/****************************************************************************
 * Copyright (C) 2013 ecsec GmbH.
 * All rights reserved.
 * Contact: ecsec GmbH (info@ecsec.de)
 *
 * This file is part of the Open eCard App.
 *
 * GNU General Public License Usage
 * This file may be used under the terms of the GNU General Public
 * License version 3.0 as published by the Free Software Foundation
 * and appearing in the file LICENSE.GPL included in the packaging of
 * this file. Please review the following information to ensure the
 * GNU General Public License version 3.0 requirements will be met:
 * http://www.gnu.org/copyleft/gpl.html.
 *
 * Other Usage
 * Alternatively, this file may be used in accordance with the terms
 * and conditions contained in a signed written agreement between
 * you and ecsec GmbH.
 *
 ***************************************************************************/

package at.gv.egiz.smcc.util;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Helper class to find shared object (.so) libraries in linux systems. The
 * algorithm to find the objects is the same as used in the dynamic loader ld.
 * There is one exception to this rule, the ELF variables DT_RPATH and
 * DT_RUNPATH are not evaluated, because they are not available in java.
 * 
 * @author Tobias Wich <tobias.wich@ecsec.de>
 */
public class LinuxLibraryFinder {

  private static final Logger logger = LoggerFactory
      .getLogger(LinuxLibraryFinder.class);

  /**
   * Gets a file object pointing to the library which has been searched. On
   * success, the file points to first file found which is readable and thus can
   * be used.
   * <p>
   * The algorithm to find the library can be found in the ld.so(8) manpage and
   * is as follows:
   * <ol>
   * <li>Check paths in {@code LD_LIBRARY_PATH} environment variable.</li>
   * <li>Check for library in {@code /etc/ld.so.cache} by executing
   * {@code ldconfig -p} and searching the output.</li>
   * <li>Check the base library paths {@code /lib} and {@code /usr/lib} or
   * {@code /lib64} and {@code /usr/lib64} depending on the architecture.</li>
   * </ol>
   * </p>
   * 
   * @param name
   *          Name of the library, such as pcsclite.
   * @param version
   *          Version suffix such as 1, 1.0 or null if no suffix is desired.
   * @return The file object to the library.
   */
  public static File getLibraryPath(String name, String version)
      throws FileNotFoundException {
    // add version only if it has a meaningful value
    version = version == null ? "" : version;
    version = version.isEmpty() ? "" : ("." + version);
    String libname = System.mapLibraryName(name) + version;

    File result;
    // LD_LIBRARY_PATH
    result = findInEnv(libname, System.getenv("LD_LIBRARY_PATH"));
    if (result != null) {
      return result;
    }
    // ld.so.cache
    result = findInLdCache(libname);
    if (result != null) {
      return result;
    }
    // base lib paths
    result = findInBaseLibPaths(libname);
    if (result != null) {
      return result;
    }

    throw new FileNotFoundException("Library " + libname
        + " not found on your system.");
  }

  private static File findInEnv(String libname, String env) {
    if (env != null) {
      for (String path : env.split(":")) {
        // append lib to path and see if it exists
        String result = path + "/" + libname;
        File test = new File(result.trim());
        if (test.canRead()) {
          return test;
        }
      }
    }
    // nothing found
    return null;
  }

  private static File findInLdCache(String libname) {
    String ldconfExec = findProgramFile("ldconfig") + " -p";
    Process p = null;
    try {
      p = Runtime.getRuntime().exec(ldconfExec);
      InputStream cacheData = p.getInputStream();
      BufferedReader cacheDataReader = new BufferedReader(
          new InputStreamReader(cacheData));
      String next;
      while ((next = cacheDataReader.readLine()) != null) {
        if (next.endsWith(libname)) {
          // extract library path from entry
          // the line can look like this:
          // libpcsclite.so.1 (libc6,x86-64) =>
          // /usr/lib/x86_64-linux-gnu/libpcsclite.so.1
          int endIdx = next.lastIndexOf("=>");
          if (endIdx != -1) {
            String result = next.substring(endIdx + 2);
            File test = new File(result.trim());
            if (test.canRead()) {
              return test;
            }
          }
        }
      }
    } catch (IOException ex) {
      logger.debug("Library {} not found in ld.so.cache.", libname);
    } finally {
      if (p != null) {
        try {
          p.getInputStream().close();
        } catch (IOException ex) {
          // dafuq?!?
        }
        try {
          p.getOutputStream().close();
        } catch (IOException ex) {
          // dafuq?!?
        }
        try {
          p.getErrorStream().close();
        } catch (IOException ex) {
          // dafuq?!?
        }
      }
    }
    return null;
  }

  private static String findProgramFile(String name) {
    String path = System.getenv().get("PATH");
    path = path == null ? "" : path;
    path = "/sbin:/usr/sbin:" + path;
    // loop through entries and find program
    for (String entry : path.split(":")) {
      String fname = entry + "/" + name;
      File f = new File(fname);
      if (f.canExecute()) {
        return fname;
      }
    }
    // nothing found, maybe the file is in the same path
    return name;
  }

  private static File findInBaseLibPaths(String libname) {
    String archSuffix = "64".equals(System.getProperty("sun.arch.data.model")) ? "64"
        : "";
    String[] basePaths = { "/lib" + archSuffix, "/usr/lib" + archSuffix };
    // look for lib in those paths
    for (String path : basePaths) {
      String fname = path + "/" + libname;
      File test = new File(fname);
      if (test.canRead()) {
        return test;
      }
    }
    return null;
  }

}