#include "cache.h"
#include "pack.h"
#include "pack-revindex.h"

struct idx_entry
{
        off_t                offset;
        const unsigned char *sha1;
        unsigned int nr;
};

static int compare_entries(const void *e1, const void *e2)
{
        const struct idx_entry *entry1 = e1;
        const struct idx_entry *entry2 = e2;
        if (entry1->offset < entry2->offset)
                return -1;
        if (entry1->offset > entry2->offset)
                return 1;
        return 0;
}

int check_pack_crc(struct packed_git *p, struct pack_window **w_curs,
                   off_t offset, off_t len, unsigned int nr)
{
        const uint32_t *index_crc;
        uint32_t data_crc = crc32(0, Z_NULL, 0);

        do {
                unsigned int avail;
                void *data = use_pack(p, w_curs, offset, &avail);
                if (avail > len)
                        avail = len;
                data_crc = crc32(data_crc, data, avail);
                offset += avail;
                len -= avail;
        } while (len);

        index_crc = p->index_data;
        index_crc += 2 + 256 + p->num_objects * (20/4) + nr;

        return data_crc != ntohl(*index_crc);
}

static int verify_packfile(struct packed_git *p,
                struct pack_window **w_curs)
{
        off_t index_size = p->index_size;
        const unsigned char *index_base = p->index_data;
        git_SHA_CTX ctx;
        unsigned char sha1[20], *pack_sig;
        off_t offset = 0, pack_sig_ofs = 0;
        uint32_t nr_objects, i;
        int err = 0;
        struct idx_entry *entries;

        /* Note that the pack header checks are actually performed by
         * use_pack when it first opens the pack file.  If anything
         * goes wrong during those checks then the call will die out
         * immediately.
         */

        git_SHA1_Init(&ctx);
        do {
                unsigned int remaining;
                unsigned char *in = use_pack(p, w_curs, offset, &remaining);
                offset += remaining;
                if (!pack_sig_ofs)
                        pack_sig_ofs = p->pack_size - 20;
                if (offset > pack_sig_ofs)
                        remaining -= (unsigned int)(offset - pack_sig_ofs);
                git_SHA1_Update(&ctx, in, remaining);
        } while (offset < pack_sig_ofs);
        git_SHA1_Final(sha1, &ctx);
        pack_sig = use_pack(p, w_curs, pack_sig_ofs, NULL);
        if (hashcmp(sha1, pack_sig))
                err = error("%s SHA1 checksum mismatch",
                            p->pack_name);
        if (hashcmp(index_base + index_size - 40, pack_sig))
                err = error("%s SHA1 does not match its inddex",
                            p->pack_name);
        unuse_pack(w_curs);

        /* Make sure everything reachable from idx is valid.  Since we
         * have verified that nr_objects matches between idx and pack,
         * we do not do scan-streaming check on the pack file.
         */
        nr_objects = p->num_objects;
        entries = xmalloc((nr_objects + 1) * sizeof(*entries));
        entries[nr_objects].offset = pack_sig_ofs;
        /* first sort entries by pack offset, since unpacking them is more efficient that way */
        for (i = 0; i < nr_objects; i++) {
                entries[i].sha1 = nth_packed_object_sha1(p, i);
                if (!entries[i].sha1)
                        die("internal error pack-check nth-packed-object");
                entries[i].offset = nth_packed_object_offset(p, i);
                entries[i].nr = i;
        }
        qsort(entries, nr_objects, sizeof(*entries), compare_entries);

        for (i = 0; i < nr_objects; i++) {
                void *data;
                enum object_type type;
                unsigned long size;

                if (p->index_version > 1) {
                        off_t offset = entries[i].offset;
                        off_t len = entries[i+1].offset - offset;
                        unsigned int nr = entries[i].nr;
                        if (check_pack_crc(p, w_curs, offset, len, nr))
                                err = error("index CRC mismatch for object %s "
                                            "from %s at offset %"PRIuMAX"",
                                            sha1_to_hex(entries[i].sha1),
                                            p->pack_name, (uintmax_t)offset);
                }
                data = unpack_entry(p, entries[i].offset, &type, &size);
                if (!data) {
                        err = error("cannot unpack %s from %s at offset %"PRIuMAX"",
                                    sha1_to_hex(entries[i].sha1), p->pack_name,
                                    (uintmax_t)entries[i].offset);
                        break;
                }
                if (check_sha1_signature(entries[i].sha1, data, size, typename(type))) {
                        err = error("packed %s from %s is corrupt",
                                    sha1_to_hex(entries[i].sha1), p->pack_name);
                        free(data);
                        break;
                }
                free(data);
        }
        free(entries);

        return err;
}

int verify_pack(struct packed_git *p)
{
        off_t index_size;
        const unsigned char *index_base;
        git_SHA_CTX ctx;
        unsigned char sha1[20];
        int err = 0;
        struct pack_window *w_curs = NULL;

        if (open_pack_index(p))
                return error("packfile %s index not opened", p->pack_name);
        index_size = p->index_size;
        index_base = p->index_data;

        /* Verify SHA1 sum of the index file */
        git_SHA1_Init(&ctx);
        git_SHA1_Update(&ctx, index_base, (unsigned int)(index_size - 20));
        git_SHA1_Final(sha1, &ctx);
        if (hashcmp(sha1, index_base + index_size - 20))
                err = error("Packfile index for %s SHA1 mismatch",
                            p->pack_name);

        /* Verify pack file */
        err |= verify_packfile(p, &w_curs);
        unuse_pack(&w_curs);

        return err;
}