NaiveTableOfContentGenerator

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Optional;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.Stream;

//Todo. Redo to tree-node parsing

public class TableOfContentGenerator {

    //Start with # symbol
    private static final Pattern HEADER_SYMBOL = Pattern.compile("^#.+");
    private static final Pattern CODE_SYMBOL = Pattern.compile("^```");
    private static final Pattern CODE_SYMBOL_OPENED_AND_CLOSED_ON_SAME_LINE = Pattern.compile("^```.*?```");
    private static boolean insideCode = false;

    record HeaderInformation(Header header, String chapterName, String anchor) {
    }

    public static void main(String[] args) throws IOException {
        System.out.println(generateTableOfContent(Files.lines(Path.of("src/main/resources/example.md"))));
    }

    public static String generateTableOfContent(Stream<String> text) {
        var headersInformation = text
                .map(String::strip)
                .map(TableOfContentGenerator::parseLine)
                .filter(Optional::isPresent)
                .map(Optional::get)
                .collect(Collectors.toList());

        StringBuilder tableOfContent = new StringBuilder();
        tableOfContent.append("# Table of Content\n\n");
        for (var headerInformation : headersInformation) {
            var formattedChapterName = "%s [%s](#%s)\n".formatted(headerInformation.header.separatorSymbol, headerInformation.chapterName, headerInformation.anchor);
            tableOfContent.append(formattedChapterName);
        }
        return tableOfContent.toString().strip();
    }

    private static Optional<HeaderInformation> parseLine(String line) {
        if (!insideCode && CODE_SYMBOL.matcher(line).find()) {
            insideCode = true;
            if (CODE_SYMBOL_OPENED_AND_CLOSED_ON_SAME_LINE.matcher(line).find()) {
                insideCode = false;
            }
        } else if (insideCode && CODE_SYMBOL.matcher(line).find()) {
            insideCode = false;
        }

        var matcher = HEADER_SYMBOL.matcher(line);
        if (matcher.find() && !insideCode) {
            var extractedHeader = matcher.group();
            var header = typeOfHeader(extractedHeader, line);
            var chapterNameWithoutHeader = line.replaceAll("^#.*?\s", "");
            var anchor = produceAnchor(chapterNameWithoutHeader);
            return Optional.of(new HeaderInformation(header, chapterNameWithoutHeader, anchor));
        }
        return Optional.empty();
    }

    private static Header typeOfHeader(String header, String line) {
        var split = header.split("\s"); //Example of line ``# This is chapter's header``
        header = split[0].strip(); //Should contain only #
        var allAreHeaderSymbols = header.codePoints().allMatch(value -> value == 35); //35 == # symbol
        if (!allAreHeaderSymbols) {
            throw new RuntimeException("Non header symbol found. Line: " + line);
        }
        return switch ((int) header.codePoints().count()) {
            case 1 -> Header.H1;
            case 2 -> Header.H2;
            case 3 -> Header.H3;
            case 4 -> Header.H4;
            case 5 -> Header.H5;
            default -> throw new RuntimeException("Invalid header");
        };
    }

    /**
     * Make all lowercase
     * Remove anything that is not a letter, number, space or hyphen, like :, ', etc
     * Change any space to a hyphen.
     */
    private static String produceAnchor(String chapterNameWithoutHeader) {
        var lowerCased = chapterNameWithoutHeader.toLowerCase();
        var removeAnythingThatIsNotLetterOrSpaceOrNumber = lowerCased.replaceAll("[^\\p{L}\\d\\s-]", "");
        return removeAnythingThatIsNotLetterOrSpaceOrNumber.replaceAll("\s", "-");
    }

    enum Header {
        H1("-"), H2("  *"), H3("    +"), H4("      -"), H5(" ".repeat(8) + "*");

        String separatorSymbol;

        Header(String separatorSymbol) {
            this.separatorSymbol = separatorSymbol;
        }
    }
}