package com.example.demo.service;

import com.example.demo.model.PdfFileRequest;
import org.apache.tomcat.util.http.fileupload.IOUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;

import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.TimeUnit;

/**
 * @author Simon
 */
@Service
public class PdfFileCreator {
    private static final Logger LOGGER = LoggerFactory.getLogger(PdfFileCreator.class);

    public void writePdfToResponse(PdfFileRequest fileRequest, HttpServletResponse response) {
        String pdfFileName = fileRequest.getFileName();
        requireNotNull(pdfFileName, "The file name of the created PDF must be set");
        requireNotEmpty(pdfFileName, "File name of the created PDF cannot be empty");

        String sourceHtmlUrl = fileRequest.getSourceHtmlUrl();
        requireNotNull(sourceHtmlUrl, "Source HTML url must be set");
        requireNotEmpty(sourceHtmlUrl, "Source HTML url cannot be empty");

        List<String> pdfCommand = Arrays.asList(
//                "wkhtmltopdf",
                "C:\\Program Files\\wkhtmltopdf\\bin\\wkhtmltopdf.exe",
                sourceHtmlUrl,
                "-"
        );
        ProcessBuilder pb = new ProcessBuilder(pdfCommand);
        Process pdfProcess;
        try {
            pdfProcess = pb.start();
            try (InputStream in = pdfProcess.getInputStream()) {
                writeCreatedPdfFileToResponse(in, response);
                waitForProcessBeforeContinueCurrentThread(pdfProcess);
                requireSuccessfulExitStatus(pdfProcess);
                setResponseHeaders(response, fileRequest);
            } catch (Exception ex) {
                writeErrorMessageToLog(ex, pdfProcess);
                throw new RuntimeException("PDF generation failed");
            } finally {
                pdfProcess.destroy();
            }
        } catch (IOException ex) {
            throw new RuntimeException("PDF generation failed", ex);
        }
    }

    private void requireNotNull(String value, String message) {
        if (value == null) {
            throw new IllegalArgumentException(message);
        }
    }

    private void requireNotEmpty(String value, String message) {
        if (value.isEmpty()) {
            throw new IllegalArgumentException(message);
        }
    }

    private void writeCreatedPdfFileToResponse(InputStream in, HttpServletResponse response) throws IOException {
        OutputStream out = response.getOutputStream();
        IOUtils.copy(in, out);
        out.flush();
    }

    private void waitForProcessBeforeContinueCurrentThread(Process process) {
        try {
            process.waitFor(2, TimeUnit.SECONDS);
        } catch (InterruptedException ex) {
            Thread.currentThread().interrupt();
        }
    }

    private void requireSuccessfulExitStatus(Process process) {
        if (process.exitValue() != 0) {
            throw new RuntimeException("PDF generation failed");
        }
    }

    private void setResponseHeaders(HttpServletResponse response, PdfFileRequest fileRequest) {
        response.setContentType("application/pdf");
        response.setHeader("Content-Disposition", "attachment; filename=\"" + fileRequest.getFileName() + "\"");
    }

    private void writeErrorMessageToLog(Exception ex, Process pdfProcess) throws IOException {
        LOGGER.error("Could not create PDF because an exception was thrown: ", ex);
        LOGGER.error("The exit value of PDF process is: {}", pdfProcess.exitValue());

        String errorMessage = getErrorMessageFromProcess(pdfProcess);
        LOGGER.error("PDF process ended with error message: {}", errorMessage);
    }

    private String getErrorMessageFromProcess(Process pdfProcess) {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(pdfProcess.getErrorStream()));
            StringWriter writer = new StringWriter();

            String line;
            while ((line = reader.readLine()) != null) {
                writer.append(line);
            }
            return writer.toString();
        } catch (IOException ex) {
            LOGGER.error("Could not extract error message from process because an exception was thrown", ex);
            return "";
        }
    }

}