/*
 * Copyright 2006 Richard Wilson <info@tinct.net>
 *
 * This file is part of NetSurf, http://www.netsurf-browser.org/
 *
 * NetSurf is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * NetSurf is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/** \file
 * Provides a central method of obtaining unique filenames.
 *
 * A maximum of 2^24 files can be allocated at any point in time.
 */

#include <dirent.h>
#include <stdbool.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include "utils/filename.h"
#include "utils/log.h"
#include "utils/url.h"
#include "utils/utils.h"

#define FULL_WORD (unsigned int)4294967295
/* '0' + '0' * 10 */
#define START_PREFIX 528

struct directory {
	int numeric_prefix;		/** numeric representation of prefix */
	char prefix[10];		/** directory prefix, eg '00/11/52/' */
	unsigned int low_used;		/** first 32 files, 1 bit per file */
	unsigned int high_used;		/** last 32 files, 1 bit per file */
	struct directory *next;		/** next directory (sorted by prefix) */
};


static struct directory *root = NULL;
static char filename_buffer[12];
static char filename_directory[256];

static struct directory *filename_create_directory(const char *prefix);
static bool filename_flush_directory(const char *folder, int depth);
static bool filename_delete_recursive(char *folder);

/**
 * Request a new, unique, filename.
 *
 * \return a pointer to a shared buffer containing the new filename or NULL on failure
 */
const char *filename_request(void) {
	struct directory *dir;
	int i = -1;

	for (dir = root; dir; dir = dir->next)
		if ((dir->low_used & dir->high_used) != FULL_WORD) {
			if (dir->low_used != FULL_WORD) {
				for (i = 0; (dir->low_used & (1 << i)); i++);
			} else {
				for (i = 0; (dir->high_used & (1 << i)); i++);
				i += 32;
			}
			break;
		}
	if (i == -1) {
		/* no available slots - create a new directory */
		dir = filename_create_directory(NULL);
		if (!dir) {
			LOG(("Failed to create a new directory."));
			return NULL;
		}
		i = 63;
	}
	if (i < 32)
		dir->low_used |= (1 << i);
	else
		dir->high_used |= (1 << (i - 32));
	sprintf(filename_buffer, "%s%.2i", dir->prefix, i);
	return filename_buffer;
}


/**
 * Claim a specific filename.
 *
 * \param  filename  the filename to claim
 * \return whether the claim was successful
 */
bool filename_claim(const char *filename) {
	char dir_prefix[9];
	int file;
	struct directory *dir;

	/* filename format is always '01/23/45/XX' */
	strncpy(dir_prefix, filename, 9);
	dir_prefix[9] = '\0';
	file = (filename[10] + filename[9] * 10 - START_PREFIX);

	/* create the directory */
	dir = filename_create_directory(dir_prefix);
	if (!dir)
		return false;

	/* update the entry */
	if (file < 32) {
		if (dir->low_used & (1 << file))
			return false;
		dir->low_used |= (1 << file);
	} else {
		if (dir->high_used & (1 << (file - 32)))
			return false;
		dir->high_used |= (1 << (file - 32));
	}
	return true;
}


/**
 * Releases a filename for future use.
 *
 * \param  filename  the filename to release
 */
void filename_release(const char *filename) {
	struct directory *dir;
	int index, file;

	/* filename format is always '01/23/45/XX' */
	index = ((filename[7] + filename[6] * 10 - START_PREFIX) |
		((filename[4] + filename[3] * 10 - START_PREFIX) << 6) |
		((filename[1] + filename[0] * 10 - START_PREFIX) << 12));
	file = (filename[10] + filename[9] * 10 - START_PREFIX);

	/* modify the correct directory entry */
	for (dir = root; dir; dir = dir->next)
		if (dir->numeric_prefix == index) {
			if (file < 32)
				dir->low_used &= ~(1 << file);
			else
				dir->high_used &= ~(1 << (file - 32));
			return;
		}
}


/**
 * Initialise the filename provider.
 */
bool filename_initialise(void) {
	char *directory, *start;

	directory = strdup(TEMP_FILENAME_PREFIX);
	if (!directory)
		return false;

	for (start = directory; *start != '\0'; start++) {
		if (*start == '/') {
			*start = '\0';
			mkdir(directory, S_IRWXU);
			*start = '/';
		}
	}
	LOG((directory));
	mkdir(directory, S_IRWXU);
	free(directory);
	return true;
}


/**
 * Deletes all files in the cache directory that are not accounted for.
 */
void filename_flush(void) {
	while (filename_flush_directory(TEMP_FILENAME_PREFIX, 0));
}


/**
 * Deletes some files in a directory that are not accounted for.
 *
 * A single call to this function may not delete all the files in
 * a directory. It should be called until it returns false.
 *
 * \param folder	the folder to search
 * \param depth		the folder depth
 * \returns whether further calls may be needed
 */
bool filename_flush_directory(const char *folder, int depth) {
	DIR *parent;
	struct dirent *entry;
	bool changed = false;
	bool del;
	int number, i;
	int prefix = 0;
	unsigned int prefix_mask = (63 << 12);
	char child[256];
	const char *prefix_start = NULL;
	struct directory *dir = NULL;

	/* find out directory details */
	if (depth > 0)
		prefix_start = folder + strlen(folder) - depth * 3 + 1;
	for (i = 0; ((i < depth) && (i < 3)); i++) {
		number = prefix_start[1] + prefix_start[0] * 10 - START_PREFIX;
		prefix |= (number << (12 - i * 6));
		prefix_mask |= (63 << (6 - i * 6));
		prefix_start += 3;
	}
	if (depth == 3) {
		for (dir = root; dir; dir = dir->next)
			if (dir->numeric_prefix == prefix)
				break;
		if ((!dir) || (dir->numeric_prefix != prefix))
			return false;
	}

	parent = opendir(folder);

	while ((entry = readdir(parent))) {
	 	struct stat statbuf;

		if (!strcmp(entry->d_name, ".") ||
				!strcmp(entry->d_name, ".."))
			continue;

		snprintf(child, 256, "%s/%s", folder, entry->d_name);
		if (stat(child, &statbuf) == -1) {
			LOG(("Unable to stat %s, even though it just got returned from readdir(): %s", child, strerror(errno)));
			continue;
		}

		/* first 3 depths are directories only, then files only */
		if (depth < 3)
			del = !S_ISDIR(statbuf.st_mode);
		else
		  	del = S_ISDIR(statbuf.st_mode);

		/* check we are a file numbered '00' -> '63' */
		if ((!del) && (entry->d_name[0] >= '0') &&
				(entry->d_name[0] <= '6') &&
				(entry->d_name[1] >= '0') &&
				(entry->d_name[1] <= '9') &&
				(entry->d_name[2] == '\0')) {
			number = atoi(entry->d_name);
			if ((number >= 0) && (number <= 63)) {
				if (depth == 3) {
					if (number < 32)
						del = !(dir->low_used &
							(1 << number));
					else
						del = !(dir->high_used &
							(1 << (number - 32)));
				} else {
					del = true;
					prefix &= ~(63 << (12 - depth * 6));
					prefix |= (number << (12 - depth * 6));
					for (dir = root; dir; dir = dir->next) {
						number = dir->numeric_prefix &
								prefix_mask;
						if (number == prefix) {
							del = false;
							break;
						}
					}
				}
			} else {
				del = true;
			}
		} else {
			del = true;
		}
		/* continue if we are a valid reference so far */
		if ((!del) && (!S_ISDIR(statbuf.st_mode)))
		    	continue;
		/* delete or recurse */
		snprintf(child, 256, "%s/%s", folder, entry->d_name);
		child[255] = '\0';
		if (del) {
			if (S_ISDIR(statbuf.st_mode))
				filename_delete_recursive(child);
			if (remove(child))
				LOG(("Failed to remove '%s'", child));
			else
				changed = true;
		} else {
			while (filename_flush_directory(child, depth + 1));
		}
	}

	closedir(parent);
	return changed;
}


/**
 * Recursively deletes the contents of a directory
 *
 * \param directory	the directory to delete
 * \return true on success, false otherwise
 */
bool filename_delete_recursive(char *folder) {
	DIR *parent;
	struct dirent *entry;
	char child[256];
	struct stat statbuf;

	parent = opendir(folder);

	while ((entry = readdir(parent))) {
		if ((!strcmp(entry->d_name, ".")) ||
				(!strcmp(entry->d_name, "..")))
			continue;
		snprintf(child, 256, "%s/%s", folder, entry->d_name);
		if (stat(child, &statbuf) == -1) {
                        LOG(("Unable to stat %s, even though it just got returned from readdir(): %s", child, strerror(errno)));
			continue;

		}
		if (S_ISDIR(statbuf.st_mode)) {
			if (!filename_delete_recursive(child)) {
				closedir(parent);
				return false;
			}
		}
		if (remove(child)) {
			LOG(("Failed to remove '%s'", child));
			closedir(parent);
			return false;
		}
	}

	closedir(parent);
	return true;
}


/**
 * Creates a new directory.
 *
 * \param  prefix  the prefix to use, or NULL to allocate a new one
 * \return a new directory structure, or NULL on memory exhaustion or
 * creation failure
 *
 * Empty directories are never deleted, except by an explicit call to
 * filename_flush().
 */
static struct directory *filename_create_directory(const char *prefix) {
	char *last_1, *last_2;
	int index;
	struct directory *old_dir, *new_dir, *prev_dir = NULL;
	char dir_prefix[16];

	/* get the lowest unique prefix, or use the provided one */
	if (!prefix) {
		for (index = 0, old_dir = root; old_dir; index++,
				prev_dir = old_dir, old_dir = old_dir->next)
			if (old_dir->numeric_prefix != index)
				break;
		sprintf(dir_prefix, "%.2i/%.2i/%.2i/",
				((index >> 12) & 63),
				((index >> 6) & 63),
				((index >> 0) & 63));
		prefix = dir_prefix;
	} else {
		/* prefix format is always '01/23/45/' */
		index = ((prefix[7] + prefix[6] * 10 - START_PREFIX) |
			((prefix[4] + prefix[3] * 10 - START_PREFIX) << 6) |
			((prefix[1] + prefix[0] * 10 - START_PREFIX) << 12));
		for (old_dir = root; old_dir; prev_dir = old_dir,
				old_dir = old_dir->next) {
			if (old_dir->numeric_prefix == index)
				return old_dir;
			else if (old_dir->numeric_prefix > index)
				break;
		}
	}

	/* allocate a new directory */
	new_dir = (struct directory *)malloc(sizeof(struct directory));
	if (!new_dir) {
		LOG(("No memory for malloc()"));
		return NULL;
	}
	strncpy(new_dir->prefix, prefix, 9);
	new_dir->prefix[9] = '\0';
	new_dir->low_used = new_dir->high_used = 0;
	new_dir->numeric_prefix = index;

	if (!prev_dir) {
		new_dir->next = root;
		root = new_dir;
	} else {
		new_dir->next = prev_dir->next;
		prev_dir->next = new_dir;
	}

	/* if the previous directory has the same parent then we can simply
	 * create the child. */
	if ((prev_dir) && (!strncmp(prev_dir->prefix, new_dir->prefix, 6))) {
		new_dir->prefix[8] = '\0';
		sprintf(filename_directory, "%s/%s",
				TEMP_FILENAME_PREFIX,
				new_dir->prefix);
		new_dir->prefix[8] = '/';
		if (!is_dir(filename_directory)) {
			if (!mkdir(filename_directory, S_IRWXU))
				return new_dir;

			/* the user has probably deleted the parent directory
			 * whilst we are running if there is an error, so we
			 * don't report this yet and try to create the
			 * structure normally. */
			LOG(("Failed to create optimised structure '%s'",
					filename_directory));
		}
	}

	/* create the directory structure */
	sprintf(filename_directory, "%s/",
			TEMP_FILENAME_PREFIX);
	last_1 = filename_directory + strlen(TEMP_FILENAME_PREFIX) + 1;
	last_2 = new_dir->prefix;
	for (int i = 0; i < 3 && *last_2; i++) {
		*last_1++ = *last_2++;
		while (*last_2 && *last_2 != '/')
			*last_1++ = *last_2++;
		if (*last_2) {
			last_1[0] = '\0';
			if (!is_dir(filename_directory)) {
				if (mkdir(filename_directory, S_IRWXU)) {
					LOG(("Failed to create directory '%s'",
							filename_directory));
					return NULL;
				}
			}
		}
	}

	return new_dir;
}


/**
 * Converts a filename into a local URL
 *
 * \param  filename  the filename to convert
 * \return a local URL allocated on heap, or NULL on failure.
 */
char *filename_as_url(const char *filename) {
	char *temp, *url;
	int length;

	length = strlen(TEMP_FILENAME_PREFIX) + strlen(filename) + 2;
	temp = malloc(length);
	if (!temp) {
	  	LOG(("No memory for malloc()"));
		return NULL;
	}
	sprintf(temp, "%s/%s", TEMP_FILENAME_PREFIX, filename);
	url = path_to_url(temp);
	free(temp);
	return url;
}