From 6330843a42081db94449790d3786dabe811a30a3 Mon Sep 17 00:00:00 2001
From: Aleksandr Gusev <sanekgusev@gmail.com>
Date: Thu, 7 Dec 2017 17:21:29 -0500
Subject: [PATCH] Support nested batches (without combining their constraints)

---
 AnchorageTests/AnchorageTests.swift | 45 +++++++++++++++++++++++++++++
 Source/Anchorage.swift              | 10 ++-----
 Source/Internal.swift               |  8 ++---
 3 files changed, 52 insertions(+), 11 deletions(-)

diff --git a/AnchorageTests/AnchorageTests.swift b/AnchorageTests/AnchorageTests.swift
index fd47497..5781ca3 100644
--- a/AnchorageTests/AnchorageTests.swift
+++ b/AnchorageTests/AnchorageTests.swift
@@ -588,6 +588,51 @@ class AnchorageTests: XCTestCase {
         XCTAssertEqual(height.firstAttribute, .height)
         XCTAssertEqual(height.secondAttribute, .height)
     }
+    
+    func testNestedBatchConstraints() {
+        var nestedConstraints: [NSLayoutConstraint] = []
+        let constraints = Anchorage.batch {
+            view1.widthAnchor == view2.widthAnchor
+            nestedConstraints = Anchorage.batch(active: false) {
+                view1.heightAnchor == view2.heightAnchor / 2 ~ .low
+            }
+            view1.leadingAnchor == view2.leadingAnchor
+        }
+        
+        let width = constraints[0]
+        let leading = constraints[1]
+        let height = nestedConstraints[0]
+        
+        assertIdentical(width.firstItem, view1)
+        assertIdentical(width.secondItem, view2)
+        XCTAssertEqual(width.constant, 0, accuracy: cgEpsilon)
+        XCTAssertEqual(width.multiplier, 1, accuracy: cgEpsilon)
+        XCTAssertEqual(width.priority.rawValue, TestPriorityRequired.rawValue, accuracy: fEpsilon)
+        XCTAssertTrue(width.isActive)
+        XCTAssertEqual(width.relation, .equal)
+        XCTAssertEqual(width.firstAttribute, .width)
+        XCTAssertEqual(width.secondAttribute, .width)
+        
+        assertIdentical(height.firstItem, view1)
+        assertIdentical(height.secondItem, view2)
+        XCTAssertEqual(height.constant, 0, accuracy: cgEpsilon)
+        XCTAssertEqual(height.multiplier, 0.5, accuracy: cgEpsilon)
+        XCTAssertEqual(height.priority.rawValue, TestPriorityLow.rawValue, accuracy: fEpsilon)
+        XCTAssertFalse(height.isActive)
+        XCTAssertEqual(height.relation, .equal)
+        XCTAssertEqual(height.firstAttribute, .height)
+        XCTAssertEqual(height.secondAttribute, .height)
+        
+        assertIdentical(leading.firstItem, view1)
+        assertIdentical(leading.secondItem, view2)
+        XCTAssertEqual(leading.constant, 0, accuracy: cgEpsilon)
+        XCTAssertEqual(leading.multiplier, 1, accuracy: cgEpsilon)
+        XCTAssertEqual(leading.priority.rawValue, TestPriorityRequired.rawValue, accuracy: fEpsilon)
+        XCTAssertTrue(leading.isActive)
+        XCTAssertEqual(leading.relation, .equal)
+        XCTAssertEqual(leading.firstAttribute, .leading)
+        XCTAssertEqual(leading.secondAttribute, .leading)
+    }
 
 }
 
diff --git a/Source/Anchorage.swift b/Source/Anchorage.swift
index 80a47b3..afa1358 100644
--- a/Source/Anchorage.swift
+++ b/Source/Anchorage.swift
@@ -397,7 +397,6 @@ infix operator ~: PriorityPrecedence
 
 /// Any Anchorage constraints created inside the passed closure are returned in the array.
 ///
-/// - Precondition: Can't be called inside or simultaneously with another batch. Batches cannot be nested.
 /// - Parameter closure: A closure that runs some Anchorage expressions.
 /// - Returns: An array of new, active `NSLayoutConstraint`s.
 @discardableResult public func batch(_ closure: () -> Void) -> [NSLayoutConstraint] {
@@ -406,19 +405,16 @@ infix operator ~: PriorityPrecedence
 
 /// Any Anchorage constraints created inside the passed closure are returned in the array.
 ///
-/// - Precondition: Can't be called inside or simultaneously with another batch. Batches cannot be nested.
 /// - Parameter active: Whether the created constraints should be active when they are returned.
 /// - Parameter closure: A closure that runs some Anchorage expressions.
 /// - Returns: An array of new `NSLayoutConstraint`s.
 public func batch(active: Bool, closure: () -> Void) -> [NSLayoutConstraint] {
-    precondition(currentBatch == nil)
+    let batch = ConstraintBatch()
+    batches.append(batch)
     defer {
-        currentBatch = nil
+        batches.removeLast()
     }
 
-    let batch = ConstraintBatch()
-    currentBatch = batch
-
     closure()
 
     if active {
diff --git a/Source/Internal.swift b/Source/Internal.swift
index 0a9ab4f..fc222a2 100644
--- a/Source/Internal.swift
+++ b/Source/Internal.swift
@@ -312,7 +312,7 @@ internal struct ConstraintBuilder {
 
 // MARK: - Batching
 
-internal var currentBatch: ConstraintBatch?
+internal var batches: [ConstraintBatch] = []
 
 internal class ConstraintBatch {
 
@@ -333,7 +333,7 @@ internal class ConstraintBatch {
 ///
 /// - Parameter closure: The work to perform inside of a batch
 internal func performInBatch(closure: () -> Void) {
-    if currentBatch == nil {
+    if batches.isEmpty {
         batch(closure)
     }
     else {
@@ -351,8 +351,8 @@ internal func finalize(constraint: NSLayoutConstraint, withPriority priority: Pr
 
     constraint.priority = priority.value
 
-    if let currentBatch = currentBatch {
-        currentBatch.add(constraint: constraint)
+    if let lastBatch = batches.last {
+        lastBatch.add(constraint: constraint)
     }
     else {
         constraint.isActive = true