/*
    * Copyright 2002-2014 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.beans.factory.config;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.AbstractMap;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.LinkedHashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.Properties;
  import java.util.Set;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.yaml.snakeyaml.Yaml;
  import org.yaml.snakeyaml.constructor.Constructor;
  import org.yaml.snakeyaml.nodes.MappingNode;
  import org.yaml.snakeyaml.parser.ParserException;
  
  import org.springframework.core.io.Resource;
  import org.springframework.util.Assert;
  import org.springframework.util.StringUtils;
  
  /**
   * Base class for Yaml factories.
   *
   * @author Dave Syer
   * @since 4.1
   */
  public abstract class YamlProcessor {
  
  	private final Log logger = LogFactory.getLog(getClass());
  
  	private ResolutionMethod resolutionMethod = ResolutionMethod.OVERRIDE;
  
  	private Resource[] resources = new Resource[0];
  
  	private List<DocumentMatcher> documentMatchers = Collections.emptyList();
  
  	private boolean matchDefault = true;
  
  
  	/**
  	 * A map of document matchers allowing callers to selectively use only
  	 * some of the documents in a YAML resource. In YAML documents are
  	 * separated by <code>---<code> lines, and each document is converted
  	 * to properties before the match is made. E.g.
  	 *
  	 * <pre class="code">
  	 * environment: dev
  	 * url: http://dev.bar.com
  	 * name: Developer Setup
  	 * ---
  	 * environment: prod
  	 * url:http://foo.bar.com
  	 * name: My Cool App
  	 * </pre>
  	 *
  	 * when mapped with
  	 * <code>documentMatchers = YamlProcessor.mapMatcher({"environment": "prod"})</code>
  	 * would end up as
  	 *
  	 * <pre class="code">
  	 * environment=prod
  	 * url=http://foo.bar.com
  	 * name=My Cool App
  	 * url=http://dev.bar.com
  	 * </pre>
  	 * @param matchers a map of keys to value patterns (regular expressions)
  	 */
  	public void setDocumentMatchers(DocumentMatcher... matchers) {
  		this.documentMatchers = Arrays.asList(matchers);
  	}
  
  	/**
  	 * Flag indicating that a document for which all the
  	 * {@link #setDocumentMatchers(DocumentMatcher...) document matchers} abstain will
  	 * nevertheless match.
  	 * @param matchDefault the flag to set (default true)
  	 */
 	public void setMatchDefault(boolean matchDefault) {
 		this.matchDefault = matchDefault;
 	}
 
 	/**
 	 * Method to use for resolving resources. Each resource will be converted to a Map, so
 	 * this property is used to decide which map entries to keep in the final output from
 	 * this factory.
 	 * @param resolutionMethod the resolution method to set (defaults to
 	 * {@link ResolutionMethod#OVERRIDE}).
 	 */
 	public void setResolutionMethod(ResolutionMethod resolutionMethod) {
 		Assert.notNull(resolutionMethod, "ResolutionMethod must not be null");
 		this.resolutionMethod = resolutionMethod;
 	}
 
 	/**
 	 * Set locations of YAML {@link Resource resources} to be loaded.
 	 * @see ResolutionMethod
 	 */
 	public void setResources(Resource... resources) {
 		this.resources = resources;
 	}
 
 
 	/**
 	 * Provide an opportunity for subclasses to process the Yaml parsed from the supplied
 	 * resources. Each resource is parsed in turn and the documents inside checked against
 	 * the {@link #setDocumentMatchers(DocumentMatcher...) matchers}. If a document
 	 * matches it is passed into the callback, along with its representation as
 	 * Properties. Depending on the {@link #setResolutionMethod(ResolutionMethod)} not all
 	 * of the documents will be parsed.
 	 * @param callback a callback to delegate to once matching documents are found
 	 * @see #createYaml()
 	 */
 	protected void process(MatchCallback callback) {
 		Yaml yaml = createYaml();
 		for (Resource resource : this.resources) {
 			boolean found = process(callback, yaml, resource);
 			if (this.resolutionMethod == ResolutionMethod.FIRST_FOUND && found) {
 				return;
 			}
 		}
 	}
 
 	/**
 	 * Create the {@link Yaml} instance to use.
 	 */
 	protected Yaml createYaml() {
 		return new Yaml(new StrictMapAppenderConstructor());
 	}
 
 	private boolean process(MatchCallback callback, Yaml yaml, Resource resource) {
 		int count = 0;
 		try {
 			if (this.logger.isDebugEnabled()) {
 				this.logger.debug("Loading from YAML: " + resource);
 			}
 			InputStream stream = resource.getInputStream();
 			try {
 				for (Object object : yaml.loadAll(stream)) {
 					if (object != null && process(asMap(object), callback)) {
 						count++;
 						if (this.resolutionMethod == ResolutionMethod.FIRST_FOUND) {
 							break;
 						}
 					}
 				}
 				if (this.logger.isDebugEnabled()) {
 					this.logger.debug("Loaded " + count + " document" + (count > 1 ? "s" : "") +
 							" from YAML resource: " + resource);
 				}
 			}
 			finally {
 				stream.close();
 			}
 		}
 		catch (IOException ex) {
 			handleProcessError(resource, ex);
 		}
 		return (count > 0);
 	}
 
 	private void handleProcessError(Resource resource, IOException ex) {
 		if (this.resolutionMethod != ResolutionMethod.FIRST_FOUND &&
 				this.resolutionMethod != ResolutionMethod.OVERRIDE_AND_IGNORE) {
 			throw new IllegalStateException(ex);
 		}
 		if (this.logger.isWarnEnabled()) {
 			this.logger.warn("Could not load map from " + resource + ": " + ex.getMessage());
 		}
 	}
 
 	@SuppressWarnings("unchecked")
 	private Map<String, Object> asMap(Object object) {
 		// YAML can have numbers as keys
 		Map<String, Object> result = new LinkedHashMap<String, Object>();
 		if (!(object instanceof Map)) {
 			// A document can be a text literal
 			result.put("document", object);
 			return result;
 		}
 
 		Map<Object, Object> map = (Map<Object, Object>) object;
 		for (Entry<Object, Object> entry : map.entrySet()) {
 			Object value = entry.getValue();
 			if (value instanceof Map) {
 				value = asMap(value);
 			}
 			Object key = entry.getKey();
 			if (key instanceof CharSequence) {
 				result.put(key.toString(), value);
 			}
 			else {
 				// It has to be a map key in this case
 				result.put("[" + key.toString() + "]", value);
 			}
 		}
 		return result;
 	}
 
 	private boolean process(Map<String, Object> map, MatchCallback callback) {
 		Properties properties = new Properties();
 		properties.putAll(getFlattenedMap(map));
 
 		if (this.documentMatchers.isEmpty()) {
 			if (this.logger.isDebugEnabled()) {
 				this.logger.debug("Merging document (no matchers set)" + map);
 			}
 			callback.process(properties, map);
 			return true;
 		}
 
 		MatchStatus result = MatchStatus.ABSTAIN;
 		for (DocumentMatcher matcher : this.documentMatchers) {
 			MatchStatus match = matcher.matches(properties);
 			result = MatchStatus.getMostSpecific(match, result);
 			if (match == MatchStatus.FOUND) {
 				if (this.logger.isDebugEnabled()) {
 					this.logger.debug("Matched document with document matcher: " + properties);
 				}
 				callback.process(properties, map);
 				return true;
 			}
 		}
 
 		if (result == MatchStatus.ABSTAIN && this.matchDefault) {
 			if (this.logger.isDebugEnabled()) {
 				this.logger.debug("Matched document with default matcher: " + map);
 			}
 			callback.process(properties, map);
 			return true;
 		}
 
 		this.logger.debug("Unmatched document");
 		return false;
 	}
 
 	/**
 	 * Return a flattened version of the given map, recursively following any nested Map
 	 * or Collection values. Entries from the resulting map retain the same order as the
 	 * source. When called with the Map from a {@link MatchCallback} the result will
 	 * contain the same values as the {@link MatchCallback} Properties.
 	 * @param source the source map
 	 * @return a flattened map
 	 * @since 4.1.3
 	 */
 	protected final Map<String, Object> getFlattenedMap(Map<String, Object> source) {
 		Map<String, Object> result = new LinkedHashMap<String, Object>();
 		buildFlattenedMap(result, source, null);
 		return result;
 	}
 
 	private void buildFlattenedMap(Map<String, Object> result, Map<String, Object> source, String path) {
 		for (Entry<String, Object> entry : source.entrySet()) {
 			String key = entry.getKey();
 			if (StringUtils.hasText(path)) {
 				if (key.startsWith("[")) {
 					key = path + key;
 				}
 				else {
 					key = path + "." + key;
 				}
 			}
 			Object value = entry.getValue();
 			if (value instanceof String) {
 				result.put(key, value);
 			}
 			else if (value instanceof Map) {
 				// Need a compound key
 				@SuppressWarnings("unchecked")
 				Map<String, Object> map = (Map<String, Object>) value;
 				buildFlattenedMap(result, map, key);
 			}
 			else if (value instanceof Collection) {
 				// Need a compound key
 				@SuppressWarnings("unchecked")
 				Collection<Object> collection = (Collection<Object>) value;
 				int count = 0;
 				for (Object object : collection) {
 					buildFlattenedMap(result,
 							Collections.singletonMap("[" + (count++) + "]", object), key);
 				}
 			}
 			else {
 				result.put(key, value == null ? "" : value);
 			}
 		}
 	}
 
 
 	/**
 	 * Callback interface used to process properties in a resulting map.
 	 */
 	public interface MatchCallback {
 
 		/**
 		 * Process the properties.
 		 * @param properties the properties to process
 		 * @param map a mutable result map
 		 */
 		void process(Properties properties, Map<String, Object> map);
 	}
 
 
 	/**
 	 * Strategy interface used to test if properties match.
 	 */
 	public interface DocumentMatcher {
 
 		/**
 		 * Test if the given properties match.
 		 * @param properties the properties to test
 		 * @return the status of the match.
 		 */
 		MatchStatus matches(Properties properties);
 	}
 
 
 	/**
 	 * Status returned from {@link DocumentMatcher#matches(java.util.Properties)}
 	 */
 	public enum MatchStatus {
 
 		/**
 		 * A match was found.
 		 */
 		FOUND,
 
 		/**
 		 * No match was found.
 		 */
 		NOT_FOUND,
 
 		/**
 		 * The matcher should not be considered.
 		 */
 		ABSTAIN;
 
 		/**
 		 * Compare two {@link MatchStatus} items, returning the most specific status.
 		 */
 		public static MatchStatus getMostSpecific(MatchStatus a, MatchStatus b) {
 			return (a.ordinal() < b.ordinal() ? a : b);
 		}
 	}
 
 
 	/**
 	 * Method to use for resolving resources.
 	 */
 	public enum ResolutionMethod {
 
 		/**
 		 * Replace values from earlier in the list.
 		 */
 		OVERRIDE,
 
 		/**
 		 * Replace values from earlier in the list, ignoring any failures.
 		 */
 		OVERRIDE_AND_IGNORE,
 
 		/**
 		 * Take the first resource in the list that exists and use just that.
 		 */
 		FIRST_FOUND
 	}
 
 
 	/**
 	 * A specialized {@link Constructor} that checks for duplicate keys.
 	 */
 	protected static class StrictMapAppenderConstructor extends Constructor {
 
 		public 	StrictMapAppenderConstructor() {
 			super();
 		}
 
 		@Override
 		protected Map<Object, Object> constructMapping(MappingNode node) {
 			try {
 				return super.constructMapping(node);
 			} catch (IllegalStateException e) {
 				throw new ParserException("while parsing MappingNode",
 						node.getStartMark(), e.getMessage(), node.getEndMark());
 			}
 		}
 
 		@Override
 		protected Map<Object, Object> createDefaultMap() {
 			final Map<Object, Object> delegate = super.createDefaultMap();
 			return new AbstractMap<Object, Object>() {
 				@Override
 				public Object put(Object key, Object value) {
 					if (delegate.containsKey(key)) {
 						throw new IllegalStateException("duplicate key: " + key);
 					}
 					return delegate.put(key, value);
 				}
 				@Override
 				public Set<Entry<Object, Object>> entrySet() {
 					return delegate.entrySet();
 				}
 			};
 		}
 
 	}
 
 }