#include <stdio.h>
#include <git2.h>
#include <stdlib.h>
#include <string.h>

static void check(int error, const char *message, const char *arg)
{
	if (!error)
		return;
	if (arg)
		fprintf(stderr, "%s '%s' (%d)\n", message, arg, error);
	else
		fprintf(stderr, "%s (%d)\n", message, error);
	exit(1);
}

static void usage(const char *message, const char *arg)
{
	if (message && arg)
		fprintf(stderr, "%s: %s\n", message, arg);
	else if (message)
		fprintf(stderr, "%s\n", message);
	fprintf(stderr, "usage: log [<options>]\n");
	exit(1);
}

struct log_state {
	git_repository *repo;
	const char *repodir;
	git_revwalk *walker;
	int hide;
	int sorting;
};

static void set_sorting(struct log_state *s, unsigned int sort_mode)
{
	if (!s->repo) {
		if (!s->repodir) s->repodir = ".";
		check(git_repository_open_ext(&s->repo, s->repodir, 0, NULL),
			"Could not open repository", s->repodir);
	}

	if (!s->walker)
		check(git_revwalk_new(&s->walker, s->repo),
			"Could not create revision walker", NULL);

	if (sort_mode == GIT_SORT_REVERSE)
		s->sorting = s->sorting ^ GIT_SORT_REVERSE;
	else
		s->sorting = sort_mode | (s->sorting & GIT_SORT_REVERSE);

	git_revwalk_sorting(s->walker, s->sorting);
}

static void push_rev(struct log_state *s, git_object *obj, int hide)
{
	hide = s->hide ^ hide;

	if (!s->walker)
		check(git_revwalk_new(&s->walker, s->repo),
			"Could not create revision walker", NULL);

	if (!obj)
		check(git_revwalk_push_head(s->walker),
			"Could not find repository HEAD", NULL);
	else if (hide)
		check(git_revwalk_hide(s->walker, git_object_id(obj)),
			"Reference does not refer to a commit", NULL);
	else
		check(git_revwalk_push(s->walker, git_object_id(obj)),
			"Reference does not refer to a commit", NULL);

	git_object_free(obj);
}

static int add_revision(struct log_state *s, const char *revstr)
{
	git_revspec revs;
	int hide = 0;

	if (!s->repo) {
		if (!s->repodir) s->repodir = ".";
		check(git_repository_open_ext(&s->repo, s->repodir, 0, NULL),
			"Could not open repository", s->repodir);
	}

	if (!revstr)
		push_rev(s, NULL, hide);
	else if (*revstr == '^') {
		revs.flags = GIT_REVPARSE_SINGLE;
		hide = !hide;
		if (!git_revparse_single(&revs.from, s->repo, revstr + 1))
			return -1;
	} else
		if (!git_revparse(&revs, s->repo, revstr))
			return -1;

	if ((revs.flags & GIT_REVPARSE_SINGLE) != 0)
		push_rev(s, revs.from, hide);
	else {
		push_rev(s, revs.to, hide);

		if ((revs.flags & GIT_REVPARSE_MERGE_BASE) != 0) {
			git_oid base;
			check(git_merge_base(&base, s->repo,
				git_object_id(revs.from), git_object_id(revs.to)),
				"Could not find merge base", revstr);
			check(git_object_lookup(&revs.to, s->repo, &base, GIT_OBJ_COMMIT),
				"Could not find merge base commit", NULL);

			push_rev(s, revs.to, hide);
		}

		push_rev(s, revs.from, !hide);
	}

	return 0;
}

static void print_time(const git_time *intime, const char *prefix)
{
	char sign, out[32];
	struct tm intm;
	int offset, hours, minutes;
	time_t t;

	offset = intime->offset;
	if (offset < 0) {
		sign = '-';
		offset = -offset;
	} else {
		sign = '+';
	}

	hours   = offset / 60;
	minutes = offset % 60;

	t = (time_t)intime->time + (intime->offset * 60);

	gmtime_r(&t, &intm);
	strftime(out, sizeof(out), "%a %b %d %T %Y", &intm);

	printf("%s%s %c%02d%02d\n", prefix, out, sign, hours, minutes);
}

struct log_options {
	int show_diff;
	int skip;
	int min_parents, max_parents;
	git_time_t before;
	git_time_t after;
	char *author;
	char *committer;
};

int main(int argc, char *argv[])
{
	int i, count = 0;
	char *a;
	struct log_state s;
	git_strarray paths;
	git_oid oid;
	git_commit *commit;
	char buf[GIT_OID_HEXSZ + 1];

	git_threads_init();

	memset(&s, 0, sizeof(s));

	for (i = 1; i < argc; ++i) {
		a = argv[i];

		if (a[0] != '-') {
			if (!add_revision(&s, a))
				++count;
			else /* try failed revision parse as filename */
				break;
		} else if (!strcmp(a, "--")) {
			++i;
			break;
		}
		else if (!strcmp(a, "--date-order"))
			set_sorting(&s, GIT_SORT_TIME);
		else if (!strcmp(a, "--topo-order"))
			set_sorting(&s, GIT_SORT_TOPOLOGICAL);
		else if (!strcmp(a, "--reverse"))
			set_sorting(&s, GIT_SORT_REVERSE);
		else if (!strncmp(a, "--git-dir=", strlen("--git-dir=")))
			s.repodir = a + strlen("--git-dir=");
		else
			usage("Unsupported argument", a);
	}

	if (!count)
		add_revision(&s, NULL);

	paths.strings = &argv[i];
	paths.count   = argc - i;

	while (!git_revwalk_next(&oid, s.walker)) {
		const git_signature *sig;
		const char *scan, *eol;

		check(git_commit_lookup(&commit, s.repo, &oid),
			"Failed to look up commit", NULL);

		git_oid_tostr(buf, sizeof(buf), &oid);
		printf("commit %s\n", buf);

		if ((count = (int)git_commit_parentcount(commit)) > 1) {
			printf("Merge:");
			for (i = 0; i < count; ++i) {
				git_oid_tostr(buf, 8, git_commit_parent_id(commit, i));
				printf(" %s", buf);
			}
			printf("\n");
		}

		if ((sig = git_commit_author(commit)) != NULL) {
			printf("Author: %s <%s>\n", sig->name, sig->email);
			print_time(&sig->when, "Date:   ");
		}
		printf("\n");

		for (scan = git_commit_message(commit); scan && *scan; ) {
			for (eol = scan; *eol && *eol != '\n'; ++eol) /* find eol */;

			printf("    %.*s\n", (int)(eol - scan), scan);
			scan = *eol ? eol + 1 : NULL;
		}
		printf("\n");

		git_commit_free(commit);
	}

	git_revwalk_free(s.walker);
	git_repository_free(s.repo);
	git_threads_shutdown();

	return 0;
}