#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>

#include "print.h"
#include "fs.h"

#include "config.h"

const static int BLOCK_ADDRESSES_PER_INODE = (FS_BLOCK_SIZE-sizeof(int)*3) / sizeof(int);
const static int BLOCK_ADDRESSES_PER_INODE_EXTENSION = (FS_BLOCK_SIZE-sizeof(int)) / sizeof(int);


static char used_file_path[FS_MAX_DEVICE_FILE_NAME_LEN+1];
static int used_file_fd;
static int write_permitted;

static char fs_cwd[FS_MAX_PATH_LEN+1];
static struct fs_header fsh_cache;
static char fs_bitmap_cache[FS_BLOCK_SIZE * FS_MAX_BITMAP_SIZE];


static int read_block(unsigned int block_no, void *data)
{
	if (lseek(used_file_fd, block_no * FS_BLOCK_SIZE, SEEK_SET) < 0) {
		pr_err("failed to seek to block %d (bs=%d) on device '%s'\n", block_no, FS_BLOCK_SIZE, used_file_path);
		return -1;
	}

	return read(used_file_fd, data, FS_BLOCK_SIZE);
}

static int write_block(unsigned int block_no, void *data)
{
	if (lseek(used_file_fd, block_no * FS_BLOCK_SIZE, SEEK_SET) < 0) {
		pr_err("failed to seek to block %d (bs=%d) on device '%s'\n", block_no, FS_BLOCK_SIZE, used_file_path);
		return -1;
	}

	return write(used_file_fd, data, FS_BLOCK_SIZE);
}

static void mark_used(unsigned int block_no)
{
	if (block_no > fsh_cache.block_count) {
		pr_err("block %d is out of filesystem block range (%d)\n", block_no, fsh_cache.block_count);
		return;
	}

	unsigned char bitmap_bit = 1 << (block_no & 0x7);
	unsigned int bitmap_block_offset = (block_no >> 3) % FS_BLOCK_SIZE;
	unsigned int bitmap_block_index = (block_no >> 3) / FS_BLOCK_SIZE;

	fs_bitmap_cache[bitmap_block_index * FS_BLOCK_SIZE + bitmap_block_offset] |= bitmap_bit;

	// write changes to device
	write_block(bitmap_block_index+1, (void *) &(fs_bitmap_cache[bitmap_block_index*FS_BLOCK_SIZE]));

	pr("Marked block_no=%d (block=%d, offset=%d, bit=%d) as used\n",
			block_no, bitmap_block_index, bitmap_block_offset, block_no & 0x7);
}

static void mark_free(unsigned int block_no)
{
	if (block_no > fsh_cache.block_count) {
		pr_err("block %d is out of fimesystem block range (%d)\n", block_no, fsh_cache.block_count);
		return;
	}

	unsigned char bitmap_bit = 1 << (block_no & 0x7);
	unsigned int bitmap_block_offset = (block_no >> 3) % FS_BLOCK_SIZE;
	unsigned int bitmap_block_index = (block_no >> 3) / FS_BLOCK_SIZE;

	fs_bitmap_cache[bitmap_block_index * FS_BLOCK_SIZE + bitmap_block_offset] &= ~bitmap_bit;

	// write changes to device
	write_block(bitmap_block_index+1, (void *) &(fs_bitmap_cache[bitmap_block_index*FS_BLOCK_SIZE]));

	pr("Marked block_no=%d (block=%d, offset=%d, bit=%d) as free\n",
			block_no, bitmap_block_index, bitmap_block_offset, bitmap_bit);
}

static int identify_fs(void)
{
	struct fs_header read_buf;
	{
		int read_amount = read_block(0, (void *) &read_buf);

		if (read_amount < 0) {
			pr_err("failed to read fs_header from storage device '%s'\n", used_file_path);
			return 0;
		}

		if (read_amount < FS_BLOCK_SIZE) {
			pr_warn("failed to read full block (read %d/%d bytes)\n", read_amount, FS_BLOCK_SIZE);
		} else if (read_amount == 0) {
			pr_err("storage device size is 0\n");
			return 0;
		}
	}

	if (read_buf.next_extension) {
		pr_info("identified filesystem version 0x%hhx with %d max inodes (on %d blocks), next header extension is at block 0x%x\n",
				read_buf.version, read_buf.max_inode_count, read_buf.block_count, read_buf.next_extension);
	} else {
		pr_info("identified filesystem version 0x%hhx with %d max inodes (on %d blocks), with no header extensions\n",
				read_buf.version, read_buf.max_inode_count, read_buf.block_count);
	}

	return read_buf.version;
}

static unsigned int find_free_block(void)
{
	unsigned int b = 0;

	int blocks_used_for_bitmap = fsh_cache.block_count / (FS_BLOCK_SIZE * 8);
	if (fsh_cache.block_count % (FS_BLOCK_SIZE * 8))
		blocks_used_for_bitmap++;

	for (int i = 0; i < blocks_used_for_bitmap; i++) {
		for (int j = 0; j < FS_BLOCK_SIZE; j++) {
			if (!(~(fs_bitmap_cache[i*FS_BLOCK_SIZE + j]))) {
				b += 8;
			} else {
				for (int k = 0; k < 8; k++, b++) {
					if (!((fs_bitmap_cache[i*FS_BLOCK_SIZE + j]) & (1 << k))) {
						return b;
					}
				}
			}
		}
	}

	return 0;
}

static void write_inode_ptr(unsigned int inode_ptr, unsigned int block_ptr)
{
	if ((inode_ptr / BLOCK_ADDRESSES_PER_INODE) == 0) {
		// inode_ptr is in the fs_header
		struct fs_header fsh;
		int read_result = read_block(0, &fsh);
		if (FS_BLOCK_SIZE != read_result) {
			if (read_result < 0) {
				pr_err("failed to read fs header from device '%s'\n", used_file_path);
			} else {
				pr_err("failed to read full header from device (read %d/%d bytes)\n", read_result, FS_BLOCK_SIZE);
			}

			return;
		}

		fsh.inode_ptrs[inode_ptr] = block_ptr;

		int write_result = write_block(0, (void *) &fsh);
		if (FS_BLOCK_SIZE != write_result) {
			if (write_result < 0) {
				pr_err("failed to write fs header to device '%s'\n", used_file_path);
			} else {
				pr_err("failed to write full block to device, written %d/%d bytes\n", write_result, FS_BLOCK_SIZE);
			}

			return;
		}

		pr("Updated inode ptr %d -> %d\n", inode_ptr, block_ptr);
	} else {
		// TODO: find block with relevant inode_ptr, extend fs_header if needed
		/*
		unsigned int relevant_block_index = ((free_block_index - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION) + 1;
		unsigned int relevant_block_record_offset = (free_block_index - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;
		*/
	}
}

char *fs_get_cwd(void)
{
	return fs_cwd;
}

int fs_chdir(void *d)
{
	memset(fs_cwd, 0, sizeof(fs_cwd));
	strcpy(fs_cwd, *((char**)d));

	return 0;
}

int fs_allow_write(void *d)
{
	if (used_file_fd <= 0) {
		pr_err("no device present\n");
		return 0;
	}

	pr_info("Allowing write operations on device '%s'\n", used_file_path);
	write_permitted = 1;

	return 0;
}

int fs_prohibit_write(void *d)
{
	if (used_file_fd <= 0) {
		pr_err("no device present\n");
		return 0;
	}

	pr_info("Prohibiting write operations on device '%s'\n", used_file_path);
	write_permitted = 0;

	return 0;
}

int fs_create(void *d)
{
	pr("[mock] Regular file '%s' created\n", *((char **) d));

	return 0;
}

int fs_use(void *d)
{
	char *fname = *((char **) d);
	int name_len = strlen(fname);

	if (name_len > FS_MAX_DEVICE_FILE_NAME_LEN) {
		pr_err("device filename too long (> %d)\n", FS_MAX_DEVICE_FILE_NAME_LEN);
		return 0;
	}

	pr("Using file '%s' as storage device\n", fname);

	strcpy(used_file_path, fname);

	if (used_file_fd > 0)
		close(used_file_fd);

	used_file_fd = open(fname, O_RDWR);

	if (used_file_fd < 0) {
		pr_err("failed to open filename '%s'\n", fname);
		return 0;
	}

	int fs_version = identify_fs();
	if (!fs_version) {
		pr_info("filesystem could not be identified on device '%s'\n", fname);
		write_permitted = 0;
	} else if (fs_version != 1) {
		pr_warn("filesystem is corrupted or has unsupported version (0x%hhx)\n", fs_version);
		write_permitted = 0;
	} else if (fs_version == 1) {
		pr_info("filesystem v1 has been identified on device '%s'\n", fname);
		write_permitted = 1;
	}

	if (write_permitted) {
		{
			int bytes_read = read_block(0, (void *) &fsh_cache);
			if (bytes_read < 0) {
				pr_err("failed to cache filesystem header\n");
				write_permitted = 0;
				return 0;
			} else if (bytes_read < FS_BLOCK_SIZE) {
				pr_err("failed to read full filesystem header (read %d/%d bytes)\n", bytes_read, FS_BLOCK_SIZE);
				write_permitted = 0;
				return 0;
			} else {
				pr("Cached filesystem header\n");
			}
		}

		int blocks_used_for_bitmap = fsh_cache.block_count / (FS_BLOCK_SIZE * 8);
		if (fsh_cache.block_count % (FS_BLOCK_SIZE * 8))
			blocks_used_for_bitmap++;

		if (blocks_used_for_bitmap > FS_MAX_BITMAP_SIZE) {
			pr_err("filesystem bitmap too large (%d blocks > %d)\n", blocks_used_for_bitmap, FS_MAX_BITMAP_SIZE);
			write_permitted = 0;
			return 0;
		}

		{
			for (int i = 0; i < blocks_used_for_bitmap; i++) {
				int bytes_read = read_block(i+1, &(fs_bitmap_cache[FS_BLOCK_SIZE*i]));

				if (bytes_read < 0) {
					pr_err("failed to cache filesystem bitmap block %d/%d\n", i+1, blocks_used_for_bitmap);
					write_permitted = 0;
					return 0;
				} else if (bytes_read < FS_BLOCK_SIZE) {
					pr_err("failed to read full filesystem bitmap block %d/%d (read %d/%d bytes)\n",
							i+1, blocks_used_for_bitmap, bytes_read, FS_BLOCK_SIZE);
					write_permitted = 0;
					return 0;
				} else {
					pr("Cached filesystem bitmap block %d/%d\n", i+1, blocks_used_for_bitmap);
				}
			}
		}

		char *root_dir_path = "/";
		fs_chdir((void *) &root_dir_path);
	}

	return 0;
}

int fs_mkfs(void *d)
{
	if (!write_permitted) {
		pr_err("device '%s' is write-protected\n", used_file_path);
		return 0;
	}

	if (used_file_fd <= 0) {
		pr_err("storage device not present\n");
		return 0;
	}

	int max_inode_count = *((int *)d);

	if (max_inode_count <= 0) {
		pr_err("max inode count must be positive (got %d)\n", max_inode_count);
		return 0;
	}

	struct stat st;
	if (fstat(used_file_fd, &st) < 0) {
		pr_err("could not stat device '%s'\n", used_file_path);
		return 0;
	}

	int block_count = st.st_size / FS_BLOCK_SIZE;
	int blocks_used_for_bitmap = block_count / (FS_BLOCK_SIZE * 8);
	if (block_count % (FS_BLOCK_SIZE * 8))
		blocks_used_for_bitmap++;

	if (blocks_used_for_bitmap > FS_MAX_BITMAP_SIZE) {
		pr_err("memory bitmap is too large (%d blocks > %d)\n", blocks_used_for_bitmap, FS_MAX_BITMAP_SIZE);
		return 0;
	}

	pr("Formatting storage device '%s' of size %d (total_block_count = %d, bitmap_blocks = %d) with %d allowed inode pointers\n", used_file_path, st.st_size, block_count, blocks_used_for_bitmap, max_inode_count);

	struct fs_header fsh = {};
	fsh.version = 0x1;
	fsh.max_inode_count = max_inode_count;
	fsh.block_count = block_count;

	pr("header size is %d bytes, writing it to the first block\n", sizeof(fsh));

	int result = write_block(0, (void *) &fsh);
	if (FS_BLOCK_SIZE != result) {
		if (result < 0) {
			pr_err("failed to write fs header to device '%s'\n", used_file_path);
		} else {
			pr_err("failed to write full block to device, written %d/%d bytes\n", result, FS_BLOCK_SIZE);
		}

		return 0;
	}

	// update fsh cache
	memcpy(&fsh_cache, &fsh, FS_BLOCK_SIZE);

	// clear fs_bitmap_cache
	memset(&fs_bitmap_cache, 0, sizeof(fs_bitmap_cache));

	int blocks_used = 1 + blocks_used_for_bitmap;

	unsigned char bitmap_block[FS_BLOCK_SIZE];
	unsigned int j = 0;

	for (int i = 0; i < blocks_used_for_bitmap; i++) {
		memset(bitmap_block, 0, FS_BLOCK_SIZE);
		for (int k = 0; k < FS_BLOCK_SIZE; k++) {
			for (int t = 0; t < 8; t++, j++) {
				if (j == blocks_used)
					goto finish_current_block;

				bitmap_block[i] |= (1 << t);
			}
		}

finish_current_block:
		{
			int bytes_written = write_block(i+1, (void *) bitmap_block);

			if (bytes_written < 0) {
				pr_err("failed to write bitmap block %d/%d on device '%s'\n",
						i+1, blocks_used_for_bitmap, used_file_path);
				return 0;
			} else if (bytes_written < FS_BLOCK_SIZE) {
				pr_err("failed to write full bitmap block %d/%d on device '%s' (written %d/%d bytes)\n",
						i+1, blocks_used_for_bitmap, used_file_path, bytes_written, FS_BLOCK_SIZE);
				return 0;
			} else {
				pr("Written bitmap block %d/%d on device '%s'\n", i+1, blocks_used_for_bitmap, used_file_path);
			}

			// update fs_bitmap_cache
			memcpy(&(fs_bitmap_cache[FS_BLOCK_SIZE*i]), &bitmap_block, FS_BLOCK_SIZE);
		}
	}


	// create root directory automatically

	struct fs_inode root_dir = {};
	root_dir.ftype = DIRECTORY;
	root_dir.ref_count = 1;

	unsigned int free_block_index = find_free_block();

	if (!free_block_index) {
		pr_err("failed to find free block for root directory\n");
		return 0;
	}

	{
		int bytes_written = write_block(free_block_index, (void *) &root_dir);
		if (bytes_written < 0) {
			pr_err("failed to write root directory block on device '%s'\n", used_file_path);
			return 0;
		} else if (bytes_written < FS_BLOCK_SIZE) {
			pr_err("failed to write full root directory block on device '%s' (written %d/%d bytes)\n",
					used_file_path, bytes_written, FS_BLOCK_SIZE);
			return 0;
		} else {
			pr("Written root directory block on device '%s'\n", used_file_path);
		}
	}
	mark_used(free_block_index);

	// inode0 -> root_dir_block
	write_inode_ptr(0, free_block_index);

	char *root_dir_path = "/";
	fs_chdir((void *) &root_dir_path);

	return 0;
}