import Foundation

let (w, h) = (101, 103)

infix operator %%: MultiplicationPrecedence
func %%<T: BinaryInteger>(lhs: T, rhs: T) -> T {
    return (lhs % rhs + rhs) % rhs
}

struct Robot : CustomStringConvertible {
    var (x, y): (Int, Int)
    let (vx, vy): (Int, Int)
    var description: String { return "p=(\(x), \(y)) v=(\(vx), \(vy))" }

    mutating func move() {
        x = (x + vx) %% w
        y = (y + vy) %% h
    }
}

func readInput(_ filePath: String) throws -> [Robot] {
    let robot = try Regex(#"p=([0-9]+),([0-9]+) v=([0-9-]+),([0-9-]+)"#)
    var robots: [Robot] = []
    let content = try String(contentsOfFile: filePath, encoding: .ascii)
    content.split(separator: "\n").forEach { line in
        if let m = line.wholeMatch(of: robot) {
            robots.append(Robot(
                x: Int(m.output[1].substring!)!,
                y: Int(m.output[2].substring!)!,
                vx: Int(m.output[3].substring!)!,
                vy: Int(m.output[4].substring!)!
            ))
        }
    }
    return robots
}

func variance(_ bots: [Robot]) -> Int {
    let (sX, sY) = bots.reduce((0, 0)) { s, bot in (s.0 + bot.x, s.1 + bot.y) }
    let (mX, mY) = (sX/bots.count, sY/bots.count)
    return bots.reduce(0) { s, bot in
        s + (mX-bot.x)*(mX-bot.x) + (mY-bot.y)*(mY-bot.y) }
}

func printRobots(_ bots: [Robot]) -> String {
    var screen: [[String]] = Array(
        repeating: Array(repeating: " ", count: 101),
        count: 52
    )
    bots.forEach { bot in
        let (q, r) = bot.y.quotientAndRemainder(dividingBy: 2)
        if screen[q][bot.x] == " " {
            screen[q][bot.x] = (r == 0) ? "▀" : "▄"
        } else {
            screen[q][bot.x] = "█"
        }
    }
    return "┌" + String(repeating: "─", count: w) + "┐\n" +
        screen.map { row in "│" + row.joined() + "│" }.joined(separator: "\n") +
        "\n└" + String(repeating: "─", count: w) + "┘"
}

var bots = try readInput(CommandLine.arguments[1])
var i = 0
var minSigma = Int.max
while true {
    i += 1
    for i in 0..<bots.count {
        bots[i].move()
    }
    let printout = printRobots(bots)
    let sigma = variance(bots)
    if sigma < minSigma {
        minSigma = sigma
        //print("\u{001B}[2J")
        print(printout)
        print("i=\(i) s²=\(sigma)")
    }
}