An algorithm I wrote to sort a list of file paths in varying levels of directories into ascending order

String+FilePathSort.swift

extension String {

    /// Compares the current string value as a file path against a second
    /// file path string in order to determine which comes first.
    ///
    /// Rules:
    /// * Item names are only compared if they are in the same directory
    /// * Items in higher parent directories always take priority
    /// * Files prefixed with "_" are automatically downgraded (Since files prefixed like that are usually ads)
    ///
    /// - Parameter secondString: The string to compare this string against
    /// - Returns: `true` if the ordering is ascending, and `false` otherwise
    public func filePathCompare(with secondString: String) -> Bool {

        // Format the inputs to remove any possible leading slashes
        var firstFilePath = self.deletingPrefix("/")
        var secondFilePath = secondString.deletingPrefix("/")

        // If one URL has less slashes (ie, the item is in a parent directory), favour that one
        let firstFolderCount = firstFilePath.countInstances(of: "/")
        let secondFolderCount = secondFilePath.countInstances(of: "/")
        if firstFolderCount != secondFolderCount {
            return firstFolderCount < secondFolderCount
        }

        // Loop through until we go past the front of either URL
        while firstFilePath.lastPathComponent != ".." && secondFilePath.lastPathComponent != ".." {
            // Get the last component of the file path
            let firstFileName = firstFilePath.lastPathComponent
            let secondFileName = secondFilePath.lastPathComponent

            // Remove the components from the file paths
            firstFilePath = firstFilePath.deletingLastPathComponent
            secondFilePath = secondFilePath.deletingLastPathComponent

            // If the truncated file paths don't match, go up one more level until they do
            if firstFilePath.compare(secondFilePath) != .orderedSame {
                continue
            }

            // Once the truncated file URLs match, this means the items being compared
            // are both in the same directory. We can do a file name compare to determine
            // the ordering

            // Always give lower priority to files pre-fixed with '_'
            if firstFileName.hasPrefix("_") { return false }
            if secondFileName.hasPrefix("_") { return true }

            // Perform a compare on just the file names
            return firstFileName.localizedCompare(secondFileName) == .orderedAscending
        }

        // Default to ascending (But this should never be called)
        return true
    }
}