// Copyright 2014 The Bazel Authors. All rights reserved.
//
// 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.devtools.build.lib.rules.java;

import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.devtools.build.lib.vfs.FileSystemUtils;
import com.google.devtools.build.lib.vfs.PathFragment;
import javax.annotation.Nullable;

/** Utility methods for use by Java-related parts of the build system. */
public final class JavaUtil {

  private JavaUtil() {}

  // ---------- Java related methods

  /*
   * TODO(bazel-team): (2009)
   *
   * This way of figuring out Java source roots is basically
   * broken. I think we need to support these two use cases:
   * (1) A user puts their shell into a directory named java.
   * (2) Someplace in the tree, there's a package named java.
   *
   * (1) is more important than (2); and (2) cannot always be guaranteed
   * due to sloppy implementations in the past; most notably the old
   * tools/boilerplate_rules.mk code for compiling Java.
   *
   * Basically, to implement correct semantics, we will need to configure
   * Java source roots based on the package path, plus some heuristics to
   * support legacy code, maybe.
   *
   * Roughly:
   * Given a path, find the source root that applies to it by
   * - walk over the elements in the package path
   * - add "java", "javatests" to them
   * - find the first element that is a maximal prefix to the Java file
   * - for experimental, some legacy support that basically has some
   * arbitrary padding before the Java sourceroot.
   */

  /**
   * Given the filename of a Java source file, returns the name of the toplevel Java class defined
   * within it.
   */
  public static String getJavaClassName(PathFragment path) {
    return FileSystemUtils.removeExtension(path.getBaseName());
  }

  /** Java source roots, used to relativize resource paths and infer main_class values. */
  public static final ImmutableSet<String> KNOWN_SOURCE_ROOTS =
      ImmutableSet.of("java", "javatests", "src", "testsrc");

  /**
   * Finds the index of the segment in a Java path fragment that precedes the source root. Starts
   * from the first "java" or "javatests" or "src" or "testsrc" segment. If the found item was
   * "src", check if this is followed by "main" or "test" and then "java" or "resources" (maven
   * layout). If the found item was "src", or "java"/"javatests" at the first segment, check for a
   * nested root directory (src, java or javatests). A nested root must be followed by
   * (com|net|org), or matching maven structure for nested "src", to be accepted, to avoid false
   * positives.
   *
   * @param path a Java source dir or file path
   * @return the index of the java segment or -1 iff no java segment was found.
   */
  private static int javaSegmentIndex(PathFragment path) {
    if (path.isAbsolute()) {
      throw new IllegalArgumentException("path must not be absolute: '" + path + "'");
    }
    int rootIndex = Iterables.indexOf(path.segments(), KNOWN_SOURCE_ROOTS::contains);
    if (rootIndex == -1) {
      return -1;
    }
    final boolean isSrc = "src".equals(path.getSegment(rootIndex));
    int checkMavenIndex = isSrc ? rootIndex : -1;
    if (rootIndex == 0 || isSrc) {
      // Check for a nested root directory.
      for (int i = rootIndex + 1, max = path.segmentCount() - 2; i <= max; i++) {
        String segment = path.getSegment(i);
        if ("src".equals(segment)
            || (isSrc && ("javatests".equals(segment) || "java".equals(segment)))) {
          String next = path.getSegment(i + 1);
          if ("com".equals(next) || "org".equals(next) || "net".equals(next)) {
            // Check for common first element of java package, to avoid false positives.
            rootIndex = i;
          } else if ("src".equals(segment)) {
            // Also accept maven style src/(main|test)/(java|resources).
            checkMavenIndex = i;
          }
          break;
        }
      }
    }
    // Check for (main|test)/(java|resources) after /src/.
    if (checkMavenIndex >= 0 && checkMavenIndex + 2 < path.segmentCount()) {
      String next = path.getSegment(checkMavenIndex + 1);
      if ("main".equals(next) || "test".equals(next)) {
        next = path.getSegment(checkMavenIndex + 2);
        if ("java".equals(next) || "resources".equals(next)) {
          rootIndex = checkMavenIndex + 2;
        }
      }
    }
    return rootIndex;
  }

  /** Given the PathFragment of a Java source file, returns the Java package to which it belongs. */
  public static String getJavaPackageName(PathFragment path) {
    int index = javaSegmentIndex(path) + 1;
    path = path.subFragment(index, path.segmentCount() - 1);
    return path.getPathString().replace('/', '.');
  }

  /**
   * Given the PathFragment of a file without extension, returns the Java fully qualified class name
   * based on the Java root relative path of the specified path or 'null' if no java root can be
   * determined.
   *
   * <p>For example, "java/foo/bar/wiz" and "javatests/foo/bar/wiz" both result in "foo.bar.wiz".
   *
   * <p>TODO(bazel-team): (2011) We need to have a more robust way to determine the Java root of a
   * relative path rather than simply trying to find the "java" or "javatests" or "src" directory.
   */
  @Nullable
  public static String getJavaFullClassname(PathFragment path) {
    PathFragment javaPath = getJavaPath(path);
    if (javaPath != null) {
      return javaPath.getPathString().replace('/', '.');
    }
    return null;
  }

  /**
   * Given the PathFragment of a Java source file, returns the Java root relative path or 'null' if
   * no java root can be determined.
   *
   * <p>For example, "{workspace}/java/foo/bar/wiz" and "{workspace}/javatests/foo/bar/wiz" both
   * result in "foo/bar/wiz".
   *
   * <p>TODO(bazel-team): (2011) We need to have a more robust way to determine the Java root of a
   * relative path rather than simply trying to find the "java" or "javatests" directory.
   */
  @Nullable
  public static PathFragment getJavaPath(PathFragment path) {
    int index = javaSegmentIndex(path);
    if (index >= 0) {
      return path.subFragment(index + 1);
    }
    return null;
  }

  /**
   * Given the PathFragment of a Java source file, returns the Java root of the specified path or
   * 'null' if no java root can be determined.
   *
   * <p>Example 1: "{workspace}/java/foo/bar/wiz" and "{workspace}/javatests/foo/bar/wiz" result in
   * "{workspace}/java" and "{workspace}/javatests" Example 2: "java/foo/bar/wiz" and
   * "javatests/foo/bar/wiz" result in "java" and "javatests"
   *
   * <p>TODO(bazel-team): (2011) We need to have a more robust way to determine the Java root of a
   * relative path rather than simply trying to find the "java" or "javatests" directory.
   */
  @Nullable
  public static PathFragment getJavaRoot(PathFragment path) {
    int index = javaSegmentIndex(path);
    if (index >= 0) {
      return path.subFragment(0, index + 1);
    }
    return null;
  }
}