DATAMONGO-1564 - Split up AggregationExpressions.

Refactored to multiple smaller Aggregation Operator classes reflecting the grouping (array operators, string operators,…) predefined by MongoDB.

Original pull request: spring-projects#429.

Author: christophstrobl

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

@@ -0,0 +1,149 @@
+/*
+ * Copyright 2016. the original author or authors.
+ *
+ * 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.
+ */
+package org.springframework.data.mongodb.core.aggregation;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+
+import org.bson.Document;
+import org.springframework.util.ObjectUtils;
+
+/**
+ * @author Christoph Strobl
+ * @since 1.10
+ */
+abstract class AbstractAggregationExpression implements AggregationExpression {
+
+	private final Object value;
+
+	protected AbstractAggregationExpression(Object value) {
+		this.value = value;
+	}
+
+	/* (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationExpression#toDocument(org.springframework.data.mongodb.core.aggregation.AggregationOperationContext)
+	 */
+	@Override
+	public Document toDocument(AggregationOperationContext context) {
+		return toDocument(this.value, context);
+	}
+
+	public Document toDocument(Object value, AggregationOperationContext context) {
+
+		Object valueToUse;
+		if (value instanceof List) {
+
+			List<Object> arguments = (List<Object>) value;
+			List<Object> args = new ArrayList<Object>(arguments.size());
+
+			for (Object val : arguments) {
+				args.add(unpack(val, context));
+			}
+			valueToUse = args;
+		} else if (value instanceof java.util.Map) {
+
+			Document dbo = new Document();
+			for (java.util.Map.Entry<String, Object> entry : ((java.util.Map<String, Object>) value).entrySet()) {
+				dbo.put(entry.getKey(), unpack(entry.getValue(), context));
+			}
+			valueToUse = dbo;
+		} else {
+			valueToUse = unpack(value, context);
+		}
+
+		return new Document(getMongoMethod(), valueToUse);
+	}
+
+	protected static List<Field> asFields(String... fieldRefs) {
+
+		if (ObjectUtils.isEmpty(fieldRefs)) {
+			return Collections.emptyList();
+		}
+
+		return Fields.fields(fieldRefs).asList();
+	}
+
+	private Object unpack(Object value, AggregationOperationContext context) {
+
+		if (value instanceof AggregationExpression) {
+			return ((AggregationExpression) value).toDocument(context);
+		}
+
+		if (value instanceof Field) {
+			return context.getReference((Field) value).toString();
+		}
+
+		if (value instanceof List) {
+
+			List<Object> sourceList = (List<Object>) value;
+			List<Object> mappedList = new ArrayList<Object>(sourceList.size());
+
+			for (Object item : sourceList) {
+				mappedList.add(unpack(item, context));
+			}
+			return mappedList;
+		}
+
+		return value;
+	}
+
+	protected List<Object> append(Object value) {
+
+		if (this.value instanceof List) {
+
+			List<Object> clone = new ArrayList<Object>((List) this.value);
+
+			if (value instanceof List) {
+				for (Object val : (List) value) {
+					clone.add(val);
+				}
+			} else {
+				clone.add(value);
+			}
+			return clone;
+		}
+
+		return Arrays.asList(this.value, value);
+	}
+
+	protected java.util.Map<String, Object> append(String key, Object value) {
+
+		if (!(this.value instanceof java.util.Map)) {
+			throw new IllegalArgumentException("o_O");
+		}
+		java.util.Map<String, Object> clone = new LinkedHashMap<String, Object>(
+				(java.util.Map<String, Object>) this.value);
+		clone.put(key, value);
+		return clone;
+
+	}
+
+	protected List<Object> values() {
+
+		if (value instanceof List) {
+			return new ArrayList<Object>((List) value);
+		}
+		if (value instanceof java.util.Map) {
+			return new ArrayList<Object>(((java.util.Map) value).values());
+		}
+		return new ArrayList<Object>(Arrays.asList(value));
+	}
+
+	protected abstract String getMongoMethod();
+}