Add Links and tests

Sources/JSONAPI/Meta/Links.swift

@@ -0,0 +1,51 @@
+//
+//  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 {}
+
+public protocol URL: Codable, Equatable {}
+
+public struct Link<URL: JSONAPI.URL, Meta: JSONAPI.Meta>: Equatable, Codable {
+	public let url: URL
+	public let meta: Meta
+}
+
+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)
+	}
+}

Sources/JSONAPI/Meta/Meta.swift

@@ -15,6 +15,10 @@
 public protocol Meta: Codable, Equatable {
 }
 
+// We make Optional a Meta if it wraps a Meta so that Metadata can be specified as
+// nullable.
+extension Optional: Meta where Wrapped: Meta {}
+
 public struct NoMetadata: Meta {
 	public static var none: NoMetadata { return NoMetadata() }
 

Tests/JSONAPITests/Links/LinksTests.swift

@@ -0,0 +1,70 @@
+//
+//  LinksTests.swift
+//  JSONAPITests
+//
+//  Created by Mathew Polzin on 11/24/18.
+//
+
+import XCTest
+import JSONAPI
+
+class LinksTests: XCTestCase {
+	func test_linkWithNoMeta() {
+		let links = decoded(type: LinksTests.Links.self, data: link_without_meta)
+
+		XCTAssertEqual(links.link.url, "https://website.com/path/file")
+		XCTAssertEqual(links.link.meta, NoMetadata())
+	}
+
+	func test_linkWithNoMeta_encode() {
+		test_DecodeEncodeEquality(type: LinksTests.Links.self, data: link_without_meta)
+	}
+
+	func test_linkWithNullMetadata() {
+		let link = decoded(type: Link<LinksTests.URL, Metadata?>.self, data: link_with_null_meta)
+
+		XCTAssertEqual(link.url, "https://website.com/path/file")
+		XCTAssertNil(link.meta)
+	}
+
+	func test_linkWithNullMetadata_encode() {
+		test_DecodeEncodeEquality(type: Link<LinksTests.URL, Metadata?>.self, data: link_with_null_meta)
+	}
+
+	func test_linkWithMetadata() {
+		let link = decoded(type: Link<LinksTests.URL, Metadata?>.self, data: link_with_metadata)
+
+		XCTAssertEqual(link.url, "https://website.com/path/file")
+		XCTAssertEqual(link.meta, Metadata(hello: "world"))
+
+		let link2 = decoded(type: Link<LinksTests.URL, Metadata>.self, data: link_with_metadata)
+
+		XCTAssertEqual(link2.url, "https://website.com/path/file")
+		XCTAssertEqual(link2.meta, Metadata(hello: "world"))
+	}
+
+	func test_linkWithMetadata_encode() {
+		test_DecodeEncodeEquality(type: Link<LinksTests.URL, Metadata?>.self, data: link_with_metadata)
+
+		test_DecodeEncodeEquality(type: Link<LinksTests.URL, Metadata>.self, data: link_with_metadata)
+	}
+
+	func test_linkFailsIfMetaNotFound() {
+		XCTAssertThrowsError(try JSONDecoder().decode(Link<LinksTests.URL, Metadata>.self, from: link_with_null_meta))
+	}
+}
+
+// MARK: - Test types
+extension LinksTests {
+	typealias URL = String
+
+	struct Links: JSONAPI.Links {
+		let link: Link<LinksTests.URL, NoMetadata>
+	}
+
+	struct Metadata: JSONAPI.Meta {
+		let hello: String
+	}
+}
+
+extension String: JSONAPI.URL {}

Tests/JSONAPITests/Links/stub/LinkStubs.swift

@@ -0,0 +1,28 @@
+//
+//  LinkStubs.swift
+//  JSONAPITests
+//
+//  Created by Mathew Polzin on 11/24/18.
+//
+
+let link_without_meta = """
+{
+	"link": "https://website.com/path/file"
+}
+""".data(using: .utf8)!
+
+let link_with_null_meta = """
+{
+	"href": "https://website.com/path/file",
+	"meta": null
+}
+""".data(using: .utf8)!
+
+let link_with_metadata = """
+{
+	"href": "https://website.com/path/file",
+	"meta": {
+		"hello": "world"
+	}
+}
+""".data(using: .utf8)!

Tests/JSONAPITests/XCTestManifests.swift

@@ -100,6 +100,18 @@ extension IncludedTests {
     ]
 }
 
+extension LinksTests {
+    static let __allTests = [
+        ("test_linkFailsIfMetaNotFound", test_linkFailsIfMetaNotFound),
+        ("test_linkWithMetadata", test_linkWithMetadata),
+        ("test_linkWithMetadata_encode", test_linkWithMetadata_encode),
+        ("test_linkWithNoMeta", test_linkWithNoMeta),
+        ("test_linkWithNoMeta_encode", test_linkWithNoMeta_encode),
+        ("test_linkWithNullMetadata", test_linkWithNullMetadata),
+        ("test_linkWithNullMetadata_encode", test_linkWithNullMetadata_encode),
+    ]
+}
+
 extension PolyTests {
     static let __allTests = [
         ("test_init_Poly0", test_init_Poly0),
@@ -156,6 +168,7 @@ public func __allTests() -> [XCTestCaseEntry] {
         testCase(DocumentTests.__allTests),
         testCase(EntityTests.__allTests),
         testCase(IncludedTests.__allTests),
+        testCase(LinksTests.__allTests),
         testCase(PolyTests.__allTests),
         testCase(RelationshipTests.__allTests),
         testCase(ResourceBodyTests.__allTests),