[PATCH/WIP v2 04/19] am: implement patch queue mechanism

@@ -6,6 +6,154 @@
 #include "cache.h"
 #include "builtin.h"
 #include "exec_cmd.h"
+#include "parse-options.h"
+#include "dir.h"
+
+struct am_state {
+	/* state directory path */
+	struct strbuf dir;
+
+	/* current and last patch numbers, 1-indexed */
+	int cur;
+	int last;
+};
+
+/**
+ * Initializes am_state with the default values.
+ */
+static void am_state_init(struct am_state *state)
+{
+	memset(state, 0, sizeof(*state));
+
+	strbuf_init(&state->dir, 0);
+}
+
+/**
+ * Release memory allocated by an am_state.
+ */
+static void am_state_release(struct am_state *state)
+{
+	strbuf_release(&state->dir);
+}
+
+/**
+ * Returns path relative to the am_state directory.
+ */
+static inline const char *am_path(const struct am_state *state, const char *path)
+{
+	return mkpath("%s/%s", state->dir.buf, path);
+}
+
+/**
+ * Returns 1 if there is an am session in progress, 0 otherwise.
+ */
+static int am_in_progress(const struct am_state *state)
+{
+	struct stat st;
+
+	if (lstat(state->dir.buf, &st) < 0 || !S_ISDIR(st.st_mode))
+		return 0;
+	if (lstat(am_path(state, "last"), &st) || !S_ISREG(st.st_mode))
+		return 0;
+	if (lstat(am_path(state, "next"), &st) || !S_ISREG(st.st_mode))
+		return 0;
+	return 1;
+}
+
+/**
+ * Reads the contents of `file`. The third argument can be used to give a hint
+ * about the file size, to avoid reallocs. Returns number of bytes read on
+ * success, -1 if the file does not exist. If trim is set, trailing whitespace
+ * will be removed from the file contents.
+ */
+static int read_state_file(struct strbuf *sb, const char *file, size_t hint, int trim)
+{
+	strbuf_reset(sb);
+	if (strbuf_read_file(sb, file, hint) >= 0) {
+		if (trim)
+			strbuf_rtrim(sb);
+
+		return sb->len;
+	}
+
+	if (errno == ENOENT)
+		return -1;
+
+	die_errno(_("could not read '%s'"), file);
+}
+
+/**
+ * Loads state from disk.
+ */
+static void am_load(struct am_state *state)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	read_state_file(&sb, am_path(state, "next"), 8, 1);
+	state->cur = strtol(sb.buf, NULL, 10);
+
+	read_state_file(&sb, am_path(state, "last"), 8, 1);
+	state->last = strtol(sb.buf, NULL, 10);
+
+	strbuf_release(&sb);
+}
+
+/**
+ * Remove the am_state directory.
+ */
+static void am_destroy(const struct am_state *state)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	strbuf_addstr(&sb, state->dir.buf);
+	remove_dir_recursively(&sb, 0);
+	strbuf_release(&sb);
+}
+
+/**
+ * Setup a new am session for applying patches
+ */
+static void am_setup(struct am_state *state)
+{
+	if (mkdir(state->dir.buf, 0777) < 0 && errno != EEXIST)
+		die_errno(_("failed to create directory '%s'"), state->dir.buf);
+
+	write_file(am_path(state, "next"), 1, "%d", state->cur);
+
+	write_file(am_path(state, "last"), 1, "%d", state->last);
+}
+
+/**
+ * Increments the patch pointer, and cleans am_state for the application of the
+ * next patch.
+ */
+static void am_next(struct am_state *state)
+{
+	state->cur++;
+	write_file(am_path(state, "next"), 1, "%d", state->cur);
+}
+
+/**
+ * Applies all queued patches.
+ */
+static void am_run(struct am_state *state)
+{
+	while (state->cur <= state->last)
+		am_next(state);
+
+	am_destroy(state);
+}
+
+static struct am_state state;
+
+static const char * const am_usage[] = {
+	N_("git am [options] [(<mbox>|<Maildir>)...]"),
+	NULL
+};
+
+static struct option am_options[] = {
+	OPT_END()
+};
 
 int cmd_am(int argc, const char **argv, const char *prefix)
 {

@@ -16,5 +164,21 @@ int cmd_am(int argc, const char **argv, const char *prefix)
 			die_errno("could not exec %s", path);
 	}
 
+	git_config(git_default_config, NULL);
+
+	am_state_init(&state);
+	strbuf_addstr(&state.dir, git_path("rebase-apply"));
+
+	argc = parse_options(argc, argv, prefix, am_options, am_usage, 0);
+
+	if (am_in_progress(&state))
+		am_load(&state);
+	else
+		am_setup(&state);
+
+	am_run(&state);
+
+	am_state_release(&state);
+
 	return 0;
 }