package org.simantics.acorn;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.OutputStream;
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;
import org.simantics.databoard.Bindings;
import org.simantics.databoard.binding.mutable.MutableVariant;
import org.simantics.databoard.serialization.Serializer;
import org.simantics.databoard.util.binary.BinaryMemory;

public class HeadState {

    public static final String HEAD_STATE = "head.state";
    public static final String SHA_1 = "SHA-1";
    
    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 (ByteArrayInputStream bais = new ByteArrayInputStream(bytes, digestLength, bytes.length - digestLength)) {
                HeadState object = (HeadState) org.simantics.databoard.Files.readFile(bais, Bindings.getBindingUnchecked(HeadState.class));
                return object;
            }
        } catch (IOException i) {
            return new HeadState();
//            throw new InvalidHeadStateException(i);
        } catch (NoSuchAlgorithmException e) {
            throw new Error("SHA-1 Algorithm not found", e);
        } catch (Throwable t) {
            throw new InvalidHeadStateException(t);
        }
    }
    
    public void save(Path directory) throws IOException {
        Path f = directory.resolve(HEAD_STATE);
        try {
            BinaryMemory rf = new BinaryMemory(4096);
            try {
                MutableVariant v = new MutableVariant(Bindings.getBindingUnchecked(HeadState.class), this);
                Serializer s = Bindings.getSerializerUnchecked( Bindings.VARIANT );
                s.serialize(rf, v);
            } finally {
                rf.close();
            }
            
            byte[] bytes = rf.toByteBuffer().array();
            
            MessageDigest sha1 = MessageDigest.getInstance(SHA_1);
            sha1.update(bytes);
            byte[] checksum = sha1.digest();
            
            try (OutputStream out = Files.newOutputStream(f)) {
                out.write(checksum);
                out.write(bytes);
            }
            FileIO.syncPath(f);
        } catch (NoSuchAlgorithmException e) {
            throw new Error("SHA-1 digest not found, should not happen", 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);
        }
    }
}