#include <stddef.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <sys/wait.h>
#include <sys/inotify.h>
#include <dlfcn.h>
#include <pthread.h>

#include "ccdl.h"

static void lib_init(struct lib *, const char *src_fname, const char *sym);
static int lib_build(struct lib *);
static void *lib_get(struct lib *);
static void lib_deinit(struct lib *);

static int ccdl_rebuild(struct ccdl *);
static struct lib *ccdl_get_old_lib(struct ccdl *);
static int ccdl_watch_run(struct ccdl *);

static const char *my_mktemp()
{
	const char *tmpdir = getenv("TMPDIR");
	if (!tmpdir) tmpdir = "/tmp";
	static char buf[256];
	ssize_t len = snprintf(buf, sizeof(buf), "%s/ccdl-XXXXXX", tmpdir);
	if (len < 0) return NULL;
	if (mkstemp(buf) < 0) return NULL;
	return buf;
}

static void lib_init(struct lib *lib, const char *src_fname, const char *sym_name)
{
	lib->src_fname = src_fname;
	lib->sym_name = sym_name;
	lib->handle = NULL;
	lib->sym = NULL;
}

static int compile(const char *src, const char *lib)
{
	if (!src || !lib) return -1;
	int child = fork();
	if (child < 0) return -1;
	if (child == 0) {
		char *cc = getenv("CC");
		if (!cc) cc = "cc";
		char *const argv[] = {
			cc, (char *)src, "-o", (char *)lib,
			"-fPIC", "-shared", "-lm",
			NULL};
		if (execvp(argv[0], argv)) err(1, "execvp");
		exit(0);
	} else {
		int wstatus;
		if (waitpid(child, &wstatus, 0) < 0) return -1;
		if (!WIFEXITED(wstatus) || WEXITSTATUS(wstatus)) return -1;
		return 0;
	}
}

static int lib_build(struct lib *lib)
{
	void *handle = lib->handle;
	if (!handle) {
		const char *src_fname = lib->src_fname;
		if (!src_fname) return -1;
		const char *lib_fname = my_mktemp();
		if (!lib_fname) {
			warn("mktemp");
			return -1;
		}
		if (compile(src_fname, lib_fname)) return -1;
		dlerror();
		handle = dlopen(lib_fname, RTLD_NOW);
		char *err = dlerror();
		if (unlink(lib_fname) < 0) warn("unlink");
		if (err) {
			warnx("dlopen: %s", err);
			return -1;
		}
		lib->handle = handle;
	}
	const char *sym_name = lib->sym_name;
	if (!sym_name) return -1;
	void *sym = dlsym(handle, sym_name);
	if (!sym) return -1;
	lib->sym = sym;
	printf("built\n");
	return 0;
}

static void *lib_get(struct lib *lib)
{
	if (!lib->sym) lib_build(lib);
	return lib->sym;
}

static void lib_deinit(struct lib *lib)
{
	if (lib->handle) {
		dlclose(lib->handle);
		lib->handle = NULL;
		lib->sym = NULL;
	}
}

void ccdl_init(struct ccdl *ccdl, const char *src_fname, const char *sym_name)
{
	lib_init(&ccdl->libs[0], src_fname, sym_name);
	lib_init(&ccdl->libs[1], src_fname, sym_name);
	ccdl->lib = &ccdl->libs[0];
}

static struct lib *ccdl_get_old_lib(struct ccdl *ccdl)
{
	return ccdl->lib == &ccdl->libs[1] ? &ccdl->libs[0] : &ccdl->libs[1];
}

void *ccdl_get(struct ccdl *ccdl)
{
	struct lib *old_lib = ccdl_get_old_lib(ccdl);
	if (old_lib) {
		lib_deinit(old_lib);
	}
	return lib_get(ccdl->lib);
}

static int ccdl_watch_run(struct ccdl *ccdl)
{
	int ifd = inotify_init();
	int wd = 0;
	if (ifd < 0) {
		warn("inotify_init");
		return -1;
	}
	if (!ccdl || !ccdl->lib || !ccdl->lib->src_fname) {
		warn("missing lib filename");
		return -1;
	}
	wd = inotify_add_watch(ifd, ccdl->lib->src_fname, IN_MODIFY);
	if (wd < 0) {
		warn("watch");
		return -1;
	}

	while (1) {
		struct inotify_event ev;
		ssize_t len = read(ifd, &ev, sizeof ev);
		//printf("readed %zd %u %u %u\n", len, sizeof ev, ev.len, ev.mask);
		if (len < 0) {
			warn("read");
			return -1;
		}
		if ((size_t)len < sizeof ev) {
			warn("small read");
			continue;
		}
		if (ev.len > 0) {
			warn("unexpected name");
			return -1;
		}
		if (ev.mask & IN_MODIFY) {
		} else if (ev.mask & IN_DELETE_SELF) {
			printf("deleted\n");
		} else if (ev.mask & IN_IGNORED) {
			// file is being replaced. replace the watch
			wd = inotify_add_watch(ifd, ccdl->lib->src_fname, IN_MODIFY);
			if (wd < 0) {
				warn("inotify_add_watch");
				return -1;
			}
		} else {
			printf("unknown mask: %u\n", ev.mask);
		}
		(void)ccdl_rebuild(ccdl);
	}

	return 0;
}

static void *ccdl_watch_run_thread(void *ccdl)
{
	return (void *)(intptr_t)ccdl_watch_run(ccdl);
}

int ccdl_watch(struct ccdl *ccdl)
{
	pthread_t *id = &ccdl->watcher_thread;
	if (pthread_create(id, NULL, ccdl_watch_run_thread, ccdl)) return -1;
	return 0;
}

static int ccdl_rebuild(struct ccdl *ccdl)
{
	struct lib *new_lib = ccdl_get_old_lib(ccdl);
	lib_deinit(new_lib);
	if (lib_build(new_lib) < 0) return -1;
	ccdl->lib = new_lib;
	return 0;
}

int ccdl_deinit(struct ccdl *ccdl)
{
	pthread_t thread = ccdl->watcher_thread;
	if (thread) {
		void *retval;
		pthread_join(thread, &retval);
		return (intptr_t)retval;
	}
	return 0;
}