src/java.desktop/share/classes/javax/swing/text/html/CSSParser.java

/*
 * Copyright (c) 1999, 2023, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package javax.swing.text.html;

import java.io.*;

/**
 * A CSS parser. This works by way of a delegate that implements the
 * {@code CSSParserCallback} interface. The delegate is notified of the following
 * events:
 * <ul>
 *   <li>Import statement: {@code handleImport}.
 *   <li>Selectors {@code handleSelector}. This is invoked for each
 *       string. For example if the Reader contained p, bar , a {}, the delegate
 *       would be notified 4 times, for 'p,' 'bar' ',' and 'a'.
 *   <li>When a rule starts, {@code startRule}.
 *   <li>Properties in the rule via the {@code handleProperty}. This
 *       is invoked once per property/value key, for example font size: foo;, would
 *       cause the delegate to be notified once with a value of 'font size'.
 *   <li>Values in the rule via the {@code handleValue}, this is notified
 *       for the total value.
 *   <li>When a rule ends, {@code endRule}.
 * </ul>
 * This will parse much more than CSS 1, and loosely implements the
 * recommendation for <i>Forward-compatible parsing</i> in section
 * 7.1 of the CSS spec found at:
 * <a href=http://www.w3.org/TR/REC-CSS1>http://www.w3.org/TR/REC-CSS1</a>.
 * <p>
 * If parsing results in an error, a {@code RuntimeException} will be thrown.
 * <p>
 * This will preserve case. If the callback wishes to treat certain portions
 * case-insensitively (such as selectors), it should use {@code toLowerCase}, or
 * something similar.
 *
 * @author Scott Violet
 */
class CSSParser {
    // Parsing something like the following:
    // (@rule | ruleset | block)*
    //
    // @rule       (block | identifier)*; (block with {} ends @rule)
    // block       matching [] () {} (that is, [()] is a block, [(){}{[]}]
    //                                is a block, ()[] is two blocks)
    // identifier  "*" | '*' | anything but a [](){} and whitespace
    //
    // ruleset     selector decblock
    // selector    (identifier | (block, except block '{}') )*
    // declblock   declaration* block*
    // declaration (identifier* stopping when identifier ends with :)
    //             (identifier* stopping when identifier ends with ;)
    //
    // comments /* */ can appear any where, and are stripped.


    // identifier - letters, digits, dashes and escaped characters
    // block starts with { ends with matching }, () [] and {} always occur
    //   in matching pairs, '' and "" also occur in pairs, except " may be


    // Indicates the type of token being parsed.
    private static final int   IDENTIFIER = 1;
    private static final int   BRACKET_OPEN = 2;
    private static final int   BRACKET_CLOSE = 3;
    private static final int   BRACE_OPEN = 4;
    private static final int   BRACE_CLOSE = 5;
    private static final int   PAREN_OPEN = 6;
    private static final int   PAREN_CLOSE = 7;
    private static final int   END = -1;

    private static final char[] charMapping = { 0, 0, '[', ']', '{', '}', '(',
                                               ')', 0};


    /** Set to true if one character has been read ahead. */
    private boolean        didPushChar;
    /** The read ahead character. */
    private int            pushedChar;
    /** Temporary place to hold identifiers. */
    private StringBuffer   unitBuffer;
    /** Used to indicate blocks. */
    private int[]          unitStack;
    /** Number of valid blocks. */
    private int            stackCount;
    /** Holds the incoming CSS rules. */
    private Reader         reader;
    /** Set to true when the first non @ rule is encountered. */
    private boolean        encounteredRuleSet;
    /** Notified of state. */
    private CSSParserCallback callback;
    /** nextToken() inserts the string here. */
    private char[]         tokenBuffer;
    /** Current number of chars in tokenBufferLength. */
    private int            tokenBufferLength;
    /** Set to true if any whitespace is read. */
    private boolean        readWS;


    // The delegate interface.
    static interface CSSParserCallback {
        /** Called when an {@code @import} is encountered. */
        void handleImport(String importString);
        // There is currently no way to distinguish between '"foo,"' and
        // 'foo,'. But this generally isn't valid CSS. If it becomes
        // a problem, handleSelector will have to be told if the string is
        // quoted.
        void handleSelector(String selector);
        void startRule();
        // Property names are mapped to lower case before being passed to
        // the delegate.
        void handleProperty(String property);
        void handleValue(String value);
        void endRule();
    }

    CSSParser() {
        unitStack = new int[2];
        tokenBuffer = new char[80];
        unitBuffer = new StringBuffer();
    }

    void parse(Reader reader, CSSParserCallback callback,
               boolean inRule) throws IOException {
        this.callback = callback;
        stackCount = tokenBufferLength = 0;
        this.reader = reader;
        encounteredRuleSet = false;
        try {
            if (inRule) {
                parseDeclarationBlock();
            }
            else {
                while (getNextStatement());
            }
        } finally {
            callback = null;
            reader = null;
        }
    }

    /**
     * Gets the next statement, returning false if the end is reached. A
     * statement is either an @rule, or a ruleset.
     */
    private boolean getNextStatement() throws IOException {
        unitBuffer.setLength(0);

        int token = nextToken((char)0);

        switch (token) {
        case IDENTIFIER:
            if (tokenBufferLength > 0) {
                if (tokenBuffer[0] == '@') {
                    parseAtRule();
                }
                else {
                    encounteredRuleSet = true;
                    parseRuleSet();
                }
            }
            return true;
        case BRACKET_OPEN:
        case BRACE_OPEN:
        case PAREN_OPEN:
            parseTillClosed(token);
            return true;

        case BRACKET_CLOSE:
        case BRACE_CLOSE:
        case PAREN_CLOSE:
            // Shouldn't happen...
            throw new RuntimeException("Unexpected top level block close");

        case END:
            return false;
        }
        return true;
    }

    /**
     * Parses an @ rule, stopping at a matching brace pair, or ;.
     */
    private void parseAtRule() throws IOException {
        // PENDING: make this more efficient.
        boolean        done = false;
        boolean isImport = (tokenBufferLength == 7 &&
                            tokenBuffer[0] == '@' && tokenBuffer[1] == 'i' &&
                            tokenBuffer[2] == 'm' && tokenBuffer[3] == 'p' &&
                            tokenBuffer[4] == 'o' && tokenBuffer[5] == 'r' &&
                            tokenBuffer[6] == 't');

        unitBuffer.setLength(0);
        while (!done) {
            int       nextToken = nextToken(';');

            switch (nextToken) {
            case IDENTIFIER:
                if (tokenBufferLength > 0 &&
                    tokenBuffer[tokenBufferLength - 1] == ';') {
                    --tokenBufferLength;
                    done = true;
                }
                if (tokenBufferLength > 0) {
                    if (unitBuffer.length() > 0 && readWS) {
                        unitBuffer.append(' ');
                    }
                    unitBuffer.append(tokenBuffer, 0, tokenBufferLength);
                }
                break;

            case BRACE_OPEN:
                if (unitBuffer.length() > 0 && readWS) {
                    unitBuffer.append(' ');
                }
                unitBuffer.append(charMapping[nextToken]);
                parseTillClosed(nextToken);
                done = true;
                // Skip a tailing ';', not really to spec.
                {
                    int nextChar = readWS();
                    if (nextChar != -1 && nextChar != ';') {
                        pushChar(nextChar);
                    }
                }
                break;

            case BRACKET_OPEN: case PAREN_OPEN:
                unitBuffer.append(charMapping[nextToken]);
                parseTillClosed(nextToken);
                break;

            case BRACKET_CLOSE: case BRACE_CLOSE: case PAREN_CLOSE:
                throw new RuntimeException("Unexpected close in @ rule");

            case END:
                done = true;
                break;
            }
        }
        if (isImport && !encounteredRuleSet) {
            callback.handleImport(unitBuffer.toString());
        }
    }

    /**
     * Parses the next rule set, which is a selector followed by a
     * declaration block.
     */
    private void parseRuleSet() throws IOException {
        if (parseSelectors()) {
            callback.startRule();
            parseDeclarationBlock();
            callback.endRule();
        }
    }

    /**
     * Parses a set of selectors, returning false if the end of the stream
     * is reached.
     */
    private boolean parseSelectors() throws IOException {
        // Parse the selectors
        int       nextToken;

        if (tokenBufferLength > 0) {
            callback.handleSelector(new String(tokenBuffer, 0,
                                               tokenBufferLength));
        }

        unitBuffer.setLength(0);
        for (;;) {
            while ((nextToken = nextToken((char)0)) == IDENTIFIER) {
                if (tokenBufferLength > 0) {
                    callback.handleSelector(new String(tokenBuffer, 0,
                                                       tokenBufferLength));
                }
            }
            switch (nextToken) {
            case BRACE_OPEN:
                return true;

            case BRACKET_OPEN: case PAREN_OPEN:
                parseTillClosed(nextToken);
                // Not too sure about this, how we handle this isn't very
                // well spec'd.
                unitBuffer.setLength(0);
                break;

            case BRACKET_CLOSE: case BRACE_CLOSE: case PAREN_CLOSE:
                throw new RuntimeException("Unexpected block close in selector");

            case END:
                // Prematurely hit end.
                return false;
            }
        }
    }

    /**
     * Parses a declaration block. Which a number of declarations followed
     * by a })].
     */
    private void parseDeclarationBlock() throws IOException {
        for (;;) {
            int token = parseDeclaration();
            switch (token) {
            case END: case BRACE_CLOSE:
                return;

            case BRACKET_CLOSE: case PAREN_CLOSE:
                // Bail
                throw new RuntimeException("Unexpected close in declaration block");
            case IDENTIFIER:
                break;
            }
        }
    }

    /**
     * Parses a single declaration, which is an identifier a : and another
     * identifier. This returns the last token seen.
     */
    // identifier+: identifier* ;|}
    private int parseDeclaration() throws IOException {
        int    token;

        if ((token = parseIdentifiers(':', false)) != IDENTIFIER) {
            return token;
        }
        // Make the property name to lowercase
        for (int counter = unitBuffer.length() - 1; counter >= 0; counter--) {
            unitBuffer.setCharAt(counter, Character.toLowerCase
                                 (unitBuffer.charAt(counter)));
        }
        callback.handleProperty(unitBuffer.toString());

        token = parseIdentifiers(';', true);
        callback.handleValue(unitBuffer.toString());
        return token;
    }

    /**
     * Parses identifiers until {@code extraChar} is encountered,
     * returning the ending token, which will be {@code IDENTIFIER} if
     * {@code extraChar} is found.
     */
    private int parseIdentifiers(char extraChar,
                                 boolean wantsBlocks) throws IOException {
        int   nextToken;
        int   ubl;

        unitBuffer.setLength(0);
        for (;;) {
            nextToken = nextToken(extraChar);

            switch (nextToken) {
            case IDENTIFIER:
                if (tokenBufferLength > 0) {
                    if (tokenBuffer[tokenBufferLength - 1] == extraChar) {
                        if (--tokenBufferLength > 0) {
                            if (readWS && unitBuffer.length() > 0) {
                                unitBuffer.append(' ');
                            }
                            unitBuffer.append(tokenBuffer, 0,
                                              tokenBufferLength);
                        }
                        return IDENTIFIER;
                    }
                    if (readWS && unitBuffer.length() > 0) {
                        unitBuffer.append(' ');
                    }
                    unitBuffer.append(tokenBuffer, 0, tokenBufferLength);
                }
                break;

            case BRACKET_OPEN:
            case BRACE_OPEN:
            case PAREN_OPEN:
                ubl = unitBuffer.length();
                if (wantsBlocks) {
                    unitBuffer.append(charMapping[nextToken]);
                }
                parseTillClosed(nextToken);
                if (!wantsBlocks) {
                    unitBuffer.setLength(ubl);
                }
                break;

            case BRACE_CLOSE:
                // No need to throw for these two, we return token and
                // caller can do whatever.
            case BRACKET_CLOSE:
            case PAREN_CLOSE:
            case END:
                // Hit the end
                return nextToken;
            }
        }
    }

    /**
     * Parses till a matching block close is encountered. This is only
     * appropriate to be called at the top level (no nesting).
     */
    private void parseTillClosed(int openToken) throws IOException {
        int       nextToken;
        boolean   done = false;

        startBlock(openToken);
        while (!done) {
            nextToken = nextToken((char)0);
            switch (nextToken) {
            case IDENTIFIER:
                if (unitBuffer.length() > 0 && readWS) {
                    unitBuffer.append(' ');
                }
                if (tokenBufferLength > 0) {
                    unitBuffer.append(tokenBuffer, 0, tokenBufferLength);
                }
                break;

            case BRACKET_OPEN: case BRACE_OPEN: case PAREN_OPEN:
                if (unitBuffer.length() > 0 && readWS) {
                    unitBuffer.append(' ');
                }
                unitBuffer.append(charMapping[nextToken]);
                startBlock(nextToken);
                break;

            case BRACKET_CLOSE: case BRACE_CLOSE: case PAREN_CLOSE:
                if (unitBuffer.length() > 0 && readWS) {
                    unitBuffer.append(' ');
                }
                unitBuffer.append(charMapping[nextToken]);
                endBlock(nextToken);
                if (!inBlock()) {
                    done = true;
                }
                break;

            case END:
                // Prematurely hit end.
                throw new RuntimeException("Unclosed block");
            }
        }
    }

    /**
     * Fetches the next token.
     */
    private int nextToken(char idChar) throws IOException {
        readWS = false;

        int     nextChar = readWS();

        switch (nextChar) {
        case '\'':
            readTill('\'');
            if (tokenBufferLength > 0) {
                tokenBufferLength--;
            }
            return IDENTIFIER;
        case '"':
            readTill('"');
            if (tokenBufferLength > 0) {
                tokenBufferLength--;
            }
            return IDENTIFIER;
        case '[':
            return BRACKET_OPEN;
        case ']':
            return BRACKET_CLOSE;
        case '{':
            return BRACE_OPEN;
        case '}':
            return BRACE_CLOSE;
        case '(':
            return PAREN_OPEN;
        case ')':
            return PAREN_CLOSE;
        case -1:
            return END;
        default:
            pushChar(nextChar);
            getIdentifier(idChar);
            return IDENTIFIER;
        }
    }

    /**
     * Gets an identifier, returning {@code true} if the length of the string is
     * greater than 0, stopping when {@code stopChar}, whitespace, or one of
     * {}()[] is hit.
     */
    // NOTE: this could be combined with readTill, as they contain somewhat
    // similar functionality.
    private boolean getIdentifier(char stopChar) throws IOException {
        boolean lastWasEscape = false;
        boolean done = false;
        int escapeCount = 0;
        int escapeChar = 0;
        int nextChar;
        int intStopChar = (int)stopChar;
        // 1 for '\', 2 for valid escape char [0-9a-fA-F], 3 for
        // stop character (white space, ()[]{}) 0 otherwise
        short type;
        int escapeOffset = 0;

        tokenBufferLength = 0;
        while (!done) {
            nextChar = readChar();
            switch (nextChar) {
            case '\\':
                type = 1;
                break;

            case '0': case '1': case '2': case '3': case '4': case '5':
            case '6': case '7': case '8': case '9':
                type = 2;
                escapeOffset = nextChar - '0';
                break;

            case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
                type = 2;
                escapeOffset = nextChar - 'a' + 10;
                break;

            case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
                type = 2;
                escapeOffset = nextChar - 'A' + 10;
                break;

            case '\'': case '"': case '[': case ']': case '{': case '}':
            case '(': case ')':
            case ' ': case '\n': case '\t': case '\r':
                type = 3;
                break;

            case '/':
                type = 4;
                break;

            case -1:
                // Reached the end
                done = true;
                type = 0;
                break;

            default:
                type = 0;
                break;
            }
            if (lastWasEscape) {
                if (type == 2) {
                    // Continue with escape.
                    escapeChar = escapeChar * 16 + escapeOffset;
                    if (++escapeCount == 4) {
                        lastWasEscape = false;
                        append((char)escapeChar);
                    }
                }
                else {
                    // no longer escaped
                    lastWasEscape = false;
                    if (escapeCount > 0) {
                        append((char)escapeChar);
                        // Make this simpler, reprocess the character.
                        pushChar(nextChar);
                    }
                    else if (!done) {
                        append((char)nextChar);
                    }
                }
            }
            else if (!done) {
                if (type == 1) {
                    lastWasEscape = true;
                    escapeChar = escapeCount = 0;
                }
                else if (type == 3) {
                    done = true;
                    pushChar(nextChar);
                }
                else if (type == 4) {
                    // Potential comment
                    nextChar = readChar();
                    if (nextChar == '*') {
                        done = true;
                        readComment();
                        readWS = true;
                    }
                    else {
                        append('/');
                        if (nextChar == -1) {
                            done = true;
                        }
                        else {
                            pushChar(nextChar);
                        }
                    }
                }
                else {
                    append((char)nextChar);
                    if (nextChar == intStopChar) {
                        done = true;
                    }
                }
            }
        }
        return (tokenBufferLength > 0);
    }

    /**
     * Reads till a {@code stopChar} is encountered, escaping characters
     * as necessary.
     */
    private void readTill(char stopChar) throws IOException {
        boolean lastWasEscape = false;
        int escapeCount = 0;
        int escapeChar = 0;
        int nextChar;
        boolean done = false;
        int intStopChar = (int)stopChar;
        // 1 for '\', 2 for valid escape char [0-9a-fA-F], 0 otherwise
        short type;
        int escapeOffset = 0;

        tokenBufferLength = 0;
        while (!done) {
            nextChar = readChar();
            switch (nextChar) {
            case '\\':
                type = 1;
                break;

            case '0': case '1': case '2': case '3': case '4':case '5':
            case '6': case '7': case '8': case '9':
                type = 2;
                escapeOffset = nextChar - '0';
                break;

            case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
                type = 2;
                escapeOffset = nextChar - 'a' + 10;
                break;

            case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
                type = 2;
                escapeOffset = nextChar - 'A' + 10;
                break;

            case -1:
                // Prematurely reached the end!
                throw new RuntimeException("Unclosed " + stopChar);

            default:
                type = 0;
                break;
            }
            if (lastWasEscape) {
                if (type == 2) {
                    // Continue with escape.
                    escapeChar = escapeChar * 16 + escapeOffset;
                    if (++escapeCount == 4) {
                        lastWasEscape = false;
                        append((char)escapeChar);
                    }
                }
                else {
                    // no longer escaped
                    if (escapeCount > 0) {
                        append((char)escapeChar);
                        if (type == 1) {
                            lastWasEscape = true;
                            escapeChar = escapeCount = 0;
                        }
                        else {
                            if (nextChar == intStopChar) {
                                done = true;
                            }
                            append((char)nextChar);
                            lastWasEscape = false;
                        }
                    }
                    else {
                        append((char)nextChar);
                        lastWasEscape = false;
                    }
                }
            }
            else if (type == 1) {
                lastWasEscape = true;
                escapeChar = escapeCount = 0;
            }
            else {
                if (nextChar == intStopChar) {
                    done = true;
                }
                append((char)nextChar);
            }
        }
    }

    private void append(char character) {
        if (tokenBufferLength == tokenBuffer.length) {
            char[] newBuffer = new char[tokenBuffer.length * 2];
            System.arraycopy(tokenBuffer, 0, newBuffer, 0, tokenBuffer.length);
            tokenBuffer = newBuffer;
        }
        tokenBuffer[tokenBufferLength++] = character;
    }

    /**
     * Parses a comment block.
     */
    private void readComment() throws IOException {
        int nextChar;

        for(;;) {
            nextChar = readChar();
            switch (nextChar) {
            case -1:
                throw new RuntimeException("Unclosed comment");
            case '*':
                nextChar = readChar();
                if (nextChar == '/') {
                    return;
                }
                else if (nextChar == -1) {
                    throw new RuntimeException("Unclosed comment");
                }
                else {
                    pushChar(nextChar);
                }
                break;
            default:
                break;
            }
        }
    }

    /**
     * Called when a block start is encountered ({[.
     */
    private void startBlock(int startToken) {
        if (stackCount == unitStack.length) {
            int[]     newUS = new int[stackCount * 2];

            System.arraycopy(unitStack, 0, newUS, 0, stackCount);
            unitStack = newUS;
        }
        unitStack[stackCount++] = startToken;
    }

    /**
     * Called when an end block is encountered )]}
     */
    private void endBlock(int endToken) {
        int    startToken;

        switch (endToken) {
        case BRACKET_CLOSE:
            startToken = BRACKET_OPEN;
            break;
        case BRACE_CLOSE:
            startToken = BRACE_OPEN;
            break;
        case PAREN_CLOSE:
            startToken = PAREN_OPEN;
            break;
        default:
            // Will never happen.
            startToken = -1;
            break;
        }
        if (stackCount > 0 && unitStack[stackCount - 1] == startToken) {
            stackCount--;
        }
        else {
            // Invalid state, should do something.
            throw new RuntimeException("Unmatched block");
        }
    }

    /**
     * @return true if currently in a block.
     */
    private boolean inBlock() {
        return (stackCount > 0);
    }

    /**
     * Skips any white space, returning the character after the white space.
     */
    private int readWS() throws IOException {
        int nextChar;
        while ((nextChar = readChar()) != -1 &&
               Character.isWhitespace((char)nextChar)) {
            readWS = true;
        }
        return nextChar;
    }

    /**
     * Reads a character from the stream.
     */
    private int readChar() throws IOException {
        if (didPushChar) {
            didPushChar = false;
            return pushedChar;
        }
        return reader.read();
        // Uncomment the following to do case insensitive parsing.
        /*
        if (retValue != -1) {
            return (int)Character.toLowerCase((char)retValue);
        }
        return retValue;
        */
    }

    /**
     * Supports one character look ahead, this will throw if called twice
     * in a row.
     */
    private void pushChar(int tempChar) {
        if (didPushChar) {
            // Should never happen.
            throw new RuntimeException("Can not handle look ahead of more than one character");
        }
        didPushChar = true;
        pushedChar = tempChar;
    }
}