// Copyright (C) 2013 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.server.change;

import static com.google.common.base.Preconditions.checkState;

import com.google.common.base.Objects;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.gerrit.common.data.PatchScript;
import com.google.gerrit.common.data.PatchScript.DisplayMethod;
import com.google.gerrit.common.data.PatchScript.FileMode;
import com.google.gerrit.extensions.restapi.CacheControl;
import com.google.gerrit.extensions.restapi.IdString;
import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
import com.google.gerrit.extensions.restapi.Response;
import com.google.gerrit.extensions.restapi.RestReadView;
import com.google.gerrit.prettify.common.SparseFileContent;
import com.google.gerrit.reviewdb.client.Account;
import com.google.gerrit.reviewdb.client.AccountDiffPreference;
import com.google.gerrit.reviewdb.client.Patch.ChangeType;
import com.google.gerrit.reviewdb.client.PatchSet;
import com.google.gerrit.server.patch.PatchScriptFactory;
import com.google.gerrit.server.project.NoSuchChangeException;
import com.google.gerrit.server.git.LargeObjectException;
import com.google.gwtorm.server.OrmException;
import com.google.inject.Inject;
import com.google.inject.Provider;
import org.eclipse.jgit.diff.Edit;
import org.eclipse.jgit.diff.ReplaceEdit;
import org.kohsuke.args4j.CmdLineException;
import org.kohsuke.args4j.CmdLineParser;
import org.kohsuke.args4j.NamedOptionDef;
import org.kohsuke.args4j.Option;
import org.kohsuke.args4j.OptionDef;
import org.kohsuke.args4j.spi.OptionHandler;
import org.kohsuke.args4j.spi.Parameters;
import org.kohsuke.args4j.spi.Setter;

import java.util.List;
import java.util.concurrent.TimeUnit;

public class GetDiff implements RestReadView<FileResource> {
  private final PatchScriptFactory.Factory patchScriptFactoryFactory;
  private final Provider<Revisions> revisions;

  @Option(name = "--base", metaVar = "REVISION")
  String base;

  @Option(name = "--ignore-whitespace")
  IgnoreWhitespace ignoreWhitespace = IgnoreWhitespace.NONE;

  @Option(name = "--context", handler = ContextOptionHandler.class)
  short context = AccountDiffPreference.DEFAULT_CONTEXT;

  @Option(name = "--intraline")
  boolean intraline;

  @Inject
  GetDiff(PatchScriptFactory.Factory patchScriptFactoryFactory,
      Provider<Revisions> revisions) {
    this.patchScriptFactoryFactory = patchScriptFactoryFactory;
    this.revisions = revisions;
  }

  @Override
  public Object apply(FileResource resource)
      throws OrmException, NoSuchChangeException, LargeObjectException, ResourceNotFoundException {
    PatchSet.Id basePatchSet = null;
    if (base != null) {
      RevisionResource baseResource = revisions.get().parse(
          resource.getRevision().getChangeResource(), IdString.fromDecoded(base));
      basePatchSet = baseResource.getPatchSet().getId();
    }
    AccountDiffPreference prefs = new AccountDiffPreference(new Account.Id(0));
    prefs.setIgnoreWhitespace(ignoreWhitespace.whitespace);
    prefs.setContext(context);
    prefs.setIntralineDifference(intraline);

    PatchScript ps = patchScriptFactoryFactory.create(
        resource.getRevision().getControl(),
        resource.getPatchKey().getFileName(),
        basePatchSet,
        resource.getPatchKey().getParentKey(),
        prefs)
          .call();

    Content content = new Content(ps);
    for (Edit edit : ps.getEdits()) {
      if (edit.getType() == Edit.Type.EMPTY) {
        continue;
      }
      content.addCommon(edit.getBeginA());

      checkState(content.nextA == edit.getBeginA(),
          "nextA = %d; want %d", content.nextA, edit.getBeginA());
      checkState(content.nextB == edit.getBeginB(),
          "nextB = %d; want %d", content.nextB, edit.getBeginB());
      switch (edit.getType()) {
        case DELETE:
        case INSERT:
        case REPLACE:
          List<Edit> internalEdit = edit instanceof ReplaceEdit
            ? ((ReplaceEdit) edit).getInternalEdits()
            : null;
          content.addDiff(edit.getEndA(), edit.getEndB(), internalEdit);
          break;
        case EMPTY:
        default:
          throw new IllegalStateException();
      }
    }
    content.addCommon(ps.getA().size());

    Result result = new Result();
    if (ps.getDisplayMethodA() != DisplayMethod.NONE) {
      result.metaA = new FileMeta();
      result.metaA.name = Objects.firstNonNull(ps.getOldName(), ps.getNewName());
      result.metaA.setContentType(ps.getFileModeA(), ps.getMimeTypeA());
    }

    if (ps.getDisplayMethodB() != DisplayMethod.NONE) {
      result.metaB = new FileMeta();
      result.metaB.name = ps.getNewName();
      result.metaB.setContentType(ps.getFileModeB(), ps.getMimeTypeB());
    }

    if (intraline) {
      if (ps.hasIntralineTimeout()) {
        result.intralineStatus = IntraLineStatus.TIMEOUT;
      } else if (ps.hasIntralineFailure()) {
        result.intralineStatus = IntraLineStatus.FAILURE;
      } else {
        result.intralineStatus = IntraLineStatus.OK;
      }
    }

    result.changeType = ps.getChangeType();
    if (ps.getPatchHeader().size() > 0) {
      result.diffHeader = ps.getPatchHeader();
    }
    result.content = content.lines;
    Response<Result> r = Response.ok(result);
    if (resource.isCacheable()) {
      r.caching(CacheControl.PRIVATE(7, TimeUnit.DAYS));
    }
    return r;
  }

  static class Result {
    FileMeta metaA;
    FileMeta metaB;
    IntraLineStatus intralineStatus;
    ChangeType changeType;
    List<String> diffHeader;
    List<ContentEntry> content;
  }

  static class FileMeta {
    String name;
    String contentType;
    String url;

    void setContentType(FileMode fileMode, String mimeType) {
      switch (fileMode) {
        case FILE:
          contentType = mimeType;
          break;
        case GITLINK:
          contentType = "x-git/gitlink";
          break;
        case SYMLINK:
          contentType = "x-git/symlink";
          break;
        default:
          throw new IllegalStateException("file mode: " + fileMode);
      }
    }
  }

  enum IntraLineStatus {
    OK,
    TIMEOUT,
    FAILURE;
  }

  private static class Content {
    final List<ContentEntry> lines;
    final SparseFileContent fileA;
    final SparseFileContent fileB;

    int nextA;
    int nextB;

    Content(PatchScript ps) {
      lines = Lists.newArrayListWithExpectedSize(ps.getEdits().size() + 2);
      fileA = ps.getA();
      fileB = ps.getB();
    }

    void addCommon(int end) {
      end = Math.min(end, fileA.size());
      if (nextA >= end) {
        return;
      }
      nextB += end - nextA;

      while (nextA < end) {
        if (fileA.contains(nextA)) {
          ContentEntry e = entry();
          e.ab = Lists.newArrayListWithCapacity(end - nextA);
          for (int i = nextA; i == nextA && i < end; i = fileA.next(i), nextA++) {
            e.ab.add(fileA.get(i));
          }
        } else {
          int endRegion = Math.min(end,
              (nextA == 0) ? fileA.first() : fileA.next(nextA - 1));
          ContentEntry e = entry();
          e.skip = endRegion - nextA;
          nextA = endRegion;
        }
      }
    }

    void addDiff(int endA, int endB, List<Edit> internalEdit) {
      int lenA = endA - nextA;
      int lenB = endB - nextB;
      checkState(lenA > 0 || lenB > 0);

      ContentEntry e = entry();
      if (lenA > 0) {
        e.a = Lists.newArrayListWithCapacity(lenA);
        for (; nextA < endA; nextA++) {
          e.a.add(fileA.get(nextA));
        }
      }
      if (lenB > 0) {
        e.b = Lists.newArrayListWithCapacity(lenB);
        for (; nextB < endB; nextB++) {
          e.b.add(fileB.get(nextB));
        }
      }
      if (internalEdit != null && !internalEdit.isEmpty()) {
        e.editA = Lists.newArrayListWithCapacity(internalEdit.size() * 2);
        e.editB = Lists.newArrayListWithCapacity(internalEdit.size() * 2);
        int lastA = 0;
        int lastB = 0;
        for (Edit edit : internalEdit) {
          if (edit.getBeginA() != edit.getEndA()) {
            e.editA.add(ImmutableList.of(edit.getBeginA() - lastA, edit.getEndA() - edit.getBeginA()));
            lastA = edit.getEndA();
          }
          if (edit.getBeginB() != edit.getEndB()) {
            e.editB.add(ImmutableList.of(edit.getBeginB() - lastB, edit.getEndB() - edit.getBeginB()));
            lastB = edit.getEndB();
          }
        }
      }
    }

    private ContentEntry entry() {
      ContentEntry e = new ContentEntry();
      lines.add(e);
      return e;
    }
  }

  enum IgnoreWhitespace {
    NONE(AccountDiffPreference.Whitespace.IGNORE_NONE),
    TRAILING(AccountDiffPreference.Whitespace.IGNORE_SPACE_AT_EOL),
    CHANGED(AccountDiffPreference.Whitespace.IGNORE_SPACE_CHANGE),
    ALL(AccountDiffPreference.Whitespace.IGNORE_ALL_SPACE);

    private final AccountDiffPreference.Whitespace whitespace;

    private IgnoreWhitespace(AccountDiffPreference.Whitespace whitespace) {
      this.whitespace = whitespace;
    }
  }

  static final class ContentEntry {
    // Common lines to both sides.
    List<String> ab;
    // Lines of a.
    List<String> a;
    // Lines of b.
    List<String> b;

    // A list of changed sections of the of the corresponding line list.
    // Each entry is a character <offset, length> pair. The offset is from the
    // beginning of the first line in the list. Also, the offset includes an
    // implied trailing newline character for each line.
    List<List<Integer>> editA;
    List<List<Integer>> editB;

    // Number of lines to skip on both sides.
    Integer skip;
  }

  public static class ContextOptionHandler extends OptionHandler<Short> {
    public ContextOptionHandler(
        CmdLineParser parser, OptionDef option, Setter<Short> setter) {
      super(parser, option, setter);
    }

    @Override
    public final int parseArguments(final Parameters params)
        throws CmdLineException {
      final String value = params.getParameter(0);
      short context;
      if ("all".equalsIgnoreCase(value)) {
        context = AccountDiffPreference.WHOLE_FILE_CONTEXT;
      } else {
        try {
          context = Short.parseShort(value, 10);
          if (context < 0) {
            throw new NumberFormatException();
          }
        } catch (NumberFormatException e) {
          throw new CmdLineException(owner,
              String.format("\"%s\" is not a valid value for \"%s\"",
                  value, ((NamedOptionDef) option).name()));
        }
      }
      setter.addValue(context);
      return 1;
    }

    @Override
    public final String getDefaultMetaVariable() {
      return "ALL|# LINES";
    }
  }
}