#include "cache.h"
#include "tree-walk.h"
#include "tree.h"

static const char *get_mode(const char *str, unsigned int *modep)
{
        unsigned char c;
        unsigned int mode = 0;

        if (*str == ' ')
                return NULL;

        while ((c = *str++) != ' ') {
                if (c < '0' || c > '7')
                        return NULL;
                mode = (mode << 3) + (c - '0');
        }
        *modep = mode;
        return str;
}

static void decode_tree_entry(struct tree_desc *desc, const char *buf, unsigned long size)
{
        const char *path;
        unsigned int mode, len;

        if (size < 24 || buf[size - 21])
                die("corrupt tree file");

        path = get_mode(buf, &mode);
        if (!path || !*path)
                die("corrupt tree file");
        len = strlen(path) + 1;

        /* Initialize the descriptor entry */
        desc->entry.path = path;
        desc->entry.mode = mode;
        desc->entry.sha1 = (const unsigned char *)(path + len);
}

void init_tree_desc(struct tree_desc *desc, const void *buffer, unsigned long size)
{
        desc->buffer = buffer;
        desc->size = size;
        if (size)
                decode_tree_entry(desc, buffer, size);
}

void *fill_tree_descriptor(struct tree_desc *desc, const unsigned char *sha1)
{
        unsigned long size = 0;
        void *buf = NULL;

        if (sha1) {
                buf = read_object_with_reference(sha1, tree_type, &size, NULL);
                if (!buf)
                        die("unable to read tree %s", sha1_to_hex(sha1));
        }
        init_tree_desc(desc, buf, size);
        return buf;
}

static void entry_clear(struct name_entry *a)
{
        memset(a, 0, sizeof(*a));
}

static void entry_extract(struct tree_desc *t, struct name_entry *a)
{
        *a = t->entry;
}

void update_tree_entry(struct tree_desc *desc)
{
        const void *buf = desc->buffer;
        const unsigned char *end = desc->entry.sha1 + 20;
        unsigned long size = desc->size;
        unsigned long len = end - (const unsigned char *)buf;

        if (size < len)
                die("corrupt tree file");
        buf = end;
        size -= len;
        desc->buffer = buf;
        desc->size = size;
        if (size)
                decode_tree_entry(desc, buf, size);
}

int tree_entry(struct tree_desc *desc, struct name_entry *entry)
{
        if (!desc->size)
                return 0;

        *entry = desc->entry;
        update_tree_entry(desc);
        return 1;
}

void setup_traverse_info(struct traverse_info *info, const char *base)
{
        int pathlen = strlen(base);
        static struct traverse_info dummy;

        memset(info, 0, sizeof(*info));
        if (pathlen && base[pathlen-1] == '/')
                pathlen--;
        info->pathlen = pathlen ? pathlen + 1 : 0;
        info->name.path = base;
        info->name.sha1 = (void *)(base + pathlen + 1);
        if (pathlen)
                info->prev = &dummy;
}

char *make_traverse_path(char *path, const struct traverse_info *info, const struct name_entry *n)
{
        int len = tree_entry_len(n->path, n->sha1);
        int pathlen = info->pathlen;

        path[pathlen + len] = 0;
        for (;;) {
                memcpy(path + pathlen, n->path, len);
                if (!pathlen)
                        break;
                path[--pathlen] = '/';
                n = &info->name;
                len = tree_entry_len(n->path, n->sha1);
                info = info->prev;
                pathlen -= len;
        }
        return path;
}

struct tree_desc_skip {
        struct tree_desc_skip *prev;
        const void *ptr;
};

struct tree_desc_x {
        struct tree_desc d;
        struct tree_desc_skip *skip;
};

static int name_compare(const char *a, int a_len,
                        const char *b, int b_len)
{
        int len = (a_len < b_len) ? a_len : b_len;
        int cmp = memcmp(a, b, len);
        if (cmp)
                return cmp;
        return (a_len - b_len);
}

static int check_entry_match(const char *a, int a_len, const char *b, int b_len)
{
        /*
         * The caller wants to pick *a* from a tree or nothing.
         * We are looking at *b* in a tree.
         *
         * (0) If a and b are the same name, we are trivially happy.
         *
         * There are three possibilities where *a* could be hiding
         * behind *b*.
         *
         * (1) *a* == "t",   *b* == "ab"  i.e. *b* sorts earlier than *a* no
         *                                matter what.
         * (2) *a* == "t",   *b* == "t-2" and "t" is a subtree in the tree;
         * (3) *a* == "t-2", *b* == "t"   and "t-2" is a blob in the tree.
         *
         * Otherwise we know *a* won't appear in the tree without
         * scanning further.
         */

        int cmp = name_compare(a, a_len, b, b_len);

        /* Most common case first -- reading sync'd trees */
        if (!cmp)
                return cmp;

        if (0 < cmp) {
                /* a comes after b; it does not matter if it is case (3)
                if (b_len < a_len && !memcmp(a, b, b_len) && a[b_len] < '/')
                        return 1;
                */
                return 1; /* keep looking */
        }

        /* b comes after a; are we looking at case (2)? */
        if (a_len < b_len && !memcmp(a, b, a_len) && b[a_len] < '/')
                return 1; /* keep looking */

        return -1; /* a cannot appear in the tree */
}

/*
 * From the extended tree_desc, extract the first name entry, while
 * paying attention to the candidate "first" name.  Most importantly,
 * when looking for an entry, if there are entries that sorts earlier
 * in the tree object representation than that name, skip them and
 * process the named entry first.  We will remember that we haven't
 * processed the first entry yet, and in the later call skip the
 * entry we processed early when update_extended_entry() is called.
 *
 * E.g. if the underlying tree object has these entries:
 *
 *    blob    "t-1"
 *    blob    "t-2"
 *    tree    "t"
 *    blob    "t=1"
 *
 * and the "first" asks for "t", remember that we still need to
 * process "t-1" and "t-2" but extract "t".  After processing the
 * entry "t" from this call, the caller will let us know by calling
 * update_extended_entry() that we can remember "t" has been processed
 * already.
 */

static void extended_entry_extract(struct tree_desc_x *t,
                                   struct name_entry *a,
                                   const char *first,
                                   int first_len)
{
        const char *path;
        int len;
        struct tree_desc probe;
        struct tree_desc_skip *skip;

        /*
         * Extract the first entry from the tree_desc, but skip the
         * ones that we already returned in earlier rounds.
         */
        while (1) {
                if (!t->d.size) {
                        entry_clear(a);
                        break; /* not found */
                }
                entry_extract(&t->d, a);
                for (skip = t->skip; skip; skip = skip->prev)
                        if (a->path == skip->ptr)
                                break; /* found */
                if (!skip)
                        break;
                /* We have processed this entry already. */
                update_tree_entry(&t->d);
        }

        if (!first || !a->path)
                return;

        /*
         * The caller wants "first" from this tree, or nothing.
         */
        path = a->path;
        len = tree_entry_len(a->path, a->sha1);
        switch (check_entry_match(first, first_len, path, len)) {
        case -1:
                entry_clear(a);
        case 0:
                return;
        default:
                break;
        }

        /*
         * We need to look-ahead -- we suspect that a subtree whose
         * name is "first" may be hiding behind the current entry "path".
         */
        probe = t->d;
        while (probe.size) {
                entry_extract(&probe, a);
                path = a->path;
                len = tree_entry_len(a->path, a->sha1);
                switch (check_entry_match(first, first_len, path, len)) {
                case -1:
                        entry_clear(a);
                case 0:
                        return;
                default:
                        update_tree_entry(&probe);
                        break;
                }
                /* keep looking */
        }
        entry_clear(a);
}

static void update_extended_entry(struct tree_desc_x *t, struct name_entry *a)
{
        if (t->d.entry.path == a->path) {
                update_tree_entry(&t->d);
        } else {
                /* we have returned this entry early */
                struct tree_desc_skip *skip = xmalloc(sizeof(*skip));
                skip->ptr = a->path;
                skip->prev = t->skip;
                t->skip = skip;
        }
}

static void free_extended_entry(struct tree_desc_x *t)
{
        struct tree_desc_skip *p, *s;

        for (s = t->skip; s; s = p) {
                p = s->prev;
                free(s);
        }
}

int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
{
        int ret = 0;
        struct name_entry *entry = xmalloc(n*sizeof(*entry));
        int i;
        struct tree_desc_x *tx = xcalloc(n, sizeof(*tx));

        for (i = 0; i < n; i++)
                tx[i].d = t[i];

        for (;;) {
                unsigned long mask, dirmask;
                const char *first = NULL;
                int first_len = 0;
                struct name_entry *e;
                int len;

                for (i = 0; i < n; i++) {
                        e = entry + i;
                        extended_entry_extract(tx + i, e, NULL, 0);
                }

                /*
                 * A tree may have "t-2" at the current location even
                 * though it may have "t" that is a subtree behind it,
                 * and another tree may return "t".  We want to grab
                 * all "t" from all trees to match in such a case.
                 */
                for (i = 0; i < n; i++) {
                        e = entry + i;
                        if (!e->path)
                                continue;
                        len = tree_entry_len(e->path, e->sha1);
                        if (!first) {
                                first = e->path;
                                first_len = len;
                                continue;
                        }
                        if (name_compare(e->path, len, first, first_len) < 0) {
                                first = e->path;
                                first_len = len;
                        }
                }

                if (first) {
                        for (i = 0; i < n; i++) {
                                e = entry + i;
                                extended_entry_extract(tx + i, e, first, first_len);
                                /* Cull the ones that are not the earliest */
                                if (!e->path)
                                        continue;
                                len = tree_entry_len(e->path, e->sha1);
                                if (name_compare(e->path, len, first, first_len))
                                        entry_clear(e);
                        }
                }

                /* Now we have in entry[i] the earliest name from the trees */
                mask = 0;
                dirmask = 0;
                for (i = 0; i < n; i++) {
                        if (!entry[i].path)
                                continue;
                        mask |= 1ul << i;
                        if (S_ISDIR(entry[i].mode))
                                dirmask |= 1ul << i;
                }
                if (!mask)
                        break;
                ret = info->fn(n, mask, dirmask, entry, info);
                if (ret < 0)
                        break;
                mask &= ret;
                ret = 0;
                for (i = 0; i < n; i++)
                        if (mask & (1ul << i))
                                update_extended_entry(tx + i, entry + i);
        }
        free(entry);
        for (i = 0; i < n; i++)
                free_extended_entry(tx + i);
        free(tx);
        return ret;
}

static int find_tree_entry(struct tree_desc *t, const char *name, unsigned char *result, unsigned *mode)
{
        int namelen = strlen(name);
        while (t->size) {
                const char *entry;
                const unsigned char *sha1;
                int entrylen, cmp;

                sha1 = tree_entry_extract(t, &entry, mode);
                update_tree_entry(t);
                entrylen = tree_entry_len(entry, sha1);
                if (entrylen > namelen)
                        continue;
                cmp = memcmp(name, entry, entrylen);
                if (cmp > 0)
                        continue;
                if (cmp < 0)
                        break;
                if (entrylen == namelen) {
                        hashcpy(result, sha1);
                        return 0;
                }
                if (name[entrylen] != '/')
                        continue;
                if (!S_ISDIR(*mode))
                        break;
                if (++entrylen == namelen) {
                        hashcpy(result, sha1);
                        return 0;
                }
                return get_tree_entry(sha1, name + entrylen, result, mode);
        }
        return -1;
}

int get_tree_entry(const unsigned char *tree_sha1, const char *name, unsigned char *sha1, unsigned *mode)
{
        int retval;
        void *tree;
        unsigned long size;
        struct tree_desc t;
        unsigned char root[20];

        tree = read_object_with_reference(tree_sha1, tree_type, &size, root);
        if (!tree)
                return -1;

        if (name[0] == '\0') {
                hashcpy(sha1, root);
                free(tree);
                return 0;
        }

        init_tree_desc(&t, tree, size);
        retval = find_tree_entry(&t, name, sha1, mode);
        free(tree);
        return retval;
}