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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.document.json;
import java.io.IOException;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.google.common.base.Preconditions;
/**
* Helper class to enable lookahead in the token stream.
*
* @author Steinar Knutsen
*/
public class TokenBuffer {
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;
}
}
private final Deque<Token> buffer;
private int nesting = 0;
public TokenBuffer() {
this(new ArrayDeque<>());
}
private TokenBuffer(Deque<Token> buffer) {
this.buffer = buffer;
if (buffer.size() > 0) {
updateNesting(buffer.peekFirst().token);
}
}
/** Returns whether any tokens are available in this */
public boolean isEmpty() { return size() == 0; }
public JsonToken next() {
buffer.removeFirst();
Token t = buffer.peekFirst();
if (t == null) {
return null;
}
updateNesting(t.token);
return t.token;
}
/** Returns the current token without changing position, or null if none */
public JsonToken currentToken() {
Token token = buffer.peekFirst();
if (token == null) return null;
return token.token;
}
/** Returns the current token name without changing position, or null if none */
public String currentName() {
Token token = buffer.peekFirst();
if (token == null) return null;
return token.name;
}
/** Returns the current token text without changing position, or null if none */
public String currentText() {
Token token = buffer.peekFirst();
if (token == null) return null;
return token.text;
}
public int size() {
return buffer.size();
}
private void add(JsonToken token, String name, String text) {
buffer.addLast(new Token(token, name, text));
}
public void bufferObject(JsonToken first, JsonParser tokens) {
bufferJsonStruct(first, tokens, JsonToken.START_OBJECT);
}
public void bufferArray(JsonToken first, JsonParser tokens) {
bufferJsonStruct(first, tokens, JsonToken.START_ARRAY);
}
private void bufferJsonStruct(JsonToken first, JsonParser tokens, JsonToken firstToken) {
int localNesting = 0;
JsonToken t = first;
Preconditions.checkArgument(first == firstToken,
"Expected %s, got %s.", firstToken.name(), t);
if (size() == 0) {
updateNesting(t);
}
localNesting = storeAndPeekNesting(t, localNesting, tokens);
while (localNesting > 0) {
t = nextValue(tokens);
localNesting = storeAndPeekNesting(t, localNesting, tokens);
}
}
private int storeAndPeekNesting(JsonToken t, int nesting, JsonParser tokens) {
addFromParser(t, tokens);
return nesting + nestingOffset(t);
}
private int nestingOffset(JsonToken t) {
if (t.isStructStart()) {
return 1;
} else if (t.isStructEnd()) {
return -1;
} else {
return 0;
}
}
private void addFromParser(JsonToken t, JsonParser tokens) {
try {
add(t, tokens.getCurrentName(), tokens.getText());
} catch (IOException e) {
// TODO something sane
throw new IllegalArgumentException(e);
}
}
private JsonToken nextValue(JsonParser tokens) {
try {
return tokens.nextValue();
} catch (IOException e) {
// TODO something sane
throw new IllegalArgumentException(e);
}
}
private void updateNesting(JsonToken t) {
nesting += nestingOffset(t);
}
public int nesting() {
return nesting;
}
public String dumpContents() {
StringBuilder b = new StringBuilder();
b.append("[nesting: ").append(nesting()).append("\n");
for (Token t : buffer) {
b.append("(").append(t.token).append(", \"").append(t.name).append("\", \"").append(t.text).append("\")\n");
}
b.append("]\n");
return b.toString();
}
public void fastForwardToEndObject() {
JsonToken t = currentToken();
while (t != JsonToken.END_OBJECT) {
t = next();
}
}
public TokenBuffer prefetchCurrentElement() {
Deque<Token> copy = new ArrayDeque<>();
if (currentToken().isScalarValue()) {
copy.add(buffer.peekFirst());
} else {
int localNesting = nesting();
int nestingBarrier = localNesting;
for (Token t : buffer) {
copy.add(t);
localNesting += nestingOffset(t.token);
if (localNesting < nestingBarrier) {
break;
}
}
}
return new TokenBuffer(copy);
}
public Token prefetchScalar(String name) {
int localNesting = nesting();
int nestingBarrier = localNesting;
Token toReturn = null;
Iterator<Token> i;
if (name.equals(currentName()) && currentToken().isScalarValue()) {
toReturn = buffer.peekFirst();
} else {
i = buffer.iterator();
i.next(); // just ignore the first value, as we know it's not what
// we're looking for, and it's nesting effect is already
// included
while (i.hasNext()) {
Token t = i.next();
if (localNesting == nestingBarrier && name.equals(t.name) && t.token.isScalarValue()) {
toReturn = t;
break;
}
localNesting += nestingOffset(t.token);
if (localNesting < nestingBarrier) {
break;
}
}
}
return toReturn;
}
public void skipToRelativeNesting(int relativeNesting) {
int initialNesting = nesting();
do {
next();
} while ( nesting() > initialNesting + relativeNesting);
}
}
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