/*******************************************************************************
 * This file is part of SWIFT.
 * Copyright (c) 2019 James Willis (james.s.willis@durham.ac.uk)
 *                    Pedro Gonnet (pedro.gonnet@gmail.com)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 ******************************************************************************/
/*
 * Generic hashmap manipulation functions
 *
 * Originally by Elliot C Back -
 * http://elliottback.com/wp/hashmap-implementation-in-c/
 *
 * Modified by Pete Warden to fix a serious performance problem, support strings
 * as keys and removed thread synchronization - http://petewarden.typepad.com
 */
#include "hashmap.h"

#include "error.h"
#include "memuse.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define INITIAL_NUM_CHUNKS (1)
#define HASHMAP_GROWTH_FACTOR (2)
#define HASHMAP_MAX_FILL_RATIO (1.0)
#define HASHMAP_MAX_CHUNK_FILL_RATIO (0.5)

/**
 * @brief Pre-allocate a number of chunks for the graveyard.
 */
void hashmap_allocate_chunks(hashmap_t *m, int num_chunks) {
  /* Allocate a fresh set of chunks. */
  hashmap_chunk_t *alloc;
  if ((alloc = (hashmap_chunk_t *)swift_calloc(
           "hashmap", num_chunks, sizeof(hashmap_chunk_t))) == NULL) {
    error("Unable to allocate chunks.");
  }

  /* Hook up the alloc, so that we can clean it up later. */
  if (m->allocs_count == m->allocs_size) {
    m->allocs_size *= 2;
    void **new_allocs =
        (void **)swift_malloc("hashmap", sizeof(void *) * m->allocs_size);
    memcpy(new_allocs, m->allocs, sizeof(void *) * m->allocs_count);
    swift_free("hashmap", m->allocs);
    m->allocs = new_allocs;
  }
  m->allocs[m->allocs_count++] = alloc;

  /* Link the chunks together. */
  for (int k = 0; k < num_chunks - 1; k++) {
    alloc[k].next = &alloc[k + 1];
  }

  /* Last chunk points to current graveyard. */
  alloc[num_chunks - 1].next = m->graveyard;

  /* Graveyard points to first new chunk. */
  m->graveyard = alloc;
}

void hashmap_init(hashmap_t *m) {
  /* Allocate the first (empty) list of chunks. */
  m->nr_chunks = INITIAL_NUM_CHUNKS;
  if ((m->chunks = (hashmap_chunk_t **)swift_calloc(
           "hashmap", m->nr_chunks, sizeof(hashmap_chunk_t *))) == NULL) {
    error("Unable to allocate hashmap chunks.");
  }

  /* The graveyard is currently empty. */
  m->graveyard = NULL;
  m->allocs = NULL;

  /* Init the array of allocations. */
  m->allocs_size = HASHMAP_ALLOCS_INITIAL_SIZE;
  if ((m->allocs = (void **)swift_malloc(
           "hashmap", sizeof(void *) * m->allocs_size)) == NULL) {
    error("Unable to allocate allocs pointer array.");
  }
  m->allocs_count = 0;

  /* Set initial sizes. */
  m->table_size = m->nr_chunks * HASHMAP_ELEMENTS_PER_CHUNK;
  m->size = 0;

  /* Inform the men. */
  if (HASHMAP_DEBUG_OUTPUT) {
    message(
        "Created hash table of size: %zu each element is %zu bytes. Allocated "
        "%zu empty chunks.",
        m->table_size * sizeof(hashmap_element_t), sizeof(hashmap_element_t),
        m->nr_chunks);
  }
}

/**
 * @brief Put a used chunk back into the recycling bin.
 */
void hashmap_release_chunk(hashmap_t *m, hashmap_chunk_t *chunk) {
  /* Clear all the chunk's data. */
  memset(chunk, 0, sizeof(hashmap_chunk_t));

  /* Hook it up with the other stiffs in the graveyard. */
  chunk->next = m->graveyard;
  m->graveyard = chunk;
}

/**
 * @brief Return a new chunk, either recycled or freshly allocated.
 */
hashmap_chunk_t *hashmap_get_chunk(hashmap_t *m) {
  int num_chunks = m->nr_chunks * HASHMAP_ALLOC_SIZE_FRACTION;
  if (!num_chunks) num_chunks = 1;
  if (m->graveyard == NULL) {
    hashmap_allocate_chunks(m, num_chunks);
  }

  hashmap_chunk_t *res = (hashmap_chunk_t *)m->graveyard;
  m->graveyard = (hashmap_chunk_t *)res->next;
  res->next = NULL;

  return res;
}

/**
 * @brief Looks for the given key and retuns a pointer to the corresponding
 * element.
 *
 * The returned element is either the one that already existed in the hashmap,
 * or a newly-reseverd element initialized to zero.
 *
 * If the hashmap is full, NULL is returned.
 *
 * We use `rand_r` as a hashing function. The key is first hashed to obtain an
 * initial global position. If there is a collision, the hashing function is
 * re-applied to the key to obtain a new offset *within the same bucket*. This
 * is repeated for at most HASHMAP_MAX_CHAIN_LENGTH steps, at which point
 * insertion fails.
 */
hashmap_element_t *hashmap_find(hashmap_t *m, hashmap_key_t key, int create_new,
                                int *chain_length, int *created_new_element) {
  /* If full, return immediately */
  if (create_new && m->size > m->table_size * HASHMAP_MAX_FILL_RATIO) {
    if (HASHMAP_DEBUG_OUTPUT) {
      message("hashmap is too full (%zu of %zu elements used), re-hashing.",
              m->size, m->table_size);
    }
    return NULL;
  }

  /* We will use rand_r as our hash function. */
  unsigned int curr = (unsigned int)key;

  /* Get offsets to the entry, its chunk, it's mask, etc. */
  const size_t offset = rand_r(&curr) % m->table_size;
  const size_t chunk_offset = offset / HASHMAP_ELEMENTS_PER_CHUNK;
  size_t offset_in_chunk = offset - chunk_offset * HASHMAP_ELEMENTS_PER_CHUNK;

  /* Allocate the chunk if needed. */
  if (m->chunks[chunk_offset] == NULL) {
    /* Quit here if we don't want to create a new entry. */
    if (!create_new) return NULL;

    /* Get a new chunk for this offset. */
    m->chunks[chunk_offset] = hashmap_get_chunk(m);
  }
  hashmap_chunk_t *chunk = m->chunks[chunk_offset];

  /* Count the number of free elements in this chunk and bail if it is too low.
   */
  int chunk_count = 0;
  for (int k = 0; k < HASHMAP_MASKS_PER_CHUNK; k++) {
    chunk_count += __builtin_popcountll(chunk->masks[k]);
  }
  if (create_new &&
      chunk_count > HASHMAP_ELEMENTS_PER_CHUNK * HASHMAP_MAX_CHUNK_FILL_RATIO) {
    if (HASHMAP_DEBUG_OUTPUT) {
      message(
          "chunk %zu is too full (%i of %i elements used, fill ratio is "
          "%.2f%%), re-hashing.",
          chunk_offset, chunk_count, HASHMAP_ELEMENTS_PER_CHUNK,
          (100.0 * m->size) / m->table_size);
    }
    return NULL;
  }

  /* Linear probing (well, not really, but whatever). */
  for (int i = 0; i < HASHMAP_MAX_CHAIN_LENGTH; i++) {
    /* Record the chain_length, if not NULL. */
    if (chain_length) *chain_length = i;

    /* Compute the offsets within the masks of this chunk. */
    const int mask_offset = offset_in_chunk / HASHMAP_BITS_PER_MASK;
    const int offset_in_mask =
        offset_in_chunk - mask_offset * HASHMAP_BITS_PER_MASK;

    /* Is the offset empty? */
    hashmap_mask_t search_mask = ((hashmap_mask_t)1) << offset_in_mask;
    if (!(chunk->masks[mask_offset] & search_mask)) {
      /* Quit here if we don't want to create a new element. */
      if (!create_new) return NULL;

      /* Mark this element as taken and increase the size counter. */
      chunk->masks[mask_offset] |= search_mask;
      m->size += 1;
      if (created_new_element) *created_new_element = 1;

      /* Set the key. */
      chunk->data[offset_in_chunk].key = key;

      /* Return a pointer to the new element. */
      return &chunk->data[offset_in_chunk];
    }

    /* Does the offset by chance contain the key we are looking for? */
    else if (chunk->data[offset_in_chunk].key == key) {
      return &chunk->data[offset_in_chunk];
    }

    /* None of the above, so this is a collision. Re-hash, but within the same
       chunk. I guess this is Hopscotch Hashing? */
    else {
      offset_in_chunk = rand_r(&curr) % HASHMAP_ELEMENTS_PER_CHUNK;
    }
  }

  /* We lucked out, so return nothing. */
  if (HASHMAP_DEBUG_OUTPUT) {
    message("maximum chain length exceeded, re-hashing.");
  }
  return NULL;
}

/**
 * @brief Grows the hashmap and rehashes all the elements
 */
void hashmap_grow(hashmap_t *m, size_t new_size) {
  /* Hold on to the old data. */
  const size_t old_table_size = m->table_size;
  hashmap_chunk_t **old_chunks = m->chunks;

  /* Re-allocate the chunk array. */
  if (new_size == 0) new_size = m->table_size * HASHMAP_GROWTH_FACTOR;
  m->nr_chunks =
      (new_size + HASHMAP_ELEMENTS_PER_CHUNK - 1) / HASHMAP_ELEMENTS_PER_CHUNK;
  m->table_size = m->nr_chunks * HASHMAP_ELEMENTS_PER_CHUNK;

  if (HASHMAP_DEBUG_OUTPUT) {
    message("Increasing hash table size from %zu (%zu kb) to %zu (%zu kb).",
            old_table_size, old_table_size * sizeof(hashmap_element_t) / 1024,
            m->table_size, m->table_size * sizeof(hashmap_element_t) / 1024);
  }

  if ((m->chunks = (hashmap_chunk_t **)swift_calloc(
           "hashmap", m->nr_chunks, sizeof(hashmap_chunk_t *))) == NULL) {
    error("Unable to allocate hashmap chunks.");
  }

  /* Reset size. */
  m->size = 0;

  /* Buffer of stray elements, in case we get overflows while re-hashing. */
  hashmap_element_t *strays = NULL;
  size_t strays_count = 0;
  size_t strays_size = 0;

  /* Iterate over the chunks and add their entries to the new table. */
  for (size_t cid = 0; cid < old_table_size / HASHMAP_ELEMENTS_PER_CHUNK;
       cid++) {
    /* Skip empty chunks. */
    hashmap_chunk_t *chunk = old_chunks[cid];
    if (!chunk) continue;

    /* Loop over the masks in this chunk. */
    for (int mid = 0; mid < HASHMAP_MASKS_PER_CHUNK; mid++) {
      /* Skip empty masks. */
      if (chunk->masks[mid] == 0) continue;

      /* Loop over the mask entries. */
      for (int eid = 0; eid < HASHMAP_BITS_PER_MASK; eid++) {
        hashmap_mask_t element_mask = ((hashmap_mask_t)1) << eid;
        if (chunk->masks[mid] & element_mask) {
          hashmap_element_t *element =
              &chunk->data[mid * HASHMAP_BITS_PER_MASK + eid];

          /* Copy the element over to the new hashmap. */
          hashmap_element_t *new_element =
              hashmap_find(m, element->key, /*create_new=*/1,
                           /*chain_length=*/NULL, /*created_new_element=*/NULL);

          if (new_element) {
            new_element->value = element->value;
          }
          /* If copying failed, then we have an overflow in the new hashmap.
             If this happens, store the offending element in the strays buffer
             for now. */
          else {
            /* (Re)allocate strays buffer? */
            if (strays_count == strays_size) {
              hashmap_element_t *temp_buff;
              strays_size = strays_size ? strays_size * 2 : 10;
              if ((temp_buff = (hashmap_element_t *)swift_malloc(
                       "hashmap_strays",
                       sizeof(hashmap_element_t) * strays_size)) == NULL)
                error("Failed to (re)allocate strays buffer.");
              memcpy(temp_buff, strays,
                     sizeof(hashmap_element_t) * strays_count);
              swift_free("hashmap_strays", strays);
              strays = temp_buff;
            }
            strays[strays_count++] = *element;
          }
        }
      }
    }

    /* We're through with this chunk, recycle it. */
    hashmap_release_chunk(m, chunk);
  }

  /* Free the old list of chunks. */
  swift_free("hashmap", old_chunks);

  /* If we have any strays, add them back to the hashmap. This will inevitably
     trigger a rehashing, but that's not our problem. */
  if (strays_count) {
    for (size_t k = 0; k < strays_count; k++) {
      hashmap_put(m, strays[k].key, strays[k].value);
    }
    swift_free("hashmap_strays", strays);
  }
}

void hashmap_put(hashmap_t *m, hashmap_key_t key, hashmap_value_t value) {
  /* Try to find an element for the given key. */
  hashmap_element_t *element =
      hashmap_find(m, key, /*create_new=*/1, /*chain_length=*/NULL,
                   /*created_new_element=*/NULL);

  /* Loop around, trying to find our place in the world. */
  while (!element) {
    hashmap_grow(m, 0);
    element = hashmap_find(m, key, /*create_new=*/1, /*chain_length=*/NULL,
                           /*created_new_element=*/NULL);
  }

  /* Set the value. */
  element->value = value;
}

hashmap_value_t *hashmap_get(hashmap_t *m, hashmap_key_t key) {
  /* Look for the given key. */
  hashmap_element_t *element =
      hashmap_find(m, key, /*create_new=*/1, /*chain_length=*/NULL,
                   /*created_new_element=*/NULL);
  while (!element) {
    hashmap_grow(m, 0);
    element = hashmap_find(m, key, /*create_new=*/1, /*chain_length=*/NULL,
                           /*created_new_element=*/NULL);
  }
  return &element->value;
}

hashmap_value_t *hashmap_get_new(hashmap_t *m, hashmap_key_t key,
                                 int *created_new_element) {
  /* Look for the given key. */
  hashmap_element_t *element = hashmap_find(
      m, key, /*create_new=*/1, /*chain_length=*/NULL, created_new_element);
  while (!element) {
    hashmap_grow(m, 0);
    element = hashmap_find(m, key, /*create_new=*/1, /*chain_length=*/NULL,
                           created_new_element);
  }
  return &element->value;
}

hashmap_value_t *hashmap_lookup(hashmap_t *m, hashmap_key_t key) {
  hashmap_element_t *element =
      hashmap_find(m, key, /*create_new=*/0, /*chain_length=*/NULL,
                   /*created_new_element=*/NULL);
  return element ? &element->value : NULL;
}

void hashmap_iterate(hashmap_t *m, hashmap_mapper_t f, void *data) {
  /* Loop over the chunks. */
  for (size_t cid = 0; cid < m->nr_chunks; cid++) {
    hashmap_chunk_t *chunk = m->chunks[cid];
    if (!chunk) continue;

    /* Loop over the masks. */
    for (int mid = 0; mid < HASHMAP_MASKS_PER_CHUNK; mid++) {
      hashmap_mask_t mask = chunk->masks[mid];
      if (!mask) continue;

      /* Loop over each element in the mask. */
      for (int eid = 0;
           eid < HASHMAP_BITS_PER_MASK &&
           mid * HASHMAP_BITS_PER_MASK + eid < HASHMAP_ELEMENTS_PER_CHUNK;
           eid++) {
        /* If the element exists, call the function on it. */
        if (mask & (((hashmap_mask_t)1) << eid)) {
          hashmap_element_t *element =
              &chunk->data[mid * HASHMAP_BITS_PER_MASK + eid];
          f(element->key, &element->value, data);
        }
      }
    }
  }
}

void hashmap_free(hashmap_t *m) {
  /* Free the list of active chunks. Note that the actual chunks will be freed
     as part of the allocs below. */
  swift_free("hashmap", m->chunks);

  /* Re-set some pointers and values, just in case. */
  m->chunks = NULL;
  m->graveyard = NULL;
  m->size = 0;
  m->table_size = 0;
  m->nr_chunks = 0;

  /* Free the chunk allocs. */
  for (size_t k = 0; k < m->allocs_count; k++) {
    swift_free("hashmap", m->allocs[k]);
  }
  swift_free("hashmap", m->allocs);
}

size_t hashmap_size(hashmap_t *m) {
  if (m != NULL)
    return m->size;
  else
    return 0;
}

#if HASHMAP_DEBUG_OUTPUT
void hashmap_count_chain_lengths(hashmap_key_t key, hashmap_value_t *value,
                                 void *data) {
  hashmap_t *m = (hashmap_t *)data;
  int count = 0;
  hashmap_find(m, key, /*create_entry=*/0, &count,
               /*created_new_element=*/NULL);
  m->chain_length_counts[count] += 1;
}
#endif

void hashmap_print_stats(hashmap_t *m) {
  /* Basic stats. */
  message("size: %zu, table_size: %zu, nr_chunks: %zu.", m->size, m->table_size,
          m->nr_chunks);

  /* Count the number of populated chunks, graveyard chunks, and allocs. */
  int chunk_counter = 0;
  for (size_t k = 0; k < m->nr_chunks; k++) {
    if (m->chunks[k]) chunk_counter += 1;
  }
  int graveyard_counter = 0;
  for (hashmap_chunk_t *finger = m->graveyard; finger != NULL;
       finger = (hashmap_chunk_t *)finger->next) {
    graveyard_counter += 1;
  }
  message(
      "populated chunks: %i (%zu kb), graveyard chunks: %i (%zu kb), allocs: "
      "%zu",
      chunk_counter, sizeof(hashmap_chunk_t) * chunk_counter / 1024,
      graveyard_counter, sizeof(hashmap_chunk_t) * graveyard_counter / 1024,
      m->allocs_count);

  /* Print fill ratios. */
  message("element-wise fill ratio: %.2f%%, chunk-wise fill ratio: %.2f%%",
          (100.0 * m->size) / m->table_size,
          (100.0 * chunk_counter) / m->nr_chunks);

#if HASHMAP_DEBUG_OUTPUT
  /* Compute the chain lengths. */
  for (int k = 0; k < HASHMAP_MAX_CHAIN_LENGTH; k++) {
    m->chain_length_counts[k] = 0;
  }
  hashmap_iterate(m, hashmap_count_chain_lengths, m);
  message("chain lengths:");
  for (int k = 0; k < HASHMAP_MAX_CHAIN_LENGTH; k++) {
    message("  chain_length_counts[%i]: %zu (%.2f%%)", k,
            m->chain_length_counts[k],
            (100.0 * m->chain_length_counts[k]) / m->size);
  }
#endif

  /* Compute chunk fill ratios. */
  size_t chunk_fill_ratio_counts[11];
  for (int k = 0; k < 11; k++) {
    chunk_fill_ratio_counts[k] = 0;
  }
  for (size_t k = 0; k < m->nr_chunks; k++) {
    hashmap_chunk_t *chunk = m->chunks[k];
    if (!chunk) {
      chunk_fill_ratio_counts[0] += 1;
    } else {
      int count = 0;
      for (int j = 0; j < HASHMAP_MASKS_PER_CHUNK; j++) {
        count += __builtin_popcountll(chunk->masks[j]);
      }
      chunk_fill_ratio_counts[(int)(10 * count / HASHMAP_MAX_CHUNK_FILL_RATIO /
                                    HASHMAP_ELEMENTS_PER_CHUNK)] += 1;
    }
  }
  message("chunk fill ratios:");
  for (int k = 0; k < 11; k++) {
    message("  %3i%% - %3i%%: %zu (%.2f%%)",
            (int)(k * 10 * HASHMAP_MAX_CHUNK_FILL_RATIO),
            (int)((k + 1) * 10 * HASHMAP_MAX_CHUNK_FILL_RATIO),
            chunk_fill_ratio_counts[k],
            (100.0 * chunk_fill_ratio_counts[k]) / m->nr_chunks);
  }

  /* Print struct sizes. */
  message("sizeof(hashmap_element_t): %zu", sizeof(hashmap_element_t));
  message("sizeof(hashmap_chunk_t): %zu", sizeof(hashmap_chunk_t));
  message("HASHMAP_TARGET_CHUNK_BYTES: %i", HASHMAP_TARGET_CHUNK_BYTES);
  message("HASHMAP_BITS_PER_ELEMENT: %i", HASHMAP_BITS_PER_ELEMENT);
  message("HASHMAP_ELEMENTS_PER_CHUNK: %i", HASHMAP_ELEMENTS_PER_CHUNK);
  message("HASHMAP_MASKS_PER_CHUNK: %i", HASHMAP_MASKS_PER_CHUNK);
}
