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Javageci jamal macro library
There is a newer version: 1.6.5
package javax0.geci.jamal;

import javax0.geci.api.GeciException;
import javax0.geci.api.Source;
import javax0.geci.tools.AbstractGeneratorEx;
import javax0.jamal.api.BadSyntax;
import javax0.jamal.api.Position;
import javax0.jamal.engine.Processor;
import javax0.jamal.tools.Input;

import java.util.regex.Pattern;

/**
 * A code generator class that reads the source files and works up all segments that look like
 *
 * {@code
 *     /*!jamal
 *      ...
 *      ... template part inside Java comment
 *      ...
 *      *\u0000/}{@code
 *      ...
 *      ... code part
 *      ...
 *      //__END__}
 * 
 * 
 * reading an using the 'template part' as Jamal macro source and processing it and replacing with the
 * result the 'code part'.
 */
public class JamalGenerator extends AbstractGeneratorEx {
    private static final Pattern START = Pattern.compile("^\\s*/\\*!jamal\\s*$");
    private static final Pattern COMMENT_END = Pattern.compile("^\\s*\\*/\\s*$");
    private static final Pattern SEGMENT_END = Pattern.compile("^\\s*//\\s*__END__\\s*$");

    @Override
    public void processEx(Source source) {
        final Processor processor;
        try {
            processor = new Processor("{%", "%}");
        } catch (IllegalArgumentException ex) {
            throw new GeciException("Jamal processor opening threw exception", ex);
        }
        var lines = source.getLines();
        try( final var output = source.open()) {
            var state = PROCESSING.COPY;
            final var macro = new StringBuilder();
            var lineNr = 0;
            int positionLineNr = 0;
            for (final var line : lines) {
                lineNr++;
                switch (state) {
                    case COPY:
                        output.write(line);
                        if (START.matcher(line).matches()) {
                            state = PROCESSING.INSOURCE;
                            macro.delete(0, macro.length());
                            positionLineNr = lineNr + 1;
                        }
                        break;
                    case INSOURCE:
                        output.write(line);
                        if (COMMENT_END.matcher(line).matches()) {
                            state = PROCESSING.OUTPUT;
                            final String result;
                            try {
                                result = processor.process(new Input(macro.toString(),
                                    new Position(source.getAbsoluteFile(), positionLineNr)));
                                macro.delete(0, macro.length());
                            } catch (BadSyntax badSyntax) {
                                throw new GeciException("Macro processing in file '"
                                                            + source.getAbsoluteFile() + "' threw exception", badSyntax);
                            }
                            output.write(result);
                        } else {
                            macro.append(line).append("\n");
                        }
                        break;
                    case OUTPUT:
                        if (SEGMENT_END.matcher(line).matches()) {
                            output.write(line);
                            state = PROCESSING.COPY;
                        }
                        break;
                }
            }
        }
    }

    private enum PROCESSING {
        COPY, INSOURCE, OUTPUT
    }
}