/**

*******************************************************************************

* @file json_object_iterator.c

*

* Copyright (c) 2009-2012 Hewlett-Packard Development Company, L.P.

*

* This library is free software; you can redistribute it and/or modify

* it under the terms of the MIT license. See COPYING for details.

*

*******************************************************************************

*/

#include <stddef.h>

#include "json.h"

#include "json_object_private.h"

#include "json_object_iterator.h"

/**

 * How It Works

 *

 * For each JSON Object, json-c maintains a linked list of zero

 * or more lh_entry (link-hash entry) structures inside the

 * Object's link-hash table (lh_table).

 *

 * Each lh_entry structure on the JSON Object's linked list

 * represents a single name/value pair.  The "next" field of the

 * last lh_entry in the list is set to NULL, which terminates

 * the list.

 *

 * We represent a valid iterator that refers to an actual

 * name/value pair via a pointer to the pair's lh_entry

 * structure set as the iterator's opaque_ field.

 *

 * We follow json-c's current pair list representation by

 * representing a valid "end" iterator (one that refers past the

 * last pair) with a NULL value in the iterator's opaque_ field.

 *

 * A JSON Object without any pairs in it will have the "head"

 * field of its lh_table structure set to NULL.  For such an

 * object, json_object_iter_begin will return an iterator with

 * the opaque_ field set to NULL, which is equivalent to the

 * "end" iterator.

 *

 * When iterating, we simply update the iterator's opaque_ field

 * to point to the next lh_entry structure in the linked list.

 * opaque_ will become NULL once we iterate past the last pair

 * in the list, which makes the iterator equivalent to the "end"

 * iterator.

 */

/// Our current representation of the "end" iterator;

///

/// @note May not always be NULL

static const void* kObjectEndIterValue = NULL;

/**

 * ****************************************************************************

 */

struct json_object_iterator

json_object_iter_begin(struct json_object* obj)

{

    struct json_object_iterator iter;

    struct lh_table* pTable;

    /// @note json_object_get_object will return NULL if passed NULL

    ///       or a non-json_type_object instance

    pTable = json_object_get_object(obj);

    JASSERT(NULL != pTable);

    /// @note For a pair-less Object, head is NULL, which matches our

    ///       definition of the "end" iterator

    iter.opaque_ = pTable->head;

    return iter;

}

/**

 * ****************************************************************************

 */

struct json_object_iterator

json_object_iter_end(const struct json_object* obj)

{

    struct json_object_iterator iter;

    JASSERT(NULL != obj);

    JASSERT(json_object_is_type(obj, json_type_object));

    iter.opaque_ = kObjectEndIterValue;

    return iter;

}

/**

 * ****************************************************************************

 */

void

json_object_iter_next(struct json_object_iterator* iter)

{

    JASSERT(NULL != iter);

    JASSERT(kObjectEndIterValue != iter->opaque_);

    iter->opaque_ = ((const struct lh_entry *)iter->opaque_)->next;

}

/**

 * ****************************************************************************

 */

const char*

json_object_iter_peek_name(const struct json_object_iterator* iter)

{

    JASSERT(NULL != iter);

    JASSERT(kObjectEndIterValue != iter->opaque_);

    return (const char*)(((const struct lh_entry *)iter->opaque_)->k);

}

/**

 * ****************************************************************************

 */

struct json_object*

json_object_iter_peek_value(const struct json_object_iterator* iter)

{

    JASSERT(NULL != iter);

    JASSERT(kObjectEndIterValue != iter->opaque_);

    return (struct json_object*)lh_entry_v((const struct lh_entry *)iter->opaque_);

}

/**

 * ****************************************************************************

 */

json_bool

json_object_iter_equal(const struct json_object_iterator* iter1,

                       const struct json_object_iterator* iter2)

{

    JASSERT(NULL != iter1);

    JASSERT(NULL != iter2);

    return (iter1->opaque_ == iter2->opaque_);

}

/**

 * ****************************************************************************

 */

struct json_object_iterator

json_object_iter_init_default(void)

{

    struct json_object_iterator iter;

    /**

     * @note Make this a negative, invalid value, such that

     *       accidental access to it would likely be trapped by the

     *       hardware as an invalid address.

     */

    iter.opaque_ = NULL;

    return iter;

}