package org.simantics.db.javacore;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.nio.file.Files;
import java.nio.file.Path;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Arrays;

import org.simantics.acorn.exception.InvalidHeadStateException;

public class HeadState implements Serializable {

    private static final long serialVersionUID = -4135031566499790077L;

    public int headChangeSetId = 0;
    public long transactionId = 1;
    public long reservedIds = 3;

    public ArrayList<String> clusters = new ArrayList<>();
    public ArrayList<String> files = new ArrayList<>();
    public ArrayList<String> stream = new ArrayList<>();
    public ArrayList<String> cs = new ArrayList<>();
//    public ArrayList<String> ccs = new ArrayList<String>();

    public static HeadState load(Path directory) throws InvalidHeadStateException {
        Path f = directory.resolve("head.state");
        try {
            byte[] bytes = Files.readAllBytes(f);
            MessageDigest sha1 = MessageDigest.getInstance("SHA-1");
            int digestLength = sha1.getDigestLength();
            sha1.update(bytes, digestLength, bytes.length - digestLength);
            byte[] newChecksum = sha1.digest();
            if (!Arrays.equals(newChecksum, Arrays.copyOfRange(bytes, 0, digestLength))) {
                throw new InvalidHeadStateException(
                        "Checksum " + Arrays.toString(newChecksum) + " does not match excpected "
                                + Arrays.toString(Arrays.copyOfRange(bytes, 0, digestLength)) + " for " + f.toAbsolutePath());
            }
            try (ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bytes, digestLength, bytes.length - digestLength))) {
                HeadState state = (HeadState) ois.readObject();
                return state;
            }
        } catch (IOException i) {
            return new HeadState();
        } catch (ClassNotFoundException c) {
//            throw new Error("HeadState class not found", c);
            return new HeadState();
        } catch (NoSuchAlgorithmException e) {
            throw new Error("SHA-1 Algorithm not found", e);
        }
    }

    public static void validateHeadStateIntegrity(Path headState) throws InvalidHeadStateException, IOException {
        try {
            byte[] bytes = Files.readAllBytes(headState);
            MessageDigest sha1 = MessageDigest.getInstance("SHA-1");
            int digestLength = sha1.getDigestLength();
            sha1.update(bytes, digestLength, bytes.length - digestLength);
            byte[] newChecksum = sha1.digest();
            if (!Arrays.equals(newChecksum, Arrays.copyOfRange(bytes, 0, digestLength))) {
                throw new InvalidHeadStateException(
                        "Checksum " + Arrays.toString(newChecksum) + " does not match excpected "
                                + Arrays.toString(Arrays.copyOfRange(bytes, 0, digestLength)) + " for " + headState.toAbsolutePath());
            }
        } catch (NoSuchAlgorithmException e) {
            throw new Error("SHA-1 digest not found, should not happen", e);
        }
    }
}