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package org.xml.sax.helpers;

import java.util.ArrayList;

import java.util.Collections;

import java.util.EmptyStackException;

import java.util.Enumeration;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

/**

 * Encapsulate Namespace logic for use by applications using SAX,

 * or internally by SAX drivers.

 *

 * <p>This class encapsulates the logic of Namespace processing: it

 * tracks the declarations currently in force for each context and

 * automatically processes qualified XML names into their Namespace

 * parts; it can also be used in reverse for generating XML qnames

 * from Namespaces.</p>

 *

 * <p>Namespace support objects are reusable, but the reset method

 * must be invoked between each session.</p>

 *

 * <p>Here is a simple session:</p>

 *

 * <pre>

 * String parts[] = new String[3];

 * NamespaceSupport support = new NamespaceSupport();

 *

 * support.pushContext();

 * support.declarePrefix("", "http://www.w3.org/1999/xhtml");

 * support.declarePrefix("dc", "http://www.purl.org/dc#");

 *

 * parts = support.processName("p", parts, false);

 * System.out.println("Namespace URI: " + parts[0]);

 * System.out.println("Local name: " + parts[1]);

 * System.out.println("Raw name: " + parts[2]);

 *

 * parts = support.processName("dc:title", parts, false);

 * System.out.println("Namespace URI: " + parts[0]);

 * System.out.println("Local name: " + parts[1]);

 * System.out.println("Raw name: " + parts[2]);

 *

 * support.popContext();

 * </pre>

 *

 * <p>Note that this class is optimized for the use case where most

 * elements do not contain Namespace declarations: if the same

 * prefix/URI mapping is repeated for each context (for example), this

 * class will be somewhat less efficient.</p>

 *

 * <p>Although SAX drivers (parsers) may choose to use this class to

 * implement namespace handling, they are not required to do so.

 * Applications must track namespace information themselves if they

 * want to use namespace information.

 *

 * @since 1.4, SAX 2.0

 * @author David Megginson

 */

public class NamespaceSupport

{

    ////////////////////////////////////////////////////////////////////

    // Constants.

    ////////////////////////////////////////////////////////////////////

    /**

     * The XML Namespace URI as a constant.

     * The value is <code>http://www.w3.org/XML/1998/namespace</code>

     * as defined in the "Namespaces in XML" * recommendation.

     *

     * <p>This is the Namespace URI that is automatically mapped

     * to the "xml" prefix.</p>

     */

    public final static String XMLNS =

        "http://www.w3.org/XML/1998/namespace";

    /**

     * The namespace declaration URI as a constant.

     * The value is <code>http://www.w3.org/xmlns/2000/</code>, as defined

     * in a backwards-incompatible erratum to the "Namespaces in XML"

     * recommendation.  Because that erratum postdated SAX2, SAX2 defaults

     * to the original recommendation, and does not normally use this URI.

     *

     *

     * <p>This is the Namespace URI that is optionally applied to

     * <em>xmlns</em> and <em>xmlns:*</em> attributes, which are used to

     * declare namespaces.  </p>

     *

     * @since 1.5, SAX 2.1alpha

     * @see #setNamespaceDeclUris

     * @see #isNamespaceDeclUris

     */

    public final static String NSDECL =

        "http://www.w3.org/xmlns/2000/";

    /**

     * An empty enumeration.

     */

    private final static Enumeration<String> EMPTY_ENUMERATION =

            Collections.enumeration(new ArrayList<String>());

    ////////////////////////////////////////////////////////////////////

    // Constructor.

    ////////////////////////////////////////////////////////////////////

    /**

     * Create a new Namespace support object.

     */

    public NamespaceSupport ()

    {

        reset();

    }

    ////////////////////////////////////////////////////////////////////

    // Context management.

    ////////////////////////////////////////////////////////////////////

    /**

     * Reset this Namespace support object for reuse.

     *

     * <p>It is necessary to invoke this method before reusing the

     * Namespace support object for a new session.  If namespace

     * declaration URIs are to be supported, that flag must also

     * be set to a non-default value.

     * </p>

     *

     * @see #setNamespaceDeclUris

     */

    public void reset ()

    {

        contexts = new Context[32];

        namespaceDeclUris = false;

        contextPos = 0;

        contexts[contextPos] = currentContext = new Context();

        currentContext.declarePrefix("xml", XMLNS);

    }

    /**

     * Start a new Namespace context.

     * The new context will automatically inherit

     * the declarations of its parent context, but it will also keep

     * track of which declarations were made within this context.

     *

     * <p>Event callback code should start a new context once per element.

     * This means being ready to call this in either of two places.

     * For elements that don't include namespace declarations, the

     * <em>ContentHandler.startElement()</em> callback is the right place.

     * For elements with such a declaration, it'd done in the first

     * <em>ContentHandler.startPrefixMapping()</em> callback.

     * A boolean flag can be used to

     * track whether a context has been started yet.  When either of

     * those methods is called, it checks the flag to see if a new context

     * needs to be started.  If so, it starts the context and sets the

     * flag.  After <em>ContentHandler.startElement()</em>

     * does that, it always clears the flag.

     *

     * <p>Normally, SAX drivers would push a new context at the beginning

     * of each XML element.  Then they perform a first pass over the

     * attributes to process all namespace declarations, making

     * <em>ContentHandler.startPrefixMapping()</em> callbacks.

     * Then a second pass is made, to determine the namespace-qualified

     * names for all attributes and for the element name.

     * Finally all the information for the

     * <em>ContentHandler.startElement()</em> callback is available,

     * so it can then be made.

     *

     * <p>The Namespace support object always starts with a base context

     * already in force: in this context, only the "xml" prefix is

     * declared.</p>

     *

     * @see org.xml.sax.ContentHandler

     * @see #popContext

     */

    public void pushContext ()

    {

        int max = contexts.length;

        contextPos++;

                                // Extend the array if necessary

        if (contextPos >= max) {

            Context newContexts[] = new Context[max*2];

            System.arraycopy(contexts, 0, newContexts, 0, max);

            max *= 2;

            contexts = newContexts;

        }

                                // Allocate the context if necessary.

        currentContext = contexts[contextPos];

        if (currentContext == null) {

            contexts[contextPos] = currentContext = new Context();

        }

                                // Set the parent, if any.

        if (contextPos > 0) {

            currentContext.setParent(contexts[contextPos - 1]);

        }

    }

    /**

     * Revert to the previous Namespace context.

     *

     * <p>Normally, you should pop the context at the end of each

     * XML element.  After popping the context, all Namespace prefix

     * mappings that were previously in force are restored.</p>

     *

     * <p>You must not attempt to declare additional Namespace

     * prefixes after popping a context, unless you push another

     * context first.</p>

     *

     * @see #pushContext

     */

    public void popContext ()

    {

        contexts[contextPos].clear();

        contextPos--;

        if (contextPos < 0) {

            throw new EmptyStackException();

        }

        currentContext = contexts[contextPos];

    }

    ////////////////////////////////////////////////////////////////////

    // Operations within a context.

    ////////////////////////////////////////////////////////////////////

    /**

     * Declare a Namespace prefix.  All prefixes must be declared

     * before they are referenced.  For example, a SAX driver (parser)

     * would scan an element's attributes

     * in two passes:  first for namespace declarations,

     * then a second pass using {@link #processName processName()} to

     * interpret prefixes against (potentially redefined) prefixes.

     *

     * <p>This method declares a prefix in the current Namespace

     * context; the prefix will remain in force until this context

     * is popped, unless it is shadowed in a descendant context.</p>

     *

     * <p>To declare the default element Namespace, use the empty string as

     * the prefix.</p>

     *

     * <p>Note that there is an asymmetry in this library: {@link

     * #getPrefix getPrefix} will not return the "" prefix,

     * even if you have declared a default element namespace.

     * To check for a default namespace,

     * you have to look it up explicitly using {@link #getURI getURI}.

     * This asymmetry exists to make it easier to look up prefixes

     * for attribute names, where the default prefix is not allowed.</p>

     *

     * @param prefix The prefix to declare, or the empty string to

     *  indicate the default element namespace.  This may never have

     *  the value "xml" or "xmlns".

     * @param uri The Namespace URI to associate with the prefix.

     * @return true if the prefix was legal, false otherwise

     *

     * @see #processName

     * @see #getURI

     * @see #getPrefix

     */

    public boolean declarePrefix (String prefix, String uri)

    {

        if (prefix.equals("xml") || prefix.equals("xmlns")) {

            return false;

        } else {

            currentContext.declarePrefix(prefix, uri);

            return true;

        }

    }

    /**

     * Process a raw XML qualified name, after all declarations in the

     * current context have been handled by {@link #declarePrefix

     * declarePrefix()}.

     *

     * <p>This method processes a raw XML qualified name in the

     * current context by removing the prefix and looking it up among

     * the prefixes currently declared.  The return value will be the

     * array supplied by the caller, filled in as follows:</p>

     *

     * <dl>

     * <dt>parts[0]</dt>

     * <dd>The Namespace URI, or an empty string if none is

     *  in use.</dd>

     * <dt>parts[1]</dt>

     * <dd>The local name (without prefix).</dd>

     * <dt>parts[2]</dt>

     * <dd>The original raw name.</dd>

     * </dl>

     *

     * <p>All of the strings in the array will be internalized.  If

     * the raw name has a prefix that has not been declared, then

     * the return value will be null.</p>

     *

     * <p>Note that attribute names are processed differently than

     * element names: an unprefixed element name will receive the

     * default Namespace (if any), while an unprefixed attribute name

     * will not.</p>

     *

     * @param qName The XML qualified name to be processed.

     * @param parts An array supplied by the caller, capable of

     *        holding at least three members.

     * @param isAttribute A flag indicating whether this is an

     *        attribute name (true) or an element name (false).

     * @return The supplied array holding three internalized strings

     *        representing the Namespace URI (or empty string), the

     *        local name, and the XML qualified name; or null if there

     *        is an undeclared prefix.

     * @see #declarePrefix

     * @see java.lang.String#intern */

    public String [] processName (String qName, String parts[],

                                  boolean isAttribute)

    {

        String myParts[] = currentContext.processName(qName, isAttribute);

        if (myParts == null) {

            return null;

        } else {

            parts[0] = myParts[0];

            parts[1] = myParts[1];

            parts[2] = myParts[2];

            return parts;

        }

    }

    /**

     * Look up a prefix and get the currently-mapped Namespace URI.

     *

     * <p>This method looks up the prefix in the current context.

     * Use the empty string ("") for the default Namespace.</p>

     *

     * @param prefix The prefix to look up.

     * @return The associated Namespace URI, or null if the prefix

     *         is undeclared in this context.

     * @see #getPrefix

     * @see #getPrefixes

     */

    public String getURI (String prefix)

    {

        return currentContext.getURI(prefix);

    }

    /**

     * Return an enumeration of all prefixes whose declarations are

     * active in the current context.

     * This includes declarations from parent contexts that have

     * not been overridden.

     *

     * <p><strong>Note:</strong> if there is a default prefix, it will not be

     * returned in this enumeration; check for the default prefix

     * using the {@link #getURI getURI} with an argument of "".</p>

     *

     * @return An enumeration of prefixes (never empty).

     * @see #getDeclaredPrefixes

     * @see #getURI

     */

    public Enumeration<String> getPrefixes ()

    {

        return currentContext.getPrefixes();

    }

    /**

     * Return one of the prefixes mapped to a Namespace URI.

     *

     * <p>If more than one prefix is currently mapped to the same

     * URI, this method will make an arbitrary selection; if you

     * want all of the prefixes, use the {@link #getPrefixes}

     * method instead.</p>

     *

     * <p><strong>Note:</strong> this will never return the empty (default) prefix;

     * to check for a default prefix, use the {@link #getURI getURI}

     * method with an argument of "".</p>

     *

     * @param uri the namespace URI

     * @return one of the prefixes currently mapped to the URI supplied,

     *         or null if none is mapped or if the URI is assigned to

     *         the default namespace

     * @see #getPrefixes(java.lang.String)

     * @see #getURI

     */

    public String getPrefix (String uri)

    {

        return currentContext.getPrefix(uri);

    }

    /**

     * Return an enumeration of all prefixes for a given URI whose

     * declarations are active in the current context.

     * This includes declarations from parent contexts that have

     * not been overridden.

     *

     * <p>This method returns prefixes mapped to a specific Namespace

     * URI.  The xml: prefix will be included.  If you want only one

     * prefix that's mapped to the Namespace URI, and you don't care

     * which one you get, use the {@link #getPrefix getPrefix}

     *  method instead.</p>

     *

     * <p><strong>Note:</strong> the empty (default) prefix is <em>never</em> included

     * in this enumeration; to check for the presence of a default

     * Namespace, use the {@link #getURI getURI} method with an

     * argument of "".</p>

     *

     * @param uri The Namespace URI.

     * @return An enumeration of prefixes (never empty).

     * @see #getPrefix

     * @see #getDeclaredPrefixes

     * @see #getURI

     */

    public Enumeration<String> getPrefixes (String uri)

    {

        List<String> prefixes = new ArrayList<>();

        Enumeration<String> allPrefixes = getPrefixes();

        while (allPrefixes.hasMoreElements()) {

            String prefix = allPrefixes.nextElement();

            if (uri.equals(getURI(prefix))) {

                prefixes.add(prefix);

            }

        }

        return Collections.enumeration(prefixes);

    }

    /**

     * Return an enumeration of all prefixes declared in this context.

     *

     * <p>The empty (default) prefix will be included in this

     * enumeration; note that this behaviour differs from that of

     * {@link #getPrefix} and {@link #getPrefixes}.</p>

     *

     * @return An enumeration of all prefixes declared in this

     *         context.

     * @see #getPrefixes

     * @see #getURI

     */

    public Enumeration<String> getDeclaredPrefixes ()

    {

        return currentContext.getDeclaredPrefixes();

    }

    /**

     * Controls whether namespace declaration attributes are placed

     * into the {@link #NSDECL NSDECL} namespace

     * by {@link #processName processName()}.  This may only be

     * changed before any contexts have been pushed.

     *

     * @since 1.5, SAX 2.1alpha

     *

     * @exception IllegalStateException when attempting to set this

     *  after any context has been pushed.

     */

    public void setNamespaceDeclUris (boolean value)

    {

        if (contextPos != 0)

            throw new IllegalStateException ();

        if (value == namespaceDeclUris)

            return;

        namespaceDeclUris = value;

        if (value)

            currentContext.declarePrefix ("xmlns", NSDECL);

        else {

            contexts[contextPos] = currentContext = new Context();

            currentContext.declarePrefix("xml", XMLNS);

        }

    }

    /**

     * Returns true if namespace declaration attributes are placed into

     * a namespace.  This behavior is not the default.

     *

     * @since 1.5, SAX 2.1alpha

     */

    public boolean isNamespaceDeclUris ()

        { return namespaceDeclUris; }

    ////////////////////////////////////////////////////////////////////

    // Internal state.

    ////////////////////////////////////////////////////////////////////

    private Context contexts[];