@tags

tags.swift

import UIKit
import PlaygroundSupport

extension String {
    subscript(range: NSRange) -> String? {
        guard range.location + range.length <= self.characters.count else {
            return nil
        }

        let r = index(startIndex, offsetBy: range.location)..<index(startIndex, offsetBy: range.location + range.length)

        return self[r]
    }

    subscript(range: CountableRange<Int>) -> String? {
        guard range.endIndex <= self.characters.count else {
            return nil
        }

        let r = index(startIndex, offsetBy: range.startIndex)..<index(startIndex, offsetBy: range.endIndex)

        return self[r]
    }
}

class Tagger: NSObject, UITextFieldDelegate {
    var tagStart: Int? = nil
    var tagRange: CountableRange<Int>? = nil

    func textField(_ textField: UITextField,
                   shouldChangeCharactersIn range: NSRange,
                   replacementString string: String) -> Bool {
        if textField.text?.characters.count == 1 && range.length == 1 {
            tagCancelled()
        }
        else if tagRange != nil {
            if string == " " {
                tagCancelled()
            }
            else if range.location == tagStart {
                tagCancelled()
            }
            else {
                tagExtended(to: range.location - range.length)
            }
        }
        else if string == "@" {
            if range.location == 0 {
                tagStarted(at: range.location)
            }
            else if let text = textField.text, text.characters.count > 0 {
                let sub = text[(range.location - 1)..<range.location]

                print("Previous string: \(String(describing: sub))")

                if sub == " " {
                    tagStarted(at: range.location)
                }
            }
        }

        print("text: \(string), range: \(NSStringFromRange(range))")

        return true
    }

    func tagStarted(at location: Int) {
        tagStart = location
        tagRange = location..<(location + 1)

        print("Started tag at: \(location), range: \(String(describing: tagRange))")
    }

    func tagExtended(to location: Int) {
        guard let start = tagStart else {
            fatalError("This really shouldn't happen")
        }

        tagRange = start..<(location + 1)

        print("Continued tag at: \(location), range: \(String(describing: tagRange))")
    }

    func tagCancelled() {
        tagStart = nil
        tagRange = nil

        print("Tag cancelled")
    }
}

class TextFieldTarget: NSObject {
    func setTargetForTextField(tf: UITextField) {
        tf.addTarget(self, action: #selector(textFieldChanged(_:)), for: .editingChanged)
    }

    func textFieldChanged(_ sender: UITextField) {
        if let range = t.tagRange, let text = sender.text {
            print("text: \(text[range])")
        }
    }
}

let target = TextFieldTarget()
let t = Tagger()
let tf = UITextField(frame: CGRect(x: 0, y: 100, width: 200, height: 30))

tf.backgroundColor = .gray
tf.textColor = .white
tf.delegate = t

target.setTargetForTextField(tf: tf)

PlaygroundPage.current.liveView = tf