import Foundation

enum GameStatus: Equatable {
    case playing
    case solved
    case error
}

@MainActor
final class ShikakuGame: ObservableObject {
    static let supportedSizes = [5, 7, 10, 15, 20, 25]

    @Published private(set) var puzzle: ShikakuPuzzle
    @Published private(set) var playerRects: [PlayerRect] = []
    @Published private(set) var errorRectIDs: Set<PlayerRect.ID> = []
    @Published private(set) var message = "Ready"
    @Published private(set) var status: GameStatus = .playing

    private var startDate = Date()
    private var solvedElapsed: TimeInterval?

    var size: Int {
        puzzle.size
    }

    var currentSeed: UInt64 {
        puzzle.seed
    }

    init(size: Int = 5) {
        self.puzzle = Self.makePuzzle(size: size)
        self.startDate = Date()
    }

    func newPuzzle(size requestedSize: Int? = nil, seed requestedSeed: UInt64? = nil) {
        let nextSize = requestedSize ?? size
        puzzle = Self.makePuzzle(size: nextSize, seed: requestedSeed)
        playerRects = []
        errorRectIDs = []
        message = "Ready"
        status = .playing
        startDate = Date()
        solvedElapsed = nil
    }

    func clear() {
        playerRects = []
        errorRectIDs = []
        message = "Cleared"
        status = .playing

        if let solvedElapsed {
            startDate = Date().addingTimeInterval(-solvedElapsed)
        }

        solvedElapsed = nil
    }

    func placeRect(_ rect: PlayerRect) {
        guard rect.area > 1 else {
            errorRectIDs = []
            status = .playing
            message = "Drag over at least 2 cells"
            return
        }

        let newCells = Set(rect.cells)
        playerRects.removeAll { !Set($0.cells).isDisjoint(with: newCells) }
        playerRects.append(rect)
        errorRectIDs = []
        status = .playing
        runAutoCheck()
    }

    func removeRect(at cell: GridPoint) {
        let oldCount = playerRects.count
        playerRects.removeAll { $0.contains(cell) }

        if playerRects.count != oldCount {
            errorRectIDs = []
            status = .playing
            message = "Ready"
            solvedElapsed = nil
        }
    }

    func checkSolution() {
        let result = ShikakuValidation.verify(size: size, playerRects: playerRects, clues: puzzle.clues)

        if result.isSolved {
            markSolved()
            errorRectIDs = []
            message = "Solved in \(formattedElapsed())"
        } else {
            status = .error
            errorRectIDs = invalidRectIDs()
            message = result.message
        }
    }

    func formattedElapsed(at date: Date = Date()) -> String {
        let elapsed = solvedElapsed ?? max(0, date.timeIntervalSince(startDate))
        let minutes = Int(elapsed) / 60
        let seconds = Int(elapsed) % 60
        return String(format: "%d:%02d", minutes, seconds)
    }

    private func runAutoCheck() {
        guard status != .solved else {
            return
        }

        let result = ShikakuValidation.verify(size: size, playerRects: playerRects, clues: puzzle.clues)
        if result.isSolved {
            markSolved()
            message = "Solved in \(formattedElapsed())"
        } else {
            status = .playing
            message = "Ready"
        }
    }

    private func markSolved() {
        if solvedElapsed == nil {
            solvedElapsed = Date().timeIntervalSince(startDate)
        }
        status = .solved
    }

    private func invalidRectIDs() -> Set<PlayerRect.ID> {
        Set(playerRects.compactMap { rect in
            let clueValues = rect.cells.compactMap { puzzle.clues[$0] }
            if clueValues.count != 1 || clueValues.first != rect.area {
                return rect.id
            }
            return nil
        })
    }

    private static func makePuzzle(size: Int, seed requestedSeed: UInt64? = nil) -> ShikakuPuzzle {
        do {
            return try ShikakuGenerator.generate(size: size, seed: requestedSeed)
        } catch {
            assertionFailure("Falling back after puzzle generation error: \(error)")
            return fallbackPuzzle(size: size)
        }
    }

    private static func fallbackPuzzle(size: Int) -> ShikakuPuzzle {
        let rect = SolutionRect(row: 0, col: 0, height: size, width: size)
        let clue = GridPoint(row: size / 2, col: size / 2)
        return ShikakuPuzzle(size: size, clues: [clue: rect.area], solution: [rect], seed: 0)
    }
}