Code koan: Normalizing URLs in Swift 4

URLNormalization.swift

// https://en.wikipedia.org/wiki/URL_normalization

import Foundation

extension URLComponents {
    typealias NormalizationRule = (_ components: URLComponents) -> URLComponents

    func normalize(with rule: NormalizationRule) -> URLComponents {
        return rule(self)
    }
}

let identity: URLComponents.NormalizationRule = { $0 } // URLComponentsNormalizationRuleIdentity

let declutterUTM: URLComponents.NormalizationRule = { components in
    var normalized = components
    normalized.queryItems = components.queryItems?.filter { !$0.name.starts(with: "utm_") }
    return normalized
}

let removeEmptyQuery: URLComponents.NormalizationRule = { components in
    if let query = components.query, query.isEmpty {
        var normalized = components
        normalized.query = nil
        return normalized
    } else {
        return components
    }
}

guard let sampleComponents = URLComponents(string: "https://github.com/hobby-kube/guide?utm_campaign=explore-email&utm_medium=email&utm_source=newsletter&utm_term=daily") else {
    fatalError("Couldn't create sample URL components")
}

var components = sampleComponents

components = components.normalize(with: identity)
print(components.string)
// Optional("https://github.com/hobby-kube/guide?utm_campaign=explore-email&utm_medium=email&utm_source=newsletter&utm_term=daily")

components = components.normalize(with: declutterUTM)
print(components.string)
// Optional("https://github.com/hobby-kube/guide?")

components = components.normalize(with: removeEmptyQuery)
print(components.string)
// Optional("https://github.com/hobby-kube/guide")