#include "cache.h"
#include "refs.h"
#include "strbuf.h"
#include "worktree.h"

static char *find_linked_symref(const char *symref, const char *branch,
				const char *id)
{
	struct strbuf sb = STRBUF_INIT;
	struct strbuf path = STRBUF_INIT;
	struct strbuf gitdir = STRBUF_INIT;
	char *existing = NULL;

	/*
	 * $GIT_COMMON_DIR/$symref (e.g. HEAD) is practically outside
	 * $GIT_DIR so resolve_ref_unsafe() won't work (it uses
	 * git_path). Parse the ref ourselves.
	 */
	if (id)
		strbuf_addf(&path, "%s/worktrees/%s/%s", get_git_common_dir(), id, symref);
	else
		strbuf_addf(&path, "%s/%s", get_git_common_dir(), symref);

	if (!strbuf_readlink(&sb, path.buf, 0)) {
		if (!starts_with(sb.buf, "refs/") ||
		    check_refname_format(sb.buf, 0))
			goto done;
	} else if (strbuf_read_file(&sb, path.buf, 0) >= 0 &&
	    starts_with(sb.buf, "ref:")) {
		strbuf_remove(&sb, 0, strlen("ref:"));
		strbuf_trim(&sb);
	} else
		goto done;
	if (strcmp(sb.buf, branch))
		goto done;
	if (id) {
		strbuf_reset(&path);
		strbuf_addf(&path, "%s/worktrees/%s/gitdir", get_git_common_dir(), id);
		if (strbuf_read_file(&gitdir, path.buf, 0) <= 0)
			goto done;
		strbuf_rtrim(&gitdir);
	} else
		strbuf_addstr(&gitdir, get_git_common_dir());
	strbuf_strip_suffix(&gitdir, ".git");

	existing = strbuf_detach(&gitdir, NULL);
done:
	strbuf_release(&path);
	strbuf_release(&sb);
	strbuf_release(&gitdir);

	return existing;
}

char *find_shared_symref(const char *symref, const char *target)
{
	struct strbuf path = STRBUF_INIT;
	DIR *dir;
	struct dirent *d;
	char *existing;

	if ((existing = find_linked_symref(symref, target, NULL)))
		return existing;

	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
	dir = opendir(path.buf);
	strbuf_release(&path);
	if (!dir)
		return NULL;

	while ((d = readdir(dir)) != NULL) {
		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
			continue;
		existing = find_linked_symref(symref, target, d->d_name);
		if (existing)
			goto done;
	}
done:
	closedir(dir);

	return existing;
}