/* cache.c: cache management
 *
 * Copyright (C) 2006 Lars Hjemli
 *
 * Licensed under GNU General Public License v2
 *   (see COPYING for full license text)
 */

#include "cgit.h"

const int NOLOCK = -1;

void cache_prepare(struct cacheitem *item)
{
	if (!cgit_query_repo) {
		item->name = xstrdup(fmt("%s/index.html", cgit_cache_root));
		item->ttl = cgit_cache_root_ttl;
	} else if (!cgit_query_page) {
		item->name = xstrdup(fmt("%s/%s/index.html", cgit_cache_root, 
			   cgit_query_repo));
		item->ttl = cgit_cache_repo_ttl;
	} else {
		item->name = xstrdup(fmt("%s/%s/%s/%s.html", cgit_cache_root, 
			   cgit_query_repo, cgit_query_page, 
			   cgit_querystring));
		if (cgit_query_has_symref)
			item->ttl = cgit_cache_dynamic_ttl;
		else if (cgit_query_has_sha1)
			item->ttl = cgit_cache_static_ttl;
		else
			item->ttl = cgit_cache_repo_ttl;
	}
}

int cache_exist(struct cacheitem *item)
{
	if (stat(item->name, &item->st)) {
		item->st.st_mtime = 0;
		return 0;
	}
	return 1;
}

int cache_create_dirs()
{
	char *path;

	if (!cgit_query_repo)
		return 0;

	path = fmt("%s/%s", cgit_cache_root, cgit_query_repo);
	if (mkdir(path, S_IRWXU) && errno!=EEXIST)
		return 0;

	if (cgit_query_page) {
		path = fmt("%s/%s/%s", cgit_cache_root, cgit_query_repo, 
			   cgit_query_page);
		if (mkdir(path, S_IRWXU) && errno!=EEXIST)
			return 0;
	}
	return 1;
}

int cache_refill_overdue(const char *lockfile)
{
	struct stat st;

	if (stat(lockfile, &st))
		return 0;
	else
		return (time(NULL) - st.st_mtime > cgit_cache_max_create_time);
}

int cache_lock(struct cacheitem *item)
{
	int i = 0;
	char *lockfile = xstrdup(fmt("%s.lock", item->name));

 top:
	if (++i > cgit_max_lock_attempts)
		die("cache_lock: unable to lock %s: %s",
		    item->name, strerror(errno));

       	item->fd = open(lockfile, O_WRONLY|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR);

	if (item->fd == NOLOCK && errno == ENOENT && cache_create_dirs())
		goto top;

	if (item->fd == NOLOCK && errno == EEXIST &&
	    cache_refill_overdue(lockfile) && !unlink(lockfile))
			goto top;

	free(lockfile);
	return (item->fd > 0);
}

int cache_unlock(struct cacheitem *item)
{
	close(item->fd);
	return (rename(fmt("%s.lock", item->name), item->name) == 0);
}

int cache_cancel_lock(struct cacheitem *item)
{
	return (unlink(fmt("%s.lock", item->name)) == 0);
}

int cache_expired(struct cacheitem *item)
{
	if (item->ttl < 0)
		return 0;
	return item->st.st_mtime + item->ttl * 60 < time(NULL);
}

s="p">{
	if (slot->cache_fd > 0) {
		close(slot->cache_fd);
		slot->cache_fd = -1;
	}
}

/* Print the content of the active cache slot (but skip the key). */
static int print_slot(struct cache_slot *slot)
{
	ssize_t i, j = 0;

	i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
	if (i != slot->keylen + 1)
		return errno;

	while((i=read(slot->cache_fd, slot->buf, sizeof(slot->buf))) > 0)
		j = write(STDOUT_FILENO, slot->buf, i);

	if (j < 0)
		return errno;
	else
		return 0;
}

/* Check if the slot has expired */
static int is_expired(struct cache_slot *slot)
{
	if (slot->ttl < 0)
		return 0;
	else
		return slot->cache_st.st_mtime + slot->ttl*60 < time(NULL);
}

/* Check if the slot has been modified since we opened it.
 * NB: If stat() fails, we pretend the file is modified.
 */
static int is_modified(struct cache_slot *slot)
{
	struct stat st;

	if (stat(slot->cache_name, &st))
		return 1;
	return (st.st_ino != slot->cache_st.st_ino ||
		st.st_mtime != slot->cache_st.st_mtime ||
		st.st_size != slot->cache_st.st_size);
}

/* Close an open lockfile */
static void close_lock(struct cache_slot *slot)
{
	if (slot->lock_fd > 0) {
		close(slot->lock_fd);
		slot->lock_fd = -1;
	}
}

/* Create a lockfile used to store the generated content for a cache
 * slot, and write the slot key + \0 into it.
 * Returns 0 on success and errno otherwise.
 */
static int lock_slot(struct cache_slot *slot)
{
	slot->lock_fd = open(slot->lock_name, O_RDWR|O_CREAT|O_EXCL,
			     S_IRUSR|S_IWUSR);
	if (slot->lock_fd == -1)
		return errno;
	write(slot->lock_fd, slot->key, slot->keylen + 1);
	return 0;
}

/* Release the current lockfile. If `replace_old_slot` is set the
 * lockfile replaces the old cache slot, otherwise the lockfile is
 * just deleted.
 */
static int unlock_slot(struct cache_slot *slot, int replace_old_slot)
{
	int err;

	if (replace_old_slot)
		err = rename(slot->lock_name, slot->cache_name);
	else
		err = unlink(slot->lock_name);
	return err;
}

/* Generate the content for the current cache slot by redirecting
 * stdout to the lock-fd and invoking the callback function
 */
static int fill_slot(struct cache_slot *slot)
{
	int tmp;

	/* Preserve stdout */
	tmp = dup(STDOUT_FILENO);
	if (tmp == -1)
		return errno;

	/* Redirect stdout to lockfile */
	if (dup2(slot->lock_fd, STDOUT_FILENO) == -1)
		return errno;

	/* Generate cache content */
	slot->fn(slot->cbdata);

	/* Restore stdout */
	if (dup2(tmp, STDOUT_FILENO) == -1)
		return errno;

	/* Close the temporary filedescriptor */
	close(tmp);
	return 0;
}

/* Crude implementation of 32-bit FNV-1 hash algorithm,
 * see http://www.isthe.com/chongo/tech/comp/fnv/ for details
 * about the magic numbers.
 */
#define FNV_OFFSET 0x811c9dc5
#define FNV_PRIME  0x01000193

unsigned long hash_str(const char *str)
{
	unsigned long h = FNV_OFFSET;
	unsigned char *s = (unsigned char *)str;

	if (!s)
		return h;

	while(*s) {
		h *= FNV_PRIME;
		h ^= *s++;
	}
	return h;
}

static int process_slot(struct cache_slot *slot)
{
	int err;

	err = open_slot(slot);
	if (!err && slot->match) {
		if (is_expired(slot)) {
			if (!lock_slot(slot)) {
				/* If the cachefile has been replaced between
				 * `open_slot` and `lock_slot`, we'll just
				 * serve the stale content from the original
				 * cachefile. This way we avoid pruning the
				 * newly generated slot. The same code-path
				 * is chosen if fill_slot() fails for some
				 * reason.
				 *
				 * TODO? check if the new slot contains the
				 * same key as the old one, since we would
				 * prefer to serve the newest content.
				 * This will require us to open yet another
				 * file-descriptor and read and compare the
				 * key from the new file, so for now we're
				 * lazy and just ignore the new file.
				 */
				if (is_modified(slot) || fill_slot(slot)) {
					unlock_slot(slot, 0);
					close_lock(slot);
				} else {
					close_slot(slot);
					unlock_slot(slot, 1);
					slot->cache_fd = slot->lock_fd;
				}
			}
		}
		print_slot(slot);
		close_slot(slot);
		return 0;
	}

	/* If the cache slot does not exist (or its key doesn't match the
	 * current key), lets try to create a new cache slot for this
	 * request. If this fails (for whatever reason), lets just generate
	 * the content without caching it and fool the caller to belive
	 * everything worked out (but print a warning on stdout).
	 */

	close_slot(slot);
	if ((err = lock_slot(slot)) != 0) {
		cache_log("[cgit] Unable to lock slot %s: %s (%d)\n",
			  slot->lock_name, strerror(err), err);
		slot->fn(slot->cbdata);
		return 0;
	}

	if ((err = fill_slot(slot)) != 0) {
		cache_log("[cgit] Unable to fill slot %s: %s (%d)\n",
			  slot->lock_name, strerror(err), err);
		unlock_slot(slot, 0);
		close_lock(slot);
		slot->fn(slot->cbdata);
		return 0;
	}
	// We've got a valid cache slot in the lock file, which
	// is about to replace the old cache slot. But if we
	// release the lockfile and then try to open the new cache
	// slot, we might get a race condition with a concurrent
	// writer for the same cache slot (with a different key).
	// Lets avoid such a race by just printing the content of
	// the lock file.
	slot->cache_fd = slot->lock_fd;
	unlock_slot(slot, 1);
	err = print_slot(slot);
	close_slot(slot);
	return err;
}

/* Print cached content to stdout, generate the content if necessary. */
int cache_process(int size, const char *path, const char *key, int ttl,
		  cache_fill_fn fn, void *cbdata)
{
	unsigned long hash;
	int len, i;
	char filename[1024];
	char lockname[1024 + 5];  /* 5 = ".lock" */
	struct cache_slot slot;

	/* If the cache is disabled, just generate the content */
	if (size <= 0) {
		fn(cbdata);
		return 0;
	}

	/* Verify input, calculate filenames */
	if (!path) {
		cache_log("[cgit] Cache path not specified, caching is disabled\n");
		fn(cbdata);
		return 0;
	}
	len = strlen(path);
	if (len > sizeof(filename) - 10) { /* 10 = "/01234567\0" */
		cache_log("[cgit] Cache path too long, caching is disabled: %s\n",
			  path);
		fn(cbdata);
		return 0;
	}
	if (!key)
		key = "";
	hash = hash_str(key) % size;
	strcpy(filename, path);
	if (filename[len - 1] != '/')
		filename[len++] = '/';
	for(i = 0; i < 8; i++) {
		sprintf(filename + len++, "%x",
			(unsigned char)(hash & 0xf));
		hash >>= 4;
	}
	filename[len] = '\0';
	strcpy(lockname, filename);
	strcpy(lockname + len, ".lock");
	slot.fn = fn;
	slot.cbdata = cbdata;
	slot.ttl = ttl;
	slot.cache_name = filename;
	slot.lock_name = lockname;
	slot.key = key;
	slot.keylen = strlen(key);
	return process_slot(&slot);
}

/* Return a strftime formatted date/time
 * NB: the result from this function is to shared memory
 */
char *sprintftime(const char *format, time_t time)
{
	static char buf[64];
	struct tm *tm;

	if (!time)
		return NULL;
	tm = gmtime(&time);
	strftime(buf, sizeof(buf)-1, format, tm);
	return buf;
}

int cache_ls(const char *path)
{
	DIR *dir;
	struct dirent *ent;
	int err = 0;
	struct cache_slot slot;
	char fullname[1024];
	char *name;

	if (!path) {
		cache_log("[cgit] cache path not specified\n");
		return -1;
	}
	if (strlen(path) > 1024 - 10) {
		cache_log("[cgit] cache path too long: %s\n",
			  path);
		return -1;
	}
	dir = opendir(path);
	if (!dir) {
		err = errno;
		cache_log("[cgit] unable to open path %s: %s (%d)\n",
			  path, strerror(err), err);
		return err;
	}
	strcpy(fullname, path);
	name = fullname + strlen(path);
	if (*(name - 1) != '/') {
		*name++ = '/';
		*name = '\0';
	}
	slot.cache_name = fullname;
	while((ent = readdir(dir)) != NULL) {
		if (strlen(ent->d_name) != 8)
			continue;
		strcpy(name, ent->d_name);
		if ((err = open_slot(&slot)) != 0) {
			cache_log("[cgit] unable to open path %s: %s (%d)\n",
				  fullname, strerror(err), err);
			continue;
		}
		printf("%s %s %10lld %s\n",
		       name,
		       sprintftime("%Y-%m-%d %H:%M:%S",
				   slot.cache_st.st_mtime),
		       slot.cache_st.st_size,
		       slot.buf);
		close_slot(&slot);
	}
	closedir(dir);
	return 0;
}

/* Print a message to stdout */
void cache_log(const char *format, ...)
{
	va_list args;
	va_start(args, format);
	vfprintf(stderr, format, args);
	va_end(args);
}