#include "cache.h"
#include "object.h"
#include "delta.h"

static int dry_run;
static int nr_entries;
static const char *base_name;
static const char unpack_usage[] = "git-unpack-objects basename";

struct pack_entry {
        unsigned int offset; /* network byte order */
        unsigned char sha1[20];
};

static void *pack_base;
static unsigned long pack_size;
static void *index_base;
static unsigned long index_size;

static struct pack_entry **pack_list;

static void *map_file(const char *suffix, unsigned long *sizep)
{
        static char pathname[PATH_MAX];
        unsigned long len;
        int fd;
        struct stat st;
        void *map;

        len = snprintf(pathname, PATH_MAX, "%s.%s", base_name, suffix);
        if (len >= PATH_MAX)
                die("bad pack base-name");
        fd = open(pathname, O_RDONLY);
        if (fd < 0 || fstat(fd, &st))
                die("unable to open '%s'", pathname);
        len = st.st_size;
        if (!len)
                die("bad pack file '%s'", pathname);
        map = mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0);
        if (-1 == (int)(long)map)
                die("unable to mmap '%s'", pathname);
        close(fd);
        *sizep = len;
        return map;
}

static int sort_by_offset(const void *_a, const void *_b)
{
        struct pack_entry *a = *(struct pack_entry **)_a;
        struct pack_entry *b = *(struct pack_entry **)_b;
        unsigned int o1, o2;

        o1 = ntohl(a->offset);
        o2 = ntohl(b->offset);
        return o1 < o2 ? -1 : 1;
}

static int check_index(void)
{
        unsigned int *array = index_base;
        unsigned int nr;
        int i;

        if (index_size < 4*256 + 20)
                return error("index file too small");
        nr = 0;
        for (i = 0; i < 256; i++) {
                unsigned int n = ntohl(array[i]);
                if (n < nr)
                        return error("non-monotonic index");
                nr = n;
        }
        /*
         * Total size:
         *  - 256 index entries 4 bytes each
         *  - 24-byte entries * nr (20-byte sha1 + 4-byte offset)
         *  - 20-byte SHA1 of the packfile
         *  - 20-byte SHA1 file checksum
         */
        if (index_size != 4*256 + nr * 24 + 20 + 20)
                return error("wrong index file size");

        nr_entries = nr;
        pack_list = xmalloc(nr * sizeof(struct pack_entry *));
        for (i = 0; i < nr; i++)
                pack_list[i] = index_base + 4*256 + i*24;

        qsort(pack_list, nr, sizeof(*pack_list), sort_by_offset);

        printf("%d entries\n", nr);
        return 0;
}

static int unpack_non_delta_entry(struct pack_entry *entry,
                                  int kind,
                                  unsigned char *data,
                                  unsigned long size,
                                  unsigned long left)
{
        int st;
        z_stream stream;
        char *buffer;
        unsigned char sha1[20];
        char *type_s;

        printf("%s %c %lu\n", sha1_to_hex(entry->sha1), kind, size);
        if (dry_run)
                return 0;

        buffer = xmalloc(size + 1);
        buffer[size] = 0;
        memset(&stream, 0, sizeof(stream));
        stream.next_in = data;
        stream.avail_in = left;
        stream.next_out = buffer;
        stream.avail_out = size;

        inflateInit(&stream);
        st = inflate(&stream, Z_FINISH);
        inflateEnd(&stream);
        if ((st != Z_STREAM_END) || stream.total_out != size)
                goto err_finish;
        switch (kind) {
        case 'C': type_s = "commit"; break;
        case 'T': type_s = "tree"; break;
        case 'B': type_s = "blob"; break;
        case 'G': type_s = "tag"; break;
        default: goto err_finish;
        }
        if (write_sha1_file(buffer, size, type_s, sha1) < 0)
                die("failed to write %s (%s)",
                    sha1_to_hex(entry->sha1), type_s);
        printf("%s %s\n", sha1_to_hex(sha1), type_s);
        if (memcmp(sha1, entry->sha1, 20))
                die("resulting %s have wrong SHA1", type_s);

 finish:
        st = 0;
        free(buffer);
        return st;
 err_finish:
        st = -1;
        goto finish;
}

static int find_pack_entry(unsigned char *sha1, struct pack_entry **ent)
{
        int *level1_ofs = index_base;
        int hi = ntohl(level1_ofs[*sha1]);
        int lo = ((*sha1 == 0x0) ? 0 : ntohl(level1_ofs[*sha1 - 1]));
        void *index = index_base + 4*256;

        do {
                int mi = (lo + hi) / 2;
                int cmp = memcmp(index + 24 * mi + 4, sha1, 20);
                if (!cmp) {
                        *ent = index + 24 * mi;
                        return 1;
                }
                if (cmp > 0)
                        hi = mi;
                else
                        lo = mi+1;
        } while (lo < hi);
        return 0;
}

/* forward declaration for a mutually recursive function */
static void unpack_entry(struct pack_entry *);

static int unpack_delta_entry(struct pack_entry *entry,
                              unsigned char *base_sha1,
                              unsigned long delta_size,
                              unsigned long left)
{
        void *data, *delta_data, *result, *base;
        unsigned long data_size, result_size, base_size;
        z_stream stream;
        int st;
        char type[20];
        unsigned char sha1[20];

        if (left < 20)
                die("truncated pack file");
        data = base_sha1 + 20;
        data_size = left - 20;
        printf("%s D %lu", sha1_to_hex(entry->sha1), delta_size);
        printf(" %s\n", sha1_to_hex(base_sha1));

        if (dry_run)
                return 0;

        /* pack+5 is the base sha1, unless we have it, we need to
         * unpack it first.
         */
        if (!has_sha1_file(base_sha1)) {
                struct pack_entry *base;
                if (!find_pack_entry(base_sha1, &base))
                        die("cannot find delta-pack base object");
                unpack_entry(base);
        }
        delta_data = xmalloc(delta_size);

        memset(&stream, 0, sizeof(stream));

        stream.next_in = data;
        stream.avail_in = data_size;
        stream.next_out = delta_data;
        stream.avail_out = delta_size;

        inflateInit(&stream);
        st = inflate(&stream, Z_FINISH);
        inflateEnd(&stream);
        if ((st != Z_STREAM_END) || stream.total_out != delta_size)
                die("delta data unpack failed");

        base = read_sha1_file(base_sha1, type, &base_size);
        if (!base)
                die("failed to read delta-pack base object %s", sha1_to_hex(base_sha1));
        result = patch_delta(base, base_size,
                             delta_data, delta_size,
                             &result_size);
        if (!result)
                die("failed to apply delta");
        free(delta_data);

        if (write_sha1_file(result, result_size, type, sha1) < 0)
                die("failed to write %s (%s)",
                    sha1_to_hex(entry->sha1), type);
        free(result);
        printf("%s %s\n", sha1_to_hex(sha1), type);
        if (memcmp(sha1, entry->sha1, 20))
                die("resulting %s have wrong SHA1", type);
        return 0;
}

static void unpack_entry(struct pack_entry *entry)
{
        unsigned long offset, size, left;
        unsigned char *pack;

        /* Have we done this one already due to deltas based on it? */
        if (lookup_object(entry->sha1))
                return;

        offset = ntohl(entry->offset);
        if (offset > pack_size - 5)
                die("object offset outside of pack file");
        pack = pack_base + offset;
        size = (pack[1] << 24) + (pack[2] << 16) + (pack[3] << 8) + pack[4];
        left = pack_size - offset - 5;
        switch (*pack) {
        case 'C': case 'T': case 'B': case 'G':
                unpack_non_delta_entry(entry, *pack, pack+5, size, left);
                break;
        case 'D':
                unpack_delta_entry(entry, pack+5, size, left);
                break;
        default:
                die("corrupted pack file");
        }
}

/*
 * We unpack from the end, older files first. Now, usually
 * there are deltas etc, so we'll not actually write the
 * objects in that order, but we might as well try..
 */
static void unpack_all(void)
{
        int i = nr_entries;

        while (--i >= 0) {
                struct pack_entry *entry = pack_list[i];
                unpack_entry(entry);
        }
}

int main(int argc, char **argv)
{
        int i;

        for (i = 1 ; i < argc; i++) {
                const char *arg = argv[i];

                if (*arg == '-') {
                        if (!strcmp(arg, "-n")) {
                                dry_run = 1;
                                continue;
                        }
                        usage(unpack_usage);
                }
                if (base_name)
                        usage(unpack_usage);
                base_name = arg;
        }
        if (!base_name)
                usage(unpack_usage);
        index_base = map_file("idx", &index_size);
        pack_base = map_file("pack", &pack_size);
        if (check_index() < 0)
                die("bad index file");
        unpack_all();
        return 0;
}