/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

parcel Lucy;

__C__
#include <stddef.h>
#include "Lucy/Object/Obj.h"
#include "Lucy/Util/SortUtils.h"

#define LUCY_SORTEX_DEFAULT_MEM_THRESHOLD 0x1000000
#ifdef LUCY_USE_SHORT_NAMES
  #define SORTEX_DEFAULT_MEM_THRESHOLD LUCY_SORTEX_DEFAULT_MEM_THRESHOLD
#endif
__END_C__

/** Abstract external sorter.
 *
 * SortExternal objects are sort pools which allow you to sort large amounts
 * of data.  To achieve this, you Feed() all values into the SortExternal
 * object, Flip() the object from write mode to read mode, then Fetch() the
 * values one at a time in sorted order.
 *
 * It's expected that the total memory footprint of the sortable objects will
 * eventually exceed a specified threshold; at that point, the SortExternal
 * object will call the abstract method Flush().  It's expected that Flush()
 * implementations will empty out the current sort cache, write a sorted "run"
 * to external storage, and add a new child SortExternal object to the top
 * level object's "runs" array to represent the flushed content.
 *
 * During the read phase, the child objects retrieve values from external
 * storage by calling the abstract method Refill().  The top-level
 * SortExternal object then interleaves multiple sorted streams to produce a
 * single unified stream of sorted values.
 */
abstract class Lucy::Util::SortExternal cnick SortEx
    inherits Lucy::Object::Obj {

    uint8_t       *cache;
    uint32_t       cache_cap;
    uint32_t       cache_max;
    uint32_t       cache_tick;
    uint8_t       *scratch;
    uint32_t       scratch_cap;
    VArray        *runs;
    uint32_t       num_slices;
    uint8_t      **slice_starts;
    uint32_t      *slice_sizes;
    uint32_t       mem_thresh;
    size_t         width;
    bool_t         flipped;

    inert SortExternal*
    init(SortExternal *self, size_t width);

    /** Compare two sortable elements.
     */
    abstract int
    Compare(SortExternal *self, void *va, void *vb);

    /** Flush all elements currently in the cache.
     *
     * Presumably this entails sorting everything, writing the sorted elements
     * to disk, spawning a child object to represent those elements, and
     * adding that child to the top level object via Add_Run().
     */
    abstract void
    Flush(SortExternal *self);

    /** Add data to the sort pool.
     *
     * @param data Pointer to the data being added, which must be exactly
     * <code>width</code> bytes in size.
     */
    void
    Feed(SortExternal *self, void *data);

    /** Flip the sortex from write mode to read mode.
     */
    void
    Flip(SortExternal *self);

    /** Fetch the next sorted item from the sort pool.  Invalid prior to
     * calling Flip(). Returns NULL when all elements have been exhausted.
     */
    nullable void*
    Fetch(SortExternal *self);

    /** Preview the next item that Fetch will return, but don't pop it.
     * Invalid prior to calling Flip().
     */
    nullable void*
    Peek(SortExternal *self);

    /** Add a run to the sortex's collection.
     */
    void
    Add_Run(SortExternal *self, decremented SortExternal *run);

    /** Refill the cache of a run.  Will only be called on child objects, not
     * the main object.
     */
    abstract uint32_t
    Refill(SortExternal *self);

    /** Sort all items currently in the main cache.
     */
    void
    Sort_Cache(SortExternal *self);

    /** Reset cache variables so that cache gives the appearance of having
     * been initialized.
     *
     * Subclasses may take steps to release items held in cache, if any.
     */
    void
    Clear_Cache(SortExternal *self);

    /** Return the number of items presently in the cache.
     */
    uint32_t
    Cache_Count(SortExternal *self);

    /** Allocate more memory to the cache.
     */
    void
    Grow_Cache(SortExternal *self, uint32_t new_cache_cap);

    void
    Set_Mem_Thresh(SortExternal *self, uint32_t mem_thresh);

    public void
    Destroy(SortExternal *self);
}