package com.nimbusds.jose;


import java.nio.charset.Charset;
import java.text.ParseException;

import net.jcip.annotations.ThreadSafe;

import com.nimbusds.jose.util.Base64URL;


/**
 * JSON Web Signature (JWS) object. This class is thread-safe.
 *
 * @author Vladimir Dzhuvinov
 * @version $version$ (2014-04-20)
 */
@ThreadSafe
public class JWSObject extends JOSEObject {


        /**
         * Enumeration of the states of a JSON Web Signature (JWS) object.
         */
        public static enum State {


                /**
                 * The JWS object is created but not signed yet.
                 */
                UNSIGNED,


                /**
                 * The JWS object is signed but its signature is not verified.
                 */
                SIGNED,


                /**
                 * The JWS object is signed and its signature was successfully verified.
                 */
                VERIFIED;
        }


        /**
         * The header.
         */
        private final ReadOnlyJWSHeader header;


        /**
         * The signing input for this JWS object.
         *
         * <p>Format:
         *
         * <pre>
         * [header-base64url].[payload-base64url]
         * </pre>
         */
        private final String signingInputString;


        /**
         * The signature, {@code null} if not signed.
         */
        private Base64URL signature;


        /**
         * The JWS object state.
         */
        private State state;


        /**
         * Creates a new to-be-signed JSON Web Signature (JWS) object with the 
         * specified header and payload. The initial state will be 
         * {@link State#UNSIGNED unsigned}.
         *
         * @param header  The JWS header. Must not be {@code null}.
         * @param payload The payload. Must not be {@code null}.
         */
        public JWSObject(final ReadOnlyJWSHeader header, final Payload payload) {

                if (header == null) {

                        throw new IllegalArgumentException("The JWS header must not be null");
                }

                this.header = header;

                if (payload == null) {

                        throw new IllegalArgumentException("The payload must not be null");
                }

                setPayload(payload);

                signingInputString = composeSigningInput(header.toBase64URL(), payload.toBase64URL());

                signature = null;

                state = State.UNSIGNED;
        }


        /**
         * Creates a new signed JSON Web Signature (JWS) object with the 
         * specified serialised parts. The state will be 
         * {@link State#SIGNED signed}.
         *
         * @param firstPart  The first part, corresponding to the JWS header. 
         *                   Must not be {@code null}.
         * @param secondPart The second part, corresponding to the payload. Must
         *                   not be {@code null}.
         * @param thirdPart  The third part, corresponding to the signature.
         *                   Must not be {@code null}.
         *
         * @throws ParseException If parsing of the serialised parts failed.
         */
        public JWSObject(final Base64URL firstPart, final Base64URL secondPart, final Base64URL thirdPart)      
                throws ParseException {

                if (firstPart == null) {

                        throw new IllegalArgumentException("The first part must not be null");
                }

                try {
                        this.header = JWSHeader.parse(firstPart);

                } catch (ParseException e) {

                        throw new ParseException("Invalid JWS header: " + e.getMessage(), 0);
                }

                if (secondPart == null) {

                        throw new IllegalArgumentException("The second part must not be null");
                }

                setPayload(new Payload(secondPart));

                signingInputString = composeSigningInput(firstPart, secondPart);

                if (thirdPart == null) {
                        throw new IllegalArgumentException("The third part must not be null");
                }

                signature = thirdPart;

                state = State.SIGNED; // but signature not verified yet!

                setParsedParts(firstPart, secondPart, thirdPart);
        }


        @Override
        public ReadOnlyJWSHeader getHeader() {

                return header;
        }


        /**
         * Composes the signing input for the specified JWS object parts.
         *
         * <p>Format:
         *
         * <pre>
         * [header-base64url].[payload-base64url]
         * </pre>
         *
         * @param firstPart  The first part, corresponding to the JWS header.
         *                   Must not be {@code null}.
         * @param secondPart The second part, corresponding to the payload. 
         *                   Must not be {@code null}.
         *
         * @return The signing input string.
         */
        private static String composeSigningInput(final Base64URL firstPart, final Base64URL secondPart) {

                StringBuilder sb = new StringBuilder(firstPart.toString());
                sb.append('.');
                sb.append(secondPart.toString());
                return sb.toString();
        }


        /**
         * Gets the signing input for this JWS object.
         *
         * <p>Format:
         *
         * <pre>
         * [header-base64url].[payload-base64url]
         * </pre>
         *
         * @return The signing input, to be passed to a JWS signer or verifier.
         */
        public byte[] getSigningInput() {

                return signingInputString.getBytes(Charset.forName("UTF-8"));
        }


        /**
         * @deprecated Use {@link #getSigningInput} instead.
         */
        @Deprecated
        public byte[] getSignableContent() {

                return getSigningInput();
        }


        /**
         * Gets the signature of this JWS object.
         *
         * @return The signature, {@code null} if the JWS object is not signed 
         *         yet.
         */
        public Base64URL getSignature() {

                return signature;
        }


        /**
         * Gets the state of this JWS object.
         *
         * @return The state.
         */
        public State getState() {

                return state;
        }


        /**
         * Ensures the current state is {@link State#UNSIGNED unsigned}.
         *
         * @throws IllegalStateException If the current state is not unsigned.
         */
        private void ensureUnsignedState() {

                if (state != State.UNSIGNED) {

                        throw new IllegalStateException("The JWS object must be in an unsigned state");
                }
        }


        /**
         * Ensures the current state is {@link State#SIGNED signed} or
         * {@link State#VERIFIED verified}.
         *
         * @throws IllegalStateException If the current state is not signed or
         *                               verified.
         */
        private void ensureSignedOrVerifiedState() {

                if (state != State.SIGNED && state != State.VERIFIED) {

                        throw new IllegalStateException("The JWS object must be in a signed or verified state");
                }
        }


        /**
         * Ensures the specified JWS signer supports the algorithm of this JWS
         * object.
         *
         * @throws JOSEException If the JWS algorithm is not supported.
         */
        private void ensureJWSSignerSupport(final JWSSigner signer)
                throws JOSEException {

                if (! signer.supportedAlgorithms().contains(getHeader().getAlgorithm())) {

                        throw new JOSEException("The \"" + getHeader().getAlgorithm() + 
                                                "\" algorithm is not supported by the JWS signer");
                }
        }


        /**
         * Ensures the specified JWS verifier accepts the algorithm and the headers 
         * of this JWS object.
         *
         * @throws JOSEException If the JWS algorithm or headers are not accepted.
         */
        private void ensureJWSVerifierAcceptance(final JWSVerifier verifier)
                throws JOSEException {

                if (! verifier.getAcceptedAlgorithms().contains(getHeader().getAlgorithm())) {

                        throw new JOSEException("The \"" + getHeader().getAlgorithm() + 
                                        "\" algorithm is not accepted by the JWS verifier");
                }
        }


        /**
         * Signs this JWS object with the specified signer. The JWS object must
         * be in a {@link State#UNSIGNED unsigned} state.
         *
         * @param signer The JWS signer. Must not be {@code null}.
         *
         * @throws IllegalStateException If the JWS object is not in an 
         *                               {@link State#UNSIGNED unsigned state}.
         * @throws JOSEException         If the JWS object couldn't be signed.
         */
        public synchronized void sign(final JWSSigner signer)
                throws JOSEException {

                ensureUnsignedState();

                ensureJWSSignerSupport(signer);

                try {
                        signature = signer.sign(getHeader(), getSigningInput());

                } catch (JOSEException e) {

                        throw e;
                                
                } catch (Exception e) {

                        // Prevent throwing unchecked exceptions at this point,
                        // see issue #20
                        throw new JOSEException(e.getMessage(), e);
                }

                state = State.SIGNED;
        }


        /**
         * Checks the signature of this JWS object with the specified verifier. 
         * The JWS object must be in a {@link State#SIGNED signed} state.
         *
         * @param verifier The JWS verifier. Must not be {@code null}.
         *
         * @return {@code true} if the signature was successfully verified, 
         *         else {@code false}.
         *
         * @throws IllegalStateException If the JWS object is not in a 
         *                               {@link State#SIGNED signed} or
         *                               {@link State#VERIFIED verified state}.
         * @throws JOSEException         If the JWS object couldn't be verified.
         */
        public synchronized boolean verify(final JWSVerifier verifier)
                throws JOSEException {

                ensureSignedOrVerifiedState();

                ensureJWSVerifierAcceptance(verifier);

                boolean verified;

                try {
                        verified = verifier.verify(getHeader(), getSigningInput(), getSignature());

                } catch (JOSEException e) {

                        throw e;

                } catch (Exception e) {

                        // Prevent throwing unchecked exceptions at this point,
                        // see issue #20
                        throw new JOSEException(e.getMessage(), e);
                }

                if (verified) {

                        state = State.VERIFIED;
                }

                return verified;
        }


        /**
         * Serialises this JWS object to its compact format consisting of 
         * Base64URL-encoded parts delimited by period ('.') characters. It 
         * must be in a {@link State#SIGNED signed} or 
         * {@link State#VERIFIED verified} state.
         *
         * <pre>
         * [header-base64url].[payload-base64url].[signature-base64url]
         * </pre>
         *
         * @return The serialised JWS object.
         *
         * @throws IllegalStateException If the JWS object is not in a 
         *                               {@link State#SIGNED signed} or
         *                               {@link State#VERIFIED verified} state.
         */
        @Override
        public String serialize() {

                ensureSignedOrVerifiedState();

                StringBuilder sb = new StringBuilder(signingInputString);
                sb.append('.');
                sb.append(signature.toString());
                return sb.toString();
        }


        /**
         * Parses a JWS object from the specified string in compact format. The
         * parsed JWS object will be given a {@link State#SIGNED} state.
         *
         * @param s The string to parse. Must not be {@code null}.
         *
         * @return The JWS object.
         *
         * @throws ParseException If the string couldn't be parsed to a valid 
         *                        JWS object.
         */
        public static JWSObject parse(final String s)
                throws ParseException {

                Base64URL[] parts = JOSEObject.split(s);

                if (parts.length != 3) {

                        throw new ParseException("Unexpected number of Base64URL parts, must be three", 0);
                }

                return new JWSObject(parts[0], parts[1], parts[2]);
        }
}