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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.document.json;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.google.common.base.Preconditions;
import java.io.IOException;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;
import java.util.function.Supplier;
/**
* Helper class to enable lookahead in the token stream.
*
* @author Steinar Knutsen
*/
public class TokenBuffer {
final Deque<Token> tokens = new ArrayDeque<>();
private int nesting = 0;
public TokenBuffer() { }
/** Returns whether any tokens are available in this */
public boolean isEmpty() { return tokens.isEmpty(); }
/** Returns the next token, or null, and updates the nesting count of this. */
public JsonToken next() {
advance();
JsonToken token = current();
updateNesting(token);
return token;
}
void advance() {
tokens.poll();
}
/** Returns the current token without changing position, or null if none */
public JsonToken current() {
return isEmpty() ? null : tokens.peek().token;
}
/** Returns the current token name without changing position, or null if none */
public String currentName() {
return isEmpty() ? null : tokens.peek().name;
}
/** Returns the current token text without changing position, or null if none */
public String currentText() {
return isEmpty() ? null : tokens.peek().text;
}
/**
* Returns a sequence of remaining tokens in this, or nulls when none remain.
* This may fill the token buffer, but not otherwise modify it.
*/
public Supplier<Token> lookahead() {
Iterator<Token> iterator = tokens.iterator();
if (iterator.hasNext()) iterator.next();
return () -> iterator.hasNext() ? iterator.next() : null;
}
private void add(JsonToken token, String name, String text) {
tokens.add(new Token(token, name, text));
}
public void bufferObject(JsonParser parser) {
bufferJsonStruct(parser, JsonToken.START_OBJECT);
}
private void bufferJsonStruct(JsonParser parser, JsonToken firstToken) {
JsonToken token = parser.currentToken();
Preconditions.checkArgument(token == firstToken,
"Expected %s, got %s.", firstToken.name(), token);
updateNesting(token);
try {
for (int nesting = addFromParser(parser); nesting > 0; nesting += addFromParser(parser))
parser.nextValue();
}
catch (IOException e) {
throw new IllegalArgumentException(e);
}
}
int nestingOffset(JsonToken token) {
if (token == null) return 0;
if (token.isStructStart()) {
return 1;
} else if (token.isStructEnd()) {
return -1;
} else {
return 0;
}
}
int addFromParser(JsonParser tokens) throws IOException {
add(tokens.currentToken(), tokens.currentName(), tokens.getText());
return nestingOffset(tokens.currentToken());
}
void updateNesting(JsonToken token) {
nesting += nestingOffset(token);
}
public int nesting() {
return nesting;
}
public void skipToRelativeNesting(int relativeNesting) {
int initialNesting = nesting();
do next();
while (nesting() > initialNesting + relativeNesting);
}
public static final class Token {
public final JsonToken token;
public final String name;
public final String text;
Token(JsonToken token, String name, String text) {
this.token = token;
this.name = name;
this.text = text;
}
@Override
public String toString() {
return "Token(" + token + ", " + name + ", " + text + ")";
}
}
}
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