From 3951b203c8a316ca6bc5f0b46c8aea4e3bd7c1f5 Mon Sep 17 00:00:00 2001
From: Fabian Guerra <fabian.guerra@mapbox.com>
Date: Tue, 17 Apr 2018 15:57:09 -0400
Subject: [ios, macos] Add atan NSExpresssion operator.

---
 platform/darwin/src/NSExpression+MGLAdditions.mm | 14 ++++++++++++--
 platform/darwin/test/MGLExpressionTests.mm       |  8 ++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index f03980f09b..d23da18597 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -70,6 +70,7 @@ const MGLExpressionInterpolationMode MGLExpressionInterpolationModeCubicBezier =
     INSTALL_METHOD(mgl_does:have:);
     INSTALL_METHOD(mgl_acos:);
     INSTALL_METHOD(mgl_asin:);
+    INSTALL_METHOD(mgl_atan:);
     
     // Install functions that resemble control structures, taking arbitrary
     // numbers of arguments. Vararg aftermarket functions need to be declared
@@ -100,19 +101,26 @@ const MGLExpressionInterpolationMode MGLExpressionInterpolationModeCubicBezier =
 }
 
 /**
-  Computes the principal value of the arc cosine.
+  Computes the principal value of the inverse cosine.
  */
 - (NSNumber *)mgl_acos:(NSNumber *)number {
     return @(acos(number.doubleValue));
 }
 
 /**
- Computes the principal value of the arc sine.
+ Computes the principal value of the inverse sine.
  */
 - (NSNumber *)mgl_asin:(NSNumber *)number {
     return @(asin(number.doubleValue));
 }
 
+/**
+ Computes the principal value of the inverse tangent.
+ */
+- (NSNumber *)mgl_atan:(NSNumber *)number {
+    return @(atan(number.doubleValue));
+}
+
 /**
  A placeholder for a method that evaluates an interpolation expression.
  */
@@ -693,6 +701,7 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             @"round": @"mgl_round:",
             @"acos" : @"mgl_acos:",
             @"asin" : @"mgl_asin:",
+            @"atan" : @"mgl_atan:",
             @"floor": @"floor:",
             @"ceil": @"ceiling:",
             @"^": @"raise:toPower:",
@@ -937,6 +946,7 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             @"mgl_round:": @"round",
             @"mgl_acos:" : @"acos",
             @"mgl_asin:" : @"asin",
+            @"mgl_atan:" : @"atan",
             // Vararg aftermarket expressions need to be declared with an explicit and implicit first argument.
             @"MGL_LET": @"let",
             @"MGL_LET:": @"let",
diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index 0fe7b22ea6..20e252c06b 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -545,6 +545,14 @@ using namespace std::string_literals;
         XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @0);
         XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
     }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"mgl_atan:" arguments:@[MGLConstantExpression(@20)]];
+        NSArray *jsonExpression = @[@"atan", @20];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        NSNumber *value = [expression expressionValueWithObject:nil context:nil];
+        XCTAssertEqualWithAccuracy(value.doubleValue, 1.52, 0.001);
+        XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
+    }
 }
 
 - (void)testStringFormattingExpressionObject {
-- 
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