package ui;

import model.asn1.exceptions.InvalidDBException;
import model.asn1.exceptions.ParseException;
import model.ca.CertificationAuthority;
import persistence.Decoder;
import persistence.FS;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Path;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;
import java.util.Scanner;

/**
 * Main program
 */
public class JCA {
    /**
     * Default db file (./data/ca.json)
     */
    private static final Path PATH_DEFAULT = Path.of("data", "ca.json");

    /**
     * Instances of the five screens;
     */
    private final UIHandler mainScreen;
    private final UIHandler mgmtScreen;
    private final UIHandler issueScreen;
    private final UIHandler templatesScreen;
    private final UIHandler templateSetScreen;
    /**
     * The CA
     */
    private CertificationAuthority ca;
    /**
     * The current screen.
     */
    private UIHandler screen;

    /**
     * There are unsaved changes.
     */
    private boolean unsaved = false;

    /**
     * EFFECTS: Init with main screen and empty CA. No private key and no CA cert.
     * Throws {@link NoSuchAlgorithmException} when crypto issue happens.
     */
    public JCA() throws NoSuchAlgorithmException, InvalidKeySpecException {
        this.mainScreen = new MainScreen(this);
        this.mgmtScreen = new MgmtScreen(this);
        this.issueScreen = new IssueScreen(this);
        this.templatesScreen = new TemplatesScreen(this);
        this.templateSetScreen = new TemplateSetScreen(this);

        setScreen(Screen.MAIN);

        this.ca = new CertificationAuthority();
    }

    /**
     * EFFECT: Checks if the CA is installed or not (according to the desired state) and print if not matching. Returns
     * true if matching.
     */
    public boolean checkCA(boolean requireInstalled) {
        if (requireInstalled && ca.getCertificate() == null) {
            System.out.println("No CA installed");
            return false;
        } else if (!requireInstalled && ca.getCertificate() != null) {
            System.out.println("CA already installed");
            return false;
        }
        return true;
    }

    /**
     * EFFECTS: Read PEM from stdin, matched the given tag.
     * Throws {@link ParseException} if the input is incorrect.
     */
    public Byte[] handleInputPEM(String desiredTag) throws ParseException {
        final Scanner scanner = new Scanner(System.in);
        StringBuilder in = new StringBuilder();
        while (true) {
            final String line = scanner.nextLine();
            in.append(line);
            in.append("\n");
            if (line.matches("-----END .*-----")) {
                break;
            }
        }
        return Utils.parsePEM(Utils.byteToByte(in.toString().getBytes(StandardCharsets.UTF_8)), desiredTag);
    }

    /**
     * EFFECT: Set the current screen with optional args. Exit the program when mode is null.
     * MODIFIES: this
     */
    public void setScreen(Screen mode, Object... args) {
        if (mode == null) {
            System.exit(0);
        }
        switch (mode) {
            case MAIN:
                this.screen = mainScreen;
                break;
            case MGMT:
                this.screen = mgmtScreen;
                break;
            case ISSUE:
                this.screen = issueScreen;
                break;
            case TEMPLATES:
                this.screen = templatesScreen;
                break;
            case TEMPLATE_SET:
                this.screen = templateSetScreen;
                break;
        }
        screen.enter(args);
    }

    /**
     * EFFECTS: Read the database file and replace all local states.
     * MODIFIES: this
     */
    private void load() {
        if (unsaved) {
            System.out.println("Current database is not saved yet.");
            return;
        }
        try {
            this.ca = Decoder.decodeCA(FS.read(PATH_DEFAULT));
        } catch (InvalidDBException | NoSuchAlgorithmException e) {
            System.out.println(e.getMessage());
            if (e.getCause() != null) {
                System.out.println(e.getCause().getMessage());
                e.getCause().printStackTrace();
            }
        }
    }

    /**
     * EFFECTS: Handle input line
     * MODIFIES: this
     */
    private void handleLine(String... args) {
        if (args[0].equals("log")) {
            ca.getLogs().forEach(System.out::println);
            return;
        }
        if ("help".equals(args[0])) {
            screen.help();
            System.out.println("log\tView audit logs");
            System.out.println("load\tLoad database");
            System.out.println("save\tSave database");
        } else if ("commit".equals(args[0])) {
            screen.commit();
        } else if ("show".equals(args[0])) {
            screen.show();
        } else if ("exit".equals(args[0])) {
            setScreen(screen.exit());
        } else if ("save".equals(args[0])) {
            save();
        } else if ("load".equals(args[0])) {
            load();
        } else {
            screen.command(args);
        }
        printPS1();
    }

    /**
     * EFFECTS: Print the '*user@JCA PS1' line
     */
    private void printPS1() {
        System.out.printf("%s%s@JCA %s ",
                unsaved ? "*" : "",
                ca.getUser(),
                screen.getPS1());
    }

    /**
     * EFFECTS: Save the DB
     */
    public void save() {
        try {
            FS.write(PATH_DEFAULT, Decoder.encodeCA(ca));
            unsaved = false;
        } catch (IOException e) {
            System.out.println(e.getMessage());
        }
    }

    /**
     * EFFECTS: Run the program
     */
    public void run() {
        printPS1();
        final Scanner scanner = new Scanner(System.in);
        while (true) {
            String[] args = scanner.nextLine().split(" ");
            if (args.length <= 0 || args[0].isBlank()) {
                printPS1();
                continue;
            }
            handleLine(args);
        }
    }

    public void setUnsaved(boolean unsaved) {
        this.unsaved = unsaved;
    }

    public CertificationAuthority getCa() {
        return ca;
    }
}