From 73693b184ca950a31bcdc3577e1b5c75dbaa66ac Mon Sep 17 00:00:00 2001
From: Konstantin Kostov <konstantin@headbright.be>
Date: Thu, 23 Jun 2022 15:35:55 +0200
Subject: [PATCH] feat(counter): support += and -= operators on Counter #4

---
 Source/Proxy/Proxy+Counter.swift | 53 +++++++++++++++++++++++++++++++-
 Tests/Proxy+CounterTests.swift   | 48 +++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+), 1 deletion(-)
 create mode 100644 Tests/Proxy+CounterTests.swift

diff --git a/Source/Proxy/Proxy+Counter.swift b/Source/Proxy/Proxy+Counter.swift
index 927f1af..6f04302 100644
--- a/Source/Proxy/Proxy+Counter.swift
+++ b/Source/Proxy/Proxy+Counter.swift
@@ -20,8 +20,59 @@ public extension Proxy where Wrapped == Counter {
     /// Decrements the counter by the value you provide.
     /// - Parameter delta: The amount to decrement the counter, defaults to `1`.
     func decrement(_ delta: Int = -1) {
-       increment(delta)
+        increment(delta)
     }
+    
+    /// Subtracts the second value from the counter by performing a `decrement`.
+    ///
+    /// - Parameters:
+    ///   - lhs: A Counter
+    ///   - rhs: The value to subtract from `lhs`.
+    static func -=(lhs: Proxy, rhs: Int) {
+        lhs.decrement(-rhs)
+    }
+    
+    /// Adds the second value to the counter by performing an `increment`.
+    ///
+    /// - Parameters:
+    ///   - lhs: A Counter
+    ///   - rhs: The value to add to `lhs`.
+    static func +=(lhs: Proxy, rhs: Int) {
+        lhs.increment(rhs)
+    }
+}
 
+public extension Proxy where Wrapped == Optional<Counter> {
+    /// Increments the counter by the value you provide.
+    /// - Parameter delta: The amount to increment the counter, defaults to `1`.
+    func increment(_ delta: Int = 1) {
+        var path = self.path
+        let pathComponent = path.popLast()
+        context.increment(path: path, key: pathComponent!.key, delta: delta)
+    }
+    
+    /// Decrements the counter by the value you provide.
+    /// - Parameter delta: The amount to decrement the counter, defaults to `1`.
+    func decrement(_ delta: Int = -1) {
+        increment(delta)
+    }
+    
+    /// Subtracts the second value from the counter by performing a `decrement`.
+    ///
+    /// - Parameters:
+    ///   - lhs: A Counter
+    ///   - rhs: The value to subtract from `lhs`.
+    static func -=(lhs: Proxy, rhs: Int) {
+        lhs.decrement(-rhs)
+    }
+    
+    /// Adds the second value to the counter by performing an `increment`.
+    ///
+    /// - Parameters:
+    ///   - lhs: A Counter
+    ///   - rhs: The value to add to `lhs`.
+    static func +=(lhs: Proxy, rhs: Int) {
+        lhs.increment(rhs)
+    }
 }
 
diff --git a/Tests/Proxy+CounterTests.swift b/Tests/Proxy+CounterTests.swift
new file mode 100644
index 0000000..ea38d38
--- /dev/null
+++ b/Tests/Proxy+CounterTests.swift
@@ -0,0 +1,48 @@
+//
+//  File.swift
+//  
+//
+//  Created by Konstantin Kostov on 23/06/2022.
+//
+
+import Foundation
+import XCTest
+@testable import Automerge
+
+class ProxyCounterTests: XCTestCase {
+    func testAssignmentExpressions() {
+        struct Schema: Codable, Equatable {
+            var counter: Counter?
+            var notOptionalCounter: Counter = 3
+        }
+        
+        var doc1 = Document(Schema())
+        let _ = doc1.change {
+            $0.counter?.set(3)
+            XCTAssertEqual($0.counter?.get(), 3)
+        }
+        
+        let _ = doc1.change {
+            $0.counter -= 1
+            $0.notOptionalCounter -= 1
+            XCTAssertEqual($0.counter?.get(), 2)
+            XCTAssertEqual($0.notOptionalCounter.get(), 2)
+        }
+        
+        let _ = doc1.change {
+            $0.counter += 2
+            $0.notOptionalCounter += 2
+            XCTAssertEqual($0.counter?.get(), 4)
+            XCTAssertEqual($0.notOptionalCounter.get(), 4)
+        }
+        
+        let _ = doc1.change {
+            $0.counter += -2
+            $0.notOptionalCounter -= 2
+            XCTAssertEqual($0.counter?.get(), 2)
+            XCTAssertEqual($0.notOptionalCounter.get(), 2)
+        }
+        
+        XCTAssertEqual(doc1.content, Schema(counter: 2, notOptionalCounter: 2))
+    }
+}