static IntraLineDiff compute()

in java/com/google/gerrit/server/patch/IntraLineLoader.java [108:267]
114 lines of code
55 McCabe index (conditional complexity)

  static IntraLineDiff compute(
      Text aText,
      Text bText,
      ImmutableList<Edit> immutableEdits,
      ImmutableSet<Edit> immutableEditsDueToRebase) {
    List<Edit> edits = new ArrayList<>(immutableEdits);
    combineLineEdits(edits, immutableEditsDueToRebase, aText, bText);

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

      if (e.getType() == Edit.Type.REPLACE) {
        CharText a = new CharText(aText, e.getBeginA(), e.getEndA());
        CharText b = new CharText(bText, e.getBeginB(), e.getEndB());
        CharTextComparator cmp = new CharTextComparator();

        List<Edit> wordEdits = MyersDiff.INSTANCE.diff(cmp, a, b);

        // 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 && cmp.equals(a, ab, b, bb)) {
            ab++;
            bb++;
          }
          while (ab < ae && bb < be && cmp.equals(a, 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.
          //
          while (0 < ab
              && ab < ae
              && a.charAt(ab - 1) != '\n'
              && cmp.equals(a, ab - 1, a, ae - 1)) {
            ab--;
            ae--;
          }
          if (!a.isLineStart(ab) || !a.contains(ab, ae, '\n')) {
            while (ab < ae && ae < a.size() && cmp.equals(a, ab, a, ae)) {
              ab++;
              ae++;
              if (a.charAt(ae - 1) == '\n') {
                break;
              }
            }
          }

          while (0 < bb
              && bb < be
              && b.charAt(bb - 1) != '\n'
              && cmp.equals(b, bb - 1, b, be - 1)) {
            bb--;
            be--;
          }
          if (!b.isLineStart(bb) || !b.contains(bb, be, '\n')) {
            while (bb < be && be < b.size() && cmp.equals(b, 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 - 1) != '\n'
              && a.charAt(ae) == '\n') {
            ae++;
          }
          if (bb < be //
              && (bb == 0 || b.charAt(bb - 1) == '\n') //
              && be < b.size()
              && b.charAt(be - 1) != '\n'
              && b.charAt(be) == '\n') {
            be++;
          }

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

        // Validate that the intra-line edits applied to the "a" text produces the "b" text. If this
        // check fails, fallback to a single replace edit that covers the whole area.
        if (isValidTransformation(a, b, wordEdits)) {
          edits.set(i, new ReplaceEdit(e, wordEdits));
        } else {
          edits.set(i, new ReplaceEdit(e, Arrays.asList(new Edit(0, a.size(), 0, b.size()))));
        }
      }
    }

    return new IntraLineDiff(edits);
  }