import Foundation
// https://gist.github.com/kristopherjohnson/543687c763cd6e524c91
/// Find first differing character between two strings
///
/// :param: s1 First String
/// :param: s2 Second String
///
/// :returns: .DifferenceAtIndex(i) or .NoDifference
public func firstDifferenceBetweenStrings(_ s1: String, _ s2: String) -> FirstDifferenceResult {
let len1 = s1.count
let len2 = s2.count
let lenMin = min(len1, len2)
for i in 0.. String {
let firstDifferenceResult = firstDifferenceBetweenStrings(s1, s2)
func diffString(at index: Int, _ s1: String, _ s2: String) -> String {
let markerArrow = "\u{2b06}" // "⬆"
let ellipsis = "\u{2026}" // "…"
/// Given a string and a range, return a string representing that substring.
///
/// If the range starts at a position other than 0, an ellipsis
/// will be included at the beginning.
///
/// If the range ends before the actual end of the string,
/// an ellipsis is added at the end.
func windowSubstring(_ s: String, _ range: NSRange) -> String {
let validRange = NSMakeRange(range.location, min(range.length, s.count - range.location))
let substring = (s as NSString).substring(with: validRange)
let prefix = range.location > 0 ? ellipsis : ""
let suffix = (s.count - range.location > range.length) ? ellipsis : ""
return "\(prefix)\(substring)\(suffix)"
}
// Show this many characters before and after the first difference
let windowLength = previewPrefixLength + 1 + previewSuffixLength
let windowIndex = max(index - previewPrefixLength, 0)
let windowRange = NSMakeRange(windowIndex, windowLength)
let sub1 = windowSubstring(s1, windowRange)
let sub2 = windowSubstring(s2, windowRange)
let markerPosition = min(previewSuffixLength, index) + (windowIndex > 0 ? 1 : 0)
let markerPrefix = String(repeating: " ", count: markerPosition)
let markerLine = "\(markerPrefix)\(markerArrow)"
return "Difference at index \(index):\n\(sub1)\n\(sub2)\n\(markerLine)"
}
switch firstDifferenceResult {
case .NoDifference: return "No difference"
case let .DifferenceAtIndex(index): return diffString(at: index, s1, s2)
}
}
/// Result type for firstDifferenceBetweenStrings()
public enum FirstDifferenceResult {
/// Strings are identical
case NoDifference
/// Strings differ at the specified index.
///
/// This could mean that characters at the specified index are different,
/// or that one string is longer than the other
case DifferenceAtIndex(Int)
}