import CommonCrypto

import Foundation

private let oauthVersion = "1.0"

private let oauthSignatureMethod = "HMAC-SHA1"

func authorizationHeader(

for method: HTTPMethod,

url: URL,

parameters: [String: Any],

consumerKey: String,

consumerSecret: String,

oauthToken: String?,

oauthTokenSecret: String?,

oauthTimestamp: String? = .none,

oauthNonce: String? = .none

) -> String {

var authorizationParameters = [String: Any]()

authorizationParameters["oauth_version"] = oauthVersion

authorizationParameters["oauth_signature_method"] = oauthSignatureMethod

authorizationParameters["oauth_consumer_key"] = consumerKey

authorizationParameters["oauth_timestamp"] = oauthTimestamp ?? String(Int(Date().timeIntervalSince1970))

authorizationParameters["oauth_nonce"] = oauthNonce ?? UUID().uuidString

if let oauthToken = oauthToken {

authorizationParameters["oauth_token"] = oauthToken

}

for (key, value) in parameters where key.hasPrefix("oauth_") {

authorizationParameters.updateValue(value, forKey: key)

}

let combinedParameters = authorizationParameters.merging(parameters) { $1 }

authorizationParameters["oauth_signature"] = oauthSignature(

for: method, url: url, parameters: combinedParameters, consumerSecret: consumerSecret,

oauthTokenSecret: oauthTokenSecret)

let authorizationParameterComponents = authorizationParameters.urlEncodedQueryString.components(

separatedBy: "&"

).sorted()

var headerComponents = [String]()

for component in authorizationParameterComponents {

let subcomponent = component.components(separatedBy: "=")

if subcomponent.count == 2 {

headerComponents.append("\(subcomponent[0])=\"\(subcomponent[1])\"")

}

}

return "OAuth " + headerComponents.joined(separator: ", ")

}

private func oauthSignature(

for method: HTTPMethod,

url: URL,

parameters: [String: Any],

consumerSecret: String,

oauthTokenSecret: String?

) -> String {

let tokenSecret = oauthTokenSecret?.urlEncodedString ?? ""

let encodedConsumerSecret = consumerSecret.urlEncodedString

let signingKey = "\(encodedConsumerSecret)&\(tokenSecret)"

let parameterComponents = parameters.urlEncodedQueryString.components(separatedBy: "&").sorted()

let parameterString = parameterComponents.joined(separator: "&")

let encodedParameterString = parameterString.urlEncodedString

let encodedURL = url.absoluteString.urlEncodedString

let signatureBaseString = "\(method.rawValue)&\(encodedURL)&\(encodedParameterString)"

let key = signingKey.data(using: .utf8)!

let msg = signatureBaseString.data(using: .utf8)!

let sha1 = msg.hmac(key: key)

return sha1.base64EncodedString(options: [])

}