/************************************************************//**
*
*	@file: io_impl.c
*	@author: Martin Fouilleul
*	@date: 09/05/2023
*
*****************************************************************/

#include<fcntl.h>
#include<sys/stat.h>
#include<unistd.h>
#include<limits.h>
#include"io_common.h"

//TODO: - file_handle to FILE* association
//      - open / close handles
//      - read / write
//      - file positioning & size

typedef struct file_slot
{
	u32 generation;
	int fd;
	io_error error;
	bool fatal;
	list_elt freeListElt;

} file_slot;

enum
{
	ORCA_MAX_FILE_SLOTS = 256,
};

typedef struct file_table
{
	file_slot slots[ORCA_MAX_FILE_SLOTS];
	u32 nextSlot;
	list_info freeList;
} file_table;

file_table __globalFileTable = {0};

file_slot* file_slot_alloc(file_table* table)
{
	file_slot* slot = list_pop_entry(&table->freeList, file_slot, freeListElt);
	if(!slot && table->nextSlot < ORCA_MAX_FILE_SLOTS)
	{
		slot = &table->slots[table->nextSlot];
		slot->generation = 1;
		table->nextSlot++;
	}
	return(slot);
}

void file_slot_recycle(file_table* table, file_slot* slot)
{
	slot->generation++;
	list_push(&table->freeList, &slot->freeListElt);
}

file_handle file_handle_from_slot(file_table* table, file_slot* slot)
{
	u64 index = slot - table->slots;
	u64 generation = slot->generation;
	file_handle handle = {.h = (generation<<32) | index };
	return(handle);
}

file_slot* file_slot_from_handle(file_table* table, file_handle handle)
{
	file_slot* slot = 0;

	u64 index = handle.h & 0xffffffff;
	u64 generation = handle.h>>32;

	if(index < ORCA_MAX_FILE_SLOTS)
	{
		file_slot* candidate = &table->slots[index];
		if(candidate->generation == generation)
		{
			slot = candidate;
		}
	}
	return(slot);
}

io_error io_convert_errno(int e)
{
	io_error error;
	switch(e)
	{
		case EPERM:
		case EACCES:
		case EROFS:
			error = IO_ERR_PERM;
			break;

		case ENOENT:
			error = IO_ERR_NO_ENTRY;
			break;

		case EINTR:
			error = IO_ERR_INTERRUPT;
			break;

		case EIO:
			error = IO_ERR_PHYSICAL;
			break;

		case ENXIO:
			error = IO_ERR_NO_DEVICE;
			break;

		case EBADF:
			// this should only happen when user tries to write/read to a file handle
			// opened with readonly/writeonly access
			error = IO_ERR_PERM;
			break;

		case ENOMEM:
			error = IO_ERR_MEM;
			break;

		case EFAULT:
		case EINVAL:
		case EDOM:
			error = IO_ERR_ARG;
			break;

		case EBUSY:
		case EAGAIN:
			error = IO_ERR_NOT_READY;
			break;

		case EEXIST:
			error = IO_ERR_EXISTS;
			break;

		case ENOTDIR:
			error = IO_ERR_NOT_DIR;
			break;

		case EISDIR:
			error = IO_ERR_DIR;
			break;

		case ENFILE:
		case EMFILE:
			error = IO_ERR_MAX_FILES;
			break;

		case EFBIG:
			error = IO_ERR_FILE_SIZE;
			break;

		case ENOSPC:
		case EDQUOT:
			error = IO_ERR_SPACE;
			break;

		case ELOOP:
			error = IO_ERR_MAX_LINKS;
			break;

		case ENAMETOOLONG:
			error = IO_ERR_PATH_LENGTH;
			break;

		case EOVERFLOW:
			error = IO_ERR_OVERFLOW;
			break;

		default:
			error = IO_ERR_UNKNOWN;
			break;
	}
	return(error);
}

typedef struct io_path_walk_result
{
	io_error error;
	int fd;

} io_path_walk_result;

io_path_walk_result io_path_walk(str8 path)
{
	io_path_walk_result result = {.fd = -1};

	mem_arena* scratch = mem_scratch();
	mem_arena_marker mark = mem_arena_mark(scratch);

	str8_list sep = {0};
	str8_list_push(scratch, &sep, STR8("/"));
	str8_list pathElements = str8_split(scratch, path, sep);

	str8 execPath = path_slice_directory(path_find_executable(scratch));
	str8_list list = {0};
	str8_list_push(scratch, &list, execPath);
	str8_list_push(scratch, &list, STR8("../app/data"));
	str8 dataPath = str8_list_join(scratch, list);

	result.fd = open(str8_to_cstring(scratch, dataPath), O_RDONLY);
	if(result.fd < 0)
	{
		result.error = io_convert_errno(errno);
		goto error;
	}
	struct stat dirStat;
	if(fstat(result.fd, &dirStat))
	{
		result.error = io_convert_errno(errno);
		goto error;
	}
	ino_t baseInode = dirStat.st_ino;
	ino_t currentInode = baseInode;

	for_list(&pathElements.list, elt, str8_elt, listElt)
	{
		str8 name = elt->string;

		if(!str8_cmp(name, STR8(".")))
		{
			//NOTE: skip
			continue;
		}
		else if(!str8_cmp(name, STR8("..")))
		{
			//NOTE: check that we don't escape 'root' dir
			if(currentInode == baseInode)
			{
				result.error = IO_ERR_WALKOUT;
				goto error;
			}
			else
			{
				// open that dir and continue
				int nextFd = openat(result.fd, "..", O_RDONLY);
				if(!nextFd)
				{
					result.error = io_convert_errno(errno);
					goto error;
				}
				else
				{
					close(result.fd);
					result.fd = nextFd;
					if(fstat(result.fd, &dirStat))
					{
						result.error = io_convert_errno(errno);
						goto error;
					}
					currentInode = dirStat.st_ino;
				}
			}
		}
		else
		{
			char* nameCStr = str8_to_cstring(scratch, name);
			struct stat st;

			if(fstatat(result.fd, nameCStr, &st, AT_SYMLINK_NOFOLLOW))
			{
				if(&elt->listElt != list_last(&pathElements.list))
				{
					result.error = io_convert_errno(errno);
					goto error;
				}
				else
				{
					continue;
				}
			}

			int type = st.st_mode & S_IFMT;

			if(type == S_IFLNK)
			{
				// symlink, check that it's relative, and insert it in elements
				char buff[PATH_MAX+1];
				int r = readlinkat(result.fd, nameCStr, buff, PATH_MAX);
				if(r<0)
				{
					result.error = io_convert_errno(errno);
					goto error;
				}
				else if(r == 0)
				{
					//NOTE: skip
				}
				else if(buff[0] == '/')
				{
					result.error = IO_ERR_WALKOUT;
					goto error;
				}
				else
				{
					buff[r] = '\0';

					str8_list linkElements = str8_split(scratch, str8_from_buffer(r, buff), sep);
					if(!list_empty(&linkElements.list))
					{
						//NOTE: insert linkElements into pathElements after elt
						list_elt* tmp = elt->listElt.next;
						elt->listElt.next = linkElements.list.first;
						linkElements.list.last->next = tmp;
						if(!tmp)
						{
							pathElements.list.last = linkElements.list.last;
						}
					}
				}
			}
			else if(type == S_IFDIR)
			{
				// dir, open it and continue
				int nextFd = openat(result.fd, nameCStr, O_RDONLY);
				if(!nextFd)
				{
					result.error = io_convert_errno(errno);
					goto error;
				}
				else
				{
					close(result.fd);
					result.fd = nextFd;
					currentInode = st.st_ino;
				}
			}
			else if(type == S_IFREG)
			{
				// regular file, check that we're at the last element
				if(&elt->listElt != list_last(&pathElements.list))
				{
					result.error = IO_ERR_NOT_DIR;
					goto error;
				}
			}
			else
			{
				result.error = IO_ERR_NOT_DIR;
				goto error;
			}
		}
	}
	goto end;

	error:
	{
		close(result.fd);
		result.fd = -1;
	}
	end:
	mem_arena_clear_to(scratch, mark);
	return(result);
}

io_cmp io_open(io_req* req)
{
	io_cmp cmp = {0};

	file_slot* slot = file_slot_alloc(&__globalFileTable);
	if(!slot)
	{
		cmp.error = IO_ERR_MAX_FILES;
		cmp.result = 0;
	}
	else
	{
		file_handle handle = file_handle_from_slot(&__globalFileTable, slot);
		cmp.result = handle.h;

		int flags = 0;
		if(req->openFlags & IO_OPEN_READ)
		{
			if(req->openFlags & IO_OPEN_WRITE)
			{
				flags = O_RDWR;
			}
			else
			{
				flags = O_RDONLY;
			}
		}
		else if(req->openFlags & IO_OPEN_WRITE)
		{
			flags = O_WRONLY;
		}

		if(req->openFlags & IO_OPEN_TRUNCATE)
		{
			flags |= O_TRUNC;
		}
		if(req->openFlags & IO_OPEN_APPEND)
		{
			flags |= O_APPEND;
		}
		if(req->openFlags & IO_OPEN_CREATE)
		{
			flags |= O_CREAT;
		}

		flags |= O_NOFOLLOW;

		mode_t mode = S_IRUSR
	            	| S_IWUSR
	            	| S_IRGRP
	            	| S_IWGRP
	            	| S_IROTH
	            	| S_IWOTH;

		//NOTE: walk path (ensuring it's inside app's data directory subtree)
		str8 path = str8_from_buffer(req->size, req->buffer);
		io_path_walk_result walkRes = io_path_walk(path);
		if(walkRes.error != IO_OK)
		{
			slot->fd = -1;
			slot->fatal = true;
			slot->error = walkRes.error;
		}
		else
		{
			//NOTE: open
			mem_arena* scratch = mem_scratch();
			mem_arena_marker mark = mem_arena_mark(scratch);

			str8 name = path_slice_filename(path);
			char* nameCStr = str8_to_cstring(scratch, name);
			int fd = openat(walkRes.fd, nameCStr, flags, mode);
			close(walkRes.fd);

			mem_arena_clear_to(scratch, mark);

			if(fd >= 0)
			{
				slot->fd = fd;
				file_handle handle = file_handle_from_slot(&__globalFileTable, slot);
				cmp.result = handle.h;
			}
			else
			{
				slot->fd = -1;
				slot->fatal = true;
				slot->error = io_convert_errno(errno);
			}
		}

		cmp.error = slot->error;
	}

	return(cmp);
}

io_cmp io_close(file_slot* slot, io_req* req)
{
	io_cmp cmp = {0};
	if(slot->fd >= 0)
	{
		close(slot->fd);
	}
	file_slot_recycle(&__globalFileTable, slot);
	return(cmp);
}

io_cmp io_size(file_slot* slot, io_req* req)
{
	io_cmp cmp = {0};

	struct stat s;
	if(fstat(slot->fd, &s))
	{
		slot->error = IO_ERR_UNKNOWN;
		cmp.error = slot->error;
	}
	else
	{
		cmp.result = s.st_size;
	}

	return(cmp);
}

io_cmp io_pos(file_slot* slot, io_req* req)
{
	io_cmp cmp = {0};
	cmp.result = lseek(slot->fd, 0, SEEK_CUR);
	if(cmp.result < 0)
	{
		switch(errno)
		{
			case EINVAL:
				slot->error = IO_ERR_ARG;
				break;

			case EOVERFLOW:
				slot->error = IO_ERR_OVERFLOW;
				break;

			default:
				slot->error = IO_ERR_UNKNOWN;
				break;
		}
		cmp.error = slot->error;
	}

	return(cmp);
}

io_cmp io_seek(file_slot* slot, io_req* req)
{
	io_cmp cmp = {0};

	int whence;
	switch(req->whence)
	{
		case IO_SEEK_CURRENT:
			whence = SEEK_CUR;
			break;

		case IO_SEEK_SET:
			whence = SEEK_SET;
			break;

		case IO_SEEK_END:
			whence = SEEK_END;
	}
	cmp.result = lseek(slot->fd, req->size, whence);

	if(cmp.result < 0)
	{
		switch(errno)
		{
			case EINVAL:
				slot->error = IO_ERR_ARG;
				break;

			case EOVERFLOW:
				slot->error = IO_ERR_OVERFLOW;
				break;

			default:
				slot->error = IO_ERR_UNKNOWN;
				break;
		}
		cmp.error = slot->error;
	}

	return(cmp);
}

io_cmp io_read(file_slot* slot, io_req* req)
{
	io_cmp cmp = {0};

	cmp.result = read(slot->fd, req->buffer, req->size);

	if(cmp.result < 0)
	{
		switch(errno)
		{
			case EAGAIN:
				slot->error = IO_ERR_NOT_READY;
				break;

			case EFAULT:
			case EINVAL:
				slot->error = IO_ERR_ARG;
				break;

			case ENOBUFS:
			case ENOMEM:
				slot->error = IO_ERR_MEM;
				break;

			default:
				slot->error = IO_ERR_UNKNOWN;
				break;
		}
		cmp.error = slot->error;
	}

	return(cmp);
}

io_cmp io_write(file_slot* slot, io_req* req)
{
	io_cmp cmp = {0};

	cmp.result = write(slot->fd, req->buffer, req->size);

	if(cmp.result < 0)
	{
		switch(errno)
		{
			case EDQUOT:
			case ENOSPC:
				slot->error = IO_ERR_SPACE;
				break;

			case EFAULT:
			case EINVAL:
				slot->error = IO_ERR_ARG;
				break;

			case EAGAIN:
				slot->error = IO_ERR_NOT_READY;
				break;

			case EFBIG:
				slot->error = IO_ERR_FILE_SIZE;
				break;

			case ENOBUFS:
			case ENOMEM:
				slot->error = IO_ERR_MEM;
				break;

			default:
				slot->error = IO_ERR_UNKNOWN;
				break;
		}
		cmp.error = slot->error;
	}

	return(cmp);
}

io_cmp io_get_error(file_slot* slot, io_req* req)
{
	io_cmp cmp = {0};
	cmp.result = slot->error;
	return(cmp);
}

io_cmp io_wait_single_req(io_req* req)
{
	mem_arena* scratch = mem_scratch();

	io_cmp cmp = {0};

	////////////////////////////////////////////////////////////////////////////////////////
	//TODO: we need to convert the req->buffer wasm pointer to a native pointer here
	////////////////////////////////////////////////////////////////////////////////////////
	//TODO: check that req->buffer lies in wasm memory with at least req->size space

	/////////////////////////////////////////////////
	//TODO: we can't read reqs from wasm memory since the pointers are not the same size
	//      (hence the layout won't be the same...)
	/////////////////////////////////////////////////

	//NOTE: for some reason, wasm3 memory doesn't start at the beginning of the block we give it.
	u32 memSize = 0;
	char* memory = (char*)m3_GetMemory(__orcaApp.runtime.m3Runtime, &memSize, 0);

	u64 bufferIndex = (u64)req->buffer & 0xffffffff;

	if(bufferIndex + req->size > memSize)
	{
		cmp.error = IO_ERR_ARG;
	}
	else
	{
		//TODO: avoid modifying req.
		req->buffer = memory + bufferIndex;

		file_slot* slot = 0;
		if(req->op != IO_OP_OPEN)
		{
			slot = file_slot_from_handle(&__globalFileTable, req->handle);
			if(!slot)
			{
				cmp.error = IO_ERR_HANDLE;
			}
			else if(slot->fatal && req->op != IO_OP_CLOSE)
			{
				cmp.error = IO_ERR_PREV;
			}
		}

		if(cmp.error == IO_OK)
		{
			switch(req->op)
			{
				case IO_OP_OPEN:
					cmp = io_open(req);
					break;

				case IO_OP_CLOSE:
					cmp = io_close(slot, req);
					break;

				case IO_OP_SIZE:
					cmp = io_size(slot, req);
					break;

				case IO_OP_READ:
					cmp = io_read(slot, req);
					break;

				case IO_OP_WRITE:
					cmp = io_write(slot, req);
					break;

				case IO_OP_POS:
					cmp = io_pos(slot, req);
					break;

				case IO_OP_SEEK:
					cmp = io_seek(slot, req);
					break;

				case IO_OP_ERROR:
					cmp = io_get_error(slot, req);
					break;

				default:
					cmp.error = IO_ERR_OP;
					break;
			}
		}
	}

	return(cmp);
}