#define PCRE2_CODE_UNIT_WIDTH 8

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <git2.h>
#include <pcre2.h>


size_t
min(const size_t lhs, const size_t rhs)
{
	return lhs > rhs ? rhs : lhs;
}


char*
relative_path_in_current_dir(git_repository* repo, const char* filename)
{
	const long maximum = pathconf(".", _PC_PATH_MAX);
	size_t len = 0 > maximum ? 1024 : maximum;
	char* buf = NULL;
	char* cwd = NULL;
	for (; NULL == cwd && 1024 * 50 > len; len *= 2) {
		if (NULL == (cwd = realloc(buf, len))) {
			if (NULL != buf)
				free(buf);
			return NULL;
		}
		buf = cwd;
		cwd = getcwd(buf, len);
		if (NULL == cwd && ERANGE != errno) {
			free(buf);
			return NULL;
		}
	}
	const char* workdir = git_repository_workdir(repo);
	const size_t prefix = min(strlen(cwd), strlen(workdir));
	if (0 != strncmp(cwd, workdir, prefix)) {
		free(cwd);
		return NULL;
	}
	const size_t relative = strlen(cwd + prefix);
	if (NULL == (buf = malloc(relative + strlen(filename) + 2))) {
		free(cwd);
		return NULL;
	}
	strcpy(buf, cwd + prefix);
	if (0 < relative)
		strcat(buf, "/");
	strcat(buf, filename);
	free(cwd);
	return buf;
}


void
gerror(void)
{
	const git_error* err = git_error_last();
	dprintf(2, "%s\n", err->message);
}


int
main(int argc, char* argv[])
{
	git_libgit2_init();
	git_repository* repo = NULL;
	int err = git_repository_open_ext(&repo, NULL, GIT_REPOSITORY_OPEN_FROM_ENV, NULL);
	if (0 > err) {
		gerror();
		return 1;
	}
	git_diff_options diffopts = GIT_DIFF_OPTIONS_INIT;
	diffopts.pathspec.strings = (char*[]){relative_path_in_current_dir(repo, "PKGBUILD")};
	diffopts.pathspec.count = 1;
	git_pathspec* pathspec = NULL;
	err = git_pathspec_new(&pathspec, &diffopts.pathspec);
	if (0 > err) {
		gerror();
		return 1;
	}
	git_revwalk* walker = NULL;
	err = git_revwalk_new(&walker, repo);
	if (0 > err) {
		gerror();
		return 1;
	}
	err = git_revwalk_push_head(walker);
	if (0 > err) {
		gerror();
		return 1;
	}
	git_oid oid;
	git_tree* earlier = NULL;
	git_tree* later = NULL;
	while (0 == git_revwalk_next(&oid, walker)) {
		git_commit* commit;
		err = git_commit_lookup(&commit, repo, &oid);
		if (0 > err) {
			gerror();
			return 1;
		}
		if (NULL != earlier)
			git_tree_free(earlier);
		earlier = later;
		err = git_commit_tree(&later, commit);
		if (0 > err) {
			gerror();
			return 1;
		}
		const int matched = 0 == git_pathspec_match_tree(NULL, later, GIT_PATHSPEC_NO_MATCH_ERROR, pathspec);
		if (matched) {
			char buf[GIT_OID_HEXSZ + 1];
			git_oid_tostr(buf, sizeof(buf), git_commit_id(commit));
			puts(buf);
		}
		git_commit_free(commit);
	}
	if (NULL != earlier)
		git_tree_free(earlier);
	if (NULL != later)
		git_tree_free(later);
	git_revwalk_free(walker);
	git_pathspec_free(pathspec);
	free(diffopts.pathspec.strings[0]);
	git_repository_free(repo);
}