biskuteri-cafe-JKomasto2/RudimentaryHTMLParser.java

/* copyright

This file is part of JKomasto2.
Written in 2022 by Usawashi <usawashi16@yahoo.co.jp>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program 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 for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.

copyright */

import cafe.biskuteri.hinoki.Tree;
import java.util.List;
import java.util.ArrayList;
import java.io.StringReader;
import java.io.Reader;
import java.io.IOException;

class
RudimentaryHTMLParser {

    public static Tree<String>
    depthlessRead(String html)
    {
        try {
            return pass3(pass2(pass1(html)));
        }
        catch (IOException eIo) {
            assert false;
            /*
            * We use only StringReaders, which only throw an
            * IOException when they are read after being closed.
            * And we don't close them.
            */
            return null;
        }
    }

//     -    -%-     -

    private static Tree<String>
    pass1(String html)
    throws IOException
    {
        Reader r = new StringReader(html);
        Tree<String> docu = new Tree<String>();
        StringBuilder text = new StringBuilder();
        StringBuilder emoji = new StringBuilder();
        StringBuilder htmlEscape = new StringBuilder();
        boolean quoted = false, inEmoji = false;
        int c; while ((c = r.read()) != -1)
        {
            if (c == '&' || htmlEscape.length() > 0)
            {
                htmlEscape.append((char)c);
                if (c == ';')
                {
                    String s = empty(htmlEscape);
                    if (quoted) text.append('\\');
                    /*
                    * If we're quoted (i.e. within unescaped
                    * quotes), we're in a tag, add escaping
                    * backslash for pass2 to work with.
                    * Only necessary for the quotes, but,
                    * might as well uniformly use.
                    */
                    if (s.equals("&lt;")) text.append('<');
                    if (s.equals("&gt;")) text.append('>');
                    if (s.equals("&amp;")) text.append('&');
                    if (s.equals("&quot;")) text.append('"');
                    if (s.equals("&apos;")) text.append('\'');
                    if (s.equals("&#39;")) text.append('\'');
                }
                continue;
            }
            if (c == '"')
            {
                text.append((char)c);
                quoted = !quoted;
                continue;
            }
            if (!quoted)
            {
                if (c == '<')
                {
                    if (text.length() > 0)
                    {
                        Tree<String> node = new Tree<>();
                        node.key = "text";
                        node.value = empty(text);
                        docu.add(node);
                    }
                    continue;
                }
                if (c == '>')
                {
                    Tree<String> node = new Tree<>();
                    node.key = "tag";
                    node.value = empty(text);
                    docu.add(node);
                    continue;
                }
            }
            text.append((char)c);
            continue;
        }
        if (text.length() > 0)
        {
            Tree<String> node = new Tree<>();
            node.key = "text";
            node.value = empty(text);
            docu.add(node);
        }
        return docu;
    }

    private static Tree<String>
    pass2(Tree<String> docu)
    throws IOException
    {
        for (Tree<String> node: docu.children)
        {
            if (!node.key.equals("tag")) continue;

            Reader r = new StringReader(node.value);
            Tree<String> part = new Tree<String>();
            boolean escaped = false, quoted = false;
            StringBuilder field = new StringBuilder();
            int c; while ((c = r.read()) != -1)
            {
                if (escaped) {
                    field.append((char)c);
                    escaped = false;
                    continue;
                }
                if (c == '\\') {
                    escaped = true;
                    continue;
                }
                if (c == '"') {
                    quoted = !quoted;
                    continue;
                }
                if (quoted) {
                    field.append((char)c);
                    continue;
                }
                if (c == '=') {
                    part.key = empty(field);
                    continue;
                }
                if (c == ' ') {
                    if (field.length() > 0) {
                        boolean v = part.key != null;
                        if (v) part.value = empty(field);
                        else part.key = empty(field);
                        node.add(part);
                        part = new Tree<String>();
                    }
                    continue;
                }
                field.append((char)c);
            }
            if (field.length() > 0) {
                boolean v = part.key != null;
                if (v) part.value = empty(field);
                else part.key = empty(field);
                node.add(part);
            }
            node.value = null;
        }
        return docu;
    }

    private static Tree<String>
    pass3(Tree<String> docu)
    {
        Tree<String> returnee = new Tree<String>();

        for (Tree<String> node: docu)
        {
            if (!node.key.equals("text"))
            {
                returnee.add(node);
                continue;
            }

            StringBuilder value = new StringBuilder();
            for (String segment: whitespaceSplit(node.value))
            {
                boolean st = segment.startsWith(":");
                boolean ed = segment.endsWith(":");

                if (st && ed)
                {
                    Tree<String> text = new Tree<String>();
                    text.key = "text";
                    text.value = empty(value);
                    returnee.add(text);

                    Tree<String> emoji = new Tree<String>();
                    emoji.key = "emoji";
                    emoji.value = segment;
                    returnee.add(emoji);
                }
                else
                {
                    value.append(segment);
                }
            }
            if (value.length() > 0)
            {
                Tree<String> text = new Tree<String>();
                text.key = "text";
                text.value = empty(value);
                returnee.add(text);
            }
        }
        return returnee;
    }

    private static String
    empty(StringBuilder b)
    {
        String s = b.toString();
        b.delete(0, b.length());
        return s;
    }

    private static List<String>
    whitespaceSplit(String text)
    {
        List<String> returnee = new ArrayList<>();
        StringBuilder segment = new StringBuilder();
        boolean isWhitespace = false;
        for (char c: text.toCharArray())
        {
            boolean diff = isWhitespace ^ Character.isWhitespace(c);
            if (diff) {
                returnee.add(empty(segment));
                isWhitespace = !isWhitespace;
            }
            segment.append(c);
        }
        returnee.add(empty(segment));

        return returnee;
    }

//    ---%-@-%---

    public static void
    main(String... args)
    {
        final String EX2 =
            "<p>2000s energy<br /><a href=\"http://www.pspad.com/en/screenshot.htm\" rel=\"nofollow noopener noreferrer\" target=\"_blank\"><span class=\"invisible\">http://www.</span><span class=\"\">pspad.com/en/screenshot.htm</span><span class=\"invisible\"></span></a></p>";
    }

}