import Foundation

struct Coord : Hashable, CustomStringConvertible {
    let (x, y): (Int, Int)
    var description: String { return "(\(x),\(y))" }
}

func readInput(_ fileName: String) throws -> [Coord] {
    let xy = try Regex(#"([0-9]+),([0-9]+)"#)
    return try String(contentsOfFile: fileName,  encoding: .ascii)
        .split(separator: "\n")
        .compactMap { $0.wholeMatch(of: xy) }
        .map { Coord(
            x: Int($0.output[1].substring!)!,
            y: Int($0.output[2].substring!)!
        ) }
}

struct Map : CustomStringConvertible {
    let walls: Set<Coord>
    let (w, h): (Int, Int)
    var description: String {
        let top = "   \u{001B}[4m" + (0..<w).map { " \($0 % 10)" }.joined() + "\u{001B}[0m\n"
        let maze = (0..<h).map { i in
            String(format: "%2d▕", i) + (0..<w).map { j in
                walls.contains(Coord(x: j, y: i)) ? "▓▓" : "  "
            }.joined() + "▌"
        }.joined(separator: "\n")
        let bot = "\n   " + String(repeating: "🬂", count: w*2) + "🬀"
        return top + maze + bot
    }

    func heur(_ a: Coord, _ b: Coord) -> Int {
        return abs(a.x - b.x) + abs(a.y - b.y)
    }
    func bfs(from start: Coord, to end: Coord) -> Bool {
        var q: Set<Coord> = [start]
        var seen: Set<Coord> = [start]
        while !q.isEmpty {
            let cell = q.removeFirst()
            if cell == end {
                return true
            }
            [(0, -1), (0, 1), (-1, 0), (1, 0)].map { dy, dx in
                Coord(x: cell.x + dx, y: cell.y + dy)}
                .filter { c in c.x >= 0 && c.y >= 0 && c.x < w && c.y < h }
                .filter { !walls.contains($0) }
                .filter { !seen.contains($0) }
                .forEach { nb in
                    seen.insert(nb)
                    q.insert(nb)
                }
        }
        return false
    }
}

@main
struct AoC {
    static func main() throws {
        let bytes = try readInput(CommandLine.arguments[1])
        let w = Int(CommandLine.arguments[2]) ?? 71
        let h = Int(CommandLine.arguments[3]) ?? 71
        let startLimit = Int(CommandLine.arguments[4]) ?? 1024
        var range = Array(startLimit..<bytes.count)
        while range.count > 1 {
            let center = range.count/2
            print("Trying \(range[center])...", terminator: "")
            let map = Map(walls: Set(bytes.prefix(range[center])), w: w, h: h)
            if map.bfs(from: Coord(x: 0, y: 0), to: Coord(x: w-1, y: h-1)) {
                print(" works")
                range = Array(range[center+1..<range.count])
            } else {
                print(" blocked")
                range = Array(range[0..<center])
            }
        }
        let map = Map(walls: Set(bytes.prefix(range[0])), w: w, h: h)
        print(map)
        if map.bfs(from: Coord(x: 0, y: 0), to: Coord(x: w-1, y: h-1)) {
            print("at \(range[0]): \(bytes[range[0]])")
        } else {
            print("at \(range[0] + 1): \(bytes[range[0] + 1])")
        }
    }
}