = Piece(kind: move.piece, color: colorToMove)
        let destinationSquare: Square = Square(file: move.file, rank: move.rank)
        let game = try Game(position: position)
        var possibleMoves = game.availableMoves().filter { return $0.end == destinationSquare }.filter { move -> Bool in
            game.board.locations(for: piece).contains(where: { move.start.location == $0 })
        }

        if let sourceFile = move.sourceFile { possibleMoves = possibleMoves.filter { $0.start.file == sourceFile } }
        if let sourceRank = move.sourceRank { possibleMoves = possibleMoves.filter { $0.start.rank == sourceRank } }

        if possibleMoves.count != 1 { throw PGNMove.ParseError.invalidMove(move.rawValue) }
        return possibleMoves.first!
    }
}