Add support for $acos & $acosh aggregation operators.

Resolves: #3707
Original Pull Request: #3858

Author: divyajnu08

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ArithmeticOperators.java

@@ -799,6 +799,26 @@ public Cosh cosh() {
 		public Cosh cosh(AngularUnit unit) {
 			return usesFieldRef() ? Cosh.coshOf(fieldReference, unit) : Cosh.coshOf(expression, unit);
 		}
+		
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the inverse cosine of a numeric value.
+		 *
+		 * @return new instance of {@link ACos}.
+		 * @since 3.3
+		 */
+		public ACos acos() {
+			return usesFieldRef() ? ACos.acosOf(fieldReference) : ACos.acosOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the inverse hyperbolic cosine of a numeric value.
+		 *
+		 * @return new instance of {@link ACosh}.
+		 * @since 3.3
+		 */
+		public ACosh acosh() {
+			return usesFieldRef() ? ACosh.acoshOf(fieldReference) : ACosh.acoshOf(expression);
+		}
 
 		/**
 		 * Creates new {@link AggregationExpression} that calculates the tangent of a numeric value given in
@@ -2664,6 +2684,104 @@ protected String getMongoMethod() {
 			return "$cosh";
 		}
 	}
+	
+	/**
+	 * An {@link AggregationExpression expression} that calculates the inverse cosine of a value.
+	 *
+	 */
+	public static class ACos extends AbstractAggregationExpression {
+
+		private ACos(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates a new {@link AggregationExpression} that calculates the inverse cosine of a value.
+		 *
+		 * @param fieldReference the name of the {@link Field field} that resolves to a numeric value.
+		 * @return new instance of {@link ACos}.
+		 */
+		public static ACos acosOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			return new ACos(Fields.field(fieldReference));
+		}
+
+		/**
+		 * Creates a new {@link AggregationExpression} that calculates the inverse cosine of a value.
+		 * <br />
+		 *
+		 * @param expression the {@link AggregationExpression expression} that resolves to a numeric value.
+		 * @return new instance of {@link ACos}.
+		 */
+		public static ACos acosOf(AggregationExpression expression) {
+			return new ACos(expression);
+		}
+
+		/**
+		 * Creates a new {@link AggregationExpression} that calculates the inverse cosine of a value.
+		 *
+		 * @param value anything ({@link Field field}, {@link AggregationExpression expression}, ...) that resolves to a
+		 *          numeric value.
+		 * @return new instance of {@link ACos}.
+		 */
+		public static ACos acosOf(Number value) {
+			return new ACos(value);
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$acos";
+		}
+	}
+
+	/**
+	 * An {@link AggregationExpression expression} that calculates the inverse hyperbolic cosine of a value
+	 *
+	 */
+	public static class ACosh extends AbstractAggregationExpression {
+
+		private ACosh(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates a new {@link AggregationExpression} that calculates the inverse hyperbolic cosine of a value.
+		 *
+		 * @param fieldReference the name of the {@link Field field} that resolves to a numeric value.
+		 * @return new instance of {@link ACosh}.
+		 */
+		public static ACosh acoshOf(String fieldReference) {
+			return new ACosh(Fields.field(fieldReference));
+		}
+
+		/**
+		 * Creates a new {@link AggregationExpression} that calculates the inverse hyperbolic cosine of a value.
+		 * <br />
+		 *
+		 * @param expression the {@link AggregationExpression expression} that resolves to a numeric value.
+		 * @return new instance of {@link ACosh}.
+		 */
+		public static ACosh acoshOf(AggregationExpression expression) {
+			return new ACosh(expression);
+		}
+
+		/**
+		 * Creates a new {@link AggregationExpression} that calculates the inverse hyperbolic cosine of a value.
+		 *
+		 * @param value anything ({@link Field field}, {@link AggregationExpression expression}, ...) that resolves to a
+		 *          numeric value.
+		 * @return new instance of {@link ACosh}.
+		 */
+		public static ACosh acoshOf(Object value) {
+			return new ACosh(value);
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$acosh";
+		}
+	}
 
 	/**
 	 * An {@link AggregationExpression expression} that calculates the tangent of a value that is measured in radians.

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/ArithmeticOperatorsUnitTests.java

@@ -138,6 +138,16 @@ void rendersCosh() {
 
 		assertThat(valueOf("angle").cosh().toDocument(Aggregation.DEFAULT_CONTEXT)).isEqualTo("{ $cosh : \"$angle\" }");
 	}
+	
+	@Test 
+	void rendersACos() {
+		assertThat(valueOf("field").acos().toDocument(Aggregation.DEFAULT_CONTEXT)).isEqualTo("{ $acos : \"$field\" }");
+	}
+
+	@Test 
+	void rendersACosh() {
+		assertThat(valueOf("field").acosh().toDocument(Aggregation.DEFAULT_CONTEXT)).isEqualTo("{ $acosh : \"$field\" }");
+	}
 
 	@Test // GH-3710
 	void rendersCoshWithValueInDegrees() {