aoc2021/Sources/16/16.swift

//
//  File.swift
//
//
//  Created by Max Nuding on 15.12.21.
//

import Foundation
import Runner


enum OperatorType: Int {
    case sum = 0
    case product = 1
    case minimum = 2
    case maximum = 3
    case value = 4
    case greaterThan = 5
    case lessThan = 6
    case equal = 7
}

protocol Packet {
    var version: Int { get }
    
    func getTotalVersion() -> Int
    func getValue() -> Int
}

struct ValuePacket: Packet {
    let version: Int
    let value: Int
    
    func getTotalVersion() -> Int { version }
    func getValue() -> Int { value }
}

struct OperatorPacket: Packet {
    let type: OperatorType
    let version: Int
    let subPackets: [Packet]
    
    func getTotalVersion() -> Int { version + subPackets.map { $0.getTotalVersion() }.reduce(0, +) }
    func getValue() -> Int {
        let spValues = subPackets.map { $0.getValue() }
        switch type {
        case .sum:
            return spValues.reduce(0, +)
        case .product:
            return spValues.reduce(1, *)
        case .minimum:
            return spValues.min()!
        case .maximum:
            return spValues.max()!
        case .greaterThan:
            return spValues.first! > spValues.last! ? 1 : 0
        case .lessThan:
            return spValues.first! < spValues.last! ? 1 : 0
        case .equal:
            return spValues.first! == spValues.last! ? 1 : 0
        case .value:
            fatalError()
        }
    }
}

class Day16: Runnable {
    let inputPath: String
    
    required init(inputPath: String) {
        self.inputPath = inputPath
    }
    
    public func run() {
        let input = try! String(contentsOfFile: inputPath)
        let parts = input
            .trimmingCharacters(in: .newlines)
        let bytes = parts.bits().joined()
        let packets = parsePacket(bytes: bytes)
        let p: Packet = packets.0
        print(p.getTotalVersion())
        print(p.getValue())
    }
    
    func parsePacket<S>(bytes: S) -> (Packet, S.SubSequence) where S:StringProtocol {
        let version = bytes[bytes.startIndex..<bytes.index(bytes.startIndex, offsetBy: 3)].binaryToDecimal()
        let typeId = bytes[bytes.index(bytes.startIndex, offsetBy: 3)..<bytes.index(bytes.startIndex, offsetBy: 6)].binaryToDecimal()
        var value: Packet
        var reminder: S.SubSequence
        switch typeId {
        case 4:
            let (v, r) = parseLiteralPacketValue(bytes: bytes)
            value = ValuePacket(version: version, value: v)
            reminder = r
        default:
            let (v, r) = parseOperatorPacker(bytes: bytes)
            value = OperatorPacket(type: OperatorType(rawValue: typeId)!, version: version, subPackets: v)
            reminder = r
        }
        return (value, reminder)
    }
    
    func parseOperatorPacker<S>(bytes: S) -> ([Packet], S.SubSequence) where S:StringProtocol  {
        let startNextBitsIndex = bytes.index(bytes.startIndex, offsetBy: 7)
        let lengthTypeId = bytes[bytes.index(bytes.startIndex, offsetBy: 6)..<startNextBitsIndex].description
        let isTotalLength = lengthTypeId == "0"
        
        let nextBitsLength = isTotalLength ? 15 : 11
        let endNextBitsIndex = bytes.index(startNextBitsIndex, offsetBy: nextBitsLength)
        let nextBits = bytes[startNextBitsIndex..<endNextBitsIndex]
        
        var number = nextBits.binaryToDecimal()
        var reminder = bytes[endNextBitsIndex...]
        var subPackets = [Packet]()
        
        while number > 0 {
            let (p, rem) = parsePacket(bytes: reminder)
            number -= isTotalLength ? (reminder.count - rem.count) : 1
            subPackets.append(p)
            reminder = rem
        }
        return (subPackets, reminder)
    }
    
    func parseLiteralPacketValue<S>(bytes: S) -> (Int, S.SubSequence) where S:StringProtocol  {
        var index = bytes.index(bytes.startIndex, offsetBy: 6)
        var ei = index
        var bits: Substring = ""
        var reminder: S.SubSequence = ""
        while true {
            let si = bytes.index(index, offsetBy: 1)
            ei = bytes.index(si, offsetBy: 4)
            bits += bytes[si..<ei]
            if bytes[index] == "0" {
                reminder = bytes[ei...]
                break
            }
            index = bytes.index(ei, offsetBy: 0)
        }
        return (bits.binaryToDecimal(), reminder)
    }
}

extension StringProtocol {
    func bits() -> [String] {
        self.map { $0.bits }
    }
    
    func binaryToDecimal() -> Int { Int(self, radix: 2)! }
}

extension Character {
    var bits: String  {
        switch self.hexDigitValue! {
        case 0:
            return "0000"
        case 1:
            return "0001"
        case 2:
            return "0010"
        case 3:
            return "0011"
        case 4:
            return "0100"
        case 5:
            return "0101"
        case 6:
            return "0110"
        case 7:
            return "0111"
        case 8:
            return "1000"
        case 9:
            return "1001"
        case 10:
            return "1010"
        case 11:
            return "1011"
        case 12:
            return "1100"
        case 13:
            return "1101"
        case 14:
            return "1110"
        case 15:
            return "1111"
        default:
            fatalError()
        }
    }
}