/*
 * Copyright (c) 1997, 2023 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package jakarta.mail.internet;

import jakarta.mail.Header;
import jakarta.mail.MessagingException;
import jakarta.mail.util.LineInputStream;
import jakarta.mail.util.StreamProvider;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;


/**
 * InternetHeaders is a utility class that manages RFC822 style
 * headers. Given an RFC822 format message stream, it reads lines
 * until the blank line that indicates end of header. The input stream
 * is positioned at the start of the body. The lines are stored
 * within the object and can be extracted as either Strings or
 * {@link jakarta.mail.Header} objects. <p>
 *
 * This class is mostly intended for service providers. MimeMessage
 * and MimeBody use this class for holding their headers.
 *
 * <hr> <strong>A note on RFC822 and MIME headers</strong><p>
 *
 * RFC822 and MIME header fields <strong>must</strong> contain only
 * US-ASCII characters. If a header contains non US-ASCII characters,
 * it must be encoded as per the rules in RFC 2047. The MimeUtility
 * class provided in this package can be used to to achieve this.
 * Callers of the <code>setHeader</code>, <code>addHeader</code>, and
 * <code>addHeaderLine</code> methods are responsible for enforcing
 * the MIME requirements for the specified headers.  In addition, these
 * header fields must be folded (wrapped) before being sent if they
 * exceed the line length limitation for the transport (1000 bytes for
 * SMTP).  Received headers may have been folded.  The application is
 * responsible for folding and unfolding headers as appropriate. <p>
 *
 * The current implementation supports the System property
 * <code>mail.mime.ignorewhitespacelines</code>, which if set to true
 * will cause a line containing only whitespace to be considered
 * a blank line terminating the header.
 *
 * @author John Mani
 * @author Bill Shannon
 * @see jakarta.mail.internet.MimeUtility
 */

public class InternetHeaders {
    private static final boolean ignoreWhitespaceLines =
            MimeUtility.getBooleanSystemProperty("mail.mime.ignorewhitespacelines",
                    false);

    /**
     * An individual internet header.  This class is only used by
     * subclasses of InternetHeaders. <p>
     *
     * An InternetHeader object with a null value is used as a placeholder
     * for headers of that name, to preserve the order of headers.
     * A placeholder InternetHeader object with a name of ":" marks
     * the location in the list of headers where new headers are
     * added by default.
     *
     * @since JavaMail 1.4
     */
    protected static final class InternetHeader extends Header {
        /*
         * Note that the value field from the superclass
         * isn't used in this class.  We extract the value
         * from the line field as needed.  We store the line
         * rather than just the value to ensure that we can
         * get back the exact original line, with the original
         * whitespace, etc.
         */
        String line;    // the entire RFC822 header "line",
        // or null if placeholder

        /**
         * Constructor that takes a line and splits out
         * the header name.
         *
         * @param l the header line
         */
        public InternetHeader(String l) {
            super("", "");    // XXX - we'll change it later
            int i = l.indexOf(':');
            if (i < 0) {
                // should never happen
                name = l.trim();
            } else {
                name = l.substring(0, i).trim();
            }
            line = l;
        }

        /**
         * Constructor that takes a header name and value.
         *
         * @param n the name of the header
         * @param v the value of the header
         */
        public InternetHeader(String n, String v) {
            super(n, "");
            if (v != null)
                line = n + ": " + v;
            else
                line = null;
        }

        /**
         * Return the "value" part of the header line.
         */
        @Override
        public String getValue() {
            int i = line.indexOf(':');
            if (i < 0)
                return line;
            // skip whitespace after ':'
            int j;
            for (j = i + 1; j < line.length(); j++) {
                char c = line.charAt(j);
                if (!(c == ' ' || c == '\t' || c == '\r' || c == '\n'))
                    break;
            }
            return line.substring(j);
        }
    }

    /*
     * The enumeration object used to enumerate an
     * InternetHeaders object.  Can return
     * either a String or a Header object.
     */
    static class MatchEnum {
        private Iterator<InternetHeader> e;    // enum object of headers List
        // XXX - is this overkill?  should we step through in index
        // order instead?
        private String[] names;    // names to match, or not
        private boolean match;    // return matching headers?
        private boolean want_line;    // return header lines?
        private InternetHeader next_header; // the next header to be returned

        /*
         * Constructor.  Initialize the enumeration for the entire
         * List of headers, the set of headers, whether to return
         * matching or non-matching headers, and whether to return
         * header lines or Header objects.
         */
        MatchEnum(List<InternetHeader> v, String[] n, boolean m, boolean l) {
            e = v.iterator();
            names = n;
            match = m;
            want_line = l;
            next_header = null;
        }

        /*
         * Any more elements in this enumeration?
         */
        public boolean hasMoreElements() {
            // if necessary, prefetch the next matching header,
            // and remember it.
            if (next_header == null)
                next_header = nextMatch();
            return next_header != null;
        }

        /*
         * Return the next element.
         */
        public Object nextElement() {
            if (next_header == null)
                next_header = nextMatch();

            if (next_header == null)
                throw new NoSuchElementException("No more headers");

            InternetHeader h = next_header;
            next_header = null;
            if (want_line)
                return h.line;
            else
                return new Header(h.getName(), h.getValue());
        }

        /*
         * Return the next Header object according to the match
         * criteria, or null if none left.
         */
        private InternetHeader nextMatch() {
            next:
            while (e.hasNext()) {
                InternetHeader h = e.next();

                // skip "place holder" headers
                if (h.line == null)
                    continue;

                // if no names to match against, return appropriately
                if (names == null)
                    return match ? null : h;

                // check whether this header matches any of the names
                for (int i = 0; i < names.length; i++) {
                    if (names[i].equalsIgnoreCase(h.getName())) {
                        if (match)
                            return h;
                        else
                            // found a match, but we're
                            // looking for non-matches.
                            // try next header.
                            continue next;
                    }
                }
                // found no matches.  if that's what we wanted, return it.
                if (!match)
                    return h;
            }
            return null;
        }
    }

    static class MatchStringEnum extends MatchEnum
            implements Enumeration<String> {

        MatchStringEnum(List<InternetHeader> v, String[] n, boolean m) {
            super(v, n, m, true);
        }

        @Override
        public String nextElement() {
            return (String) super.nextElement();
        }

    }

    static class MatchHeaderEnum extends MatchEnum
            implements Enumeration<Header> {

        MatchHeaderEnum(List<InternetHeader> v, String[] n, boolean m) {
            super(v, n, m, false);
        }

        @Override
        public Header nextElement() {
            return (Header) super.nextElement();
        }

    }

    /**
     * The actual list of Headers, including placeholder entries.
     * Placeholder entries are Headers with a null value and
     * are never seen by clients of the InternetHeaders class.
     * Placeholder entries are used to keep track of the preferred
     * order of headers.  Headers are never actually removed from
     * the list, they're converted into placeholder entries.
     * New headers are added after existing headers of the same name
     * (or before in the case of <code>Received</code> and
     * <code>Return-Path</code> headers).  If no existing header
     * or placeholder for the header is found, new headers are
     * added after the special placeholder with the name ":".
     *
     * @since JavaMail 1.4
     */
    protected List<InternetHeader> headers;

    /**
     * Create an empty InternetHeaders object.  Placeholder entries
     * are inserted to indicate the preferred order of headers.
     */
    public InternetHeaders() {
        headers = new ArrayList<>(40);
        headers.add(new InternetHeader("Return-Path", null));
        headers.add(new InternetHeader("Received", null));
        headers.add(new InternetHeader("Resent-Date", null));
        headers.add(new InternetHeader("Resent-From", null));
        headers.add(new InternetHeader("Resent-Sender", null));
        headers.add(new InternetHeader("Resent-To", null));
        headers.add(new InternetHeader("Resent-Cc", null));
        headers.add(new InternetHeader("Resent-Bcc", null));
        headers.add(new InternetHeader("Resent-Message-Id", null));
        headers.add(new InternetHeader("Date", null));
        headers.add(new InternetHeader("From", null));
        headers.add(new InternetHeader("Sender", null));
        headers.add(new InternetHeader("Reply-To", null));
        headers.add(new InternetHeader("To", null));
        headers.add(new InternetHeader("Cc", null));
        headers.add(new InternetHeader("Bcc", null));
        headers.add(new InternetHeader("Message-Id", null));
        headers.add(new InternetHeader("In-Reply-To", null));
        headers.add(new InternetHeader("References", null));
        headers.add(new InternetHeader("Subject", null));
        headers.add(new InternetHeader("Comments", null));
        headers.add(new InternetHeader("Keywords", null));
        headers.add(new InternetHeader("Errors-To", null));
        headers.add(new InternetHeader("MIME-Version", null));
        headers.add(new InternetHeader("Content-Type", null));
        headers.add(new InternetHeader("Content-Transfer-Encoding", null));
        headers.add(new InternetHeader("Content-MD5", null));
        headers.add(new InternetHeader(":", null));
        headers.add(new InternetHeader("Content-Length", null));
        headers.add(new InternetHeader("Status", null));
    }

    /**
     * Read and parse the given RFC822 message stream till the
     * blank line separating the header from the body. The input
     * stream is left positioned at the start of the body. The
     * header lines are stored internally. <p>
     *
     * For efficiency, wrap a BufferedInputStream around the actual
     * input stream and pass it as the parameter. <p>
     *
     * No placeholder entries are inserted; the original order of
     * the headers is preserved.
     *
     * @param is RFC822 input stream
     * @throws MessagingException for any I/O error reading the stream
     */
    public InternetHeaders(InputStream is) throws MessagingException {
        this(is, false);
    }

    /**
     * Read and parse the given RFC822 message stream till the
     * blank line separating the header from the body. The input
     * stream is left positioned at the start of the body. The
     * header lines are stored internally. <p>
     *
     * For efficiency, wrap a BufferedInputStream around the actual
     * input stream and pass it as the parameter. <p>
     *
     * No placeholder entries are inserted; the original order of
     * the headers is preserved.
     *
     * @param is        RFC822 input stream
     * @param allowutf8 if UTF-8 encoded headers are allowed
     * @throws MessagingException for any I/O error reading the stream
     * @since JavaMail 1.6
     */
    public InternetHeaders(InputStream is, boolean allowutf8)
            throws MessagingException {
        headers = new ArrayList<>(40);
        load(is, allowutf8);
    }

    /**
     * Read and parse the given RFC822 message stream till the
     * blank line separating the header from the body. Store the
     * header lines inside this InternetHeaders object. The order
     * of header lines is preserved. <p>
     *
     * Note that the header lines are added into this InternetHeaders
     * object, so any existing headers in this object will not be
     * affected.  Headers are added to the end of the existing list
     * of headers, in order.
     *
     * @param is RFC822 input stream
     * @throws MessagingException for any I/O error reading the stream
     */
    public void load(InputStream is) throws MessagingException {
        load(is, false);
    }

    /**
     * Read and parse the given RFC822 message stream till the
     * blank line separating the header from the body. Store the
     * header lines inside this InternetHeaders object. The order
     * of header lines is preserved. <p>
     *
     * Note that the header lines are added into this InternetHeaders
     * object, so any existing headers in this object will not be
     * affected.  Headers are added to the end of the existing list
     * of headers, in order.
     *
     * @param is        RFC822 input stream
     * @param allowutf8 if UTF-8 encoded headers are allowed
     * @throws MessagingException for any I/O error reading the stream
     * @since JavaMail 1.6
     */
    public void load(InputStream is, boolean allowutf8)
            throws MessagingException {
        // Read header lines until a blank line. It is valid
        // to have BodyParts with no header lines.
        String line;
        LineInputStream lis = StreamProvider.provider().inputLineStream(is, allowutf8);
        String prevline = null;    // the previous header line, as a string
        // a buffer to accumulate the header in, when we know it's needed
        StringBuilder lineBuffer = new StringBuilder();

        try {
            // if the first line being read is a continuation line,
            // we ignore it if it's otherwise empty or we treat it as
            // a non-continuation line if it has non-whitespace content
            boolean first = true;
            do {
                line = lis.readLine();
                if (line != null &&
                        (line.startsWith(" ") || line.startsWith("\t"))) {
                    // continuation of header
                    if (prevline != null) {
                        lineBuffer.append(prevline);
                        prevline = null;
                    }
                    if (first) {
                        String lt = line.trim();
                        if (lt.length() > 0)
                            lineBuffer.append(lt);
                    } else {
                        if (lineBuffer.length() > 0)
                            lineBuffer.append("\r\n");
                        lineBuffer.append(line);
                    }
                } else {
                    // new header
                    if (prevline != null)
                        addHeaderLine(prevline);
                    else if (lineBuffer.length() > 0) {
                        // store previous header first
                        addHeaderLine(lineBuffer.toString());
                        lineBuffer.setLength(0);
                    }
                    prevline = line;
                }
                first = false;
            } while (line != null && !isEmpty(line));
        } catch (IOException ioex) {
            throw new MessagingException("Error in input stream", ioex);
        }
    }

    /**
     * Is this line an empty (blank) line?
     */
    private static final boolean isEmpty(String line) {
        return line.length() == 0 ||
                (ignoreWhitespaceLines && line.trim().length() == 0);
    }

    /**
     * Return all the values for the specified header. The
     * values are String objects.  Returns <code>null</code>
     * if no headers with the specified name exist.
     *
     * @param name header name
     * @return array of header values, or null if none
     */
    public String[] getHeader(String name) {
        Iterator<InternetHeader> e = headers.iterator();
        // XXX - should we just step through in index order?
        List<String> v = new ArrayList<>(); // accumulate return values

        while (e.hasNext()) {
            InternetHeader h = e.next();
            if (name.equalsIgnoreCase(h.getName()) && h.line != null) {
                v.add(h.getValue());
            }
        }
        if (v.size() == 0)
            return (null);
        // convert List to an array for return
        String[] r = new String[v.size()];
        r = v.toArray(r);
        return (r);
    }

    /**
     * Get all the headers for this header name, returned as a single
     * String, with headers separated by the delimiter. If the
     * delimiter is <code>null</code>, only the first header is
     * returned.  Returns <code>null</code>
     * if no headers with the specified name exist.
     *
     * @param delimiter delimiter
     * @param name      header name
     * @return the value fields for all headers with
     * this name, or null if none
     */
    public String getHeader(String name, String delimiter) {
        String[] s = getHeader(name);

        if (s == null)
            return null;

        if ((s.length == 1) || delimiter == null)
            return s[0];

        StringBuilder r = new StringBuilder(s[0]);
        for (int i = 1; i < s.length; i++) {
            r.append(delimiter);
            r.append(s[i]);
        }
        return r.toString();
    }

    /**
     * Change the first header line that matches name
     * to have value, adding a new header if no existing header
     * matches. Remove all matching headers but the first. <p>
     *
     * Note that RFC822 headers can only contain US-ASCII characters
     *
     * @param name  header name
     * @param value header value
     */
    public void setHeader(String name, String value) {
        boolean found = false;

        for (int i = 0; i < headers.size(); i++) {
            InternetHeader h = headers.get(i);
            if (name.equalsIgnoreCase(h.getName())) {
                if (!found) {
                    int j;
                    if (h.line != null && (j = h.line.indexOf(':')) >= 0) {
                        h.line = h.line.substring(0, j + 1) + " " + value;
                        // preserves capitalization, spacing
                    } else {
                        h.line = name + ": " + value;
                    }
                    found = true;
                } else {
                    headers.remove(i);
                    i--;    // have to look at i again
                }
            }
        }

        if (!found) {
            addHeader(name, value);
        }
    }

    /**
     * Add a header with the specified name and value to the header list. <p>
     *
     * The current implementation knows about the preferred order of most
     * well-known headers and will insert headers in that order.  In
     * addition, it knows that <code>Received</code> headers should be
     * inserted in reverse order (newest before oldest), and that they
     * should appear at the beginning of the headers, preceeded only by
     * a possible <code>Return-Path</code> header.  <p>
     *
     * Note that RFC822 headers can only contain US-ASCII characters.
     *
     * @param name  header name
     * @param value header value
     */
    public void addHeader(String name, String value) {
        int pos = headers.size();
        boolean addReverse =
                name.equalsIgnoreCase("Received") ||
                        name.equalsIgnoreCase("Return-Path");
        if (addReverse)
            pos = 0;
        for (int i = headers.size() - 1; i >= 0; i--) {
            InternetHeader h = headers.get(i);
            if (name.equalsIgnoreCase(h.getName())) {
                if (addReverse) {
                    pos = i;
                } else {
                    headers.add(i + 1, new InternetHeader(name, value));
                    return;
                }
            }
            // marker for default place to add new headers
            if (!addReverse && h.getName().equals(":"))
                pos = i;
        }
        headers.add(pos, new InternetHeader(name, value));
    }

    /**
     * Remove all header entries that match the given name
     *
     * @param name header name
     */
    public void removeHeader(String name) {
        for (int i = 0; i < headers.size(); i++) {
            InternetHeader h = headers.get(i);
            if (name.equalsIgnoreCase(h.getName())) {
                h.line = null;
                //headers.remove(i);
                //i--;    // have to look at i again
            }
        }
    }

    /**
     * Return all the headers as an Enumeration of
     * {@link jakarta.mail.Header} objects.
     *
     * @return Enumeration of Header objects
     */
    public Enumeration<Header> getAllHeaders() {
        return (new MatchHeaderEnum(headers, null, false));
    }

    /**
     * Return all matching {@link jakarta.mail.Header} objects.
     *
     * @param names the headers to return
     * @return Enumeration of matching Header objects
     */
    public Enumeration<Header> getMatchingHeaders(String[] names) {
        return (new MatchHeaderEnum(headers, names, true));
    }

    /**
     * Return all non-matching {@link jakarta.mail.Header} objects.
     *
     * @param names the headers to not return
     * @return Enumeration of non-matching Header objects
     */
    public Enumeration<Header> getNonMatchingHeaders(String[] names) {
        return (new MatchHeaderEnum(headers, names, false));
    }

    /**
     * Add an RFC822 header line to the header store.
     * If the line starts with a space or tab (a continuation line),
     * add it to the last header line in the list.  Otherwise,
     * append the new header line to the list.  <p>
     *
     * Note that RFC822 headers can only contain US-ASCII characters
     *
     * @param line raw RFC822 header line
     */
    public void addHeaderLine(String line) {
        try {
            char c = line.charAt(0);
            if (c == ' ' || c == '\t') {
                InternetHeader h = headers.get(headers.size() - 1);
                h.line += "\r\n" + line;
            } else
                headers.add(new InternetHeader(line));
        } catch (StringIndexOutOfBoundsException e) {
            // line is empty, ignore it
            return;
        } catch (NoSuchElementException e) {
            // XXX - list is empty?
        }
    }

    /**
     * Return all the header lines as an Enumeration of Strings.
     *
     * @return Enumeration of Strings of all header lines
     */
    public Enumeration<String> getAllHeaderLines() {
        return (getNonMatchingHeaderLines(null));
    }

    /**
     * Return all matching header lines as an Enumeration of Strings.
     *
     * @param names the headers to return
     * @return Enumeration of Strings of all matching header lines
     */
    public Enumeration<String> getMatchingHeaderLines(String[] names) {
        return (new MatchStringEnum(headers, names, true));
    }

    /**
     * Return all non-matching header lines
     *
     * @param names the headers to not return
     * @return Enumeration of Strings of all non-matching header lines
     */
    public Enumeration<String> getNonMatchingHeaderLines(String[] names) {
        return (new MatchStringEnum(headers, names, false));
    }
}
