NSDateFormatter extension for localizing non-standard dateFormats.

DateFormatter+LocalizedFormats.swift

import Foundation

/// Removes key/value pairs from the format dictionary where another pair covers it.
///
/// The format dictionary should have locale identifiers as the keys, where language, script and country codes are separated by underscores (_), and the date format as the value.
///
/// Example: Given the following dictionary: ["en": "MMM d", "en_US": "MMM d"], "en_US" is unnessary because "en" (the language without the country) has the same format.
///
/// - parameter formats: The format dictionary to be reduced.
/// - parameter defaultFormat: A format that can be removed from the dictionary because it is the default. Defaults to `nil`.
/// - returns: The reduced format dictionary.
private func reducedFormatsFromFormats(formats: [String:String], defaultFormat: String? = nil) -> [String:String] {
    var final = [String:String]()
    for (key, format) in formats {
        guard format != defaultFormat else { continue }
        let components = key.components(separatedBy: "_")
        if components.count == 3 {
            let superKey = "\(components[0])_\(components[1])"
            if format != formats[superKey] {
                final[key] = format
            }
        } else if components.count == 2 {
            let superKey = components[0]
            if format != formats[superKey] {
                final[key] = format
            }
        } else {
            final[key] = format
        }
    }
    return final
}

/// Prints Swift code for the dictionary.
///
/// - parameter formats: The dictionary.
private func printFormats(formats: [String:String]) {
    print("let formats = [")
    for (key, format) in formats.sorted(by: { $0.1 < $1.1 }) {
        print("\t\"\(key)\": \"\(format)\",")
    }
    print("]")
}

private var cachedFormatters = [String:DateFormatter]()

extension DateFormatter {
    /// Creates an `DateFormatter` using a format from *formats* that coincides with *locale*.
    ///
    /// - Parameters:
    ///   - formats: A dictionary of [<locale>:<format>].
    ///   - defaultFormat: The default format to use if one isn't found in *formats*.
    ///   - locale: The locale with which to format the date.
    ///   - cacheKey: A key to use to cache the formatter. Should be unique for the given formats.
    /// - Returns: A date formatter configured to the locale and appropriate format.
    class func from(formats: [String:String], defaultFormat: String, locale: Locale = Locale.current, cacheKey: String) -> DateFormatter {
        // Get the locale ID and check the cached formatters
        let localeCacheKey = locale.identifier + "|" + cacheKey
        if let formatter = cachedFormatters[localeCacheKey] {
            return formatter
        }
        
        // Get the language, script, and country codes of the locale
        let language = locale.languageCode!
        let script = locale.scriptCode
        let region = locale.regionCode
        
        // Create an array of possible locale identifiers in the order of preference
        var codes = [String]()
        if let script = script, let country = region {
            codes.append("\(language)_\(script)_\(country)")
        }
        if let region = region {
            codes.append("\(language)_\(region)")
        }
        if let script = script {
            codes.append("\(language)_\(script)")
        }
        codes.append(language)
        
        // Get a format from the dictionary
        var dateFormat = defaultFormat
        for code in codes {
            if let format = formats[code] {
                dateFormat = format
                break
            }
        }
        
        // Create a formatter
        let formatter = DateFormatter()
        formatter.locale = locale
        formatter.dateFormat = dateFormat
        cachedFormatters[localeCacheKey] = formatter
        return formatter
    }
    
    /// Returns an `DateFormatter` that shows the date as a short month and the day, e.g. Apr 2.
    ///
    /// This method will cache the date formatter so that calling it more than once will return the same one.
    /// Changes made to it will affect later calls.
    ///
    /// - parameter locale: The locale the date should be formatted in. Defaults to the current locale.
    /// - returns: The date formatter.
    class func forShortMonthAndDate(using locale: Locale = Locale.current) -> DateFormatter {
        let shortMonthAndDateFormats = [
            "af": "dd MMM", "ak": "MMM d", "as": "MMM d", "bo": "MMMཚེས་d", "br": "MMM d", "brx": "MMM d", "bs": "dd. MMM", "chr": "MMM d", "ckb": "MMM d",
            "cs": "d. MMM", "da": "d. MMM", "de": "d. MMM", "dsb": "d. MMM", "dz": "ཟླ་MMM ཚེས་dd", "ee": "MMM d", "en": "MMM d", "en_150": "dd MMM", "en_AD": "dd MMM",
            "en_AL": "dd MMM", "en_AT": "dd MMM", "en_BA": "dd MMM", "en_BE": "dd MMM", "en_BW": "dd MMM", "en_BZ": "dd MMM", "en_CH": "dd MMM", "en_CY": "dd MMM",
            "en_CZ": "dd MMM", "en_DE": "dd MMM", "en_DK": "dd MMM", "en_EE": "dd MMM", "en_ES": "dd MMM", "en_FI": "dd MMM", "en_FR": "dd MMM", "en_GR": "dd MMM",
            "en_HR": "dd MMM", "en_HU": "dd MMM", "en_IS": "dd MMM", "en_IT": "dd MMM", "en_LT": "dd MMM", "en_LU": "dd MMM", "en_LV": "dd MMM", "en_ME": "dd MMM",
            "en_MT": "dd MMM", "en_NL": "dd MMM", "en_NO": "dd MMM", "en_PL": "dd MMM", "en_PT": "dd MMM", "en_RO": "dd MMM", "en_RU": "dd MMM", "en_SE": "dd MMM",
            "en_SI": "dd MMM", "en_SK": "dd MMM", "en_TR": "dd MMM", "en_ZA": "dd MMM", "en_ZW": "dd MMM", "eo": "MMM-dd", "es_CL": "dd-MM", "es_CO": "d/MM",
            "es_GT": "d/MM", "es_MX": "dd/MM", "es_PA": "MM/dd", "es_PR": "MM/dd", "es_US": "MMM d", "et": "d. MMM", "eu": "MMM d", "fi": "d. MMM", "fil": "MMM d",
            "fo": "d. MMM", "fur": "dd/MM", "gsw": "dd.MM", "gv": "MMM d", "he": "d בMMM", "hi": "dd/MM", "hr": "d. MMM", "hsb": "d. MMM", "hu": "MMM d.",
            "hy": "dd MMM", "ii": "MMM d", "is": "d. MMM", "it": "dd MMM", "iu": "MMM d", "ja": "M月d日", "jgo": "MMM d", "kl": "MMM d", "kn": "MMM d",
            "ko": "M월 d일", "kok": "MMM d", "ks": "MMM d", "ksh": "d. MMM", "kw": "MMM d", "ky": "MMM d", "lb": "d. MMM", "lkt": "MMM d", "lt": "MM-dd",
            "lv": "d. MMM", "mgo": "MMM d", "mk": "dd MMM", "ml": "MMM d", "mn": "MMM d", "mt": "dd MMM", "nb": "d. MMM", "ne": "MMM d", "nn": "d. MMM",
            "om": "dd MMM", "os": "dd MMM", "pt": "dd/MM", "qu": "MMM d", "rm": "dd-MM", "rw": "MMM d", "sah": "MMM d", "se": "MMM d", "seh": "dd/MM",
            "si": "MMM d", "sk": "d. MMM", "sl": "d. MMM", "smn": "MMM d", "so": "dd-MMM", "sr": "dd. MMM", "tg": "MMM d", "ti": "dd MMM", "ug": "MMM d",
            "uz": "MMM d", "vi": "dd-MM", "wae": "d. MMM", "zh": "M月d日", "zu": "MMM d",
            ]
        return from(formats: shortMonthAndDateFormats, defaultFormat: "d MMM", locale: locale, cacheKey: "shortMonthAndDateFormat")
    }
}