// Copyright (C) 2009 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.patch;

import static com.google.gerrit.common.data.PatchScriptSettings.Whitespace.IGNORE_NONE;

import com.google.gerrit.common.data.PatchScriptSettings.Whitespace;
import com.google.gerrit.reviewdb.Change;
import com.google.gerrit.reviewdb.PatchSet;
import com.google.gerrit.reviewdb.Project;
import com.google.gerrit.server.cache.Cache;
import com.google.gerrit.server.cache.CacheModule;
import com.google.gerrit.server.cache.EvictionPolicy;
import com.google.gerrit.server.cache.SelfPopulatingCache;
import com.google.gerrit.server.config.GerritServerConfig;
import com.google.gerrit.server.git.GitRepositoryManager;
import com.google.inject.Inject;
import com.google.inject.Module;
import com.google.inject.Singleton;
import com.google.inject.TypeLiteral;
import com.google.inject.name.Named;

import org.eclipse.jgit.diff.Edit;
import org.eclipse.jgit.diff.MyersDiff;
import org.eclipse.jgit.diff.ReplaceEdit;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.Config;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.FileMode;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectLoader;
import org.eclipse.jgit.lib.ObjectWriter;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.patch.FileHeader;
import org.eclipse.jgit.patch.FileHeader.PatchType;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevTree;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.treewalk.TreeWalk;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.regex.Pattern;

/** Provides a cached list of {@link PatchListEntry}. */
@Singleton
public class PatchListCacheImpl implements PatchListCache {
  private static final String CACHE_NAME = "diff";
  private static final boolean dynamic = false;

  private static final Pattern BLANK_LINE_RE =
      Pattern.compile("^[ \\t]*(|[{}]|/\\*\\*?|\\*)[ \\t]*$");
  private static final Pattern CONTROL_BLOCK_START_RE =
      Pattern.compile("[{:][ \\t]*$");

  public static Module module() {
    return new CacheModule() {
      @Override
      protected void configure() {
        final TypeLiteral<Cache<PatchListKey, PatchList>> type =
            new TypeLiteral<Cache<PatchListKey, PatchList>>() {};
        disk(type, CACHE_NAME) //
            .memoryLimit(128) // very large items, cache only a few
            .evictionPolicy(EvictionPolicy.LRU) // prefer most recent
        ;
        bind(PatchListCacheImpl.class);
        bind(PatchListCache.class).to(PatchListCacheImpl.class);
      }
    };
  }

  private final GitRepositoryManager repoManager;
  private final SelfPopulatingCache<PatchListKey, PatchList> self;
  private final boolean computeIntraline;

  @Inject
  PatchListCacheImpl(final GitRepositoryManager grm,
      @GerritServerConfig final Config config,
      @Named(CACHE_NAME) final Cache<PatchListKey, PatchList> raw) {
    repoManager = grm;
    computeIntraline = config.getBoolean("cache", "diff", "intraline", true);
    self = new SelfPopulatingCache<PatchListKey, PatchList>(raw) {
      @Override
      protected PatchList createEntry(final PatchListKey key) throws Exception {
        return compute(key);
      }
    };
  }

  public PatchList get(final PatchListKey key) {
    if (dynamic) {
      try {
        return compute(key);
      } catch (Exception e) {
        throw new RuntimeException("Cannot lookup " + key, e);
      }
    }
    return self.get(key);
  }

  public PatchList get(final Change change, final PatchSet patchSet) {
    return get(change, patchSet, IGNORE_NONE);
  }

  public PatchList get(final Change change, final PatchSet patchSet,
      final Whitespace whitespace) {
    final Project.NameKey projectKey = change.getProject();
    final ObjectId a = null;
    final ObjectId b = ObjectId.fromString(patchSet.getRevision().get());
    return get(new PatchListKey(projectKey, a, b, whitespace));
  }

  private PatchList compute(final PatchListKey key)
      throws MissingObjectException, IncorrectObjectTypeException, IOException {
    final Repository repo = repoManager.openRepository(key.projectKey.get());
    try {
      return readPatchList(key, repo);
    } finally {
      repo.close();
    }
  }

  private PatchList readPatchList(final PatchListKey key, final Repository repo)
      throws IOException {
    final RevWalk rw = new RevWalk(repo);
    final RevCommit b = rw.parseCommit(key.getNewId());
    final AnyObjectId a = aFor(key, repo, b);

    final List<String> args = new ArrayList<String>();
    args.add("git");
    args.add("--git-dir=.");
    args.add("diff-tree");
    args.add("-M");
    switch (key.getWhitespace()) {
      case IGNORE_NONE:
        break;
      case IGNORE_SPACE_AT_EOL:
        args.add("--ignore-space-at-eol");
        break;
      case IGNORE_SPACE_CHANGE:
        args.add("--ignore-space-change");
        break;
      case IGNORE_ALL_SPACE:
        args.add("--ignore-all-space");
        break;
      default:
        throw new IOException("Unsupported whitespace " + key.getWhitespace());
    }
    if (a == null /* want combined diff */) {
      args.add("--cc");
      args.add(b.name());
    } else {
      args.add("--unified=1");
      args.add(a.name());
      args.add(b.name());
    }

    final org.eclipse.jgit.patch.Patch p = new org.eclipse.jgit.patch.Patch();
    final Process diffProcess = exec(repo, args);
    try {
      diffProcess.getOutputStream().close();
      diffProcess.getErrorStream().close();

      final InputStream in = diffProcess.getInputStream();
      try {
        p.parse(in);
      } finally {
        in.close();
      }
    } finally {
      try {
        final int rc = diffProcess.waitFor();
        if (rc != 0) {
          throw new IOException("git diff-tree exited abnormally: " + rc);
        }
      } catch (InterruptedException ie) {
      }
    }

    RevTree aTree = a != null ? rw.parseTree(a) : null;
    RevTree bTree = b.getTree();

    final int cnt = p.getFiles().size();
    final PatchListEntry[] entries = new PatchListEntry[cnt];
    for (int i = 0; i < cnt; i++) {
      entries[i] = newEntry(repo, aTree, bTree, p.getFiles().get(i));
    }
    return new PatchList(a, b, computeIntraline, entries);
  }

  private PatchListEntry newEntry(Repository repo, RevTree aTree,
      RevTree bTree, FileHeader fileHeader) throws IOException {
    final FileMode oldMode = fileHeader.getOldMode();
    final FileMode newMode = fileHeader.getNewMode();

    if (oldMode == FileMode.GITLINK || newMode == FileMode.GITLINK) {
      return new PatchListEntry(fileHeader, Collections.<Edit> emptyList());
    }

    if (aTree == null // want combined diff
        || fileHeader.getPatchType() != PatchType.UNIFIED
        || fileHeader.getHunks().isEmpty()) {
      return new PatchListEntry(fileHeader, Collections.<Edit> emptyList());
    }

    List<Edit> edits = fileHeader.toEditList();
    if (edits.isEmpty()) {
      return new PatchListEntry(fileHeader, Collections.<Edit> emptyList());
    }
    if (!computeIntraline) {
      return new PatchListEntry(fileHeader, edits);
    }

    switch (fileHeader.getChangeType()) {
      case ADD:
      case DELETE:
        return new PatchListEntry(fileHeader, edits);
    }

    Text aContent = null;
    Text bContent = null;

    for (int i = 0; i < edits.size(); i++) {
      Edit e = edits.get(i);

      if (e.getType() == Edit.Type.REPLACE) {
        if (aContent == null) {
          edits = new ArrayList<Edit>(edits);
          aContent = read(repo, fileHeader.getOldName(), aTree);
          bContent = read(repo, fileHeader.getNewName(), bTree);
          combineLineEdits(edits, aContent, bContent);
          i = -1; // restart the entire scan after combining lines.
          continue;
        }

        CharText a = new CharText(aContent, e.getBeginA(), e.getEndA());
        CharText b = new CharText(bContent, e.getBeginB(), e.getEndB());

        List<Edit> wordEdits = new MyersDiff(a, b).getEdits();

        // Combine edits that are really close together. If they are
        // just a few characters apart we tend to get better results
        // by joining them together and taking the whole span.
        //
        for (int j = 0; j < wordEdits.size() - 1;) {
          Edit c = wordEdits.get(j);
          Edit n = wordEdits.get(j + 1);

          if (n.getBeginA() - c.getEndA() <= 5
              || n.getBeginB() - c.getEndB() <= 5) {
            int ab = c.getBeginA();
            int ae = n.getEndA();

            int bb = c.getBeginB();
            int be = n.getEndB();

            if (canCoalesce(a, c.getEndA(), n.getBeginA())
                && canCoalesce(b, c.getEndB(), n.getBeginB())) {
              wordEdits.set(j, new Edit(ab, ae, bb, be));
              wordEdits.remove(j + 1);
              continue;
            }
          }

          j++;
        }

        // Apply some simple rules to fix up some of the edits. Our
        // logic above, along with our per-character difference tends
        // to produce some crazy stuff.
        //
        for (int j = 0; j < wordEdits.size(); j++) {
          Edit c = wordEdits.get(j);
          int ab = c.getBeginA();
          int ae = c.getEndA();

          int bb = c.getBeginB();
          int be = c.getEndB();

          // Sometimes the diff generator produces an INSERT or DELETE
          // right up against a REPLACE, but we only find this after
          // we've also played some shifting games on the prior edit.
          // If that happened to us, coalesce them together so we can
          // correct this mess for the user. If we don't we wind up
          // with silly stuff like "es" -> "es = Addresses".
          //
          if (1 < j) {
            Edit p = wordEdits.get(j - 1);
            if (p.getEndA() == ab || p.getEndB() == bb) {
              if (p.getEndA() == ab && p.getBeginA() < p.getEndA()) {
                ab = p.getBeginA();
              }
              if (p.getEndB() == bb && p.getBeginB() < p.getEndB()) {
                bb = p.getBeginB();
              }
              wordEdits.remove(--j);
            }
          }

          // We sometimes collapsed an edit together in a strange way,
          // such that the edges of each text is identical. Fix by
          // by dropping out that incorrectly replaced region.
          //
          while (ab < ae && bb < be && a.equals(ab, b, bb)) {
            ab++;
            bb++;
          }
          while (ab < ae && bb < be && a.equals(ae - 1, b, be - 1)) {
            ae--;
            be--;
          }

          // The leading part of an edit and its trailing part in the same
          // text might be identical. Slide down that edit and use the tail
          // rather than the leading bit. If however the edit is only on a
          // whitespace block try to shift it to the left margin, assuming
          // that it is an indentation change.
          //
          boolean aShift = true;
          if (ab < ae && isOnlyWhitespace(a, ab, ae)) {
            int lf = findLF(wordEdits, j, a, ab);
            if (lf < ab && a.charAt(lf) == '\n') {
              int nb = lf + 1;
              int p = 0;
              while (p < ae - ab) {
                if (a.equals(ab + p, a, ab + p))
                  p++;
                else
                  break;
              }
              if (p == ae - ab) {
                ab = nb;
                ae = nb + p;
                aShift = false;
              }
            }
          }
          if (aShift) {
            while (0 < ab && ab < ae && a.charAt(ab - 1) != '\n'
                && a.equals(ab - 1, a, ae - 1)) {
              ab--;
              ae--;
            }
            if (!a.isLineStart(ab) || !a.contains(ab, ae, '\n')) {
              while (ab < ae && ae < a.size() && a.equals(ab, a, ae)) {
                ab++;
                ae++;
                if (a.charAt(ae - 1) == '\n') {
                  break;
                }
              }
            }
          }

          boolean bShift = true;
          if (bb < be && isOnlyWhitespace(b, bb, be)) {
            int lf = findLF(wordEdits, j, b, bb);
            if (lf < bb && b.charAt(lf) == '\n') {
              int nb = lf + 1;
              int p = 0;
              while (p < be - bb) {
                if (b.equals(bb + p, b, bb + p))
                  p++;
                else
                  break;
              }
              if (p == be - bb) {
                bb = nb;
                be = nb + p;
                bShift = false;
              }
            }
          }
          if (bShift) {
            while (0 < bb && bb < be && b.charAt(bb - 1) != '\n'
                && b.equals(bb - 1, b, be - 1)) {
              bb--;
              be--;
            }
            if (!b.isLineStart(bb) || !b.contains(bb, be, '\n')) {
              while (bb < be && be < b.size() && b.equals(bb, b, be)) {
                bb++;
                be++;
                if (b.charAt(be - 1) == '\n') {
                  break;
                }
              }
            }
          }

          // If most of a line was modified except the LF was common, make
          // the LF part of the modification region. This is easier to read.
          //
          if (ab < ae //
              && (ab == 0 || a.charAt(ab - 1) == '\n') //
              && ae < a.size() && a.charAt(ae) == '\n') {
            ae++;
          }
          if (bb < be //
              && (bb == 0 || b.charAt(bb - 1) == '\n') //
              && be < b.size() && b.charAt(be) == '\n') {
            be++;
          }

          wordEdits.set(j, new Edit(ab, ae, bb, be));
        }

        edits.set(i, new ReplaceEdit(e, wordEdits));
      }
    }

    return new PatchListEntry(fileHeader, edits);
  }

  private static void combineLineEdits(List<Edit> edits, Text a, Text b) {
    for (int j = 0; j < edits.size() - 1;) {
      Edit c = edits.get(j);
      Edit n = edits.get(j + 1);

      // Combine edits that are really close together. Right now our rule
      // is, coalesce two line edits which are only one line apart if that
      // common context line is either a "pointless line", or is identical
      // on both sides and starts a new block of code. These are mostly
      // block reindents to add or remove control flow operators.
      //
      final int ad = n.getBeginA() - c.getEndA();
      final int bd = n.getBeginB() - c.getEndB();
      if ((1 <= ad && isBlankLineGap(a, c.getEndA(), n.getBeginA()))
          || (1 <= bd && isBlankLineGap(b, c.getEndB(), n.getBeginB()))
          || (ad == 1 && bd == 1 && isControlBlockStart(a, c.getEndA()))) {
        int ab = c.getBeginA();
        int ae = n.getEndA();

        int bb = c.getBeginB();
        int be = n.getEndB();

        edits.set(j, new Edit(ab, ae, bb, be));
        edits.remove(j + 1);
        continue;
      }

      j++;
    }
  }

  private static boolean isBlankLineGap(Text a, int b, int e) {
    for (; b < e; b++) {
      if (!BLANK_LINE_RE.matcher(a.getLine(b)).matches()) {
        return false;
      }
    }
    return true;
  }

  private static boolean isControlBlockStart(Text a, int idx) {
    final String l = a.getLine(idx);
    return CONTROL_BLOCK_START_RE.matcher(l).find();
  }

  private static boolean canCoalesce(CharText a, int b, int e) {
    while (b < e) {
      if (a.charAt(b++) == '\n') {
        return false;
      }
    }
    return true;
  }

  private static int findLF(List<Edit> edits, int j, CharText t, int b) {
    int lf = b;
    int limit = 0 < j ? edits.get(j - 1).getEndB() : 0;
    while (limit < lf && t.charAt(lf) != '\n') {
      lf--;
    }
    return lf;
  }

  private static boolean isOnlyWhitespace(CharText t, final int b, final int e) {
    for (int c = b; c < e; c++) {
      if (!Character.isWhitespace(t.charAt(c))) {
        return false;
      }
    }
    return b < e;
  }

  private static Text read(Repository repo, String path, RevTree tree)
      throws IOException {
    TreeWalk tw = TreeWalk.forPath(repo, path, tree);
    if (tw == null || tw.getFileMode(0).getObjectType() != Constants.OBJ_BLOB) {
      return Text.EMPTY;
    }
    ObjectLoader ldr = repo.openObject(tw.getObjectId(0));
    if (ldr == null) {
      return Text.EMPTY;
    }
    return new Text(ldr.getCachedBytes());
  }

  private static AnyObjectId aFor(final PatchListKey key,
      final Repository repo, final RevCommit b) throws IOException {
    if (key.getOldId() != null) {
      return key.getOldId();
    }

    switch (b.getParentCount()) {
      case 0:
        return emptyTree(repo);
      case 1:
        return b.getParent(0);
      default:
        // merge commit, return null to force combined diff behavior
        return null;
    }
  }

  private static Process exec(final Repository repo, final List<String> args)
      throws IOException {
    final String[] argv = args.toArray(new String[args.size()]);
    return Runtime.getRuntime().exec(argv, null, repo.getDirectory());
  }

  private static ObjectId emptyTree(final Repository repo) throws IOException {
    return new ObjectWriter(repo).writeCanonicalTree(new byte[0]);
  }
}