#include <ctype.h>
#include "cache.h"
#include "object.h"
#include "delta.h"
#include "csum-file.h"

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

/*
 * The object type is a single-character shorthand:
 *  - 'C' for "Commit"
 *  - 'T' for "Tree"
 *  - 'B' for "Blob"
 *  - 'G' for "taG"
 *  - 'D' for "Delta"
 */
struct object_entry {
        unsigned char sha1[20];
        unsigned long size;
        unsigned long offset;
        unsigned int depth;
        unsigned int hash;
        unsigned char 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 const char *base_name;
static unsigned char pack_file_sha1[20];

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(otherbuf, othersize,
                               buf, size, &delta_size, ~0UL);
        if (!delta_buf || delta_size != entry->delta_size)
                die("delta size changed");
        free(buf);
        free(otherbuf);
        return delta_buf;
}

static unsigned long write_object(struct sha1file *f, struct object_entry *entry)
{
        unsigned long size;
        char type[10];
        void *buf = read_sha1_file(entry->sha1, type, &size);
        char header[25];
        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] = entry->type;
        hdrlen = 5;
        if (entry->delta) {
                header[0] = 'D';
                memcpy(header+5, entry->delta, 20);
                buf = delta_against(buf, size, entry);
                size = entry->delta_size;
                hdrlen = 25;
        }
        datalen = htonl(size);
        memcpy(header+1, &datalen, 4);
        sha1write(f, header, hdrlen);
        datalen = sha1write_compressed(f, buf, size);
        free(buf);
        return hdrlen + datalen;
}

static void write_pack_file(void)
{
        int i;
        struct sha1file *f = sha1create("%s.%s", base_name, "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);
        }
        sha1close(f, pack_file_sha1, 1);
        mb = offset >> 20;
        offset &= 0xfffff;
}

static void write_index_file(void)
{
        int i;
        struct sha1file *f = sha1create("%s.%s", base_name, "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;
        }
        sha1write(f, array, 256 * sizeof(int));

        /*
         * 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);
                sha1write(f, &offset, 4);
                sha1write(f, entry->sha1, 20);
        }
        sha1write(f, pack_file_sha1, 20);
        sha1close(f, NULL, 1);
}

static void add_object_entry(unsigned char *sha1, unsigned int hash)
{
        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);
        entry->hash = hash;
        nr_objects = idx+1;
}

static void check_object(struct object_entry *entry)
{
        char type[20];

        if (!sha1_object_info(entry->sha1, type, &entry->size)) {
                if (!strcmp(type, "commit")) {
                        entry->type = 'C';
                } else if (!strcmp(type, "tree")) {
                        entry->type = 'T';
                } else if (!strcmp(type, "blob")) {
                        entry->type = 'B';
                } else if (!strcmp(type, "tag")) {
                        entry->type = 'G';
                } else
                        die("unable to pack object %s of type %s",
                            sha1_to_hex(entry->sha1), type);
        }
        else
                die("unable to get type of object %s",
                    sha1_to_hex(entry->sha1));
}

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->hash < b->hash)
                return -1;
        if (a->hash > b->hash)
                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 _backwards_ in a list sorted by type and
 * by size, so that we see progressively smaller and smaller files.
 * That's because we prefer deltas to be from the bigger file
 * to the smaller - deletes are potentially cheaper, but perhaps
 * more importantly, the bigger file is likely the more recent
 * one.
 */
static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
{
        struct object_entry *cur_entry = cur->entry;
        struct object_entry *old_entry = old->entry;
        unsigned long size, oldsize, delta_size, sizediff;
        long max_size;
        void *delta_buf;

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

        size = cur_entry->size;
        if (size < 50)
                return -1;
        oldsize = old_entry->size;
        sizediff = oldsize > size ? oldsize - size : size - oldsize;
        if (sizediff > size / 8)
                return -1;
        if (old_entry->depth >= max_depth)
                return 0;

        /*
         * 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).
         */
        max_size = size / 2 - 20;
        if (cur_entry->delta)
                max_size = cur_entry->delta_size-1;
        if (sizediff >= max_size)
                return -1;
        delta_buf = diff_delta(old->data, oldsize,
                               cur->data, size, &delta_size, max_size);
        if (!delta_buf)
                return 0;
        cur_entry->delta = old_entry;
        cur_entry->delta_size = delta_size;
        cur_entry->depth = old_entry->depth + 1;
        free(delta_buf);
        return 0;
}

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

        memset(array, 0, array_size);
        i = nr_objects;
        idx = 0;
        while (--i >= 0) {
                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);
                j = window;
                while (--j > 0) {
                        unsigned int other_idx = idx + j;
                        struct unpacked *m;
                        if (other_idx >= window)
                                other_idx -= window;
                        m = array + other_idx;
                        if (!m->entry)
                                break;
                        if (try_delta(n, m, depth) < 0)
                                break;
                }
                idx++;
                if (idx >= window)
                        idx = 0;
        }
}

int main(int argc, char **argv)
{
        char line[PATH_MAX + 20];
        int window = 10, depth = 10;
        int i;

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

                if (*arg == '-') {
                        if (!strncmp("--window=", arg, 9)) {
                                char *end;
                                window = strtoul(arg+9, &end, 0);
                                if (!arg[9] || *end)
                                        usage(pack_usage);
                                continue;
                        }
                        if (!strncmp("--depth=", arg, 8)) {
                                char *end;
                                depth = strtoul(arg+8, &end, 0);
                                if (!arg[8] || *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 int hash;
                char *p;
                unsigned char sha1[20];

                if (get_sha1_hex(line, sha1))
                        die("expected sha1, got garbage");
                hash = 0;
                p = line+40;
                while (*p) {
                        unsigned char c = *p++;
                        if (isspace(c))
                                continue;
                        hash = hash * 11 + c;
                }
                add_object_entry(sha1, hash);
        }
        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 (window && depth)
                find_deltas(sorted_by_type, window+1, depth);

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