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With inspiration from other libraries
// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html#License
/*
**********************************************************************
* Copyright (c) 2003-2011, International Business Machines
* Corporation and others. All Rights Reserved.
**********************************************************************
* Author: Alan Liu
* Created: September 23 2003
* Since: ICU 2.8
**********************************************************************
*/
package com.ibm.icu.impl;
import java.text.ParsePosition;
import com.ibm.icu.text.SymbolTable;
import com.ibm.icu.text.UTF16;
/**
* An iterator that returns 32-bit code points. This class is deliberately
* not related to any of the JDK or ICU4J character iterator classes
* in order to minimize complexity.
* @author Alan Liu
* @since ICU 2.8
*/
public class RuleCharacterIterator {
// TODO: Ideas for later. (Do not implement if not needed, lest the
// code coverage numbers go down due to unused methods.)
// 1. Add a copy constructor, equals() method, clone() method.
// 2. Rather than return DONE, throw an exception if the end
// is reached -- this is an alternate usage model, probably not useful.
// 3. Return isEscaped from next(). If this happens,
// don't keep an isEscaped member variable.
/**
* Text being iterated.
*/
private String text;
/**
* Position of iterator.
*/
private ParsePosition pos;
/**
* Symbol table used to parse and dereference variables. May be null.
*/
private SymbolTable sym;
/**
* Current variable expansion, or null if none.
*/
private char[] buf;
/**
* Position within buf[]. Meaningless if buf == null.
*/
private int bufPos;
/**
* Flag indicating whether the last character was parsed from an escape.
*/
private boolean isEscaped;
/**
* Value returned when there are no more characters to iterate.
*/
public static final int DONE = -1;
/**
* Bitmask option to enable parsing of variable names. If (options &
* PARSE_VARIABLES) != 0, then an embedded variable will be expanded to
* its value. Variables are parsed using the SymbolTable API.
*/
public static final int PARSE_VARIABLES = 1;
/**
* Bitmask option to enable parsing of escape sequences. If (options &
* PARSE_ESCAPES) != 0, then an embedded escape sequence will be expanded
* to its value. Escapes are parsed using Utility.unescapeAt().
*/
public static final int PARSE_ESCAPES = 2;
/**
* Bitmask option to enable skipping of whitespace. If (options &
* SKIP_WHITESPACE) != 0, then Unicode Pattern_White_Space characters will be silently
* skipped, as if they were not present in the input.
*/
public static final int SKIP_WHITESPACE = 4;
/**
* Constructs an iterator over the given text, starting at the given
* position.
* @param text the text to be iterated
* @param sym the symbol table, or null if there is none. If sym is null,
* then variables will not be deferenced, even if the PARSE_VARIABLES
* option is set.
* @param pos upon input, the index of the next character to return. If a
* variable has been dereferenced, then pos will not increment as
* characters of the variable value are iterated.
*/
public RuleCharacterIterator(String text, SymbolTable sym,
ParsePosition pos) {
if (text == null || pos.getIndex() > text.length()) {
throw new IllegalArgumentException();
}
this.text = text;
this.sym = sym;
this.pos = pos;
buf = null;
}
/**
* Returns true if this iterator has no more characters to return.
*/
public boolean atEnd() {
return buf == null && pos.getIndex() == text.length();
}
/**
* Returns the next character using the given options, or DONE if there
* are no more characters, and advance the position to the next
* character.
* @param options one or more of the following options, bitwise-OR-ed
* together: PARSE_VARIABLES, PARSE_ESCAPES, SKIP_WHITESPACE.
* @return the current 32-bit code point, or DONE
*/
public int next(int options) {
int c = DONE;
isEscaped = false;
for (;;) {
c = _current();
_advance(UTF16.getCharCount(c));
if (c == SymbolTable.SYMBOL_REF && buf == null &&
(options & PARSE_VARIABLES) != 0 && sym != null) {
String name = sym.parseReference(text, pos, text.length());
// If name == null there was an isolated SYMBOL_REF;
// return it. Caller must be prepared for this.
if (name == null) {
break;
}
bufPos = 0;
buf = sym.lookup(name);
if (buf == null) {
throw new IllegalArgumentException(
"Undefined variable: " + name);
}
// Handle empty variable value
if (buf.length == 0) {
buf = null;
}
continue;
}
if ((options & SKIP_WHITESPACE) != 0 &&
PatternProps.isWhiteSpace(c)) {
continue;
}
if (c == '\\' && (options & PARSE_ESCAPES) != 0) {
int offset[] = new int[] { 0 };
c = Utility.unescapeAt(lookahead(), offset);
jumpahead(offset[0]);
isEscaped = true;
if (c < 0) {
throw new IllegalArgumentException("Invalid escape");
}
}
break;
}
return c;
}
/**
* Returns true if the last character returned by next() was
* escaped. This will only be the case if the option passed in to
* next() included PARSE_ESCAPED and the next character was an
* escape sequence.
*/
public boolean isEscaped() {
return isEscaped;
}
/**
* Returns true if this iterator is currently within a variable expansion.
*/
public boolean inVariable() {
return buf != null;
}
/**
* Returns an object which, when later passed to setPos(), will
* restore this iterator's position. Usage idiom:
*
* RuleCharacterIterator iterator = ...;
* Object pos = iterator.getPos(null); // allocate position object
* for (;;) {
* pos = iterator.getPos(pos); // reuse position object
* int c = iterator.next(...);
* ...
* }
* iterator.setPos(pos);
*
* @param p a position object previously returned by getPos(),
* or null. If not null, it will be updated and returned. If
* null, a new position object will be allocated and returned.
* @return a position object which may be passed to setPos(),
* either `p,' or if `p' == null, a newly-allocated object
*/
public Object getPos(Object p) {
if (p == null) {
return new Object[] {buf, new int[] {pos.getIndex(), bufPos}};
}
Object[] a = (Object[]) p;
a[0] = buf;
int[] v = (int[]) a[1];
v[0] = pos.getIndex();
v[1] = bufPos;
return p;
}
/**
* Restores this iterator to the position it had when getPos()
* returned the given object.
* @param p a position object previously returned by getPos()
*/
public void setPos(Object p) {
Object[] a = (Object[]) p;
buf = (char[]) a[0];
int[] v = (int[]) a[1];
pos.setIndex(v[0]);
bufPos = v[1];
}
/**
* Skips ahead past any ignored characters, as indicated by the given
* options. This is useful in conjunction with the lookahead() method.
*
* Currently, this only has an effect for SKIP_WHITESPACE.
* @param options one or more of the following options, bitwise-OR-ed
* together: PARSE_VARIABLES, PARSE_ESCAPES, SKIP_WHITESPACE.
*/
public void skipIgnored(int options) {
if ((options & SKIP_WHITESPACE) != 0) {
for (;;) {
int a = _current();
if (!PatternProps.isWhiteSpace(a)) break;
_advance(UTF16.getCharCount(a));
}
}
}
/**
* Returns a string containing the remainder of the characters to be
* returned by this iterator, without any option processing. If the
* iterator is currently within a variable expansion, this will only
* extend to the end of the variable expansion. This method is provided
* so that iterators may interoperate with string-based APIs. The typical
* sequence of calls is to call skipIgnored(), then call lookahead(), then
* parse the string returned by lookahead(), then call jumpahead() to
* resynchronize the iterator.
* @return a string containing the characters to be returned by future
* calls to next()
*/
public String lookahead() {
if (buf != null) {
return new String(buf, bufPos, buf.length - bufPos);
} else {
return text.substring(pos.getIndex());
}
}
/**
* Advances the position by the given number of 16-bit code units.
* This is useful in conjunction with the lookahead() method.
* @param count the number of 16-bit code units to jump over
*/
public void jumpahead(int count) {
if (count < 0) {
throw new IllegalArgumentException();
}
if (buf != null) {
bufPos += count;
if (bufPos > buf.length) {
throw new IllegalArgumentException();
}
if (bufPos == buf.length) {
buf = null;
}
} else {
int i = pos.getIndex() + count;
pos.setIndex(i);
if (i > text.length()) {
throw new IllegalArgumentException();
}
}
}
/**
* Returns a string representation of this object, consisting of the
* characters being iterated, with a '|' marking the current position.
* Position within an expanded variable is not indicated.
* @return a string representation of this object
*/
@Override
public String toString() {
int b = pos.getIndex();
return text.substring(0, b) + '|' + text.substring(b);
}
/**
* Returns the current 32-bit code point without parsing escapes, parsing
* variables, or skipping whitespace.
* @return the current 32-bit code point
*/
private int _current() {
if (buf != null) {
return UTF16.charAt(buf, 0, buf.length, bufPos);
} else {
int i = pos.getIndex();
return (i < text.length()) ? UTF16.charAt(text, i) : DONE;
}
}
/**
* Advances the position by the given amount.
* @param count the number of 16-bit code units to advance past
*/
private void _advance(int count) {
if (buf != null) {
bufPos += count;
if (bufPos == buf.length) {
buf = null;
}
} else {
pos.setIndex(pos.getIndex() + count);
if (pos.getIndex() > text.length()) {
pos.setIndex(text.length());
}
}
}
}