NSRegularExpression+Substituation.swift

import Foundation

extension NSRegularExpression
{
	public func substitutingMatches(in string: String, options: NSRegularExpression.MatchingOptions = [], subsituated substitution: @escaping (NSTextCheckingResult)->(String?)) -> String
	{
		let nsString = string as NSString
		let length = nsString.length
		let entireString = NSRange(location: 0, length: length)
		
		var tmpStr = ""
		var index = 0
		
		let semaphore = DispatchSemaphore(value: 0)
		let assemblyQueue = DispatchQueue(label: "Assembly Queue")
		
		DispatchQueue.global(qos: .utility).async {
			
			defer {
				assemblyQueue.async {
					semaphore.signal()
				}
			}
			
			let matches = self.matches(in: string, options: options, range: entireString)
			
			guard matches.count > 0 else
			{
				tmpStr = string
				return
			}
			
			for match in matches
			{
				assemblyQueue.async {
					let substitutedRange = match.rangeAt(match.numberOfRanges-1)
					
					// append part until match
					if substitutedRange.location > index
					{
						let substring = nsString.substring(with: NSRange(location: index, length: substitutedRange.location - index))
						tmpStr += substring
					}
				}
				
				assemblyQueue.async
				{
					let substitutedRange = match.rangeAt(match.numberOfRanges-1)
					
					if let newString = substitution(match)
					{
						tmpStr += newString
					}
					else
					{
						let substring = nsString.substring(with: NSRange(location: index, length: substitutedRange.location - index))
						tmpStr += substring
					}

					index = NSMaxRange(substitutedRange)
				}
			}
			
			// append suffix if necessary
			assemblyQueue.async {
				if index < length
				{
					let substring = nsString.substring(with: NSRange(location: index, length: length - index))
					tmpStr += substring
				}
			}
		}
		
		semaphore.wait()
		
		return tmpStr
	}
}