package org.expeditee.encryption.io;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.lang.reflect.Method;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Base64;
import java.util.List;
import java.util.function.BiConsumer;
import java.util.function.Predicate;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

import org.expeditee.core.Point;
import org.expeditee.encryption.CryptographyConstants;
import org.expeditee.encryption.items.surrogates.EncryptionDetail;
import org.expeditee.encryption.items.surrogates.Label;
//import org.expeditee.encryption.items.surrogates.Label;
import org.expeditee.encryption.items.surrogates.Label.LabelResult;
import org.expeditee.encryption.items.surrogates.Label.LabelInfo;
import org.expeditee.gui.Frame;
import org.expeditee.gui.FrameIO;
import org.expeditee.io.Conversion;
import org.expeditee.io.DefaultFrameWriter;
import org.expeditee.io.ExpReader;
import org.expeditee.items.Constraint;
import org.expeditee.items.Item;
import org.expeditee.items.Text;
import org.expeditee.settings.identity.secrets.KeyList;

public class EncryptedExpReader extends ExpReader implements CryptographyConstants {
	
	private static final String ENCRYPTED_EXP_FLAG = "EncryptedExp";
	private static final String labelProfile = "Profile";
	private static final String labelNone = "None";
	private SecretKey personalKey;
	private boolean accessDenied = false;
	private boolean _readingSurrogates;
	private static final Predicate<String> endOfSection = s -> s.equals(EncryptedExpWriter.TERMINATOR + "") || s.equals(EncryptedExpWriter.TERMINATOR_WITH_CONTINUATION);

	public static boolean isEncryptedExpediteeFile(final String path) throws IOException {
		BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream(path), "UTF-8"));
		String firstLine = in.readLine();
		in.close();
		if (firstLine == null) return false;
		return firstLine.startsWith(ENCRYPTED_EXP_FLAG);
	}
	
	public EncryptedExpReader(String frameName) {
		super(frameName);
	}
	
	public int getVersionEnc(String fullpath) {
		try {
			BufferedReader reader = new EncryptedLineReader(new BufferedReader(new FileReader(fullpath)));
			String next = "";
			// First read the header lines until we get the version number
			while (reader.ready() && !(next = reader.readLine()).equals("Z")) {
				if (isValidLine(next)) {
					Character tag = getTag(next);
					String value = getValue(next);
					if (tag.equals('V')) {
						reader.close();
						return Integer.parseInt(value);
					}
				}
			}
			reader.close();
		} catch (Exception e) {
		}
		return -1;
	}
	
	@Override
	public Frame readFrame(final String fullPath) throws IOException {
		Reader in = new InputStreamReader(new FileInputStream(fullPath), "UTF-8");
		return readFrame(new EncryptedLineReader(in));
	}
	
	@Override
	public Frame readFrame(BufferedReader reader) throws IOException {
		if (accessDenied) { return null; }
		
		_readingSurrogates = false;
		_reader = reader;
		String next = "";
		Frame newFrame = new Frame();
		List<DelayedAction> delayedActions = new ArrayList<DelayedAction>();
		newFrame.setName(_frameName);
		
		try {
			// First read all the header lines
			next = readTheHeader(newFrame);
			
			// Now read all the items
			next = readTheItems(newFrame, delayedActions);
			
			// Read the lines
			next = readTheLines(newFrame);

			// Read the constraints
			next = readTheConstraints();
			
			if (next.equals(EncryptedExpWriter.TERMINATOR_WITH_CONTINUATION)) {
				// Read the surrogates
				_readingSurrogates = true;
				next = readTheItems(newFrame, delayedActions);
				_readingSurrogates = false;
			}
			
			for(DelayedAction action: delayedActions) {
				action.exec();
			}

			// Read the stats
			next = readTheStats(newFrame);
		} catch (Exception e) {
			e.printStackTrace();
			System.out.println("Error reading frame file line: " + next + " " + e.getMessage());
		}
		
		_reader.close();
		FrameIO.setSavedProperties(newFrame);
		newFrame.setChanged(false);

		return newFrame;
	}
	
	protected String readTheItems(Frame newFrame, List<DelayedAction> delayedActions) throws IOException {
		BiConsumer<Item, String> primaryAdd = (item, line) -> newFrame.addItem(item);
		BiConsumer<Item, String> surrogateAdd = (item, line) -> {
			int parentID = Integer.parseInt(line.split(" ")[1]);
			Item parent = newFrame.getItemWithID(parentID);
			newFrame.addToSurrogatesOnLoad(item, parent);
		};
		
		if (_readingSurrogates) {
			return readLineAfterLine(true, surrogateAdd, delayedActions);
		} else {
			return readLineAfterLine(false, primaryAdd, delayedActions);
		}
	}
	
	@Override
	protected String readTheConstraints() throws IOException, Exception {
		String next = null;
		while (_reader.ready() && !endOfSection.test(next = _reader.readLine())) {
			if (isValidLine(next)) {
				Point idtype = separateValues(next.substring(2));
				// The next line must be the endpoints
				if (!_reader.ready()) {
					throw new Exception("Unexpected end of file");
				}
				next = _reader.readLine();
				Point startend = separateValues(next.substring(2));

				Item a = _linePoints.get(startend.getX());
				Item b = _linePoints.get(startend.getY());

				new Constraint(a, b, idtype.getX(), idtype.getY());
			}
		}
		return next;
	}
	
	private String readLineAfterLine(boolean isSurrogate, BiConsumer<Item, String> storeResult, List<DelayedAction> delayedActions) throws IOException {
		String next = null;
		Item currentItem = null;
		
		while (_reader.ready() && !endOfSection.test(next = _reader.readLine())) {
			if (!isValidLine(next)) {
				continue;
			}
			
			String tag = getTagEnc(next);
			if (next.startsWith(DefaultFrameWriter.TYPE_AND_ID_STR + " ")) {
				currentItem = newItem(next);
				_linePoints.put(currentItem.getID(), currentItem);
				if (!isSurrogate) {
					storeResult.accept(currentItem, next);
				}
				EncryptionDetail unencryptedOnSave = new EncryptionDetail(EncryptionDetail.Type.UnencryptedOnSave);
				currentItem.setEncryptionDetailForTag(tag + "", unencryptedOnSave);
			} else if (next.startsWith("SurrogateFor")) {
				if (isSurrogate) {
					storeResult.accept(currentItem, next);
				}
			} else if (currentItem != null && actionShouldBeDelayed(tag.charAt(0))) { 
				delayedActions.add(new DelayedAction(currentItem, next));
			} else if (currentItem != null) {
				processBodyLine(currentItem, next);
			} else {
				System.err.println("Error while reading in frame (ExpReader): Found body line but no current item to apply it to.");
			}
		}
		
		return next;
	}
 	
	@Override
	protected void processBodyLine(Item item, String line) {
		// separate the tag from the value
		String tag = getTagEnc(line);
		String value = getValue(line);
		boolean isEncryptedLine = isEncryptedLine(line);
		
		if (item.isSurrogate() && isEncryptedLine) {
			// Surrogates should never have encrypted body lines.
			return;
		}
		
		// Attempt to decrypt the line if necessary.
		if (isEncryptedLine) {
			LabelInfo res = Label.getLabel(item.getEncryptionLabel());
			if (res.is(LabelResult.SuccessResolveLabelToKey)) {
				EncryptionDetail reencryptOnSave = new EncryptionDetail(EncryptionDetail.Type.ReencryptOnSave);
				item.setEncryptionDetailForTag(tag, reencryptOnSave);
				SecretKey key = new SecretKeySpec(res.key, SymmetricAlgorithm);
				byte[] decryptedBytes = DecryptSymmetric(Base64.getDecoder().decode(value), key);
				value = new String(decryptedBytes);				
			} else {
				EncryptionDetail undecipheredValueOnSave = new EncryptionDetail(EncryptionDetail.Type.UseUndecipheredValueOnSave);
				undecipheredValueOnSave.setUndecipheredValue(getValue(line));
				item.setEncryptionDetailForTag(tag, undecipheredValueOnSave);
				return;
			}
		} else {
			EncryptionDetail unencryptedOnSave = new EncryptionDetail(EncryptionDetail.Type.UnencryptedOnSave);
			item.setEncryptionDetailForTag(tag, unencryptedOnSave);
			if (item.isSurrogate()) {
				item.setTagNotInherited(tag);
			}
		}
		
		// Process the line
		Method toRun = tag.startsWith("_") ? _ItemTagsExt.get(tag) : _ItemTags.get(tag.charAt(0));
		if (toRun == null) {
			System.out.println("Error accessing tag method: " + tag);
		}
		Object[] vals = Conversion.Convert(toRun, value);
		try {
			if (vals != null) {
				toRun.invoke(item, vals);
			}
		} catch (Exception e) {
			System.out.println("Error running tag method: " + tag);
			e.printStackTrace();
		}
	}
	
	protected static String getValue(String line) {
		String[] split = line.split(" ");
		if (split.length >= 2) {
			return line.substring(split[0].length()).trim();
		} else {
			return null;
		}
	}
	
	private static String getTagEnc(String line) {
		char charAtZero = line.charAt(0);
		if (charAtZero == '_') {
			return line.split(" ")[0];
		} else {
			return charAtZero + "";
		}
	}
		
	private static boolean isEncryptedLine(String line) {
		if (line.startsWith("S") || line.startsWith("_el")) {
			return false;
		}		
		if (line.length() > 2) {
			return line.charAt(1) == 'E';
		} else {
			return false;
		}
	}
	
	private static byte[] DecryptSymmetric(final byte[] toDecrypt, final SecretKey key) {
		try {
			final Cipher cipher = Cipher.getInstance(SymmetricAlgorithm + SymmetricAlgorithmParameters);
			cipher.init(Cipher.DECRYPT_MODE, key);
			final byte[] decryptedBytes = cipher.doFinal(toDecrypt);
			int indexOfZero = decryptedBytes.length - 1;
			for (int i = decryptedBytes.length - 1; i >= 0; i--) {
				if (decryptedBytes[i] != (byte) 0) {
					indexOfZero = i + 1;
					break;
				}
			}
			if (indexOfZero < 0) { return decryptedBytes; }
			else { return Arrays.copyOf(decryptedBytes, indexOfZero); }
		} catch (final NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException
				| IllegalBlockSizeException | BadPaddingException e) {
			e.printStackTrace();
			return null;
		}
	}

	private class EncryptedLineReader extends BufferedReader {
		private boolean noneMode = false;
		
		public EncryptedLineReader(Reader in) {
			super(in);
		}
		
		@Override
		/**
		 * Reads a line from an encrypted exp file that uses an encryption specified by the first line of the file.
		 * Returns that line to process, null if the currently logged in users doesn't own the appropriate key (access denied).
		 */
		public String readLine() throws IOException {
			String line = super.readLine();
			
			if (line.isEmpty()) {
				return "";
			}
			
			if (noneMode) {
				return line;
			}
			
			if (line.startsWith(ENCRYPTED_EXP_FLAG)) {
				String label = line.replace(ENCRYPTED_EXP_FLAG, "");
				// if using Profile label, use personal key
				if (label.equals(labelProfile)) {
					Text text = KeyList.PersonalKey.get();
					byte[] keyBytes = Base64.getDecoder().decode(text.getData().get(0));
					personalKey = new SecretKeySpec(keyBytes, SymmetricAlgorithm);
					return readLine();
				} else if (label.equals(labelNone)) {
					noneMode = true;
					return readLine();
				} else {
					personalKey = resolveLabel(label);
					if (personalKey == null) {
						return null;
					} else {
						return readLine();
					}
				}
			}
			
			// decrypt line and return result
			byte[] toDecrypt = Base64.getDecoder().decode(line);
			byte[] decrypted = DecryptSymmetric(toDecrypt, personalKey);
			if (decrypted == null) {
				accessDenied = true;
				return null; // access denied
			} else {
				String decryptedLine = new String(decrypted);
				if (decryptedLine.startsWith("Z")) { 
					return decryptedLine.trim();
				} else { 
					return decryptedLine;
				}
			}
		}
		
		private SecretKeySpec resolveLabel(String label) {
			LabelInfo res = Label.getLabel(label);
			if (res.is(LabelResult.SuccessResolveLabelToKey)) {
				byte[] keyBytes = res.key;
				return new SecretKeySpec(keyBytes, SymmetricAlgorithm);
			}
			return null;
		}
	}
}