JSONAPI/Sources/JSONAPI/Meta/Links.swift

//
//  Links.swift
//  JSONAPI
//
//  Created by Mathew Polzin on 11/24/18.
//

/// A Links structure should contain nothing but JSONAPI.Link properties.
public protocol Links: Codable, Equatable {}

/// Use NoLinks where no links should belong to a JSON API component
public struct NoLinks: Links, CustomStringConvertible {
	public static var none: NoLinks { return NoLinks() }
	public init() {}

	public var description: String { return "No Links" }
}

public protocol JSONAPIURL: Codable, Equatable {}

public struct Link<URL: JSONAPI.JSONAPIURL, Meta: JSONAPI.Meta>: Equatable, Codable {
	public let url: URL
	public let meta: Meta

	public init(url: URL, meta: Meta) {
		self.url = url
		self.meta = meta
	}
}

extension Link where Meta == NoMetadata {
	public init(url: URL) {
		self.init(url: url, meta: .none)
	}
}

public extension Link {
	private enum CodingKeys: String, CodingKey {
		case href
		case meta
	}

	init(from decoder: Decoder) throws {
		guard Meta.self == NoMetadata.self,
			let noMeta = NoMetadata() as? Meta else {
				let container = try decoder.container(keyedBy: CodingKeys.self)
				meta = try container.decode(Meta.self, forKey: .meta)
				url = try container.decode(URL.self, forKey: .href)
				return
		}
		let container = try decoder.singleValueContainer()
		url = try container.decode(URL.self)
		meta = noMeta
	}

	func encode(to encoder: Encoder) throws {
		guard Meta.self == NoMetadata.self else {
			var container = encoder.container(keyedBy: CodingKeys.self)
			try container.encode(url, forKey: .href)
			try container.encode(meta, forKey: .meta)
			return
		}
		var container = encoder.singleValueContainer()

		try container.encode(url)
	}
}