//

// Transformer.swift

// JSONAPI

//

// Created by Mathew Polzin on 11/17/18.

//

/// A Transformer simply defines a static function that transforms a value.

public protocol Transformer {

/// ReversibleTransformers define a function that reverses the transform

/// operation.

public protocol ReversibleTransformer: Transformer {

/// The IdentityTransformer does not perform any transformation on a value.

public enum IdentityTransformer<T>: ReversibleTransformer {

public static func transform(_ value: T) throws -> T { return value }

public static func reverse(_ value: T) throws -> T { return value }

// MARK: - Validator

/// A Validator is a Transformer that throws an error if an invalid value

/// is passed to it but it does not change the type of the value. Any

/// Transformer will perform validation in one sense so a Validator is

/// really just semantic sugar (it can provide clarity in its use).

/// To enforce the semantics, any change of the value in your implementation

/// of `Validator.transform()` will be ignored.

public protocol Validator: ReversibleTransformer where From == To {

extension Validator {

public static func reverse(_ value: To) throws -> To {

let _ = try transform(value)

return value

}

/// Validate the given value and then return it if valid.

/// throws an erro if invalid.

/// - returns: The same value passed in, if it was valid.

public static func validate(_ value: To) throws -> To {

let _ = try transform(value)

return value

}