loopfollow/LoopFollow/Helpers/DictionaryKeyPath.swift

// For details, see
// http://stackoverflow.com/questions/40261857/remove-nested-key-from-dictionary
import Foundation

extension Dictionary {
    subscript(keyPath keyPath: String) -> Any? {
        get {
            guard let keyPath = Dictionary.keyPathKeys(forKeyPath: keyPath)
                else { return nil }
            return getValue(forKeyPath: keyPath)
        }
        set {
            guard let keyPath = Dictionary.keyPathKeys(forKeyPath: keyPath),
                let newValue = newValue else { return }
            self.setValue(newValue, forKeyPath: keyPath)
        }
    }

    static private func keyPathKeys(forKeyPath: String) -> [Key]? {
        let keys = forKeyPath.components(separatedBy: ".")
            .reversed().flatMap({ $0 as? Key })
        return keys.isEmpty ? nil : keys
    }

    // recursively (attempt to) access queried subdictionaries
    // (keyPath will never be empty here; the explicit unwrapping is safe)
    private func getValue(forKeyPath keyPath: [Key]) -> Any? {
        guard let value = self[keyPath.last!] else { return nil }
        return keyPath.count == 1 ? value : (value as? [Key: Any])
                .flatMap { $0.getValue(forKeyPath: Array(keyPath.dropLast())) }
    }

    // recursively (attempt to) access the queried subdictionaries to
    // finally replace the "inner value", given that the key path is valid
    private mutating func setValue(_ value: Any, forKeyPath keyPath: [Key]) {
        guard self[keyPath.last!] != nil else { return }
        if keyPath.count == 1 {
            (value as? Value).map { self[keyPath.last!] = $0 }
        }
        else if var subDict = self[keyPath.last!] as? [Key: Value] {
            subDict.setValue(value, forKeyPath: Array(keyPath.dropLast()))
            (subDict as? Value).map { self[keyPath.last!] = $0 }
        }
    }
}