Add custom encoding and decoding

Author: florianpircher

Sources/LightTableDelta/Delta.swift

@@ -23,6 +23,11 @@ public enum Delta<Element> {
 	public typealias Element = Element
 	public typealias Side = DeltaSide
 
+	enum CodingKeys: String, CodingKey {
+		case source = "A"
+		case target = "B"
+	}
+	
 	/// A source element.
 	///
 	/// Conceptually, this is a value that was deleted and thus no target element is available.
@@ -238,8 +243,47 @@ public enum Delta<Element> {
 }
 
 extension Delta: Equatable where Element: Equatable {}
+
 extension Delta: Hashable where Element: Hashable {}
-extension Delta: Encodable where Element: Encodable {}
-extension Delta: Decodable where Element: Decodable {}
+
+extension Delta: Encodable where Element: Encodable {
+	public func encode(to encoder: any Encoder) throws {
+		switch self {
+		case .deleted(let source):
+			var container = encoder.container(keyedBy: CodingKeys.self)
+			try container.encode(source, forKey: .source)
+		case .added(let target):
+			var container = encoder.container(keyedBy: CodingKeys.self)
+			try container.encode(target, forKey: .target)
+		case .modified(let source, let target):
+			var container = encoder.container(keyedBy: CodingKeys.self)
+			try container.encode(source, forKey: .source)
+			try container.encode(target, forKey: .target)
+		}
+	}
+}
+
+extension Delta: Decodable where Element: Decodable {
+	public init(from decoder: any Decoder) throws {
+		let container = try decoder.container(keyedBy: CodingKeys.self)
+		let source = try container.decodeIfPresent(Element.self, forKey: .source)
+		let target = try container.decodeIfPresent(Element.self, forKey: .target)
+		
+		if let source, let target {
+			self = .modified(source: source, target: target)
+		}
+		else if let source {
+			self = .deleted(source: source)
+		}
+		else if let target {
+			self = .added(target: target)
+		}
+		else {
+			throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "No source or target value."))
+		}
+	}
+}
+
 extension Delta: Sendable where Element: Sendable {}
+
 extension Delta: BitwiseCopyable where Element: BitwiseCopyable {}

Tests/LightTableDeltaTests/LightTableDeltaTests.swift

@@ -1 +1,39 @@
+import Testing
+import Foundation
+import LightTableDelta
 
+@Test func encoding() async throws {
+	let encoder = JSONEncoder()
+	encoder.outputFormatting = .sortedKeys
+	
+	let jsonDataDeleted = try encoder.encode(Delta.deleted(source: 3))
+	let jsonDeleted = String(decoding: jsonDataDeleted, as: UTF8.self)
+	#expect(jsonDeleted == #"{"A":3}"#)
+	
+	let jsonDataAdded = try encoder.encode(Delta.added(target: 5))
+	let jsonAdded = String(decoding: jsonDataAdded, as: UTF8.self)
+	#expect(jsonAdded == #"{"B":5}"#)
+	
+	let jsonDataModified = try encoder.encode(Delta.modified(source: 3, target: 5))
+	let jsonModified = String(decoding: jsonDataModified, as: UTF8.self)
+	#expect(jsonModified == #"{"A":3,"B":5}"#)
+}
+
+@Test func decoding() async throws {
+	let decoder = JSONDecoder()
+	
+	let jsonDataDeleted = Data(#"{"A":3}"#.utf8)
+	let deltaDeleted = try decoder.decode(Delta<Int>.self, from: jsonDataDeleted)
+	#expect(deltaDeleted == .deleted(source: 3))
+	
+	let jsonDataAdded = Data( #"{"B":5}"#.utf8)
+	let deltaAdded = try decoder.decode(Delta<Int>.self, from: jsonDataAdded)
+	#expect(deltaAdded == .added(target: 5))
+	
+	let jsonDataModified =  Data(#"{"A":3,"B":5}"#.utf8)
+	let deltaModified = try decoder.decode(Delta<Int>.self, from: jsonDataModified)
+	#expect(deltaModified == .modified(source: 3, target: 5))
+	
+	let jsonDataEmpty =  Data("{}".utf8)
+	#expect(throws: DecodingError.self, performing: { try decoder.decode(Delta<Int>.self, from: jsonDataEmpty) })
+}