import static com.google.common.collect.Lists.newArrayList;
import static com.google.common.collect.Sets.newHashSet;

import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.List;
import java.util.Set;

public class ExceptionUtils {
  private static final String INDENT = "\t";
  private static List<String> _suppressedPackages = newArrayList("org.h2", "org.hibernate", "$Proxy", "org.junit", "java.lang.reflect.Method", "sun.", "org.eclipse", "junit.framework");

  public static String getFilteredStackTrace(Throwable t) {
    return getFilteredStackTrace(t, true);
  }

  public static String getFilteredStackTrace(Throwable t, boolean shouldFilter) {
    try {
      StringWriter sw = new StringWriter();
      PrintWriter pw = new PrintWriter(sw);
      writeCleanStackTrace(t, pw, shouldFilter);
      return sw.getBuffer().toString();
    }
    catch (Exception e) {
      e.printStackTrace();
      return e.toString();
    }
  }

  private static void writeCleanStackTrace(Throwable t, PrintWriter s, boolean wantsFilter) {
    s.print("Exception: ");
    printExceptionChain(t, s);
    Set<String> skippedPackages = newHashSet();
    int skippedLines = 0;
    boolean shouldFilter = wantsFilter && filtersEnabled();
    for (StackTraceElement traceElement : getBottomThrowable(t).getStackTrace()) {
      String forbiddenPackageName = null;
      if (shouldFilter) {
        forbiddenPackageName = tryGetForbiddenPackageName(traceElement);
      }

      if (forbiddenPackageName == null) {
        if (skippedPackages.size() > 0) {
          //37 lines skipped for [org.h2, org.hibernate, sun., java.lang.reflect.Method, $Proxy]
          s.println(getSkippedPackagesMessage(skippedPackages, skippedLines));
        }
        //at hib.HibExample.test(HibExample.java:18)
        s.println(INDENT + "at " + traceElement);
        skippedPackages.clear();
        skippedLines = 0;
      }
      else {
        skippedLines++;
        skippedPackages.add(forbiddenPackageName);
      }
    }
    if (skippedLines > 0) {
      s.println(getSkippedPackagesMessage(skippedPackages, skippedLines));
    }
  }

  //37 lines skipped for [org.h2, org.hibernate, sun., java.lang.reflect.Method, $Proxy]
  private static String getSkippedPackagesMessage(Set<String> skippedPackages, int skippedLines) {
    return INDENT + skippedLines + " line" + (skippedLines == 1 ? "" : "s") + " skipped for " + skippedPackages;
  }

  private static Throwable getBottomThrowable(Throwable t) {
    while (t.getCause() != null) {
      t = t.getCause();
    }
    return t;
  }

  /**
   * Check configuration to see if filtering is enabled system-wide
   */
  private static boolean filtersEnabled() {
    return true;
  }

  private static void printExceptionChain(Throwable t, PrintWriter s) {
    s.println(t);
    if (t.getCause() != null) {
      s.print("Caused by: ");
      printExceptionChain(t.getCause(), s);
    }
  }

  /**
   * Checks to see if the class is part of a forbidden package. If so, it returns the package name from the list of suppressed packages that matches, otherwise it returns null.
   */
  private static String tryGetForbiddenPackageName(StackTraceElement traceElement) {
    String classAndMethod = traceElement.getClassName() + "." + traceElement.getMethodName();
    for (String pkg : _suppressedPackages) {
      if (classAndMethod.startsWith(pkg)) {
        return pkg;
      }
    }
    return null;
  }
}