// Copyright (C) 2019 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.fixes;

import static java.nio.charset.StandardCharsets.UTF_8;

import com.google.common.collect.ImmutableList;
import com.google.gerrit.entities.Comment;
import com.google.gerrit.entities.FixReplacement;
import com.google.gerrit.extensions.restapi.ResourceConflictException;
import com.google.gerrit.jgit.diff.ReplaceEdit;
import com.google.gerrit.server.patch.Text;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import org.eclipse.jgit.diff.Edit;

/**
 * Produces final version of an input content with all fixes applied together with list of edits.
 */
public class FixCalculator {
  private static final Comparator<FixReplacement> ASC_RANGE_FIX_REPLACEMENT_COMPARATOR =
      Comparator.comparing(fixReplacement -> fixReplacement.range);

  private FixCalculator() {}

  /**
   * Returns a result of applying fixes to an original content.
   *
   * @param originalContent is a text to which fixes must be applied
   * @param fixReplacements is a list of fixes to be applied
   * @throws ResourceConflictException if the fixReplacements contains invalid data (for example, if
   *     an item points to an invalid range or if some ranges are intersected).
   */
  public static String getNewFileContent(
      String originalContent, List<FixReplacement> fixReplacements)
      throws ResourceConflictException {
    FixResult fixResult = calculateFix(new Text(originalContent.getBytes(UTF_8)), fixReplacements);
    return fixResult.text.getString(0, fixResult.text.size(), false);
  }

  /**
   * Returns a result of applying fixes to an original content and list of applied edits.
   *
   * @param originalText is a text to which fixes must be applied
   * @param fixReplacements is a list of fixes to be applied
   * @return {@link FixResult}
   * @throws ResourceConflictException if the fixReplacements contains invalid data (for example, if
   *     an item points to an invalid range or if some ranges are intersected).
   */
  public static FixResult calculateFix(Text originalText, List<FixReplacement> fixReplacements)
      throws ResourceConflictException {
    List<FixReplacement> sortedReplacements = new ArrayList<>(fixReplacements);
    sortedReplacements.sort(ASC_RANGE_FIX_REPLACEMENT_COMPARATOR);
    if (!sortedReplacements.isEmpty() && sortedReplacements.get(0).range.startLine <= 0) {
      throw new ResourceConflictException(
          String.format(
              "Cannot calculate fix replacement for range %s",
              toString(sortedReplacements.get(0).range)));
    }
    ContentBuilder builder = new ContentBuilder(originalText);
    for (FixReplacement fixReplacement : sortedReplacements) {
      try {
        builder.addReplacement(fixReplacement);
      } catch (IndexOutOfBoundsException e) {
        throw new ResourceConflictException(
            String.format(
                "Cannot calculate fix replacement for range %s", toString(fixReplacement.range)),
            e);
      }
    }
    return builder.build();
  }

  private static String toString(Comment.Range range) {
    return String.format(
        "(%s:%s - %s:%s)", range.startLine, range.startChar, range.endLine, range.endChar);
  }

  private static class ContentBuilder {
    private static class FixRegion {
      int startSrcLine;
      int startDstLine;
      int startSrcPos;
      int startDstPos;
      List<Edit> internalEdits;

      FixRegion() {
        this.internalEdits = new ArrayList<>();
      }
    }

    private final ContentProcessor contentProcessor;
    final ImmutableList.Builder<Edit> edits;
    FixRegion currentRegion;

    ContentBuilder(Text src) {
      this.contentProcessor = new ContentProcessor(src);
      this.edits = new ImmutableList.Builder<>();
    }

    void addReplacement(FixReplacement replacement) {
      if (shouldStartNewEdit(replacement)) {
        finishExistingEdit();
      }
      // processSrcContent expects that line number is 0-based,
      // but replacement.range.startLine is 1-based, so subtract 1
      processSrcContent(replacement.range.startLine - 1, replacement.range.startChar, true);
      processReplacement(replacement);
    }

    Text getNewText() {
      return new Text(contentProcessor.sb.toString().getBytes(UTF_8));
    }

    void finish() {
      finishExistingEdit();
      if (contentProcessor.hasMoreLines()) {
        contentProcessor.appendLinesToEndOfContent();
      }
    }

    public FixResult build() {
      finish();
      return new FixResult(edits.build(), this.getNewText());
    }

    private void finishExistingEdit() {
      if (contentProcessor.srcPosition.column > 0 || contentProcessor.dstPosition.column > 0) {
        contentProcessor.processToEndOfLine(true);
      }
      if (currentRegion != null) {
        int endSrc = contentProcessor.srcPosition.line;
        if (contentProcessor.srcPosition.column > 0) {
          endSrc++;
        }
        int endDst = contentProcessor.dstPosition.line;
        if (contentProcessor.dstPosition.column > 0) {
          endDst++;
        }
        ReplaceEdit edit =
            new ReplaceEdit(
                currentRegion.startSrcLine,
                endSrc,
                currentRegion.startDstLine,
                endDst,
                currentRegion.internalEdits);
        currentRegion = null;
        edits.add(edit);
      }
    }

    private boolean shouldStartNewEdit(FixReplacement replacement) {
      if (currentRegion == null) {
        return true;
      }
      // New edit must be started if there is at least one unchanged line after the last edit
      // Subtract 1 from replacement.range.startLine because it is a 1-based line number,
      // and contentProcessor.srcPosition.line is a 0-based line number
      return replacement.range.startLine - 1 > contentProcessor.srcPosition.line + 1;
    }

    private void processSrcContent(int toLine, int toColumn, boolean append)
        throws IndexOutOfBoundsException {
      // toLine >= currentSrcLineIndex
      if (toLine == contentProcessor.srcPosition.line) {
        contentProcessor.processLineToColumn(toColumn, append);
      } else {
        contentProcessor.processToEndOfLine(append);
        contentProcessor.processMultiline(toLine, append);
        contentProcessor.processLineToColumn(toColumn, append);
      }
    }

    private void processReplacement(FixReplacement fix) {
      if (currentRegion == null) {
        currentRegion = new FixRegion();
        currentRegion.startSrcLine = contentProcessor.srcPosition.line;
        currentRegion.startSrcPos = contentProcessor.srcPosition.getLineStartPos();
        currentRegion.startDstLine = contentProcessor.dstPosition.line;
        currentRegion.startDstPos = contentProcessor.dstPosition.getLineStartPos();
      }
      int srcStartPos = contentProcessor.srcPosition.textPos;
      int dstStartPos = contentProcessor.dstPosition.textPos;
      contentProcessor.appendReplacement(fix.replacement);
      processSrcContent(fix.range.endLine - 1, fix.range.endChar, false);

      currentRegion.internalEdits.add(
          new Edit(
              srcStartPos - currentRegion.startSrcPos,
              contentProcessor.srcPosition.textPos - currentRegion.startSrcPos,
              dstStartPos - currentRegion.startDstPos,
              contentProcessor.dstPosition.textPos - currentRegion.startDstPos));
    }
  }

  private static class ContentProcessor {
    static class ContentPosition {
      int line;
      int column;
      int textPos;

      void appendMultilineContent(int lineCount, int charCount) {
        line += lineCount;
        column = 0;
        textPos += charCount;
      }

      void appendLineEndedWithEOLMark(int charCount) {
        textPos += charCount;
        line++;
        column = 0;
      }

      void appendStringWithoutEOLMark(int charCount) {
        textPos += charCount;
        column += charCount;
      }

      int getLineStartPos() {
        return textPos - column;
      }
    }

    private final StringBuilder sb;
    final ContentPosition srcPosition;
    final ContentPosition dstPosition;
    String currentSrcLine;
    Text src;
    boolean endOfSource;

    ContentProcessor(Text src) {
      this.src = src;
      sb = new StringBuilder(src.size());
      srcPosition = new ContentPosition();
      dstPosition = new ContentPosition();
      endOfSource = src.size() == 0;
    }

    void processMultiline(int toLine, boolean append) {
      if (endOfSource || toLine <= srcPosition.line) {
        return;
      }
      int fromLine = srcPosition.line;
      String lines = src.getString(fromLine, toLine, false);
      int lineCount = toLine - fromLine;
      int charCount = lines.length();
      srcPosition.appendMultilineContent(lineCount, charCount);

      if (append) {
        sb.append(lines);
        dstPosition.appendMultilineContent(lineCount, charCount);
      }
      currentSrcLine = null;
      endOfSource = srcPosition.line >= src.size();
    }

    void processToEndOfLine(boolean append) {
      if (endOfSource) {
        return;
      }
      String srcLine = getCurrentSrcLine();
      int from = srcPosition.column;
      int charCount = srcLine.length() - from;
      boolean lastLineNoEOLMark = srcPosition.line >= src.size() - 1 && src.isMissingNewlineAtEnd();
      if (!lastLineNoEOLMark) {
        srcPosition.appendLineEndedWithEOLMark(charCount);
        endOfSource = srcPosition.line >= src.size();
      } else {
        srcPosition.appendStringWithoutEOLMark(charCount);
        endOfSource = true;
      }
      if (append) {
        sb.append(srcLine, from, srcLine.length());
        if (!lastLineNoEOLMark) {
          dstPosition.appendLineEndedWithEOLMark(charCount);
        } else {
          dstPosition.appendStringWithoutEOLMark(charCount);
        }
      }
      currentSrcLine = null;
    }

    void processLineToColumn(int to, boolean append) throws IndexOutOfBoundsException {
      if (to == 0) {
        return;
      }
      String srcLine = getCurrentSrcLine();
      if (to > srcLine.length()) {
        throw new IndexOutOfBoundsException("Parameter to is out of string");
      } else if (to == srcLine.length()) {
        if (srcPosition.line < src.size() - 1 || !src.isMissingNewlineAtEnd()) {
          throw new IndexOutOfBoundsException("The processLineToColumn shouldn't add end of line");
        }
      }
      int from = srcPosition.column;
      int charCount = to - from;
      srcPosition.appendStringWithoutEOLMark(charCount);
      if (append) {
        sb.append(srcLine, from, to);
        dstPosition.appendStringWithoutEOLMark(charCount);
      }
    }

    void appendLinesToEndOfContent() {
      processMultiline(src.size(), true);
    }

    void appendReplacement(String replacement) {
      if (replacement.length() == 0) {
        return;
      }
      sb.append(replacement);
      int lastNewLinePos = -1;
      int newLineMarkCount = 0;
      while (true) {
        int index = replacement.indexOf('\n', lastNewLinePos + 1);
        if (index < 0) {
          break;
        }
        lastNewLinePos = index;
        newLineMarkCount++;
      }
      if (newLineMarkCount > 0) {
        dstPosition.appendMultilineContent(newLineMarkCount, lastNewLinePos + 1);
      }
      dstPosition.appendStringWithoutEOLMark(replacement.length() - lastNewLinePos - 1);
    }

    boolean hasMoreLines() {
      return !endOfSource;
    }

    private String getCurrentSrcLine() {
      if (currentSrcLine == null) {
        currentSrcLine = src.getString(srcPosition.line, srcPosition.line + 1, false);
      }
      return currentSrcLine;
    }
  }

  /** The result of applying fix to a file content */
  public static class FixResult {
    /** List of edits to transform an original text to a final text (with all fixes applied) */
    public final ImmutableList<Edit> edits;
    /** Final text with all applied fixes */
    public final Text text;

    FixResult(ImmutableList<Edit> edits, Text text) {
      this.edits = edits;
      this.text = text;
    }
  }
}