Allows convenient navigation between capture groups for NSRegularExpression

RegexGroup.swift

import Foundation

public final class RegexGroup: CustomDebugStringConvertible {
    
    public internal(set) var subgroups = [RegexGroup]()
    public internal(set) var value = Substring()
    
    func contains(range: Range<String.Index>) -> Bool {
        return range.lowerBound >= value.startIndex && range.upperBound <= value.endIndex
    }
    
    public var debugDescription: String { "RegexGroup(\(value))" }
    
}

extension NSTextCheckingResult {
    
    func group(in value: String) -> RegexGroup? {
        var stack = [RegexGroup]()
        for i in 0..<numberOfRanges {
            let nsRange = self.range(at: i)
            guard nsRange.location != NSNotFound else { continue }
            let startIndex = value.index(value.startIndex, offsetBy: nsRange.location)
            let endIndex = value.index(startIndex, offsetBy: nsRange.length)
            let range = startIndex..<endIndex
            guard !range.isEmpty else { continue }
            let group = RegexGroup()
            group.value = value[range]
            while var parentGroup = stack.last, !parentGroup.contains(range: range) {
                stack.popLast()
            }
            stack.last?.subgroups.append(group)
            stack.append(group)
        }
        return stack.first
    }
    
}

extension NSRegularExpression {
    
    func firstGroup(in string: String) -> RegexGroup? {
        let stringRange = NSRange(location: 0, length: string.count)
        return firstMatch(in: string, range: stringRange)?.group(in: string)
    }
    
    func allGroups(in string: String) -> [RegexGroup] {
        let stringRange = NSRange(location: 0, length: string.count)
        return matches(in: string, range: stringRange).compactMap { $0.group(in: string) }
    }
    
}

let timePattern = #"((\d{2})((\d{2}))((F)(\d*))?)"#
let regex = try! NSRegularExpression(pattern: timePattern)

dump(regex.allGroups(in: "1900F-1800"))
dump(regex.firstGroup(in: "1234F3"))