NS-free regex pattern-finding implementation

Sources/Lingo/StringInterpolator.swift

@@ -2,21 +2,18 @@ import Foundation
 
 final class StringInterpolator {
 
-    private static let regularExpression = try! NSRegularExpression(pattern: "\\%\\{[^\\}]*\\}", options: []) // swiftlint:disable:this force_try
-    
+    private static let regexPattern = "\\%\\{[^\\}]*\\}"
+
     /// Input string is in format: "You have %{count} unread messages".
     /// The function finds all placeholders and replaces them with a value specified in interpolations dictionary
     func interpolate(_ rawString: String, with interpolations: [String: Any]) -> String {
-        var result = rawString
-        let matches = StringInterpolator.regularExpression.matches(in: rawString, options: [], range: NSRange.init(location: 0, length: rawString.count))
 
-        for match in matches {
-            let range: NSRange = match.range
+        let ranges: [Range<String.Index>] = findRanges(in: rawString, startingFrom: rawString.startIndex)
+
+        return ranges.reduce(into: rawString) { result, range in
 
             // Extract whole capture group string. Will contain string like: "%{count}"
-            let startIndex = rawString.index(rawString.startIndex, offsetBy: range.location)
-            let endIndex = rawString.index(startIndex, offsetBy: range.length)
-            let matchedString = String(rawString[startIndex..<endIndex])
+            let matchedString = String(rawString[range.lowerBound..<range.upperBound])
 
             // Extract the key from `matchedString`. Will contain string like: "count"
             let keyStartIndex = matchedString.index(matchedString.startIndex, offsetBy: 2)
@@ -26,9 +23,22 @@ final class StringInterpolator {
             if let interpolation = interpolations[key] {
                 result = result.replacingOccurrences(of: matchedString, with: "\(interpolation)")
             }
+
+        }
+    }
+
+    func findRanges(in text: String, startingFrom start: String.Index) -> [Range<String.Index>] {
+        let end = text.endIndex
+        guard let range = text.range(of: Self.regexPattern, options: .regularExpression,
+                                     range: start..<end) else {
+            return ([])
         }
-
-        return result
+        let cursor = range.upperBound
+
+        let recursiveResult = self.findRanges(in: text, startingFrom: cursor)
+
+        return ([range] + recursiveResult)
+
     }
 
 }