//
//  GameController.swift
//  TetrisKit
//
//  Created by Shadowfacts on 10/13/19.
//  Copyright © 2019 Shadowfacts. All rights reserved.
//

import Foundation
import Combine

public class GameController: ObservableObject {
    
    public let width = 10
    public let height = 20
    
    var state: GameState = .waitingForStart
    
    @Published public var board: GameBoard

    @Published public var currentPiece: GamePiece? {
        didSet {
            updateCurrentPieceAtDropPoint()
        }
    }
    @Published public var currentPieceAtDropPoint: GamePiece?
    @Published public var nextTetrominoes: [Tetromino] = [.random(), .random(), .random()]
    @Published public var heldTetromino: Tetromino?

    public var ended: Bool {
        return (0..<width).first(where: { board[$0, 0] }) != nil
    }

    public init() {
        self.board = GameBoard(width: width, height: height)
        self.currentPiece = nil
    }
    
    public func start() {
        state = .playing(.normal)
        nextPiece()
    }
    
    func nextPiece() {
        let tetromino = nextTetrominoes.removeFirst()
        currentPiece = GamePiece(tetromino: tetromino, topLeft: ((width - tetromino.shape.count) / 2, 0))
        nextTetrominoes.append(.random())
    }
    
    func finalizePiece() {
        self.board.set(piece: currentPiece!)
        clearLines()
        nextPiece()
        
        state = .playing(.normal)
    }
    
    func clearLines() {
        var row = height - 1
        while row >= 0 {
            if board.rowFull(row) {
                board.tiles.remove(at: row)
            }
            row -= 1
        }
        for _ in 0..<height - board.tiles.count {
            board.tiles.insert(Array(repeating: nil, count: width), at: 0)
        }
    }
    
    public func step() {
        guard case .playing(_) = state,
            let currentPiece = currentPiece else { return }
        
        let modifiedPiece = currentPiece.moved(by: (0, 1))
        if overlapsAny(modifiedPiece) {
            finalizePiece()
        } else {
            self.currentPiece = modifiedPiece
        }
    }
    
    public func rotate(direction: RotationDirection) {
        guard case let .playing(playState) = state,
            playState != .dropped,
            let currentPiece = currentPiece else { return }
        
        let modifiedPiece = currentPiece.rotated(direction)
        if !overlapsAny(modifiedPiece) {
            self.currentPiece = modifiedPiece
        }
    }
    
    public func left() {
        guard case let .playing(playState) = state,
            playState != .dropped,
            let currentPiece = currentPiece else { return }
        let modifiedPiece = currentPiece.moved(by: (-1, 0))
        if !overlapsAny(modifiedPiece) {
            self.currentPiece = modifiedPiece
        }
    }
    
    public func right() {
        guard case let .playing(playState) = state,
            playState != .dropped,
            let currentPiece = currentPiece else { return }
        let modifiedPiece = currentPiece.moved(by: (1, 0))
        if !overlapsAny(modifiedPiece) {
            self.currentPiece = modifiedPiece
        }
    }
    
    public func drop() {
        guard case let .playing(playState) = state, playState != .dropped else { return }
        currentPiece = currentPieceAtDropPoint
        state = .playing(.dropped)
    }
    
    public func hold() {
        guard case .playing(.normal) = state,
            let currentPiece = currentPiece else { return }
        if let heldTetromino = heldTetromino {
            self.heldTetromino = currentPiece.tetromino
            self.currentPiece = GamePiece(tetromino: heldTetromino, topLeft: ((width - heldTetromino.shape.count) / 2, 0))
        } else {
            heldTetromino = currentPiece.tetromino
            nextPiece()
        }
        state = .playing(.switched)
    }
    
    private func updateCurrentPieceAtDropPoint() {
        guard let currentPiece = currentPiece else { return }
        var prev = currentPiece
        currentPieceAtDropPoint = currentPiece
        while !overlapsAny(currentPieceAtDropPoint!) {
            prev = currentPieceAtDropPoint!
            currentPieceAtDropPoint = currentPieceAtDropPoint!.moved(by: (0, 1))
        }
        currentPieceAtDropPoint = prev
    }

    public func overlapsAny(_ piece: GamePiece) -> Bool {
        let (left, top) = piece.topLeft
        for y in 0..<piece.tiles.count {
            for x in 0..<piece.tiles.first!.count where piece.tiles[y][x] {
                if top + y >= height || left + x < 0 || left + x >= width || board[left + x, top + y] {
                    return true
                }
            }
        }
        return false
    }

}

enum GameState {
    case waitingForStart
    case playing(PlayState)
}

enum PlayState {
    case normal
    case dropped
    case switched
}