/*
 * Copyright 2013 Google Inc.
 *
 * 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.common.jimfs;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.collect.ComparisonChain;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import java.io.File;
import java.io.IOException;
import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.LinkOption;
import java.nio.file.Path;
import java.nio.file.ProviderMismatchException;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.AbstractList;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Deque;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;

/**
 * Jimfs implementation of {@link Path}. Creation of new {@code Path} objects is delegated to the
 * file system's {@link PathService}.
 *
 * @author Colin Decker
 */
final class JimfsPath implements Path {

  @NullableDecl private final Name root;
  private final ImmutableList<Name> names;
  private final PathService pathService;

  public JimfsPath(PathService pathService, @NullableDecl Name root, Iterable<Name> names) {
    this.pathService = checkNotNull(pathService);
    this.root = root;
    this.names = ImmutableList.copyOf(names);
  }

  /** Returns the root name, or null if there is no root. */
  @NullableDecl
  public Name root() {
    return root;
  }

  /** Returns the list of name elements. */
  public ImmutableList<Name> names() {
    return names;
  }

  /**
   * Returns the file name of this path. Unlike {@link #getFileName()}, this may return the name of
   * the root if this is a root path.
   */
  @NullableDecl
  public Name name() {
    if (!names.isEmpty()) {
      return Iterables.getLast(names);
    }
    return root;
  }

  /**
   * Returns whether or not this is the empty path, with no root and a single, empty string, name.
   */
  public boolean isEmptyPath() {
    return root == null && names.size() == 1 && names.get(0).toString().isEmpty();
  }

  @Override
  public FileSystem getFileSystem() {
    return pathService.getFileSystem();
  }

  /**
   * Equivalent to {@link #getFileSystem()} but with a return type of {@code JimfsFileSystem}.
   * {@code getFileSystem()}'s return type is left as {@code FileSystem} to make testing paths
   * easier (as long as methods that access the file system in some way are not called, the file
   * system can be a fake file system instance).
   */
  public JimfsFileSystem getJimfsFileSystem() {
    return (JimfsFileSystem) pathService.getFileSystem();
  }

  @Override
  public boolean isAbsolute() {
    return root != null;
  }

  @Override
  public JimfsPath getRoot() {
    if (root == null) {
      return null;
    }
    return pathService.createRoot(root);
  }

  @Override
  public JimfsPath getFileName() {
    return names.isEmpty() ? null : getName(names.size() - 1);
  }

  @Override
  public JimfsPath getParent() {
    if (names.isEmpty() || (names.size() == 1 && root == null)) {
      return null;
    }

    return pathService.createPath(root, names.subList(0, names.size() - 1));
  }

  @Override
  public int getNameCount() {
    return names.size();
  }

  @Override
  public JimfsPath getName(int index) {
    checkArgument(
        index >= 0 && index < names.size(),
        "index (%s) must be >= 0 and < name count (%s)",
        index,
        names.size());
    return pathService.createFileName(names.get(index));
  }

  @Override
  public JimfsPath subpath(int beginIndex, int endIndex) {
    checkArgument(
        beginIndex >= 0 && endIndex <= names.size() && endIndex > beginIndex,
        "beginIndex (%s) must be >= 0; endIndex (%s) must be <= name count (%s) and > beginIndex",
        beginIndex,
        endIndex,
        names.size());
    return pathService.createRelativePath(names.subList(beginIndex, endIndex));
  }

  /** Returns true if list starts with all elements of other in the same order. */
  private static boolean startsWith(List<?> list, List<?> other) {
    return list.size() >= other.size() && list.subList(0, other.size()).equals(other);
  }

  @Override
  public boolean startsWith(Path other) {
    JimfsPath otherPath = checkPath(other);
    return otherPath != null
        && getFileSystem().equals(otherPath.getFileSystem())
        && Objects.equals(root, otherPath.root)
        && startsWith(names, otherPath.names);
  }

  @Override
  public boolean startsWith(String other) {
    return startsWith(pathService.parsePath(other));
  }

  @Override
  public boolean endsWith(Path other) {
    JimfsPath otherPath = checkPath(other);
    if (otherPath == null) {
      return false;
    }

    if (otherPath.isAbsolute()) {
      return compareTo(otherPath) == 0;
    }
    return startsWith(names.reverse(), otherPath.names.reverse());
  }

  @Override
  public boolean endsWith(String other) {
    return endsWith(pathService.parsePath(other));
  }

  @Override
  public JimfsPath normalize() {
    if (isNormal()) {
      return this;
    }

    Deque<Name> newNames = new ArrayDeque<>();
    for (Name name : names) {
      if (name.equals(Name.PARENT)) {
        Name lastName = newNames.peekLast();
        if (lastName != null && !lastName.equals(Name.PARENT)) {
          newNames.removeLast();
        } else if (!isAbsolute()) {
          // if there's a root and we have an extra ".." that would go up above the root, ignore it
          newNames.add(name);
        }
      } else if (!name.equals(Name.SELF)) {
        newNames.add(name);
      }
    }

    return Iterables.elementsEqual(newNames, names) ? this : pathService.createPath(root, newNames);
  }

  /**
   * Returns whether or not this path is in a normalized form. It's normal if it both contains no
   * "." names and contains no ".." names in a location other than the start of the path.
   */
  private boolean isNormal() {
    if (getNameCount() == 0 || (getNameCount() == 1 && !isAbsolute())) {
      return true;
    }

    boolean foundNonParentName = isAbsolute(); // if there's a root, the path doesn't start with ..
    boolean normal = true;
    for (Name name : names) {
      if (name.equals(Name.PARENT)) {
        if (foundNonParentName) {
          normal = false;
          break;
        }
      } else {
        if (name.equals(Name.SELF)) {
          normal = false;
          break;
        }

        foundNonParentName = true;
      }
    }
    return normal;
  }

  /** Resolves the given name against this path. The name is assumed not to be a root name. */
  JimfsPath resolve(Name name) {
    if (name.toString().isEmpty()) {
      return this;
    }
    return pathService.createPathInternal(
        root, ImmutableList.<Name>builder().addAll(names).add(name).build());
  }

  @Override
  public JimfsPath resolve(Path other) {
    JimfsPath otherPath = checkPath(other);
    if (otherPath == null) {
      throw new ProviderMismatchException(other.toString());
    }

    if (isEmptyPath() || otherPath.isAbsolute()) {
      return otherPath;
    }
    if (otherPath.isEmptyPath()) {
      return this;
    }
    return pathService.createPath(
        root, ImmutableList.<Name>builder().addAll(names).addAll(otherPath.names).build());
  }

  @Override
  public JimfsPath resolve(String other) {
    return resolve(pathService.parsePath(other));
  }

  @Override
  public JimfsPath resolveSibling(Path other) {
    JimfsPath otherPath = checkPath(other);
    if (otherPath == null) {
      throw new ProviderMismatchException(other.toString());
    }

    if (otherPath.isAbsolute()) {
      return otherPath;
    }
    JimfsPath parent = getParent();
    if (parent == null) {
      return otherPath;
    }
    return parent.resolve(other);
  }

  @Override
  public JimfsPath resolveSibling(String other) {
    return resolveSibling(pathService.parsePath(other));
  }

  @Override
  public JimfsPath relativize(Path other) {
    JimfsPath otherPath = checkPath(other);
    if (otherPath == null) {
      throw new ProviderMismatchException(other.toString());
    }

    checkArgument(
        Objects.equals(root, otherPath.root), "Paths have different roots: %s, %s", this, other);

    if (equals(other)) {
      return pathService.emptyPath();
    }

    if (isEmptyPath()) {
      return otherPath;
    }

    ImmutableList<Name> otherNames = otherPath.names;
    int sharedSubsequenceLength = 0;
    for (int i = 0; i < Math.min(getNameCount(), otherNames.size()); i++) {
      if (names.get(i).equals(otherNames.get(i))) {
        sharedSubsequenceLength++;
      } else {
        break;
      }
    }

    int extraNamesInThis = Math.max(0, getNameCount() - sharedSubsequenceLength);

    ImmutableList<Name> extraNamesInOther =
        (otherNames.size() <= sharedSubsequenceLength)
            ? ImmutableList.<Name>of()
            : otherNames.subList(sharedSubsequenceLength, otherNames.size());

    List<Name> parts = new ArrayList<>(extraNamesInThis + extraNamesInOther.size());

    // add .. for each extra name in this path
    parts.addAll(Collections.nCopies(extraNamesInThis, Name.PARENT));
    // add each extra name in the other path
    parts.addAll(extraNamesInOther);

    return pathService.createRelativePath(parts);
  }

  @Override
  public JimfsPath toAbsolutePath() {
    return isAbsolute() ? this : getJimfsFileSystem().getWorkingDirectory().resolve(this);
  }

  @Override
  public JimfsPath toRealPath(LinkOption... options) throws IOException {
    return getJimfsFileSystem()
        .getDefaultView()
        .toRealPath(this, pathService, Options.getLinkOptions(options));
  }

  @Override
  public WatchKey register(
      WatchService watcher, WatchEvent.Kind<?>[] events, WatchEvent.Modifier... modifiers)
      throws IOException {
    checkNotNull(modifiers);
    return register(watcher, events);
  }

  @Override
  public WatchKey register(WatchService watcher, WatchEvent.Kind<?>... events) throws IOException {
    checkNotNull(watcher);
    checkNotNull(events);
    if (!(watcher instanceof AbstractWatchService)) {
      throw new IllegalArgumentException(
          "watcher (" + watcher + ") is not associated with this file system");
    }

    AbstractWatchService service = (AbstractWatchService) watcher;
    return service.register(this, Arrays.asList(events));
  }

  @Override
  public URI toUri() {
    return getJimfsFileSystem().toUri(this);
  }

  @Override
  public File toFile() {
    // documented as unsupported for anything but the default file system
    throw new UnsupportedOperationException();
  }

  @Override
  public Iterator<Path> iterator() {
    return asList().iterator();
  }

  private List<Path> asList() {
    return new AbstractList<Path>() {
      @Override
      public Path get(int index) {
        return getName(index);
      }

      @Override
      public int size() {
        return getNameCount();
      }
    };
  }

  @Override
  public int compareTo(Path other) {
    // documented to throw CCE if other is associated with a different FileSystemProvider
    JimfsPath otherPath = (JimfsPath) other;
    return ComparisonChain.start()
        .compare(getJimfsFileSystem().getUri(), ((JimfsPath) other).getJimfsFileSystem().getUri())
        .compare(this, otherPath, pathService)
        .result();
  }

  @Override
  public boolean equals(@NullableDecl Object obj) {
    return obj instanceof JimfsPath && compareTo((JimfsPath) obj) == 0;
  }

  @Override
  public int hashCode() {
    return pathService.hash(this);
  }

  @Override
  public String toString() {
    return pathService.toString(this);
  }

  @NullableDecl
  private JimfsPath checkPath(Path other) {
    if (checkNotNull(other) instanceof JimfsPath && other.getFileSystem().equals(getFileSystem())) {
      return (JimfsPath) other;
    }
    return null;
  }
}