#include "git-compat-util.h"

#include "gettext.h"

#include "pack-revindex.h"

#include "odb.h"

#include "packfile.h"

#include "strbuf.h"

#include "trace2.h"

#include "parse.h"

#include "repository.h"

#include "midx.h"

#include "csum-file.h"

struct revindex_entry {

  off_t offset;

  unsigned int nr;

};

/*

 * Pack index for existing packs give us easy access to the offsets into

 * corresponding pack file where each object's data starts, but the entries

 * do not store the size of the compressed representation (uncompressed

 * size is easily available by examining the pack entry header).  It is

 * also rather expensive to find the sha1 for an object given its offset.

 *

 * The pack index file is sorted by object name mapping to offset;

 * this revindex array is a list of offset/index_nr pairs

 * ordered by offset, so if you know the offset of an object, next offset

 * is where its packed representation ends and the index_nr can be used to

 * get the object sha1 from the main index.

 */

/*

 * This is a least-significant-digit radix sort.

 *

 * It sorts each of the "n" items in "entries" by its offset field. The "max"

 * parameter must be at least as large as the largest offset in the array,

 * and lets us quit the sort early.

 */

static void sort_revindex(struct revindex_entry *entries, unsigned n, off_t max)

{

  /*

   * We use a "digit" size of 16 bits. That keeps our memory

   * usage reasonable, and we can generally (for a 4G or smaller

   * packfile) quit after two rounds of radix-sorting.

   */

#define DIGIT_SIZE (16)

#define BUCKETS (1 << DIGIT_SIZE)

  /*

   * We want to know the bucket that a[i] will go into when we are using

   * the digit that is N bits from the (least significant) end.

   */

#define BUCKET_FOR(a, i, bits) (((a)[(i)].offset >> (bits)) & (BUCKETS-1))

  /*

   * We need O(n) temporary storage. Rather than do an extra copy of the

   * partial results into "entries", we sort back and forth between the

   * real array and temporary storage. In each iteration of the loop, we

   * keep track of them with alias pointers, always sorting from "from"

   * to "to".

   */

  struct revindex_entry *tmp, *from, *to;

  int bits;

  unsigned *pos;

  ALLOC_ARRAY(pos, BUCKETS);

  ALLOC_ARRAY(tmp, n);

  from = entries;

  to = tmp;

  /*

   * If (max >> bits) is zero, then we know that the radix digit we are

   * on (and any higher) will be zero for all entries, and our loop will

   * be a no-op, as everybody lands in the same zero-th bucket.

   */

  for (bits = 0; max >> bits; bits += DIGIT_SIZE) {

    unsigned i;

    MEMZERO_ARRAY(pos, BUCKETS);

    /*

     * We want pos[i] to store the index of the last element that

     * will go in bucket "i" (actually one past the last element).

     * To do this, we first count the items that will go in each

     * bucket, which gives us a relative offset from the last

     * bucket. We can then cumulatively add the index from the

     * previous bucket to get the true index.

     */

    for (i = 0; i < n; i++)

      pos[BUCKET_FOR(from, i, bits)]++;

    for (i = 1; i < BUCKETS; i++)

      pos[i] += pos[i-1];

    /*

     * Now we can drop the elements into their correct buckets (in

     * our temporary array).  We iterate the pos counter backwards

     * to avoid using an extra index to count up. And since we are

     * going backwards there, we must also go backwards through the

     * array itself, to keep the sort stable.

     *

     * Note that we use an unsigned iterator to make sure we can

     * handle 2^32-1 objects, even on a 32-bit system. But this

     * means we cannot use the more obvious "i >= 0" loop condition

     * for counting backwards, and must instead check for

     * wrap-around with UINT_MAX.

     */

    for (i = n - 1; i != UINT_MAX; i--)

      to[--pos[BUCKET_FOR(from, i, bits)]] = from[i];

    /*

     * Now "to" contains the most sorted list, so we swap "from" and

     * "to" for the next iteration.

     */

    SWAP(from, to);

  }

  /*

   * If we ended with our data in the original array, great. If not,

   * we have to move it back from the temporary storage.

   */

  if (from != entries)

    COPY_ARRAY(entries, tmp, n);

  free(tmp);

  free(pos);

#undef BUCKET_FOR

#undef BUCKETS

#undef DIGIT_SIZE

}

/*

 * Ordered list of offsets of objects in the pack.

 */

static void create_pack_revindex(struct packed_git *p)

{

  const unsigned num_ent = p->num_objects;

  unsigned i;

  const char *index = p->index_data;

  const unsigned hashsz = p->repo->hash_algo->rawsz;

  ALLOC_ARRAY(p->revindex, num_ent + 1);

  index += 4 * 256;

  if (p->index_version > 1) {

    const uint32_t *off_32 =

      (uint32_t *)(index + 8 + (size_t)p->num_objects * (hashsz + 4));

    const uint32_t *off_64 = off_32 + p->num_objects;

    for (i = 0; i < num_ent; i++) {

      const uint32_t off = ntohl(*off_32++);

      if (!(off & 0x80000000)) {

        p->revindex[i].offset = off;

      } else {

        p->revindex[i].offset = get_be64(off_64);

        off_64 += 2;

      }

      p->revindex[i].nr = i;

    }

  } else {

    for (i = 0; i < num_ent; i++) {

      const uint32_t hl = *((uint32_t *)(index + (hashsz + 4) * i));

      p->revindex[i].offset = ntohl(hl);

      p->revindex[i].nr = i;

    }

  }

  /*

   * This knows the pack format -- the hash trailer

   * follows immediately after the last object data.

   */

  p->revindex[num_ent].offset = p->pack_size - hashsz;

  p->revindex[num_ent].nr = -1;

  sort_revindex(p->revindex, num_ent, p->pack_size);

}

static int create_pack_revindex_in_memory(struct packed_git *p)

{

  if (git_env_bool(GIT_TEST_REV_INDEX_DIE_IN_MEMORY, 0))

    die("dying as requested by '%s'",

        GIT_TEST_REV_INDEX_DIE_IN_MEMORY);

  if (open_pack_index(p))

    return -1;

  create_pack_revindex(p);

  return 0;

}

static char *pack_revindex_filename(struct packed_git *p)

{

  size_t len;

  if (!strip_suffix(p->pack_name, ".pack", &len))

    BUG("pack_name does not end in .pack");

  return xstrfmt("%.*s.rev", (int)len, p->pack_name);

}

#define RIDX_HEADER_SIZE (12)

static size_t ridx_min_size(const struct git_hash_algo *algo)

{

  return RIDX_HEADER_SIZE + (2 * algo->rawsz);

}

struct revindex_header {

  uint32_t signature;

  uint32_t version;

  uint32_t hash_id;

};

static int load_revindex_from_disk(const struct git_hash_algo *algo,

           char *revindex_name,

           uint32_t num_objects,

           const uint32_t **data_p, size_t *len_p)

{

  int fd, ret = 0;

  struct stat st;

  void *data = NULL;

  size_t revindex_size;

  struct revindex_header *hdr;

  if (git_env_bool(GIT_TEST_REV_INDEX_DIE_ON_DISK, 0))

    die("dying as requested by '%s'", GIT_TEST_REV_INDEX_DIE_ON_DISK);

  fd = git_open(revindex_name);

  if (fd < 0) {

    /* "No file" means return 1. */

    ret = 1;

    goto cleanup;

  }

  if (fstat(fd, &st)) {

    ret = error_errno(_("failed to read %s"), revindex_name);

    goto cleanup;

  }

  revindex_size = xsize_t(st.st_size);

  if (revindex_size < ridx_min_size(algo)) {

    ret = error(_("reverse-index file %s is too small"), revindex_name);

    goto cleanup;

  }

  if (revindex_size - ridx_min_size(algo) != st_mult(sizeof(uint32_t), num_objects)) {

    ret = error(_("reverse-index file %s is corrupt"), revindex_name);

    goto cleanup;

  }

  data = xmmap(NULL, revindex_size, PROT_READ, MAP_PRIVATE, fd, 0);

  hdr = data;

  if (ntohl(hdr->signature) != RIDX_SIGNATURE) {

    ret = error(_("reverse-index file %s has unknown signature"), revindex_name);

    goto cleanup;

  }

  if (ntohl(hdr->version) != 1) {

    ret = error(_("reverse-index file %s has unsupported version %"PRIu32),

          revindex_name, ntohl(hdr->version));

    goto cleanup;

  }

  if (!(ntohl(hdr->hash_id) == 1 || ntohl(hdr->hash_id) == 2)) {

    ret = error(_("reverse-index file %s has unsupported hash id %"PRIu32),

          revindex_name, ntohl(hdr->hash_id));

    goto cleanup;

  }

cleanup:

  if (ret) {

    if (data)

      munmap(data, revindex_size);

  } else {

    *len_p = revindex_size;

    *data_p = (const uint32_t *)data;

  }

  if (fd >= 0)

    close(fd);

  return ret;

}

int load_pack_revindex_from_disk(struct packed_git *p)

{

  char *revindex_name;

  int ret;

  if (open_pack_index(p))

    return -1;

  revindex_name = pack_revindex_filename(p);

  ret = load_revindex_from_disk(p->repo->hash_algo,

              revindex_name,

              p->num_objects,

              &p->revindex_map,

              &p->revindex_size);

  if (ret)

    goto cleanup;

  p->revindex_data = (const uint32_t *)((const char *)p->revindex_map + RIDX_HEADER_SIZE);

cleanup:

  free(revindex_name);

  return ret;

}

int load_pack_revindex(struct repository *r, struct packed_git *p)

{

  if (p->revindex || p->revindex_data)

    return 0;

  prepare_repo_settings(r);

  if (r->settings.pack_read_reverse_index &&

      !load_pack_revindex_from_disk(p))

    return 0;

  else if (!create_pack_revindex_in_memory(p))

    return 0;

  return -1;

}

/*

 * verify_pack_revindex verifies that the on-disk rev-index for the given

 * pack-file is the same that would be created if written from scratch.

 *

 * A negative number is returned on error.

 */

int verify_pack_revindex(struct packed_git *p)

{

  int res = 0;

  /* Do not bother checking if not initialized. */

  if (!p->revindex_map || !p->revindex_data)

    return res;

  if (!hashfile_checksum_valid(p->repo->hash_algo,

             (const unsigned char *)p->revindex_map, p->revindex_size)) {

    error(_("invalid checksum"));

    res = -1;

  }

  /* This may fail due to a broken .idx. */

  if (create_pack_revindex_in_memory(p))

    return res;

  for (size_t i = 0; i < p->num_objects; i++) {

    uint32_t nr = p->revindex[i].nr;

    uint32_t rev_val = get_be32(p->revindex_data + i);

    if (nr != rev_val) {

      error(_("invalid rev-index position at %"PRIu64": %"PRIu32" != %"PRIu32""),

            (uint64_t)i, nr, rev_val);

      res = -1;

    }

  }

  return res;

}

static int can_use_midx_ridx_chunk(struct multi_pack_index *m)

{

  if (!m->chunk_revindex)

    return 0;

  if (m->chunk_revindex_len != st_mult(sizeof(uint32_t), m->num_objects)) {

    error(_("multi-pack-index reverse-index chunk is the wrong size"));

    return 0;

  }

  return 1;

}

int load_midx_revindex(struct multi_pack_index *m)

{

  struct strbuf revindex_name = STRBUF_INIT;

  int ret;

  if (m->revindex_data)

    return 0;

  if (can_use_midx_ridx_chunk(m)) {

    /*

     * If the MIDX `m` has a `RIDX` chunk, then use its contents for

     * the reverse index instead of trying to load a separate `.rev`

     * file.

     *

     * Note that we do *not* set `m->revindex_map` here, since we do

     * not want to accidentally call munmap() in the middle of the

     * MIDX.

     */

    trace2_data_string("load_midx_revindex", m->source->odb->repo,

           "source", "midx");

    m->revindex_data = (const uint32_t *)m->chunk_revindex;

    return 0;

  }

  trace2_data_string("load_midx_revindex", m->source->odb->repo,

         "source", "rev");

  if (m->has_chain)

    get_split_midx_filename_ext(m->source, &revindex_name,

              get_midx_checksum(m),

              MIDX_EXT_REV);

  else

    get_midx_filename_ext(m->source, &revindex_name,

              get_midx_checksum(m),

              MIDX_EXT_REV);

  ret = load_revindex_from_disk(m->source->odb->repo->hash_algo,

              revindex_name.buf,

              m->num_objects,

              &m->revindex_map,

              &m->revindex_len);

  if (ret)

    goto cleanup;

  m->revindex_data = (const uint32_t *)((const char *)m->revindex_map + RIDX_HEADER_SIZE);

cleanup:

  strbuf_release(&revindex_name);

  return ret;

}

int close_midx_revindex(struct multi_pack_index *m)

{

  if (!m || !m->revindex_map)

    return 0;

  munmap((void*)m->revindex_map, m->revindex_len);

  m->revindex_map = NULL;

  m->revindex_data = NULL;

  m->revindex_len = 0;

  return 0;

}

int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos)

{

  unsigned lo, hi;

  if (load_pack_revindex(p->repo, p) < 0)

    return -1;

  lo = 0;

  hi = p->num_objects + 1;

  do {

    const unsigned mi = lo + (hi - lo) / 2;

    off_t got = pack_pos_to_offset(p, mi);

    if (got == ofs) {

      *pos = mi;

      return 0;

    } else if (ofs < got)

      hi = mi;

    else

      lo = mi + 1;

  } while (lo < hi);

  error("bad offset for revindex");

  return -1;

}

uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos)

{

  if (!(p->revindex || p->revindex_data))

    BUG("pack_pos_to_index: reverse index not yet loaded");

  if (p->num_objects <= pos)

    BUG("pack_pos_to_index: out-of-bounds object at %"PRIu32, pos);

  if (p->revindex)

    return p->revindex[pos].nr;

  else

    return get_be32(p->revindex_data + pos);

}

off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos)

{

  if (!(p->revindex || p->revindex_data))

    BUG("pack_pos_to_index: reverse index not yet loaded");

  if (p->num_objects < pos)

    BUG("pack_pos_to_offset: out-of-bounds object at %"PRIu32, pos);

  if (p->revindex)

    return p->revindex[pos].offset;

  else if (pos == p->num_objects)

    return p->pack_size - p->repo->hash_algo->rawsz;

  else

    return nth_packed_object_offset(p, pack_pos_to_index(p, pos));

}

uint32_t pack_pos_to_midx(struct multi_pack_index *m, uint32_t pos)

{

  while (m && pos < m->num_objects_in_base)

    m = m->base_midx;

  if (!m)

    BUG("NULL multi-pack-index for object position: %"PRIu32, pos);

  if (!m->revindex_data)

    BUG("pack_pos_to_midx: reverse index not yet loaded");

  if (m->num_objects + m->num_objects_in_base <= pos)

    BUG("pack_pos_to_midx: out-of-bounds object at %"PRIu32, pos);

  return get_be32(m->revindex_data + pos - m->num_objects_in_base);

}

struct midx_pack_key {

  uint32_t pack;

  off_t offset;

  uint32_t preferred_pack;

  struct multi_pack_index *midx;

};

static int midx_pack_order_cmp(const void *va, const void *vb)

{

  const struct midx_pack_key *key = va;

  struct multi_pack_index *midx = key->midx;

  size_t pos = (uint32_t *)vb - (const uint32_t *)midx->revindex_data;

  uint32_t versus = pack_pos_to_midx(midx, pos + midx->num_objects_in_base);

  uint32_t versus_pack = nth_midxed_pack_int_id(midx, versus);

  off_t versus_offset;

  uint32_t key_preferred = key->pack == key->preferred_pack;

  uint32_t versus_preferred = versus_pack == key->preferred_pack;

  /*

   * First, compare the preferred-ness, noting that the preferred pack

   * comes first.

   */

  if (key_preferred && !versus_preferred)

    return -1;

  else if (!key_preferred && versus_preferred)

    return 1;

  /* Then, break ties first by comparing the pack IDs. */

  if (key->pack < versus_pack)

    return -1;

  else if (key->pack > versus_pack)

    return 1;

  /* Finally, break ties by comparing offsets within a pack. */

  versus_offset = nth_midxed_offset(midx, versus);

  if (key->offset < versus_offset)

    return -1;

  else if (key->offset > versus_offset)

    return 1;

  return 0;

}

static int midx_key_to_pack_pos(struct multi_pack_index *m,

        struct midx_pack_key *key,

        uint32_t *pos)

{

  uint32_t *found;

  if (key->pack >= m->num_packs + m->num_packs_in_base)

    BUG("MIDX pack lookup out of bounds (%"PRIu32" >= %"PRIu32")",

        key->pack, m->num_packs + m->num_packs_in_base);

  /*

   * The preferred pack sorts first, so determine its identifier by

   * looking at the first object in pseudo-pack order.

   *

   * Note that if no --preferred-pack is explicitly given when writing a

   * multi-pack index, then whichever pack has the lowest identifier

   * implicitly is preferred (and includes all its objects, since ties are

   * broken first by pack identifier).

   */

  if (midx_preferred_pack(key->midx, &key->preferred_pack) < 0)

    return error(_("could not determine preferred pack"));

  found = bsearch(key, m->revindex_data, m->num_objects,

      sizeof(*m->revindex_data),

      midx_pack_order_cmp);

  if (!found)

    return -1;

  *pos = (found - m->revindex_data) + m->num_objects_in_base;

  return 0;

}

int midx_to_pack_pos(struct multi_pack_index *m, uint32_t at, uint32_t *pos)

{

  struct midx_pack_key key;

  while (m && at < m->num_objects_in_base)

    m = m->base_midx;

  if (!m)

    BUG("NULL multi-pack-index for object position: %"PRIu32, at);

  if (!m->revindex_data)

    BUG("midx_to_pack_pos: reverse index not yet loaded");

  if (m->num_objects + m->num_objects_in_base <= at)

    BUG("midx_to_pack_pos: out-of-bounds object at %"PRIu32, at);

  key.pack = nth_midxed_pack_int_id(m, at);

  key.offset = nth_midxed_offset(m, at);

  key.midx = m;

  return midx_key_to_pack_pos(m, &key, pos);

}

int midx_pair_to_pack_pos(struct multi_pack_index *m, uint32_t pack_int_id,

        off_t ofs, uint32_t *pos)

{

  struct midx_pack_key key = {

    .pack = pack_int_id,

    .offset = ofs,

    .midx = m,

  };

  return midx_key_to_pack_pos(m, &key, pos);

}