package name.nathanmcrae.numbersstation;

import com.leakyabstractions.result.api.Result;
import com.leakyabstractions.result.core.Results;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.lang.management.ManagementFactory;
import java.lang.ProcessHandle;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javafx.util.Pair;

public class LinuxScheduler {
    private static final Logger logger = Logger.getLogger(Main.class.getName());

    public static Result<Boolean, String> registerSchedule(StationSettings settings) {
        try {
            String taskName = "numbers-station-main_" + settings.getName();

            Process listProcess = new ProcessBuilder("crontab", "-l").start();
            if (!listProcess.waitFor(5, TimeUnit.SECONDS)) {
                String message = "Failed to query " + taskName + " task: process timed out";
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }

            Pair<String, String> output = WindowsScheduler.captureProcessOutput(listProcess);
            if(listProcess.exitValue() != 0) {
                String message = "Failed to get user id. Exit code: " + listProcess.exitValue() + ". stdout: " + output.getKey() + "\n\tstderr: " + output.getValue();
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }

            String currentCrontab = output.getKey();

            String cronEntry = "# " + taskName + "\n" + cronExpression(settings) + "\n\n";

            Pattern pattern = Pattern.compile("# " + taskName + "\\n[^\\n]+\\n\\n");

            Matcher matcher = pattern.matcher(currentCrontab);

            StringBuilder sb = new StringBuilder();

            if (matcher.find()) {
                matcher.appendReplacement(sb, cronEntry);

                boolean foundMultiple = false;
                while (matcher.find()) {
                    foundMultiple = true;
                    matcher.appendReplacement(sb, "");
                }

                if (foundMultiple) {
                    logger.log(Level.WARNING, "Found multiple instances of '" + taskName + "' prior to replacement");
                }

                matcher.appendTail(sb);
            } else {
                sb.append(currentCrontab);
                sb.append(cronEntry);
            }

            String newCrontab = sb.toString();

            Process addProcess = new ProcessBuilder("crontab", "-").start();
            Writer w = new OutputStreamWriter(addProcess.getOutputStream(), "UTF-8");
            System.out.println(newCrontab);
            w.write(newCrontab);
            w.flush();
            w.close();
            if (!addProcess.waitFor(5, TimeUnit.SECONDS)) {
                String message = "Failed to register " + taskName + " task: process timed out";
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }

            if(addProcess.exitValue() != 0) {
                Pair<String, String> addOutput = WindowsScheduler.captureProcessOutput(addProcess);
                String message = "Failed to get user id. Exit code: " + addProcess.exitValue() + ". stdout: " + addOutput.getKey() + ". stderr: " + addOutput.getValue();
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }
        } catch (CronExpressionException | IOException | InterruptedException e) {
            String message = "Exception while registering schedule";
            logger.log(Level.SEVERE, message, e);
            return Results.failure(message);
        }

        return Results.success(true);
    }

    public static Result<Boolean, String> scheduleExists(StationSettings settings) {
        try {
            String taskName = "numbers-station-main_" + settings.getName();

            Process listProcess = new ProcessBuilder("crontab", "-l").start();
            if (!listProcess.waitFor(5, TimeUnit.SECONDS)) {
                String message = "Failed to query " + taskName + " task: process timed out";
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }

            Pair<String, String> output = WindowsScheduler.captureProcessOutput(listProcess);
            if(listProcess.exitValue() != 0) {
                String message = "Failed to get user id. Exit code: " + listProcess.exitValue() + ". stdout: " + output.getKey() + "\n\tstderr: " + output.getValue();
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }

            String currentCrontab = output.getKey();

            String cronEntry = "# " + taskName + "\n" + cronExpression(settings) + "\n\n";

            Pattern pattern = Pattern.compile("# " + taskName + "\\n[^\\n]+\\n\\n");

            Matcher matcher = pattern.matcher(currentCrontab);

            if (matcher.find()) {
                return Results.success(true);
            } else {
                return Results.success(true);
            }
        } catch (CronExpressionException | IOException | InterruptedException e) {
            String message = "Exception while checking for schedule";
            logger.log(Level.SEVERE, message, e);
            return Results.failure(message);
        }
    }

    public static Result<Boolean, String> removeSchedule(StationSettings settings) {
        try {
            String taskName = "numbers-station-main_" + settings.getName();

            Process listProcess = new ProcessBuilder("crontab", "-l").start();
            if (!listProcess.waitFor(5, TimeUnit.SECONDS)) {
                String message = "Failed to query " + taskName + " task: process timed out";
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }

            Pair<String, String> output = WindowsScheduler.captureProcessOutput(listProcess);
            if(listProcess.exitValue() != 0) {
                String message = "Failed to get user id. Exit code: " + listProcess.exitValue() + ". stdout: " + output.getKey() + "\n\tstderr: " + output.getValue();
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }

            String currentCrontab = output.getKey();

            String cronEntry = "# " + taskName + "\n" + cronExpression(settings) + "\n\n";

            Pattern pattern = Pattern.compile("# " + taskName + "\\n[^\\n]+\\n\\n");

            Matcher matcher = pattern.matcher(currentCrontab);

            StringBuilder sb = new StringBuilder();

            while (matcher.find()) {
                matcher.appendReplacement(sb, "");
            }

            String newCrontab = sb.toString();

            Process addProcess = new ProcessBuilder("crontab", "-").start();
            Writer w = new OutputStreamWriter(addProcess.getOutputStream(), "UTF-8");
            System.out.println(newCrontab);
            w.write(newCrontab);
            w.flush();
            w.close();
            if (!addProcess.waitFor(5, TimeUnit.SECONDS)) {
                String message = "Failed to register " + taskName + " task: process timed out";
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }

            if(addProcess.exitValue() != 0) {
                Pair<String, String> addOutput = WindowsScheduler.captureProcessOutput(addProcess);
                String message = "Failed to get user id. Exit code: " + addProcess.exitValue() + ". stdout: " + addOutput.getKey() + ". stderr: " + addOutput.getValue();
                logger.log(Level.SEVERE, message);
                return Results.failure(message);
            }
        } catch (CronExpressionException | IOException | InterruptedException e) {
            String message = "Exception while removing schedule";
            logger.log(Level.SEVERE, message, e);
            return Results.failure(message);
        }

        return Results.success(true);
    }

    /**
     *  * * * * * {command to execute}
     *  | | | | |
     *  | | | | day of the week (0–6) (Sunday to Saturday;
     *  | | | month (1–12)             7 is also Sunday on some systems)
     *  | | day of the month (1–31)
     *  | hour (0–23)
     *  minute (0–59)
     */
    public static String cronExpression(StationSettings settings) throws CronExpressionException {
        LocalDateTime scheduleDateTime = settings.getScheduleStart().withZoneSameInstant(ZoneId.systemDefault()).toLocalDateTime();

        String minute = Integer.toString(scheduleDateTime.getMinute());
        String hour = Integer.toString(scheduleDateTime.getHour());
        String dayOfMonth = Integer.toString(scheduleDateTime.getDayOfMonth());
        String dayOfWeek = Integer.toString(scheduleDateTime.getDayOfMonth());

        String scheduleString = "";
        switch(settings.getMessagePeriod()) {
            case DAILY:
                scheduleString = minute + " " + hour + " * * *";
                break;
            case WEEKLY:
                scheduleString = minute + " " + hour + " * * " + dayOfWeek;
                break;
            case MONTHLY:
                scheduleString = minute + " " + hour + " " + dayOfMonth + " * *";
                break;
            default:
                throw new CronExpressionException("Message period not implemented: '" + settings.getMessagePeriod() + "'");
        }

        String processName = ManagementFactory.getRuntimeMXBean().getName();
        long pid = Long.parseLong(processName.split("@")[0]);
        ProcessHandle currentProcess = ProcessHandle.of(pid).orElseThrow();
        Path executablePath = currentProcess.info().command().map(Paths::get).orElseThrow();
        logger.info("Executable Path: " + executablePath);
        return scheduleString + " " + executablePath.toString() + " --station \"" + settings.getName() + "\"";
    }

    public static class CronExpressionException extends Exception {
        public CronExpressionException(String message) {
            super(message);
        }
    }
}