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/*
* 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 io.trino.likematcher;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
import static com.google.common.base.Preconditions.checkArgument;
import static java.util.Objects.requireNonNull;
public class FjsMatcher
implements Matcher
{
private final List pattern;
private final int start;
private final int end;
private final boolean exact;
private volatile Fjs matcher;
public FjsMatcher(List pattern, int start, int end, boolean exact)
{
this.pattern = requireNonNull(pattern, "pattern is null");
this.start = start;
this.end = end;
this.exact = exact;
}
@Override
public boolean match(byte[] input, int offset, int length)
{
Fjs matcher = this.matcher;
if (matcher == null) {
matcher = new Fjs(pattern, start, end, exact);
this.matcher = matcher;
}
return matcher.match(input, offset, length);
}
private static class Fjs
{
private final boolean exact;
private final List patterns = new ArrayList<>();
private final List bmsShifts = new ArrayList<>();
private final List kmpShifts = new ArrayList<>();
public Fjs(List pattern, int start, int end, boolean exact)
{
this.exact = exact;
for (int i = start; i <= end; i++) {
Pattern element = pattern.get(i);
switch (element) {
case Pattern.Literal literal -> {
checkArgument(i == 0 || !(pattern.get(i - 1) instanceof Pattern.Literal), "Multiple consecutive literals found");
byte[] bytes = literal.value().getBytes(StandardCharsets.UTF_8);
patterns.add(bytes);
bmsShifts.add(computeBmsShifts(bytes));
kmpShifts.add(computeKmpShifts(bytes));
}
case Pattern.Any any -> throw new IllegalArgumentException("'any' pattern not supported");
case null, default -> {}
}
}
}
private static int[] computeKmpShifts(byte[] pattern)
{
int[] result = new int[pattern.length + 1];
result[0] = -1;
int j = -1;
for (int i = 1; i < result.length; i++) {
while (j >= 0 && pattern[i - 1] != pattern[j]) {
j = result[j];
}
j++;
result[i] = j;
}
return result;
}
private static int[] computeBmsShifts(byte[] pattern)
{
int[] result = new int[256];
for (int i = 0; i < pattern.length; i++) {
result[pattern[i] & 0xFF] = i + 1;
}
return result;
}
private static int find(byte[] input, final int offset, final int length, byte[] pattern, int[] bmsShifts, int[] kmpShifts)
{
if (pattern.length > length || pattern.length == 0) {
return -1;
}
final int inputLimit = offset + length;
int i = offset;
while (true) {
// Attempt to match the last position of the pattern
// As long as it doesn't match, skip ahead based on the Boyer-Moore-Sunday heuristic
int matchEnd = i + pattern.length - 1;
while (matchEnd < inputLimit - 1 && input[matchEnd] != pattern[pattern.length - 1]) {
int shift = pattern.length + 1 - bmsShifts[input[matchEnd + 1] & 0xFF];
matchEnd += shift;
}
if (matchEnd == inputLimit - 1 && match(input, inputLimit - pattern.length, pattern)) {
return inputLimit - pattern.length;
}
else if (matchEnd >= inputLimit - 1) {
return -1;
}
// At this point, we know the last position of the pattern matches with some
// position in the input text given by "matchEnd"
// Use KMP to match the first length-1 characters of the pattern
i = matchEnd - (pattern.length - 1);
int j = findLongestMatch(input, i, pattern, 0, pattern.length - 1);
if (j == pattern.length - 1) {
return i;
}
i += j;
j = kmpShifts[j];
// Continue to match the whole pattern using KMP
while (j >= 0) {
int size = findLongestMatch(input, i, pattern, j, Math.min(inputLimit - i, pattern.length - j));
i += size;
j += size;
if (j == pattern.length) {
return i - j;
}
j = kmpShifts[j];
}
i++;
}
}
private static int findLongestMatch(byte[] input, int inputOffset, byte[] pattern, int patternOffset, int length)
{
for (int i = 0; i < length; i++) {
if (input[inputOffset + i] != pattern[patternOffset + i]) {
return i;
}
}
return length;
}
private static boolean match(byte[] input, int offset, byte[] pattern)
{
for (int i = 0; i < pattern.length; i++) {
if (input[offset + i] != pattern[i]) {
return false;
}
}
return true;
}
public boolean match(byte[] input, int offset, int length)
{
int start = offset;
int remaining = length;
for (int i = 0; i < patterns.size(); i++) {
if (remaining == 0) {
return false;
}
byte[] term = patterns.get(i);
int position = find(input, start, remaining, term, bmsShifts.get(i), kmpShifts.get(i));
if (position == -1) {
return false;
}
position += term.length;
remaining -= position - start;
start = position;
}
return !exact || remaining == 0;
}
}
}
