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

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

static int entry_compare(struct name_entry *a, struct name_entry *b)
{
	return base_name_compare(
			a->path, a->pathlen, a->mode,
			b->path, b->pathlen, b->mode);
}

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->sha1 = tree_entry_extract(t, &a->path, &a->mode);
	a->pathlen = strlen(a->path);
}

void update_tree_entry(struct tree_desc *desc)
{
	void *buf = desc->buf;
	unsigned long size = desc->size;
	int len = strlen(buf) + 1 + 20;

	if (size < len)
		die("corrupt tree file");
	desc->buf = buf + len;
	desc->size = size - len;
}

const unsigned char *tree_entry_extract(struct tree_desc *desc, const char **pathp, unsigned int *modep)
{
	void *tree = desc->buf;
	unsigned long size = desc->size;
	int len = strlen(tree)+1;
	const unsigned char *sha1 = tree + len;
	const char *path = strchr(tree, ' ');
	unsigned int mode;

	if (!path || size < len + 20 || sscanf(tree, "%o", &mode) != 1)
		die("corrupt tree file");
	*pathp = path+1;
	*modep = canon_mode(mode);
	return sha1;
}

void traverse_trees(int n, struct tree_desc *t, const char *base, traverse_callback_t callback)
{
	struct name_entry *entry = xmalloc(n*sizeof(*entry));

	for (;;) {
		struct name_entry entry[3];
		unsigned long mask = 0;
		int i, last;

		last = -1;
		for (i = 0; i < n; i++) {
			if (!t[i].size)
				continue;
			entry_extract(t+i, entry+i);
			if (last >= 0) {
				int cmp = entry_compare(entry+i, entry+last);

				/*
				 * Is the new name bigger than the old one?
				 * Ignore it
				 */
				if (cmp > 0)
					continue;
				/*
				 * Is the new name smaller than the old one?
				 * Ignore all old ones
				 */
				if (cmp < 0)
					mask = 0;
			}
			mask |= 1ul << i;
			last = i;
		}
		if (!mask)
			break;

		/*
		 * Update the tree entries we've walked, and clear
		 * all the unused name-entries.
		 */
		for (i = 0; i < n; i++) {
			if (mask & (1ul << i)) {
				update_tree_entry(t+i);
				continue;
			}
			entry_clear(entry + i);
		}
		callback(n, mask, entry, base);
	}
	free(entry);
}