thodg/libgit2

diff --git a/examples/.gitignore b/examples/.gitignore
index 7114939..b652e28 100644
--- a/examples/.gitignore
+++ b/examples/.gitignore
@@ -8,4 +8,5 @@ init
 log
 rev-parse
 status
+tag
 *.dSYM
diff --git a/examples/Makefile b/examples/Makefile
index 2e7f68f..e866b7f 100644
--- a/examples/Makefile
+++ b/examples/Makefile
@@ -3,7 +3,7 @@
 CC = gcc
 CFLAGS = -g -I../include -I../src -Wall -Wextra -Wmissing-prototypes -Wno-missing-field-initializers
 LFLAGS = -L../build -lgit2 -lz
-APPS = general showindex diff rev-list cat-file status log rev-parse init blame
+APPS = general showindex diff rev-list cat-file status log rev-parse init blame tag
 
 all: $(APPS)
 
diff --git a/examples/tag.c b/examples/tag.c
new file mode 100644
index 0000000..2d5a3d2
--- /dev/null
+++ b/examples/tag.c
@@ -0,0 +1,314 @@
+/*
+ * libgit2 "tag" example - shows how to list, create and delete tags
+ *
+ * Written by the libgit2 contributors
+ *
+ * To the extent possible under law, the author(s) have dedicated all copyright
+ * and related and neighboring rights to this software to the public domain
+ * worldwide. This software is distributed without any warranty.
+ *
+ * You should have received a copy of the CC0 Public Domain Dedication along
+ * with this software. If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ */
+
+#include "common.h"
+
+/**
+ * The following example partially reimplements the `git tag` command
+ * and some of its options.
+ *
+ * These commands should work:
+
+ * - Tag name listing (`tag`)
+ * - Filtered tag listing with messages (`tag -n3 -l "v0.1*"`)
+ * - Lightweight tag creation (`tag test v0.18.0`)
+ * - Tag creation (`tag -a -m "Test message" test v0.18.0`)
+ * - Tag deletion (`tag -d test`)
+ *
+ * The command line parsing logic is simplified and doesn't handle
+ * all of the use cases.
+ */
+
+/** tag_options represents the parsed command line options */
+typedef struct {
+	const char *message;
+	const char *pattern;
+	const char *tag_name;
+	const char *target;
+	int num_lines;
+	int force;
+} tag_options;
+
+/** tag_state represents the current program state for dragging around */
+typedef struct {
+	git_repository *repo;
+	tag_options *opts;
+} tag_state;
+
+/** An action to execute based on the command line arguments */
+typedef void (*tag_action)(tag_state *state);
+typedef struct args_info args_info;
+
+static void check(int result, const char *message)
+{
+	if (result) fatal(message, NULL);
+}
+
+/** Tag listing: Print individual message lines */
+static void print_list_lines(const char *message, const tag_state *state)
+{
+	const char *msg = message;
+	int num = state->opts->num_lines - 1;
+
+	if (!msg) return;
+
+	/** first line - headline */
+	while(*msg && *msg != '\n') printf("%c", *msg++);
+
+	/** skip over new lines */
+	while(*msg && *msg == '\n') msg++;
+
+	printf("\n");
+
+	/** print just headline? */
+	if (num == 0) return;
+	if (*msg && msg[1]) printf("\n");
+
+	/** print individual commit/tag lines */
+	while (*msg && num-- >= 2) {
+		printf("    ");
+
+		while (*msg && *msg != '\n') printf("%c", *msg++);
+
+		/** handle consecutive new lines */
+		if (*msg && *msg == '\n' && msg[1] == '\n') {
+			num--;
+			printf("\n");
+		}
+		while(*msg && *msg == '\n') msg++;
+
+		printf("\n");
+	}
+}
+
+/** Tag listing: Print an actual tag object */
+static void print_tag(git_tag *tag, const tag_state *state)
+{
+	printf("%-16s", git_tag_name(tag));
+
+	if (state->opts->num_lines) {
+		const char *msg = git_tag_message(tag);
+		print_list_lines(msg, state);
+	} else {
+		printf("\n");
+	}
+}
+
+/** Tag listing: Print a commit (target of a lightweight tag) */
+static void print_commit(git_commit *commit, const char *name,
+		const tag_state *state)
+{
+	printf("%-16s", name);
+
+	if (state->opts->num_lines) {
+		const char *msg = git_commit_message(commit);
+		print_list_lines(msg, state);
+	} else {
+		printf("\n");
+	}
+}
+
+/** Tag listing: Fallback, should not happen */
+static void print_name(const char *name)
+{
+	printf("%s\n", name);
+}
+
+/** Tag listing: Lookup tags based on ref name and dispatch to print */
+static int each_tag(const char *name, tag_state *state)
+{
+	git_repository *repo = state->repo;
+	git_object *obj;
+
+	check_lg2(git_revparse_single(&obj, repo, name),
+			"Failed to lookup rev", name);
+
+	switch (git_object_type(obj)) {
+		case GIT_OBJ_TAG:
+			print_tag((git_tag *) obj, state);
+			break;
+		case GIT_OBJ_COMMIT:
+			print_commit((git_commit *) obj, name, state);
+			break;
+		default:
+			print_name(name);
+	}
+
+	git_object_free(obj);
+	return 0;
+}
+
+static void action_list_tags(tag_state *state)
+{
+	const char *pattern = state->opts->pattern;
+	git_strarray tag_names = {0};
+	size_t i;
+
+	check_lg2(git_tag_list_match(&tag_names, pattern ? pattern : "*", state->repo),
+			"Unable to get list of tags", NULL);
+
+	for(i = 0; i < tag_names.count; i++) {
+		each_tag(tag_names.strings[i], state);
+	}
+
+	git_strarray_free(&tag_names);
+}
+
+static void action_delete_tag(tag_state *state)
+{
+	tag_options *opts = state->opts;
+	git_object *obj;
+	char oid[GIT_OID_HEXSZ + 1];
+
+	check(!opts->tag_name, "Name required");
+
+	check_lg2(git_revparse_single(&obj, state->repo, opts->tag_name),
+			"Failed to lookup rev", opts->tag_name);
+
+	check_lg2(git_tag_delete(state->repo, opts->tag_name),
+			"Unable to delete tag", opts->tag_name);
+
+	git_oid_tostr(oid, sizeof(oid), git_object_id(obj));
+
+	printf("Deleted tag '%s' (was %s)\n", opts->tag_name, oid);
+
+	git_object_free(obj);
+}
+
+static void action_create_lighweight_tag(tag_state *state)
+{
+	git_repository *repo = state->repo;
+	tag_options *opts = state->opts;
+	git_oid oid;
+	git_object *target;
+
+	check(!opts->tag_name, "Name required");
+
+	if (!opts->target) opts->target = "HEAD";
+
+	check(!opts->target, "Target required");
+
+	check_lg2(git_revparse_single(&target, repo, opts->target),
+			"Unable to resolve spec", opts->target);
+
+	check_lg2(git_tag_create_lightweight(&oid, repo, opts->tag_name,
+				target, opts->force), "Unable to create tag", NULL);
+
+	git_object_free(target);
+}
+
+static void action_create_tag(tag_state *state)
+{
+	git_repository *repo = state->repo;
+	tag_options *opts = state->opts;
+	git_signature *tagger;
+	git_oid oid;
+	git_object *target;
+
+	check(!opts->tag_name, "Name required");
+	check(!opts->message, "Message required");
+
+	if (!opts->target) opts->target = "HEAD";
+
+	check_lg2(git_revparse_single(&target, repo, opts->target),
+			"Unable to resolve spec", opts->target);
+
+	check_lg2(git_signature_default(&tagger, repo),
+			"Unable to create signature", NULL);
+
+	check_lg2(git_tag_create(&oid, repo, opts->tag_name,
+				target, tagger, opts->message, opts->force), "Unable to create tag", NULL);
+
+	git_object_free(target);
+	git_signature_free(tagger);
+}
+
+static void print_usage()
+{
+	fprintf(stderr, "usage: see `git help tag`\n");
+	exit(1);
+}
+
+/** Parse command line arguments and choose action to run when done */
+static void parse_options(tag_action *action, tag_options *opts, int argc, char **argv)
+{
+	args_info args = ARGS_INFO_INIT;
+	*action = &action_list_tags;
+
+	for (args.pos = 1; args.pos < argc; ++args.pos) {
+		const char *curr = argv[args.pos];
+
+		if (curr[0] != '-') {
+			if (!opts->tag_name)
+				opts->tag_name = curr;
+			else if (!opts->target)
+				opts->target = curr;
+			else
+				print_usage();
+
+			if (*action != &action_create_tag)
+				*action = &action_create_lighweight_tag;
+		} else if (!strcmp(curr, "-n")) {
+			opts->num_lines = 1;
+			*action = &action_list_tags;
+		} else if (!strcmp(curr, "-a")) {
+			*action = &action_create_tag;
+		} else if (!strcmp(curr, "-f")) {
+			opts->force = 1;
+		} else if (match_int_arg(&opts->num_lines, &args, "-n", 0)) {
+			*action = &action_list_tags;
+		} else if (match_str_arg(&opts->pattern, &args, "-l")) {
+			*action = &action_list_tags;
+		} else if (match_str_arg(&opts->tag_name, &args, "-d")) {
+			*action = &action_delete_tag;
+		} else if (match_str_arg(&opts->message, &args, "-m")) {
+			*action = &action_create_tag;
+		}
+	}
+}
+
+/** Initialize tag_options struct */
+static void tag_options_init(tag_options *opts)
+{
+	memset(opts, 0, sizeof(*opts));
+
+	opts->message   = NULL;
+	opts->pattern   = NULL;
+	opts->tag_name  = NULL;
+	opts->target    = NULL;
+	opts->num_lines = 0;
+	opts->force     = 0;
+}
+
+int main(int argc, char **argv)
+{
+	git_threads_init();
+
+	git_repository *repo;
+	check_lg2(git_repository_open_ext(&repo, ".", 0, NULL),
+			"Could not open repository", NULL);
+
+	tag_options opts;
+	tag_options_init(&opts);
+	tag_action action;
+	parse_options(&action, &opts, argc, argv);
+
+	tag_state state = {repo, &opts};
+	action(&state);
+
+	git_repository_free(repo);
+	git_threads_shutdown();
+
+	return 0;
+}