[PATCH/RFC/GSoC 05/17] rebase-options: implement rebase_options_load() and rebase_options_save()

[Paul Tan <pyokagan@gmail.com>]

These functions can be used for loading and saving common rebase options
into a state directory.

Signed-off-by: Paul Tan <pyokagan@gmail.com>
---
 rebase-common.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 rebase-common.h |  4 ++++
 2 files changed, 73 insertions(+)

diff --git a/rebase-common.c b/rebase-common.c
index 5a49ac4..1835f08 100644
--- a/rebase-common.c
+++ b/rebase-common.c
@@ -26,3 +26,72 @@ void rebase_options_swap(struct rebase_options *dst, struct rebase_options *src)
 	*dst = *src;
 	*src = tmp;
 }
+
+static int state_file_exists(const char *dir, const char *file)
+{
+	return file_exists(mkpath("%s/%s", dir, file));
+}
+
+static int read_state_file(struct strbuf *sb, const char *dir, const char *file)
+{
+	const char *path = mkpath("%s/%s", dir, file);
+	strbuf_reset(sb);
+	if (strbuf_read_file(sb, path, 0) >= 0)
+		return sb->len;
+	else
+		return error(_("could not read '%s'"), path);
+}
+
+int rebase_options_load(struct rebase_options *opts, const char *dir)
+{
+	struct strbuf sb = STRBUF_INIT;
+	const char *filename;
+
+	/* opts->orig_refname */
+	if (read_state_file(&sb, dir, "head-name") < 0)
+		return -1;
+	strbuf_trim(&sb);
+	if (starts_with(sb.buf, "refs/heads/"))
+		opts->orig_refname = strbuf_detach(&sb, NULL);
+	else if (!strcmp(sb.buf, "detached HEAD"))
+		opts->orig_refname = NULL;
+	else
+		return error(_("could not parse %s"), mkpath("%s/%s", dir, "head-name"));
+
+	/* opts->onto */
+	if (read_state_file(&sb, dir, "onto") < 0)
+		return -1;
+	strbuf_trim(&sb);
+	if (get_oid_hex(sb.buf, &opts->onto) < 0)
+		return error(_("could not parse %s"), mkpath("%s/%s", dir, "onto"));
+
+	/*
+	 * We always write to orig-head, but interactive rebase used to write
+	 * to head. Fall back to reading from head to cover for the case that
+	 * the user upgraded git with an ongoing interactive rebase.
+	 */
+	filename = state_file_exists(dir, "orig-head") ? "orig-head" : "head";
+	if (read_state_file(&sb, dir, filename) < 0)
+		return -1;
+	strbuf_trim(&sb);
+	if (get_oid_hex(sb.buf, &opts->orig_head) < 0)
+		return error(_("could not parse %s"), mkpath("%s/%s", dir, filename));
+
+	strbuf_release(&sb);
+	return 0;
+}
+
+static int write_state_text(const char *dir, const char *file, const char *string)
+{
+	return write_file(mkpath("%s/%s", dir, file), "%s", string);
+}
+
+void rebase_options_save(const struct rebase_options *opts, const char *dir)
+{
+	const char *head_name = opts->orig_refname;
+	if (!head_name)
+		head_name = "detached HEAD";
+	write_state_text(dir, "head-name", head_name);
+	write_state_text(dir, "onto", oid_to_hex(&opts->onto));
+	write_state_text(dir, "orig-head", oid_to_hex(&opts->orig_head));
+}
diff --git a/rebase-common.h b/rebase-common.h
index db5146a..051c056 100644
--- a/rebase-common.h
+++ b/rebase-common.h
@@ -20,4 +20,8 @@ void rebase_options_release(struct rebase_options *);
 
 void rebase_options_swap(struct rebase_options *dst, struct rebase_options *src);
 
+int rebase_options_load(struct rebase_options *, const char *dir);
+
+void rebase_options_save(const struct rebase_options *, const char *dir);
+
 #endif /* REBASE_COMMON_H */
-- 
2.7.0