[ios, macos] Change the format for case expressions to a flat structure. (#11450)

* [ios, macos] Change the format for case expressions to a flat structure.

* [ios, macos] Add support for multiple branches case expression.

* [ios, macos] Add multiple branch tests to case expressions.

* [ios, macos] Case operator now has iOS 8 support.

4 files changed, 89 insertions, 32 deletions

diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index 5ad565c398..bd747dc97e 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -464,17 +464,22 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
         } else if ([op isEqualToString:@"var"]) {
             return [NSExpression expressionForVariable:argumentObjects.firstObject];
         } else if ([op isEqualToString:@"case"]) {
-            NSPredicate *conditional = [NSPredicate mgl_predicateWithJSONObject:argumentObjects.firstObject];
-            NSExpression *trueExpression = [NSExpression mgl_expressionWithJSONObject:argumentObjects[1]];
-            NSExpression *falseExpression;
-            if (argumentObjects.count > 3) {
-                NSArray *falseObjects = [@[@"case"] arrayByAddingObjectsFromArray:
-                                         [argumentObjects subarrayWithRange:NSMakeRange(2, argumentObjects.count - 2)]];
-                falseExpression = [NSExpression mgl_expressionWithJSONObject:falseObjects];
-            } else {
-                falseExpression = [NSExpression mgl_expressionWithJSONObject:argumentObjects[2]];
+            NSArray *caseExpressions = argumentObjects;
+            NSExpression *firstConditional = [NSExpression expressionWithFormat:@"%@", [NSPredicate mgl_predicateWithJSONObject:caseExpressions[0]]];
+            NSMutableArray *arguments = [NSMutableArray array];
+            
+            for (NSUInteger index = 1; index < caseExpressions.count; index++) {
+                if ([caseExpressions[index] isKindOfClass:[NSArray class]]) {
+                    NSPredicate *conditional = [NSPredicate mgl_predicateWithJSONObject:caseExpressions[index]];
+                    NSExpression *argument = [NSExpression expressionWithFormat:@"%@", conditional];
+                    [arguments addObject:argument];
+                } else {
+                    [arguments addObject:[NSExpression mgl_expressionWithJSONObject:caseExpressions[index]]];
+                }
+                
             }
-            return [NSExpression expressionForConditional:conditional trueExpression:trueExpression falseExpression:falseExpression];
+            
+            return [NSExpression expressionForFunction:firstConditional selectorName:@"mgl_case:" arguments:arguments];
         } else {
             [NSException raise:NSInvalidArgumentException
                         format:@"Expression operator %@ not yet implemented.", op];
@@ -666,6 +671,20 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
                 }];
                 [expressionObject addObject:self.operand.mgl_jsonExpressionObject];
                 return expressionObject;
+            } else if ([function isEqualToString:@"mgl_case:"]) {
+                NSPredicate *firstConditional = (NSPredicate *)self.operand.constantValue;
+                NSMutableArray *expressionObject = [NSMutableArray arrayWithObjects:@"case", firstConditional.mgl_jsonExpressionObject, nil];
+                
+                for (NSExpression *option in self.arguments) {
+                    if ([option respondsToSelector:@selector(constantValue)] && [option.constantValue isKindOfClass:[NSComparisonPredicate class]]) {
+                        NSPredicate *predicate = (NSPredicate *)option.constantValue;
+                        [expressionObject addObject:predicate.mgl_jsonExpressionObject];
+                    } else {
+                        [expressionObject addObject:option.mgl_jsonExpressionObject];
+                    }
+                }
+                
+                return expressionObject;
             } else if ([function isEqualToString:@"median:"] ||
                        [function isEqualToString:@"mode:"] ||
                        [function isEqualToString:@"stddev:"] ||
@@ -690,7 +709,17 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
         }
             
         case NSConditionalExpressionType: {
-            NSMutableArray *arguments = [NSMutableArray arrayWithObjects:self.predicate.mgl_jsonExpressionObject, self.trueExpression.mgl_jsonExpressionObject, nil];
+            NSMutableArray *arguments = [NSMutableArray arrayWithObjects:self.predicate.mgl_jsonExpressionObject, nil];
+            
+            if (self.trueExpression.expressionType == NSConditionalExpressionType) {
+                // Fold nested conditionals into a single case expression.
+                NSArray *trueArguments = self.trueExpression.mgl_jsonExpressionObject;
+                trueArguments = [trueArguments subarrayWithRange:NSMakeRange(1, trueArguments.count - 1)];
+                [arguments addObjectsFromArray:trueArguments];
+            } else {
+                [arguments addObject:self.trueExpression.mgl_jsonExpressionObject];
+            }
+            
             if (self.falseExpression.expressionType == NSConditionalExpressionType) {
                 // Fold nested conditionals into a single case expression.
                 NSArray *falseArguments = self.falseExpression.mgl_jsonExpressionObject;
diff --git a/platform/darwin/src/NSPredicate+MGLAdditions.h b/platform/darwin/src/NSPredicate+MGLAdditions.h
index 89e9e65c64..cce7561add 100644
--- a/platform/darwin/src/NSPredicate+MGLAdditions.h
+++ b/platform/darwin/src/NSPredicate+MGLAdditions.h
@@ -16,4 +16,6 @@
 
 @property (nonatomic, readonly) id mgl_jsonExpressionObject;
 
+- (id)mgl_case:(id)firstValue, ...;
+
 @end
diff --git a/platform/darwin/src/NSPredicate+MGLAdditions.mm b/platform/darwin/src/NSPredicate+MGLAdditions.mm
index 63c8307803..2d5b646ff2 100644
--- a/platform/darwin/src/NSPredicate+MGLAdditions.mm
+++ b/platform/darwin/src/NSPredicate+MGLAdditions.mm
@@ -324,4 +324,29 @@ NSArray *MGLSubpredicatesWithJSONObjects(NSArray *objects) {
     return nil;
 }
 
+- (id)mgl_case:(id)firstValue, ... {
+
+    if ([self evaluateWithObject:nil]) {
+        return firstValue;
+    }
+    
+    id eachExpression;
+    va_list argumentList;
+    va_start(argumentList, firstValue);
+    
+    while ((eachExpression = va_arg(argumentList, id))) {
+        if ([eachExpression isKindOfClass:[NSComparisonPredicate class]]) {
+            id valueExpression = va_arg(argumentList, id);
+            if ([eachExpression evaluateWithObject:nil]) {
+                return valueExpression;
+            }
+        } else {
+            return eachExpression;
+        }
+    }
+    va_end(argumentList);
+    
+    return nil;
+}
+
 @end
diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index a5ed2f7bf5..3f36a0cf61 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -573,28 +573,29 @@ using namespace std::string_literals;
 }
 
 - (void)testConditionalExpressionObject {
-    // FIXME: This test crashes because iOS 8 doesn't have `+[NSExpression expressionForConditional:trueExpression:falseExpression:]`.
-    // https://github.com/mapbox/mapbox-gl-native/issues/11007
-    if (@available(iOS 9.0, *)) {
-        {
-            NSPredicate *conditional = [NSPredicate predicateWithFormat:@"1 = 2"];
-            NSExpression *trueExpression = [NSExpression expressionForConstantValue:@YES];
-            NSExpression *falseExpression = [NSExpression expressionForConstantValue:@NO];
-            NSExpression *expression = [NSExpression expressionForConditional:conditional trueExpression:trueExpression falseExpression:falseExpression];
-            NSArray *jsonExpression = @[@"case", @[@"==", @1, @2], @YES, @NO];
-            XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
-            XCTAssertEqualObjects([NSExpression expressionWithFormat:@"TERNARY(1 = 2, TRUE, FALSE)"].mgl_jsonExpressionObject, jsonExpression);
-            XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @NO);
-            XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
-        }
-        {
-            NSExpression *expression = [NSExpression expressionWithFormat:@"TERNARY(0 = 1, TRUE, TERNARY(1 = 2, TRUE, FALSE))"];
-            NSArray *jsonExpression = @[@"case", @[@"==", @0, @1], @YES, @[@"==", @1, @2], @YES, @NO];
-            XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
-            XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @NO);
-            XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
-        }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(%@, 'mgl_case:', %@, %@)",
+                                    [NSExpression expressionWithFormat:@"%@", [NSPredicate predicateWithFormat:@"1 = 2"]],
+                                                                                                 MGLConstantExpression(@YES),
+                                                                                                 MGLConstantExpression(@NO)];
+        NSArray *jsonExpression = @[@"case", @[@"==", @1, @2], @YES, @NO];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @NO);
     }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(%@, 'mgl_case:', %@, %@, %@, %@)",
+                                    [NSExpression expressionWithFormat:@"%@", [NSPredicate predicateWithFormat:@"1 = 2"]],
+                                                                                                 MGLConstantExpression(@YES),
+                                                                                                 [NSExpression expressionWithFormat:@"%@", [NSPredicate predicateWithFormat:@"1 = 1"]],
+                                                                                                 MGLConstantExpression(@YES),
+                                                                                                 MGLConstantExpression(@NO)];
+        NSArray *jsonExpression = @[@"case", @[@"==", @1, @2], @YES, @[@"==", @1, @1], @YES, @NO];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @YES);
+    }
+    
 }
 
 @end