#include "cache.h"
#include "delta.h"
#include "pack.h"
#include "csum-file.h"

static const char index_pack_usage[] =
"git-index-pack [-o index-file] pack-file";

struct object_entry
{
        unsigned long offset;
        enum object_type type;
        enum object_type real_type;
        unsigned char sha1[20];
};

struct delta_entry
{
        struct object_entry *obj;
        unsigned char base_sha1[20];
};

static const char *pack_name;
static unsigned char *pack_base;
static unsigned long pack_size;
static struct object_entry *objects;
static struct delta_entry *deltas;
static int nr_objects;
static int nr_deltas;

static void open_pack_file(void)
{
        int fd;
        struct stat st;

        fd = open(pack_name, O_RDONLY);
        if (fd < 0)
                die("cannot open packfile '%s': %s", pack_name,
                    strerror(errno));
        if (fstat(fd, &st)) {
                int err = errno;
                close(fd);
                die("cannot fstat packfile '%s': %s", pack_name,
                    strerror(err));
        }
        pack_size = st.st_size;
        pack_base = mmap(NULL, pack_size, PROT_READ, MAP_PRIVATE, fd, 0);
        if (pack_base == MAP_FAILED) {
                int err = errno;
                close(fd);
                die("cannot mmap packfile '%s': %s", pack_name,
                    strerror(err));
        }
        close(fd);
}

static void parse_pack_header(void)
{
        const struct pack_header *hdr;
        unsigned char sha1[20];
        SHA_CTX ctx;

        /* Ensure there are enough bytes for the header and final SHA1 */
        if (pack_size < sizeof(struct pack_header) + 20)
                die("packfile '%s' is too small", pack_name);

        /* Header consistency check */
        hdr = (void *)pack_base;
        if (hdr->hdr_signature != htonl(PACK_SIGNATURE))
                die("packfile '%s' signature mismatch", pack_name);
        if (hdr->hdr_version != htonl(PACK_VERSION))
                die("packfile '%s' version %d different from ours %d",
                    pack_name, ntohl(hdr->hdr_version), PACK_VERSION);

        nr_objects = ntohl(hdr->hdr_entries);

        /* Check packfile integrity */
        SHA1_Init(&ctx);
        SHA1_Update(&ctx, pack_base, pack_size - 20);
        SHA1_Final(sha1, &ctx);
        if (memcmp(sha1, pack_base + pack_size - 20, 20))
                die("packfile '%s' SHA1 mismatch", pack_name);
}

static void bad_object(unsigned long offset, const char *format,
                       ...) NORETURN __attribute__((format (printf, 2, 3)));

static void bad_object(unsigned long offset, const char *format, ...)
{
        va_list params;
        char buf[1024];

        va_start(params, format);
        vsnprintf(buf, sizeof(buf), format, params);
        va_end(params);
        die("packfile '%s': bad object at offset %lu: %s",
            pack_name, offset, buf);
}

static void *unpack_entry_data(unsigned long offset,
                               unsigned long *current_pos, unsigned long size)
{
        unsigned long pack_limit = pack_size - 20;
        unsigned long pos = *current_pos;
        z_stream stream;
        void *buf = xmalloc(size);

        memset(&stream, 0, sizeof(stream));
        stream.next_out = buf;
        stream.avail_out = size;
        stream.next_in = pack_base + pos;
        stream.avail_in = pack_limit - pos;
        inflateInit(&stream);

        for (;;) {
                int ret = inflate(&stream, 0);
                if (ret == Z_STREAM_END)
                        break;
                if (ret != Z_OK)
                        bad_object(offset, "inflate returned %d", ret);
        }
        inflateEnd(&stream);
        if (stream.total_out != size)
                bad_object(offset, "size mismatch (expected %lu, got %lu)",
                           size, stream.total_out);
        *current_pos = pack_limit - stream.avail_in;
        return buf;
}

static void *unpack_raw_entry(unsigned long offset,
                              enum object_type *obj_type,
                              unsigned long *obj_size,
                              unsigned char *delta_base,
                              unsigned long *next_obj_offset)
{
        unsigned long pack_limit = pack_size - 20;
        unsigned long pos = offset;
        unsigned char c;
        unsigned long size;
        unsigned shift;
        enum object_type type;
        void *data;

        c = pack_base[pos++];
        type = (c >> 4) & 7;
        size = (c & 15);
        shift = 4;
        while (c & 0x80) {
                if (pos >= pack_limit)
                        bad_object(offset, "object extends past end of pack");
                c = pack_base[pos++];
                size += (c & 0x7fUL) << shift;
                shift += 7;
        }

        switch (type) {
        case OBJ_DELTA:
                if (pos + 20 >= pack_limit)
                        bad_object(offset, "object extends past end of pack");
                memcpy(delta_base, pack_base + pos, 20);
                pos += 20;
                /* fallthru */
        case OBJ_COMMIT:
        case OBJ_TREE:
        case OBJ_BLOB:
        case OBJ_TAG:
                data = unpack_entry_data(offset, &pos, size);
                break;
        default:
                bad_object(offset, "bad object type %d", type);
        }

        *obj_type = type;
        *obj_size = size;
        *next_obj_offset = pos;
        return data;
}

static int find_delta(const unsigned char *base_sha1)
{
        int first = 0, last = nr_deltas;

        while (first < last) {
                int next = (first + last) / 2;
                struct delta_entry *delta = &deltas[next];
                int cmp;

                cmp = memcmp(base_sha1, delta->base_sha1, 20);
                if (!cmp)
                        return next;
                if (cmp < 0) {
                        last = next;
                        continue;
                }
                first = next+1;
        }
        return -first-1;
}

static int find_deltas_based_on_sha1(const unsigned char *base_sha1,
                                     int *first_index, int *last_index)
{
        int first = find_delta(base_sha1);
        int last = first;
        int end = nr_deltas - 1;

        if (first < 0)
                return -1;
        while (first > 0 && !memcmp(deltas[first-1].base_sha1, base_sha1, 20))
                --first;
        while (last < end && !memcmp(deltas[last+1].base_sha1, base_sha1, 20))
                ++last;
        *first_index = first;
        *last_index = last;
        return 0;
}

static void sha1_object(const void *data, unsigned long size,
                        enum object_type type, unsigned char *sha1)
{
        SHA_CTX ctx;
        char header[50];
        int header_size;
        const char *type_str;

        switch (type) {
        case OBJ_COMMIT: type_str = "commit"; break;
        case OBJ_TREE:   type_str = "tree"; break;
        case OBJ_BLOB:   type_str = "blob"; break;
        case OBJ_TAG:    type_str = "tag"; break;
        default:
                die("bad type %d", type);
        }

        header_size = sprintf(header, "%s %lu", type_str, size) + 1;

        SHA1_Init(&ctx);
        SHA1_Update(&ctx, header, header_size);
        SHA1_Update(&ctx, data, size);
        SHA1_Final(sha1, &ctx);
}

static void resolve_delta(struct delta_entry *delta, void *base_data,
                          unsigned long base_size, enum object_type type)
{
        struct object_entry *obj = delta->obj;
        void *delta_data;
        unsigned long delta_size;
        void *result;
        unsigned long result_size;
        enum object_type delta_type;
        unsigned char base_sha1[20];
        unsigned long next_obj_offset;
        int j, first, last;

        obj->real_type = type;
        delta_data = unpack_raw_entry(obj->offset, &delta_type,
                                      &delta_size, base_sha1,
                                      &next_obj_offset);
        result = patch_delta(base_data, base_size, delta_data, delta_size,
                             &result_size);
        free(delta_data);
        if (!result)
                bad_object(obj->offset, "failed to apply delta");
        sha1_object(result, result_size, type, obj->sha1);
        if (!find_deltas_based_on_sha1(obj->sha1, &first, &last)) {
                for (j = first; j <= last; j++)
                        resolve_delta(&deltas[j], result, result_size, type);
        }
        free(result);
}

static int compare_delta_entry(const void *a, const void *b)
{
        const struct delta_entry *delta_a = a;
        const struct delta_entry *delta_b = b;
        return memcmp(delta_a->base_sha1, delta_b->base_sha1, 20);
}

static void parse_pack_objects(void)
{
        int i;
        unsigned long offset = sizeof(struct pack_header);
        unsigned char base_sha1[20];
        void *data;
        unsigned long data_size;

        /*
         * First pass:
         * - find locations of all objects;
         * - calculate SHA1 of all non-delta objects;
         * - remember base SHA1 for all deltas.
         */
        for (i = 0; i < nr_objects; i++) {
                struct object_entry *obj = &objects[i];
                obj->offset = offset;
                data = unpack_raw_entry(offset, &obj->type, &data_size,
                                        base_sha1, &offset);
                obj->real_type = obj->type;
                if (obj->type == OBJ_DELTA) {
                        struct delta_entry *delta = &deltas[nr_deltas++];
                        delta->obj = obj;
                        memcpy(delta->base_sha1, base_sha1, 20);
                } else
                        sha1_object(data, data_size, obj->type, obj->sha1);
                free(data);
        }
        if (offset != pack_size - 20)
                die("packfile '%s' has junk at the end", pack_name);

        /* Sort deltas by base SHA1 for fast searching */
        qsort(deltas, nr_deltas, sizeof(struct delta_entry),
              compare_delta_entry);

        /*
         * Second pass:
         * - for all non-delta objects, look if it is used as a base for
         *   deltas;
         * - if used as a base, uncompress the object and apply all deltas,
         *   recursively checking if the resulting object is used as a base
         *   for some more deltas.
         */
        for (i = 0; i < nr_objects; i++) {
                struct object_entry *obj = &objects[i];
                int j, first, last;

                if (obj->type == OBJ_DELTA)
                        continue;
                if (find_deltas_based_on_sha1(obj->sha1, &first, &last))
                        continue;
                data = unpack_raw_entry(obj->offset, &obj->type, &data_size,
                                        base_sha1, &offset);
                for (j = first; j <= last; j++)
                        resolve_delta(&deltas[j], data, data_size, obj->type);
                free(data);
        }

        /* Check for unresolved deltas */
        for (i = 0; i < nr_deltas; i++) {
                if (deltas[i].obj->real_type == OBJ_DELTA)
                        die("packfile '%s' has unresolved deltas",  pack_name);
        }
}

static int sha1_compare(const void *_a, const void *_b)
{
        struct object_entry *a = *(struct object_entry **)_a;
        struct object_entry *b = *(struct object_entry **)_b;
        return memcmp(a->sha1, b->sha1, 20);
}

static void write_index_file(const char *index_name, unsigned char *sha1)
{
        struct sha1file *f;
        struct object_entry **sorted_by_sha, **list, **last;
        unsigned int array[256];
        int i;
        SHA_CTX ctx;

        if (nr_objects) {
                sorted_by_sha =
                        xcalloc(nr_objects, sizeof(struct object_entry *));
                list = sorted_by_sha;
                last = sorted_by_sha + nr_objects;
                for (i = 0; i < nr_objects; ++i)
                        sorted_by_sha[i] = &objects[i];
                qsort(sorted_by_sha, nr_objects, sizeof(sorted_by_sha[0]),
                      sha1_compare);

        }
        else
                sorted_by_sha = list = last = NULL;

        unlink(index_name);
        f = sha1create("%s", index_name);

        /*
         * Write the first-level table (the list is sorted,
         * but we use a 256-entry lookup to be able to avoid
         * having to do eight extra binary search iterations).
         */
        for (i = 0; i < 256; i++) {
                struct object_entry **next = list;
                while (next < last) {
                        struct object_entry *obj = *next;
                        if (obj->sha1[0] != i)
                                break;
                        next++;
                }
                array[i] = htonl(next - sorted_by_sha);
                list = next;
        }
        sha1write(f, array, 256 * sizeof(int));

        /* recompute the SHA1 hash of sorted object names.
         * currently pack-objects does not do this, but that
         * can be fixed.
         */
        SHA1_Init(&ctx);
        /*
         * Write the actual SHA1 entries..
         */
        list = sorted_by_sha;
        for (i = 0; i < nr_objects; i++) {
                struct object_entry *obj = *list++;
                unsigned int offset = htonl(obj->offset);
                sha1write(f, &offset, 4);
                sha1write(f, obj->sha1, 20);
                SHA1_Update(&ctx, obj->sha1, 20);
        }
        sha1write(f, pack_base + pack_size - 20, 20);
        sha1close(f, NULL, 1);
        free(sorted_by_sha);
        SHA1_Final(sha1, &ctx);
}

int main(int argc, char **argv)
{
        int i;
        char *index_name = NULL;
        char *index_name_buf = NULL;
        unsigned char sha1[20];

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

                if (*arg == '-') {
                        if (!strcmp(arg, "-o")) {
                                if (index_name || (i+1) >= argc)
                                        usage(index_pack_usage);
                                index_name = argv[++i];
                        } else
                                usage(index_pack_usage);
                        continue;
                }

                if (pack_name)
                        usage(index_pack_usage);
                pack_name = arg;
        }

        if (!pack_name)
                usage(index_pack_usage);
        if (!index_name) {
                int len = strlen(pack_name);
                if (len < 5 || strcmp(pack_name + len - 5, ".pack"))
                        die("packfile name '%s' does not end with '.pack'",
                            pack_name);
                index_name_buf = xmalloc(len);
                memcpy(index_name_buf, pack_name, len - 5);
                strcpy(index_name_buf + len - 5, ".idx");
                index_name = index_name_buf;
        }

        open_pack_file();
        parse_pack_header();
        objects = xcalloc(nr_objects, sizeof(struct object_entry));
        deltas = xcalloc(nr_objects, sizeof(struct delta_entry));
        parse_pack_objects();
        free(deltas);
        write_index_file(index_name, sha1);
        free(objects);
        free(index_name_buf);

        printf("%s\n", sha1_to_hex(sha1));

        return 0;
}