/**
 * Universität Ulm
 * Grundlagen der Betriebssysteme - Labor
 * Versuch 1 : Kommandozeilen-Interpreter
 * Aufgabe 1 : Erstellen einer minimalen Shell
 * @author Julian Bestler (julian.bestler@uni-ulm.de)
 * @version 1.0
 */

import static cTools.KernelWrapper.*;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.File;

class Shell {
    final static int STD_IN = 0;
    final static int STD_OUT = 1;

    public static void main(String[] args) throws Exception {
        String login = "";
        try {
            login = System.getProperty("user.name") + "@" + java.net.InetAddress.getLocalHost().getHostName();
        }
        atch (Exception ex) {
        }

        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        while (true) {

            System.out.print(login + " " + System.getProperty("user.dir") + ">> "); // Display
                                                // prompt
            String[] commands = reader.readLine().split("\\|"); // Read commands

            int in = 0;
            int[] fd = new int[2];

            for (int i = 0; i < commands.length; i++) {
                String cmd = new String(commands[i].trim().replace("'", ""));
                if (cmd.compareToIgnoreCase("Exit") == 0) {
                    exit(0);
                }
                /***************************************
                 *** Replace * with all filenames in the directory
                 ***************************************/
                File[] currentFolder = new File(System.getProperty("user.dir")).listFiles();
                String filenames = "";
                for (int j = 0; j < currentFolder.length; j++) {
                    if (currentFolder[j].isFile()) {
                        filenames += " " + currentFolder[j];
                    }
                }
                System.out.println("Replacing * by " + filenames);
                cmd = cmd.replaceFirst("\\*", filenames);

                /****************************************
                 *** Redirection operators < and >
                 ****************************************/
                Boolean stdinRedirect = cmd.contains("<");
                Boolean stdoutRedirect = cmd.contains(">");
                int stdin_old = 0;
                int stdout_old = 1;

                if (stdinRedirect) { // redirect stdin
                    stdin_old = dup2(STD_IN, 2); // back up original stdin
                    close(STD_IN); // close original stdin
                    open(cmd.substring(cmd.indexOf("<") + 1, cmd.length()).trim(), O_RDONLY);   // open
                                                            // new
                                                            // stdin
                    cmd = cmd.substring(0, cmd.indexOf("<"));   // remove redirect
                                            // from command
                                            // string
                }
                if (stdoutRedirect) {
                    stdout_old = dup2(STD_OUT, 3); // back up original stdout
                    close(STD_OUT); // close original stdout
                    open(cmd.substring(cmd.indexOf(">") + 1, cmd.length()).trim(), O_WRONLY | O_CREAT);     // open
                                                                // or
                                                                // create
                                                                // new
                                                                // stdout
                    cmd = cmd.substring(0, cmd.indexOf(">"));   // remove redirect
                                            // from command
                                            // string
                }

                String[] opt = cmd.split(" ");
                String path = null;

                File pgm = new File(opt[0]);
                if (pgm.isFile() && pgm.canExecute()) { // Maybe it's an
                                    // absolute path
                    path = opt[0];
                } else { // Else search in path variable for program location
                    for (String folder : System.getenv("PATH").split(":")) {
                        pgm = new File(folder + "/" + opt[0]);
                        if (pgm.isFile() && pgm.canExecute()) {
                            path = folder + "/" + opt[0];
                            break;
                        }
                    }
                }

                if (path == null) {
                    System.err.println("No executable program found!");
                } else {
                    if (i < commands.length - 1) {
                        pipe(fd);
                        execute(in, fd[1], path, opt);
                        close(fd[1]);
                        in = fd[0];
                    } else {
                        int pid = fork();
                        if (pid == 0) {
                            if (in != 0) {
                                dup2(in, 0);
                            }
                            execv(path, opt);
                        } else {
                            int[] status = new int[1];
                            waitpid(pid, status, 0);
                        }
                    }
                }

                // Restore original stdin / stdout
                if (stdinRedirect) {
                    close(STD_IN);
                    dup2(stdin_old, STD_IN);
                    close(stdin_old);
                }
                if (stdoutRedirect) {
                    close(STD_OUT);
                    dup2(stdout_old, STD_OUT);
                    close(stdout_old);
                }
            }
        }
    }

    private static void execute(int in, int out, String pgm, String[] argv) {
        int pid = fork();
        if (pid == 0) {
            if (in != 0) {
                dup2(in, 0);
                close(in);
            }
            if (out != 1) {
                dup2(out, 1);
                close(out);
            }
            execv(pgm, argv);
        }
    }
}