/*******************************************************************************
 * Copyright (c) 2000, 2018 IBM Corporation and others.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 * 
 * SPDX-License-Identifier: EPL-2.0
 *
 *******************************************************************************/
package org.eclipse.dltk.ui.documentation;

import java.io.CharArrayReader;
import java.io.IOException;
import java.io.Reader;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import org.eclipse.core.runtime.IAdaptable;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.dltk.core.DLTKCore;
import org.eclipse.dltk.core.IMember;
import org.eclipse.dltk.core.IModelElement;
import org.eclipse.dltk.core.ModelException;
import org.eclipse.dltk.utils.AdaptUtils;
import org.eclipse.dltk.utils.NatureExtensionManager;
import org.eclipse.jface.resource.ImageDescriptor;

/**
 * Helper needed to get access to script documentation.
 *
 * <p>
 * This class is not intended to be subclassed or instantiated by clients.
 * </p>
 */
public class ScriptDocumentationAccess {
	private static final String DOCUMENTATION_PROVIDERS_EXTENSION_POINT = "org.eclipse.dltk.ui.scriptDocumentationProviders"; //$NON-NLS-1$

	private static final NatureExtensionManager<IScriptDocumentationProvider> providers = new NatureExtensionManager<IScriptDocumentationProvider>(
			DOCUMENTATION_PROVIDERS_EXTENSION_POINT, IScriptDocumentationProvider.class) {
		@Override
		protected void initializeDescriptors(List<Object> descriptors) {
			Collections.sort(descriptors, new Comparator<Object>() {
				int priority(IConfigurationElement element) {
					try {
						return Integer.parseInt(element.getAttribute("priority"));
					} catch (NumberFormatException e) {
						return 0;
					}
				}

				@Override
				public int compare(Object o1, Object o2) {
					return priority((IConfigurationElement) o2) - priority((IConfigurationElement) o1);
				}
			});
		}

		@Override
		protected IScriptDocumentationProvider[] createEmptyResult() {
			return new IScriptDocumentationProvider[0];
		}
	};

	private ScriptDocumentationAccess() {
		// do not instantiate
	}

	private static IScriptDocumentationProvider[] getProviders(String nature) {
		return providers.getInstances(nature);
	}

	private static interface Operation {
		Reader getInfo(IScriptDocumentationProvider provider);
	}

	private static interface Operation2 {
		IDocumentationResponse getInfo(IScriptDocumentationProvider provider);
	}

	private static final int BUFF_SIZE = 2048;

	private static Reader merge(String nature, Operation operation) {
		StringBuilder buffer = new StringBuilder();
		char[] buff = null;
		for (IScriptDocumentationProvider p : getProviders(nature)) {
			Reader reader = operation.getInfo(p);
			if (reader != null) {
				if (buffer.length() != 0) {
					buffer.append("<hr/>"); //$NON-NLS-1$
				}
				if (buff == null) {
					buff = new char[BUFF_SIZE];
				}
				try {
					int len;
					while ((len = reader.read(buff, 0, BUFF_SIZE)) != -1) {
						buffer.append(buff, 0, len);
					}
				} catch (IOException e) {
					if (DLTKCore.DEBUG) {
						e.printStackTrace();
					}
				}
			}
		}
		if (buffer.length() > 0) {
			char[] cnt = new char[buffer.length()];
			buffer.getChars(0, buffer.length(), cnt, 0);
			return new CharArrayReader(cnt);
		}
		return null;
	}

	private static IDocumentationResponse merge(String nature, Operation2 operation) {
		for (IScriptDocumentationProvider p : getProviders(nature)) {
			final IDocumentationResponse response = operation.getInfo(p);
			if (response != null) {
				return response;
			}
		}
		return null;
	}

	/**
	 * Gets a reader for an IMember documentation. Content are found using
	 * documentation documentationProviders, contributed via extension point. The
	 * content does contain HTML code describing member. It may be for ex. header
	 * comment or a man page. (if <code>allowExternal</code> is <code>true</code>)
	 *
	 * @param member         The member to get documentation for.
	 * @param allowInherited For procedures and methods: if member doesn't have it's
	 *                       own documentation, look into parent types methods.
	 * @param allowExternal  Allows external documentation like man-pages.
	 * @return Reader for a content, or <code>null</code> if no documentation is
	 *         found.
	 * @throws ModelException is thrown when the elements documentation can not be
	 *                        accessed
	 * @since 3.0
	 */
	public static Reader getHTMLContentReader(String nature, final Object member, final boolean allowInherited,
			final boolean allowExternal) {
		return merge(nature, (Operation) provider -> {
			if (provider instanceof IScriptDocumentationProviderExtension2) {
				final IScriptDocumentationProviderExtension2 ext = (IScriptDocumentationProviderExtension2) provider;
				final IDocumentationResponse response = ext.getDocumentationFor(member);
				return DocumentationUtils.getReader(response);
			} else if (member instanceof IMember) {
				return provider.getInfo((IMember) member, allowInherited, allowExternal);
			} else {
				return null;
			}
		});
	}

	/**
	 * @since 3.0
	 */
	public static IDocumentationResponse getDocumentation(String nature, final Object member,
			final IAdaptable context) {
		return merge(nature, (Operation2) provider -> {
			if (provider instanceof IScriptDocumentationProviderExtension2) {
				final IScriptDocumentationProviderExtension2 ext = (IScriptDocumentationProviderExtension2) provider;
				final IDocumentationResponse response = ext.getDocumentationFor(member);
				if (response != null && response.getTitle() == null) {
					final IScriptDocumentationTitleAdapter titleAdapter = AdaptUtils.getAdapter(context,
							IScriptDocumentationTitleAdapter.class);
					if (titleAdapter != null) {
						final String title = titleAdapter.getTitle(member);
						// TODO (alex) image
						if (title != null && title.length() != 0) {
							return new DocumentationResponseDelegate(response) {
								@Override
								public String getTitle() {
									return title;
								}

								private boolean imageEvaluated;
								private ImageDescriptor image;

								@Override
								public ImageDescriptor getImage() {
									final ImageDescriptor result = super.getImage();
									if (result != null) {
										return result;
									}
									if (!imageEvaluated) {
										image = titleAdapter.getImage(member);
										imageEvaluated = true;
									}
									return image;
								}
							};
						}
					}
				}
				return response;
			} else if (member instanceof IMember) {
				final IMember m = (IMember) member;
				return DocumentationUtils.wrap(member, context, provider.getInfo(m, true, true));
			} else {
				return null;
			}
		});
	}

	/**
	 * Gets a reader for an keyword documentation. Content are found using ALL
	 * documentation documentationProviders, contributed via extension point. The
	 * content does contain HTML code describing member.
	 *
	 * @param content The keyword to find.
	 * @return Reader for a content, or <code>null</code> if no documentation is
	 *         found.
	 * @throws ModelException is thrown when the elements documentation can not be
	 *                        accessed
	 */
	@Deprecated
	public static Reader getHTMLContentReader(String nature, final String content) throws ModelException {
		return merge(nature, (Operation) provider -> provider.getInfo(content));
	}

	/**
	 * Returns the documentation for the specified keyword
	 *
	 * @param nature
	 * @param context
	 * @param keyword
	 * @since 2.0
	 */
	public static Reader getKeywordDocumentation(String nature, final IModelElement context, final String keyword)
			throws ModelException {
		return merge(nature, (Operation) provider -> {
			if (provider instanceof IScriptDocumentationProviderExtension) {
				final IScriptDocumentationProviderExtension ext = (IScriptDocumentationProviderExtension) provider;
				final IDocumentationResponse response = ext.describeKeyword(keyword, context);
				return DocumentationUtils.getReader(response);
			}
			return provider.getInfo(keyword);
		});
	}
}