Twitter text counter 280 characters

TwitterText.swift

import Foundation

struct WeightRange {
    let range: ClosedRange<UInt32>
    let weight: Int
}

struct TwitterText {
    static func lengthOf(tweet: String) -> Int {
        let defaultWeight = 200
        let scale = 100
        let ranges = [
            WeightRange(range: 0...4351, weight: 100),
            WeightRange(range: 8192...8205, weight: 100),
            WeightRange(range: 8208...8223, weight: 100),
            WeightRange(range: 8242...8247, weight: 100)
        ]

        let (cleanText, urlLength) = cleanAndCountURLs(text: tweet)
        var weightedLength = urlLength * scale

        for char in cleanText.unicodeScalars {
            var weight = defaultWeight
            for item in ranges where item.range ~= char.value {
                weight = item.weight
                continue
            }
            weightedLength += weight
        }
        weightedLength /= scale
        return weightedLength
    }

    private static func cleanAndCountURLs(text: String) -> (String, Int) {
        var output = text
        var lenght = 0
        let detector = try! NSDataDetector(types: NSTextCheckingResult.CheckingType.link.rawValue)
        let matches = detector.matches(in: text, options: [], range: NSRange(location: 0, length: text.utf16.count))

        matches.forEach {
            output = (text as NSString).replacingCharacters(in: $0.range, with: "")
            lenght += 23
        }
        return (output, lenght)
    }
}

Sample:

var str = "日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本語日本 https://google.com"

TwitterText.lengthOf(tweet: str) // 280

@hebertialmeida this was super helpful thanks a lot. There is one tiny issue though, NSDataDetector fails to handle some short URLs for example url like es.pn returns a length of 5 where as the twitter app correctly calculates it as 23. I have faced this issue and I am not sure how to go about solving this.

I see this note in the Objective C library for URL-

IFUnicodeURL is a category for NSURL which will allow it to support Internationalized domain names in URLs.

This uses code from IDN SDK from Verisign, Inc. The entire IDN SDK source package is included in IDNSDK-1.1.0.zip. I have pulled out and slightly modified (to avoid compiler and analyzer warnings) the files and headers needed so that building this in XCode is as easy as adding the IFUnicodeURL folder to your project.

@annjaun I think any URLs on twitter should count as 23, but yeah, detecting this kind of URL will probably require a custom regex implementation if it is not handled by NSDataDetector .

Twitter also count es.pn as 23: