PreProcessor.groovy

package com.initvoid.jconfig

import groovy.transform.CompileStatic

import java.util.regex.Pattern

@CompileStatic
class PreProcessor
{
    static Pattern HELP_PATTERN = ~/^\s*(---)?\s*help\s*(---)?/
    static int     INIT_LENGTH  = -1

    static void process (InputStream inputStream, OutputStream outputStream)
    {
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream)
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream)
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader)

        String line
        boolean active = false
        int baseIndent = INIT_LENGTH

        while ((line = bufferedReader.readLine()) != null)
        {
            if (line.matches(HELP_PATTERN))
            {
                active = true
                baseIndent = INIT_LENGTH
            }
            else if (active)
            {
                int indentLength = indentLength(line)

                if (baseIndent == INIT_LENGTH)
                {
                    baseIndent = indentLength
                }
                else if (indentLength < baseIndent && line.trim().length() > 0)
                {
                    outputStreamWriter.write('\u001F')
                    active = false
                }
            }
            outputStreamWriter.write(line)

            outputStreamWriter.write('\n')
        }

        if (active)
        {
            outputStreamWriter.write('\u001F')
        }

        outputStreamWriter.flush()
    }

    static int indentLength (String line)
    {
        int lineLength = line.length()
        int indentLength = -1

        for (int i = 0; i < lineLength; i++)
            if (line[i] == '\t')
                indentLength = (indentLength & ~7) + 8
            else if (line[i] == ' ')
                indentLength++
            else
                break

        return indentLength
    }

    static void main (String[] args)
    {
        def url = 'https://raw.githubusercontent.com/torvalds/linux/master/arch/x86/Kconfig'.toURL()
        def bufferedInputStream    = url.newInputStream()
        def byteArrayOutputStream  = new ByteArrayOutputStream()

        process(bufferedInputStream, byteArrayOutputStream)

        def result = byteArrayOutputStream.toString()

        println result

        'nop'
    }

}