checkstyle {
    toolVersion = "7.0"
    ignoreFailures = true
    configFile rootProject.file("checkstyle/checkstyle.xml")
    configProperties = [ "checkstyleFilterFile" : file('checkstyle/filter.xml')]
}

task checkstyleChanged(type: Checkstyle) {
    source 'changedfiles'
    include '**/*.java'
    classpath = files()
    ignoreFailures = true
    showViolations = true

    copyChangedFilesForCheckstyle()

    reports {
        html {
            destination "${project.rootDir}/build/reports/checkstyle/checkstyle_changed.html"
        }
        xml {
            destination "${project.rootDir}/build/reports/checkstyle/checkstyle_changed.xml"
        }
    }
}

/**
 * Compares the current set of changed files to HEAD and copies them to a temporary
 * folder. This is a prerequisite to run checkstyle on changed files only.
 */
def copyChangedFilesForCheckstyle() {
    ByteArrayOutputStream systemOutStream = new ByteArrayOutputStream()
    ("git diff --name-status HEAD~1").execute().waitForProcessOutput(systemOutStream, System.err)
    def allFiles = systemOutStream.toString().trim().split('\n')
    systemOutStream.close()

    Pattern statusPattern = Pattern.compile("([^D])\\t+(.+)")
    // Contains all files that are not deleted
    ArrayList<String> files = new ArrayList<>()
    for (file in allFiles) {
        Matcher matcher = statusPattern.matcher(file)
        if (matcher.find()) {
            files.add(matcher.group(2))
        }
    }

    String dst = "./changedfiles/"
    String rootDir = "./"
    new File(dst).deleteDir()
    mkdir(dst)

    for (file in files) {
        File srcFile = new File(rootDir + file)
        if (!srcFile.exists()) {
            continue
        }
        String dstFileName = dst + file
        String dstDirOnly = dstFileName.substring(0, dstFileName.lastIndexOf("/"))
        File dstDir = new File(dstDirOnly)
        File dstFile = new File(dstFileName)
        dstDir.mkdirs()
        Files.copy(srcFile.toPath(), dstFile.toPath())
    }
}