// Copyright (C) 2008 The Android Open Source Project
//
// 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 com.google.gerrit.httpd.raw;

import com.google.common.hash.Hasher;
import com.google.common.hash.Hashing;
import com.google.common.collect.Lists;
import com.google.common.primitives.Bytes;
import com.google.gerrit.common.data.GerritConfig;
import com.google.gerrit.common.data.HostPageData;
import com.google.gerrit.extensions.registration.DynamicSet;
import com.google.gerrit.extensions.webui.WebUiPlugin;
import com.google.gerrit.httpd.HtmlDomUtil;
import com.google.gerrit.httpd.WebSession;
import com.google.gerrit.server.CurrentUser;
import com.google.gerrit.server.IdentifiedUser;
import com.google.gerrit.server.config.GerritServerConfig;
import com.google.gerrit.server.config.SitePaths;
import com.google.gwtexpui.linker.server.Permutation;
import com.google.gwtexpui.linker.server.PermutationSelector;
import com.google.gwtexpui.server.CacheHeaders;
import com.google.gwtjsonrpc.server.JsonServlet;
import com.google.gwtjsonrpc.server.RPCServletUtils;
import com.google.inject.Inject;
import com.google.inject.Provider;
import com.google.inject.Singleton;

import org.eclipse.jgit.lib.Config;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.StringWriter;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/** Sends the Gerrit host page to clients. */
@SuppressWarnings("serial")
@Singleton
public class HostPageServlet extends HttpServlet {
  private static final Logger log =
      LoggerFactory.getLogger(HostPageServlet.class);
  private static final boolean IS_DEV = Boolean.getBoolean("Gerrit.GwtDevMode");
  private static final String HPD_ID = "gerrit_hostpagedata";

  private final Provider<CurrentUser> currentUser;
  private final Provider<WebSession> session;
  private final GerritConfig config;
  private final DynamicSet<WebUiPlugin> plugins;
  private final HostPageData.Theme signedOutTheme;
  private final HostPageData.Theme signedInTheme;
  private final SitePaths site;
  private final Document template;
  private final String noCacheName;
  private final PermutationSelector selector;
  private final boolean refreshHeaderFooter;
  private volatile Page page;

  @Inject
  HostPageServlet(final Provider<CurrentUser> cu, final Provider<WebSession> w,
      final SitePaths sp, final ThemeFactory themeFactory,
      final GerritConfig gc, final ServletContext servletContext,
      final DynamicSet<WebUiPlugin> webUiPlugins,
      @GerritServerConfig final Config cfg)
      throws IOException, ServletException {
    currentUser = cu;
    session = w;
    config = gc;
    plugins = webUiPlugins;
    signedOutTheme = themeFactory.getSignedOutTheme();
    signedInTheme = themeFactory.getSignedInTheme();
    site = sp;
    refreshHeaderFooter = cfg.getBoolean("site", "refreshHeaderFooter", true);
    boolean checkUserAgent = cfg.getBoolean("site", "checkUserAgent", true);

    final String pageName = "HostPage.html";
    template = HtmlDomUtil.parseFile(getClass(), pageName);
    if (template == null) {
      throw new FileNotFoundException("No " + pageName + " in webapp");
    }

    if (HtmlDomUtil.find(template, "gerrit_module") == null) {
      throw new ServletException("No gerrit_module in " + pageName);
    }
    if (HtmlDomUtil.find(template, HPD_ID) == null) {
      throw new ServletException("No " + HPD_ID + " in " + pageName);
    }

    String src = "gerrit_ui/gerrit_ui.nocache.js";
    if (!IS_DEV) {
      Element devmode = HtmlDomUtil.find(template, "gwtdevmode");
      if (devmode != null) {
        devmode.getParentNode().removeChild(devmode);
      }

      InputStream in = servletContext.getResourceAsStream("/" + src);
      if (in != null) {
        Hasher md = Hashing.md5().newHasher();
        try {
          try {
            final byte[] buf = new byte[1024];
            int n;
            while ((n = in.read(buf)) > 0) {
              md.putBytes(buf, 0, n);
            }
          } finally {
            in.close();
          }
        } catch (IOException e) {
          throw new IOException("Failed reading " + src, e);
        }
        src += "?content=" + md.hash().toString();
      } else {
        log.debug("No " + src + " in webapp root; keeping noncache.js URL");
      }
    }

    noCacheName = src;
    selector = new PermutationSelector("gerrit_ui");
    if (checkUserAgent && !IS_DEV) {
      selector.init(servletContext);
    }
    page = new Page();
  }

  private void json(final Object data, final StringWriter w) {
    JsonServlet.defaultGsonBuilder().create().toJson(data, w);
  }

  private Page get() {
    Page p = page;
    if (refreshHeaderFooter && p.isStale()) {
      final Page newPage;
      try {
        newPage = new Page();
      } catch (IOException e) {
        log.error("Cannot refresh site header/footer", e);
        return p;
      }
      p = newPage;
      page = p;
    }
    return p;
  }

  @Override
  protected void doGet(final HttpServletRequest req,
      final HttpServletResponse rsp) throws IOException {
    final Page.Content page = select(req);
    final StringWriter w = new StringWriter();
    final CurrentUser user = currentUser.get();
    if (user instanceof IdentifiedUser) {
      w.write(HPD_ID + ".account=");
      json(((IdentifiedUser) user).getAccount(), w);
      w.write(";");

      w.write(HPD_ID + ".xGerritAuth=");
      json(session.get().getXGerritAuth(), w);
      w.write(";");

      w.write(HPD_ID + ".accountDiffPref=");
      json(((IdentifiedUser) user).getAccountDiffPreference(), w);
      w.write(";");

      w.write(HPD_ID + ".theme=");
      json(signedInTheme, w);
      w.write(";");
    } else {
      w.write(HPD_ID + ".theme=");
      json(signedOutTheme, w);
      w.write(";");
    }
    plugins(w);

    final byte[] hpd = w.toString().getBytes("UTF-8");
    final byte[] raw = Bytes.concat(page.part1, hpd, page.part2);
    final byte[] tosend;
    if (RPCServletUtils.acceptsGzipEncoding(req)) {
      rsp.setHeader("Content-Encoding", "gzip");
      tosend = HtmlDomUtil.compress(raw);
    } else {
      tosend = raw;
    }

    CacheHeaders.setNotCacheable(rsp);
    rsp.setContentType("text/html");
    rsp.setCharacterEncoding(HtmlDomUtil.ENC);
    rsp.setContentLength(tosend.length);
    final OutputStream out = rsp.getOutputStream();
    try {
      out.write(tosend);
    } finally {
      out.close();
    }
  }

  private void plugins(StringWriter w) {
    List<String> urls = Lists.newArrayList();
    for (WebUiPlugin u : plugins) {
      urls.add(String.format("plugins/%s/%s",
          u.getPluginName(),
          u.getJavaScriptResourcePath()));
    }
    if (!urls.isEmpty()) {
      w.write(HPD_ID + ".plugins=");
      json(urls, w);
      w.write(";");
    }
  }

  private Page.Content select(HttpServletRequest req) {
    Page pg = get();
    if ("1".equals(req.getParameter("dbg"))) {
      return pg.debug;
    } else if ("0".equals(req.getParameter("s"))) {
      // If s=0 is used in the URL, the user has explicitly asked us
      // to not perform selection on the server side, perhaps due to
      // it incorrectly guessing their user agent.
      return pg.get(null);
    }
    return pg.get(selector.select(req));
  }

  private static class FileInfo {
    private final File path;
    private final long time;

    FileInfo(final File p) {
      path = p;
      time = path.lastModified();
    }

    boolean isStale() {
      return time != path.lastModified();
    }
  }

  private class Page {
    private final FileInfo css;
    private final FileInfo header;
    private final FileInfo footer;
    private final Map<Permutation, Content> permutations;
    private final Content debug;

    Page() throws IOException {
      Document hostDoc = HtmlDomUtil.clone(template);

      css = injectCssFile(hostDoc, "gerrit_sitecss", site.site_css);
      header = injectXmlFile(hostDoc, "gerrit_header", site.site_header);
      footer = injectXmlFile(hostDoc, "gerrit_footer", site.site_footer);

      final HostPageData pageData = new HostPageData();
      pageData.config = config;

      final StringWriter w = new StringWriter();
      w.write("var " + HPD_ID + "=");
      json(pageData, w);
      w.write(";");

      final Element data = HtmlDomUtil.find(hostDoc, HPD_ID);
      asScript(data);
      data.appendChild(hostDoc.createTextNode(w.toString()));
      data.appendChild(hostDoc.createComment(HPD_ID));

      permutations = new HashMap<Permutation, Content>();
      for (Permutation p : selector.getPermutations()) {
        final Document d = HtmlDomUtil.clone(hostDoc);
        Element nocache = HtmlDomUtil.find(d, "gerrit_module");
        nocache.getParentNode().removeChild(nocache);
        p.inject(d);
        permutations.put(p, new Content(d));
      }

      Element nocache = HtmlDomUtil.find(hostDoc, "gerrit_module");
      asScript(nocache);
      nocache.removeAttribute("id");
      nocache.setAttribute("src", noCacheName);
      permutations.put(null, new Content(hostDoc));

      nocache.setAttribute("src", "gerrit_ui/gerrit_dbg.nocache.js");
      debug = new Content(hostDoc);
    }

    Content get(Permutation p) {
      Content c = permutations.get(p);
      if (c == null) {
        c = permutations.get(null);
      }
      return c;
    }

    boolean isStale() {
      return css.isStale() || header.isStale() || footer.isStale();
    }

    private void asScript(final Element scriptNode) {
      scriptNode.setAttribute("type", "text/javascript");
      scriptNode.setAttribute("language", "javascript");
    }

    class Content {
      final byte[] part1;
      final byte[] part2;

      Content(Document hostDoc) throws IOException {
        final String raw = HtmlDomUtil.toString(hostDoc);
        final int p = raw.indexOf("<!--" + HPD_ID);
        if (p < 0) {
          throw new IOException("No tag in transformed host page HTML");
        }
        part1 = raw.substring(0, p).getBytes("UTF-8");
        part2 = raw.substring(raw.indexOf('>', p) + 1).getBytes("UTF-8");
      }
    }

    private FileInfo injectCssFile(final Document hostDoc, final String id,
        final File src) throws IOException {
      final FileInfo info = new FileInfo(src);
      final Element banner = HtmlDomUtil.find(hostDoc, id);
      if (banner == null) {
        return info;
      }

      while (banner.getFirstChild() != null) {
        banner.removeChild(banner.getFirstChild());
      }

      String css = HtmlDomUtil.readFile(src.getParentFile(), src.getName());
      if (css == null) {
        return info;
      }

      banner.appendChild(hostDoc.createCDATASection("\n" + css + "\n"));
      return info;
    }

    private FileInfo injectXmlFile(final Document hostDoc, final String id,
        final File src) throws IOException {
      final FileInfo info = new FileInfo(src);
      final Element banner = HtmlDomUtil.find(hostDoc, id);
      if (banner == null) {
        return info;
      }

      while (banner.getFirstChild() != null) {
        banner.removeChild(banner.getFirstChild());
      }

      Document html = HtmlDomUtil.parseFile(src);
      if (html == null) {
        return info;
      }

      final Element content = html.getDocumentElement();
      banner.appendChild(hostDoc.importNode(content, true));
      return info;
    }
  }
}