Implement NSPredicate-based query (#531)

*   implement queryFilteredUsingPredicate in FIRQuery;
*   add unit test and integration test for queryFilteredUsingPredicate;
*   project change of adding the FIRQueryTests.m file;
*   refactoring queryFilteredUsingPredicate to split logic into two helpers;

7 files changed, 204 insertions, 0 deletions

diff --git a/Firestore/CHANGELOG.md b/Firestore/CHANGELOG.md
index 0c5bcdc..e6ecf11 100644
--- a/Firestore/CHANGELOG.md
+++ b/Firestore/CHANGELOG.md
@@ -4,6 +4,7 @@
   with persistence enabled.
 
 - [fixed] Addressed race condition during the teardown of idle streams (#490).
+- [feature] Queries can now be created from an NSPredicate.
 
 # v0.9.3
 - [changed] Improved performance loading documents matching a query.
diff --git a/Firestore/Example/Firestore.xcodeproj/project.pbxproj b/Firestore/Example/Firestore.xcodeproj/project.pbxproj
index 437b661..5657b95 100644
--- a/Firestore/Example/Firestore.xcodeproj/project.pbxproj
+++ b/Firestore/Example/Firestore.xcodeproj/project.pbxproj
@@ -61,6 +61,7 @@
 		6ED54761B845349D43DB6B78 /* Pods_Firestore_Example.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 75A6FE51C1A02DF38F62FAAD /* Pods_Firestore_Example.framework */; };
 		71719F9F1E33DC2100824A3D /* LaunchScreen.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = 71719F9D1E33DC2100824A3D /* LaunchScreen.storyboard */; };
 		873B8AEB1B1F5CCA007FD442 /* Main.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = 873B8AEA1B1F5CCA007FD442 /* Main.storyboard */; };
+		ABAEEF4F1FD5F8B100C966CB /* FIRQueryTests.m in Sources */ = {isa = PBXBuildFile; fileRef = ABAEEF4E1FD5F8B100C966CB /* FIRQueryTests.m */; };
 		AFE6114F0D4DAECBA7B7C089 /* Pods_Firestore_IntegrationTests.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = B2FA635DF5D116A67A7441CD /* Pods_Firestore_IntegrationTests.framework */; };
 		C4E749275AD0FBDF9F4716A8 /* Pods_SwiftBuildTest.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 32AD40BF6B0E849B07FFD05E /* Pods_SwiftBuildTest.framework */; };
 		D5B2532E4676014F57A7EAB9 /* FSTStreamTests.m in Sources */ = {isa = PBXBuildFile; fileRef = D5B25C0D4AADFCA3ADB883E4 /* FSTStreamTests.m */; };
@@ -230,6 +231,7 @@
 		8E002F4AD5D9B6197C940847 /* Firestore.podspec */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text; name = Firestore.podspec; path = ../Firestore.podspec; sourceTree = "<group>"; };
 		9D52E67EE96AA7E5D6F69748 /* Pods-Firestore_IntegrationTests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-Firestore_IntegrationTests.debug.xcconfig"; path = "Pods/Target Support Files/Pods-Firestore_IntegrationTests/Pods-Firestore_IntegrationTests.debug.xcconfig"; sourceTree = "<group>"; };
 		9EF477AD4B2B643FD320867A /* Pods-Firestore_Example.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-Firestore_Example.debug.xcconfig"; path = "Pods/Target Support Files/Pods-Firestore_Example/Pods-Firestore_Example.debug.xcconfig"; sourceTree = "<group>"; };
+		ABAEEF4E1FD5F8B100C966CB /* FIRQueryTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = FIRQueryTests.m; sourceTree = "<group>"; };
 		B2FA635DF5D116A67A7441CD /* Pods_Firestore_IntegrationTests.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Pods_Firestore_IntegrationTests.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		CE00BABB5A3AAB44A4C209E2 /* Pods-Firestore_Tests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-Firestore_Tests.debug.xcconfig"; path = "Pods/Target Support Files/Pods-Firestore_Tests/Pods-Firestore_Tests.debug.xcconfig"; sourceTree = "<group>"; };
 		D3CC3DC5338DCAF43A211155 /* README.md */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = net.daringfireball.markdown; name = README.md; path = ../README.md; sourceTree = "<group>"; };
@@ -584,6 +586,7 @@
 			isa = PBXGroup;
 			children = (
 				DE51B1841F0D48AC0013853F /* FIRGeoPointTests.m */,
+				ABAEEF4E1FD5F8B100C966CB /* FIRQueryTests.m */,
 			);
 			path = API;
 			sourceTree = "<group>";
@@ -1161,6 +1164,7 @@
 			files = (
 				DE2EF0881F3D0B6E003D0CDC /* FSTTreeSortedDictionaryTests.m in Sources */,
 				DE51B1FD1F0D492C0013853F /* FSTSpecTests.m in Sources */,
+				ABAEEF4F1FD5F8B100C966CB /* FIRQueryTests.m in Sources */,
 				DE51B2001F0D493A0013853F /* FSTComparisonTests.m in Sources */,
 				DE51B1CC1F0D48C00013853F /* FIRGeoPointTests.m in Sources */,
 				DE51B1E11F0D490D0013853F /* FSTMemoryRemoteDocumentCacheTests.m in Sources */,
diff --git a/Firestore/Example/Tests/API/FIRQueryTests.m b/Firestore/Example/Tests/API/FIRQueryTests.m
new file mode 100644
index 0000000..bd0d860
--- /dev/null
+++ b/Firestore/Example/Tests/API/FIRQueryTests.m
@@ -0,0 +1,75 @@
+/*
+ * Copyright 2017 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+@import FirebaseFirestore;
+
+#import <XCTest/XCTest.h>
+
+#import "Firestore/Source/API/FIRFirestore+Internal.h"
+#import "Firestore/Source/API/FIRQuery+Internal.h"
+#import "Firestore/Source/Core/FSTQuery.h"
+#import "Firestore/Source/Model/FSTPath.h"
+
+#import "Firestore/Example/Tests/Util/FSTHelpers.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface FIRQueryTests : XCTestCase
+@end
+
+@implementation FIRQueryTests
+
+- (void)testFilteringWithPredicate {
+  // Everything is dummy for unit test here. Filtering does not require any app
+  // specific setting as far as we do not fetch data.
+  FIRFirestore *firestore = [[FIRFirestore alloc] initWithProjectID:@"abc"
+                                                           database:@"abc"
+                                                     persistenceKey:@"db123"
+                                                credentialsProvider:nil
+                                                workerDispatchQueue:nil
+                                                        firebaseApp:nil];
+  FSTResourcePath *path = [FSTResourcePath pathWithString:@"foo"];
+  FIRQuery *query = [FIRQuery referenceWithQuery:[FSTQuery queryWithPath:path]
+                                       firestore:firestore];
+  FIRQuery *query1 = [query queryWhereField:@"f" isLessThanOrEqualTo:@1];
+  FIRQuery *query2 = [query queryFilteredUsingPredicate:
+                      [NSPredicate predicateWithFormat:@"f<=1"]];
+  FIRQuery *query3 = [[query queryWhereField:@"f1" isLessThan:@2]
+                      queryWhereField:@"f2" isEqualTo:@3];
+  FIRQuery *query4 = [query queryFilteredUsingPredicate:
+                      [NSPredicate predicateWithFormat:@"f1<2 && f2==3"]];
+  FIRQuery *query5 = [[[[[query queryWhereField:@"f1" isLessThan:@2]
+                         queryWhereField:@"f2" isEqualTo:@3]
+                        queryWhereField:@"f1" isLessThanOrEqualTo:@"four"]
+                       queryWhereField:@"f1" isGreaterThanOrEqualTo:@"five"]
+                      queryWhereField:@"f1" isGreaterThan:@6];
+  FIRQuery *query6 = [query queryFilteredUsingPredicate:
+                      [NSPredicate predicateWithFormat:
+                       @"f1<2 && f2==3 && f1<='four' && f1>='five' && f1>6"]];
+  FIRQuery *query7 = [query queryFilteredUsingPredicate:
+                      [NSPredicate predicateWithFormat:
+                       @"2>f1 && 3==f2 && 'four'>=f1 && 'five'<=f1 && 6<f1"]];
+  XCTAssertEqualObjects(query1, query2);
+  XCTAssertNotEqualObjects(query2, query3);
+  XCTAssertEqualObjects(query3, query4);
+  XCTAssertNotEqualObjects(query4, query5);
+  XCTAssertEqualObjects(query5, query6);
+  XCTAssertEqualObjects(query6, query7);
+}
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/Firestore/Example/Tests/Integration/API/FIRQueryTests.m b/Firestore/Example/Tests/Integration/API/FIRQueryTests.m
index 180b423..ccc635e 100644
--- a/Firestore/Example/Tests/Integration/API/FIRQueryTests.m
+++ b/Firestore/Example/Tests/Integration/API/FIRQueryTests.m
@@ -111,6 +111,23 @@
   XCTAssertEqualObjects(FIRQuerySnapshotGetIDs(snapshot), (@[ @"b", @"a" ]));
 }
 
+- (void)testQueryWithPredicate {
+  FIRCollectionReference *collRef = [self collectionRefWithDocuments:@{
+    @"a" : @{@"a" : @1},
+    @"b" : @{@"a" : @2},
+    @"c" : @{@"a" : @3}
+  }];
+
+  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"a < 3"];
+  FIRQuery *query = [collRef queryFilteredUsingPredicate:predicate];
+  query = [query queryOrderedByFieldPath:[[FIRFieldPath alloc] initWithFields:@[ @"a" ]]
+                              descending:YES];
+
+  FIRQuerySnapshot *snapshot = [self readDocumentSetForRef:query];
+
+  XCTAssertEqualObjects(FIRQuerySnapshotGetIDs(snapshot), (@[ @"b", @"a" ]));
+}
+
 - (void)testFilterOnInfinity {
   FIRCollectionReference *collRef = [self collectionRefWithDocuments:@{
     @"a" : @{@"inf" : @(INFINITY)},
diff --git a/Firestore/Source/API/FIRQuery+Internal.h b/Firestore/Source/API/FIRQuery+Internal.h
index 3c2b2a7..b443c2f 100644
--- a/Firestore/Source/API/FIRQuery+Internal.h
+++ b/Firestore/Source/API/FIRQuery+Internal.h
@@ -23,6 +23,8 @@ NS_ASSUME_NONNULL_BEGIN
 /** Internal FIRQuery API we don't want exposed in our public header files. */
 @interface FIRQuery (Internal)
 + (FIRQuery *)referenceWithQuery:(FSTQuery *)query firestore:(FIRFirestore *)firestore;
+- (FIRQuery *)queryFilteredUsingComparisonPredicate:(NSPredicate *)predicate;
+- (FIRQuery *)queryFilteredUsingCompoundPredicate:(NSPredicate *)predicate;
 @property(nonatomic, strong, readonly) FSTQuery *query;
 @end
 
diff --git a/Firestore/Source/API/FIRQuery.m b/Firestore/Source/API/FIRQuery.m
index 12e79c5..9ab854a 100644
--- a/Firestore/Source/API/FIRQuery.m
+++ b/Firestore/Source/API/FIRQuery.m
@@ -256,6 +256,98 @@ addSnapshotListenerInternalWithOptions:(FSTListenOptions *)internalOptions
                                  value:value];
 }
 
+- (FIRQuery *)queryFilteredUsingComparisonPredicate:(NSPredicate *)predicate {
+  NSComparisonPredicate *comparison = (NSComparisonPredicate *)predicate;
+  if (comparison.comparisonPredicateModifier != NSDirectPredicateModifier) {
+    FSTThrowInvalidArgument(@"Invalid query. Predicate cannot have an "
+                            "aggregate modifier.");
+  }
+  NSString *path;
+  id value = nil;
+  if ([comparison.leftExpression expressionType] == NSKeyPathExpressionType &&
+      [comparison.rightExpression expressionType] == NSConstantValueExpressionType) {
+    path = comparison.leftExpression.keyPath;
+    value = comparison.rightExpression.constantValue;
+    switch (comparison.predicateOperatorType) {
+      case NSEqualToPredicateOperatorType:
+        return [self queryWhereField:path isEqualTo:value];
+      case NSLessThanPredicateOperatorType:
+        return [self queryWhereField:path isLessThan:value];
+      case NSLessThanOrEqualToPredicateOperatorType:
+        return [self queryWhereField:path isLessThanOrEqualTo:value];
+      case NSGreaterThanPredicateOperatorType:
+        return [self queryWhereField:path isGreaterThan:value];
+      case NSGreaterThanOrEqualToPredicateOperatorType:
+        return [self queryWhereField:path isGreaterThanOrEqualTo:value];
+      default:
+        ;  // Fallback below to throw assertion.
+    }
+  } else if ([comparison.leftExpression expressionType] == NSConstantValueExpressionType &&
+             [comparison.rightExpression expressionType] == NSKeyPathExpressionType) {
+    path = comparison.rightExpression.keyPath;
+    value = comparison.leftExpression.constantValue;
+    switch (comparison.predicateOperatorType) {
+      case NSEqualToPredicateOperatorType:
+        return [self queryWhereField:path isEqualTo:value];
+      case NSLessThanPredicateOperatorType:
+        return [self queryWhereField:path isGreaterThan:value];
+      case NSLessThanOrEqualToPredicateOperatorType:
+        return [self queryWhereField:path isGreaterThanOrEqualTo:value];
+      case NSGreaterThanPredicateOperatorType:
+        return [self queryWhereField:path isLessThan:value];
+      case NSGreaterThanOrEqualToPredicateOperatorType:
+        return [self queryWhereField:path isLessThanOrEqualTo:value];
+      default:
+        ;  // Fallback below to throw assertion.
+    }
+  } else {
+    FSTThrowInvalidArgument(@"Invalid query. Predicate comparisons must "
+                            "include a key path and a constant.");
+  }
+  // Fallback cases of unsupported comparison operator.
+  switch (comparison.predicateOperatorType) {
+    case NSCustomSelectorPredicateOperatorType:
+      FSTThrowInvalidArgument(@"Invalid query. Custom predicate filters are "
+                              "not supported.");
+      break;
+    default:
+      FSTThrowInvalidArgument(@"Invalid query. Operator type %lu is not supported.",
+                              (unsigned long)comparison.predicateOperatorType);
+  }
+}
+
+- (FIRQuery *)queryFilteredUsingCompoundPredicate:(NSPredicate *)predicate {
+  NSCompoundPredicate *compound = (NSCompoundPredicate *)predicate;
+  if (compound.compoundPredicateType != NSAndPredicateType ||
+      compound.subpredicates.count == 0) {
+    FSTThrowInvalidArgument(@"Invalid query. Only compound queries using AND "
+                            "are supported.");
+  }
+  FIRQuery *query = self;
+  for (NSPredicate *pred in compound.subpredicates) {
+    query = [query queryFilteredUsingPredicate:pred];
+  }
+  return query;
+}
+
+- (FIRQuery *)queryFilteredUsingPredicate:(NSPredicate *)predicate {
+  if ([predicate isKindOfClass:[NSComparisonPredicate class]]) {
+    return [self queryFilteredUsingComparisonPredicate:predicate];
+  } else if ([predicate isKindOfClass:[NSCompoundPredicate class]]) {
+    return [self queryFilteredUsingCompoundPredicate:predicate];
+  } else if ([predicate isKindOfClass:
+              [[NSPredicate predicateWithBlock:
+                ^BOOL(id obj, NSDictionary *bindings) { return true; }] class]]) {
+    FSTThrowInvalidArgument(@"Invalid query. Block-based predicates are not "
+                            "supported. Please use predicateWithFormat to "
+                            "create predicates instead.");
+  } else {
+    FSTThrowInvalidArgument(@"Invalid query. Expect comparison or compound of "
+                            "comparison predicate. Please use "
+                            "predicateWithFormat to create predicates.");
+  }
+}
+
 - (FIRQuery *)queryOrderedByField:(NSString *)field {
   return
       [self queryOrderedByFieldPath:[FIRFieldPath pathWithDotSeparatedString:field] descending:NO];
diff --git a/Firestore/Source/Public/FIRQuery.h b/Firestore/Source/Public/FIRQuery.h
index 0f3aeed..ff15ac6 100644
--- a/Firestore/Source/Public/FIRQuery.h
+++ b/Firestore/Source/Public/FIRQuery.h
@@ -256,6 +256,19 @@ NS_SWIFT_NAME(Query)
            isGreaterThanOrEqualTo:(id)value NS_SWIFT_NAME(whereField(_:isGreaterThanOrEqualTo:));
 // clang-format on
 
+/**
+ * Creates and returns a new `FIRQuery` with the additional filter that documents must
+ * satisfy the specified predicate.
+ *
+ * @param predicate The predicate the document must satisfy. Can be either comparison
+ *     or compound of comparison. In particular, block-based predicate is not supported.
+ *
+ * @return The created `FIRQuery`.
+ */
+// clang-format off
+- (FIRQuery *)queryFilteredUsingPredicate:(NSPredicate *)predicate NS_SWIFT_NAME(filter(using:));
+// clang-format on
+
 #pragma mark - Sorting Data
 /**
  * Creates and returns a new `FIRQuery` that's additionally sorted by the specified field.