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

static const char pack_usage[] = "git-pack-objects [--window=N] base-name < object-list";

enum object_type {
        OBJ_NONE,
        OBJ_COMMIT,
        OBJ_TREE,
        OBJ_BLOB,
        OBJ_DELTA       // NOTE! This is _not_ the same as a "delta" object in the filesystem
};

struct object_entry {
        unsigned char sha1[20];
        unsigned long size;
        unsigned long offset;
        unsigned int depth;
        unsigned int flags;
        enum object_type type;
        unsigned long delta_size;
        struct object_entry *delta;
};

static struct object_entry **sorted_by_sha, **sorted_by_type;
static struct object_entry *objects = NULL;
static int nr_objects = 0, nr_alloc = 0;
static int delta_window = 10;
static const char *base_name;

struct myfile {
        int fd;
        unsigned long chars;
        unsigned char buffer[8192];
};

static FILE *create_file(const char *suffix)
{
        static char filename[PATH_MAX];
        unsigned len;

        len = snprintf(filename, PATH_MAX, "%s.%s", base_name, suffix);
        if (len >= PATH_MAX)
                die("you wascally wabbit, you");
        return fopen(filename, "w");
}

static unsigned long fwrite_compressed(void *in, unsigned long size, FILE *f)
{
        z_stream stream;
        unsigned long maxsize;
        void *out;

        memset(&stream, 0, sizeof(stream));
        deflateInit(&stream, Z_DEFAULT_COMPRESSION);
        maxsize = deflateBound(&stream, size);
        out = xmalloc(maxsize);

        /* Compress it */
        stream.next_in = in;
        stream.avail_in = size;

        stream.next_out = out;
        stream.avail_out = maxsize;

        while (deflate(&stream, Z_FINISH) == Z_OK)
                /* nothing */;
        deflateEnd(&stream);

        size = stream.total_out;
        fwrite(out, size, 1, f);
        free(out);
        return size;
}

static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
{
        unsigned long othersize, delta_size;
        char type[10];
        void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
        void *delta_buf;

        if (!otherbuf)
                die("unable to read %s", sha1_to_hex(entry->delta->sha1));
        delta_buf = diff_delta(buf, size, otherbuf, othersize, &delta_size);
        if (delta_size != entry->delta_size)
                die("delta size changed");
        free(buf);
        free(otherbuf);
        return delta_buf;
}

static unsigned long write_object(FILE *f, struct object_entry *entry)
{
        unsigned long size;
        char type[10];
        void *buf = read_sha1_file(entry->sha1, type, &size);
        char header[21];
        unsigned hdrlen, datalen;

        if (!buf)
                die("unable to read %s", sha1_to_hex(entry->sha1));
        if (size != entry->size)
                die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);

        /*
         * The object header is a byte of 'type' followed by four bytes of
         * length, except for deltas that has the 20 bytes of delta sha
         * instead.
         */
        header[0] = ".CTB"[entry->type];
        datalen = htonl(size);
        memcpy(header+1, &datalen, 4);
        hdrlen = 5;
        if (entry->delta) {
                header[0] = 'D';
                memcpy(header+1, entry->delta, 20);
                buf = delta_against(buf, size, entry);
                size = entry->delta_size;
                hdrlen = 21;
        }
        fwrite(header, hdrlen, 1, f);
        datalen = fwrite_compressed(buf, size, f);
        free(buf);
        return hdrlen + datalen;
}

static void write_pack_file(void)
{
        int i;
        FILE *f = create_file("pack");
        unsigned long offset = 0;
        unsigned long mb;

        for (i = 0; i < nr_objects; i++) {
                struct object_entry *entry = objects + i;
                entry->offset = offset;
                offset += write_object(f, entry);
        }
        fclose(f);
        mb = offset >> 20;
        offset &= 0xfffff;
}

static void write_index_file(void)
{
        int i;
        FILE *f = create_file("idx");
        struct object_entry **list = sorted_by_sha;
        struct object_entry **last = list + nr_objects;
        unsigned int array[256];

        /*
         * 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 *entry = *next;
                        if (entry->sha1[0] != i)
                                break;
                        next++;
                }
                array[i] = htonl(next - sorted_by_sha);
                list = next;
        }
        fwrite(array, 256, sizeof(int), f);

        /*
         * Write the actual SHA1 entries..
         */
        list = sorted_by_sha;
        for (i = 0; i < nr_objects; i++) {
                struct object_entry *entry = *list++;
                unsigned int offset = htonl(entry->offset);
                fwrite(&offset, 4, 1, f);
                fwrite(entry->sha1, 20, 1, f);
        }
        fclose(f);
}

static void add_object_entry(unsigned char *sha1)
{
        unsigned int idx = nr_objects;
        struct object_entry *entry;

        if (idx >= nr_alloc) {
                unsigned int needed = (idx + 1024) * 3 / 2;
                objects = xrealloc(objects, needed * sizeof(*entry));
                nr_alloc = needed;
        }
        entry = objects + idx;
        memset(entry, 0, sizeof(*entry));
        memcpy(entry->sha1, sha1, 20);
        nr_objects = idx+1;
}

static void check_object(struct object_entry *entry)
{
        char buffer[128];
        char type[10];
        unsigned long mapsize;
        z_stream stream;
        void *map;

        map = map_sha1_file(entry->sha1, &mapsize);
        if (!map)
                die("unable to map %s", sha1_to_hex(entry->sha1));
        if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0)
                die("unable to unpack %s header", sha1_to_hex(entry->sha1));
        munmap(map, mapsize);
        if (parse_sha1_header(buffer, type, &entry->size) < 0)
                die("unable to parse %s header", sha1_to_hex(entry->sha1));
        if (!strcmp(type, "commit")) {
                entry->type = OBJ_COMMIT;
        } else if (!strcmp(type, "tree")) {
                entry->type = OBJ_TREE;
        } else if (!strcmp(type, "blob")) {
                entry->type = OBJ_BLOB;
        } else
                die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type);
}

static void get_object_details(void)
{
        int i;
        struct object_entry *entry = objects;

        for (i = 0; i < nr_objects; i++)
                check_object(entry++);
}

typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);

static entry_sort_t current_sort;

static int sort_comparator(const void *_a, const void *_b)
{
        struct object_entry *a = *(struct object_entry **)_a;
        struct object_entry *b = *(struct object_entry **)_b;
        return current_sort(a,b);
}

static struct object_entry **create_sorted_list(entry_sort_t sort)
{
        struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
        int i;

        for (i = 0; i < nr_objects; i++)
                list[i] = objects + i;
        current_sort = sort;
        qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
        return list;
}

static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
{
        return memcmp(a->sha1, b->sha1, 20);
}

static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
{
        if (a->type < b->type)
                return -1;
        if (a->type > b->type)
                return 1;
        if (a->size < b->size)
                return -1;
        if (a->size > b->size)
                return 1;
        return a < b ? -1 : (a > b);
}

struct unpacked {
        struct object_entry *entry;
        void *data;
};

/*
 * We search for deltas in a list sorted by type and by size, and
 * walk the "old" chain backwards in the list, so if the type
 * has changed or the size difference is too big, there's no point
 * in even continuing the walk, since the other old objects are
 * going to be even smaller or of a different type. So return -1
 * once we determine that there's no point even trying.
 */
static int try_delta(struct unpacked *cur, struct unpacked *old)
{
        struct object_entry *cur_entry = cur->entry;
        struct object_entry *old_entry = old->entry;
        unsigned long size, oldsize, delta_size;
        void *delta_buf;

        /* Don't bother doing diffs between different types */
        if (cur_entry->type != old_entry->type)
                return -1;

        /* Size is guaranteed to be larger than or equal to oldsize */
        size = cur_entry->size;
        oldsize = old_entry->size;
        if (size - oldsize > oldsize / 4)
                return -1;

        /*
         * NOTE!
         *
         * We always delta from the bigger to the smaller, since that's
         * more space-efficient (deletes don't have to say _what_ they
         * delete).
         */
        delta_buf = diff_delta(cur->data, size, old->data, oldsize, &delta_size);
        if (!delta_buf)
                die("unable to create delta");
        if (delta_size + 20 < size / 2) {
                if (!cur_entry->delta || cur_entry->delta_size > delta_size) {
                        cur_entry->delta = old_entry;
                        cur_entry->delta_size = delta_size;
                }
        }
        free(delta_buf);
        return 0;
}

static void find_deltas(struct object_entry **list, int window)
{
        unsigned int i;
        unsigned int array_size = window * sizeof(struct unpacked);
        struct unpacked *array = xmalloc(array_size);

        memset(array, 0, array_size);
        for (i = 0; i < nr_objects; i++) {
                unsigned int idx = i % window;
                struct object_entry *entry = list[i];
                struct unpacked *n = array + idx;
                unsigned long size;
                char type[10];
                int j;

                free(n->data);
                n->entry = entry;
                n->data = read_sha1_file(entry->sha1, type, &size);
                if (size != entry->size)
                        die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
                for (j = 0; j < window; j++) {
                        unsigned int other_idx = idx - 1 - j;
                        struct unpacked *m;
                        if (other_idx < 0)
                                other_idx += window;
                        m = array + other_idx;
                        if (!m->entry)
                                break;
                        if (try_delta(n, m) < 0)
                                break;
                }
        }
}

int main(int argc, char **argv)
{
        char line[128];
        int i;

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

                if (*arg == '-') {
                        if (!strncmp("--window=", arg, 9)) {
                                char *end;
                                delta_window = strtoul(arg+9, &end, 0);
                                if (!arg[9] || *end)
                                        usage(pack_usage);
                                continue;
                        }
                        usage(pack_usage);
                }
                if (base_name)
                        usage(pack_usage);
                base_name = arg;
        }

        if (!base_name)
                usage(pack_usage);

        while (fgets(line, sizeof(line), stdin) != NULL) {
                unsigned char sha1[20];
                if (get_sha1_hex(line, sha1))
                        die("expected sha1, got garbage");
                add_object_entry(sha1);
        }
        get_object_details();

        printf("Packing %d objects\n", nr_objects);

        sorted_by_sha = create_sorted_list(sha1_sort);
        sorted_by_type = create_sorted_list(type_size_sort);
        if (delta_window)
                find_deltas(sorted_by_type, delta_window);

        write_pack_file();
        write_index_file();
        return 0;
}