A helper for translating Advent of Code puzzle input into usable values.

aoc19-day3-input.swift

//: # Advent of Code 2019
//: ### Day 3 - Crossed Wires
//:
//: [Prev](@prev) <---> [Next](@next)

import Foundation

struct Wire: StringInitable, CustomStringConvertible {
    enum Direction: String {
        case up = "U"
        case down = "D"
        case right = "R"
        case left = "L"
    }

    let direction: Direction
    let length: Int

    init?(_ string: String) {
        guard
            let dirChar = string.first,
            let dir = Direction(rawValue: String(dirChar)),
            let len = Int(string.dropFirst())
        else { return nil }
        self.direction = dir
        self.length = len
    }

    var description: String {
        "Wire[\(direction.rawValue), \(length)]"
    }
}

//: Load data.
let parser = DataParser<Wire>()
guard let parseResult = try? parser.parseCSVLines(fileName: "input") else {
    fatalError("Could not read in data.")
}

print(parseResult)

DataParser.swift

import Foundation

/// A type that can be initialized from a string value.
///
public protocol StringInitable {
    /// Initialize the object with a string.
    ///
    /// - Note: This operation can fail if the string is not valid for this object type.
    ///
    init?(_ string: String)
}

extension Int: StringInitable {}

extension String: StringInitable {}

/// A helper object that can parse raw string data into structured values.
///
public struct DataParser<T: StringInitable> {

    /// Parsing-specific errors.
    public enum Error: Swift.Error {

        /// Unable to load or parse the input.
        case unableToReadInput
    }

    public init() {}

    /// Parse where input values are separated by newlines.
    ///
    public func parseLines(fileName: String) throws -> [T] {
        return try loadDataString(from: fileName)
            .split(separator: "\n")
            .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
            .compactMap { T($0) }
    }

    /// Parse where input values are separated by commas.
    ///
    public func parseCSV(fileName: String) throws -> [T] {
        return try loadDataString(from: fileName)
            .split(separator: ",")
            .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
            .compactMap { T($0) }
    }

    /// Parse where there are multiple lines and each line is comma-separated.
    ///
    public func parseCSVLines(fileName: String) throws -> [[T]] {
        return try loadDataString(from: fileName)
            .split(separator: "\n")
            .map { line in
                line
                    .split(separator: ",")
                    .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
                    .compactMap { T($0) }
            }
    }

    /// Attempt to load the input file from the Resources folder.
    ///
    private func loadDataString(from fileName: String) throws -> String {
        guard let dataURL = Bundle.main.url(forResource: fileName, withExtension: nil) else {
            throw Error.unableToReadInput
        }
        return try String(contentsOf: dataURL)
    }
}