'use strict';

const {

SafeMap,

Symbol,

} = primordials;

// Private symbols

const kFd = Symbol('kFd');

const kEntry = Symbol('kEntry');

// VFS FDs use bit 30 set to avoid conflicts with real OS fds.

// Real fds are small non-negative integers; VFS fds start at 0x40000000.

const VFS_FD_MASK = 0x40000000;

let nextFd = 0;

// Global registry of open virtual file descriptors

const openFDs = new SafeMap();

/**

* Represents an open virtual file descriptor.

* Wraps a VirtualFileHandle from the provider.

*/

class VirtualFD {

/**

* @param {number} fd The file descriptor number

* @param {VirtualFileHandle} entry The virtual file handle

*/

constructor(fd, entry) {

this[kFd] = fd;

this[kEntry] = entry;

}

/**

* Gets the file descriptor number.

* @returns {number}

*/

get fd() {

return this[kFd];

}

/**

* Gets the file handle.

* @returns {VirtualFileHandle}

*/

get entry() {

return this[kEntry];

}

}

/**

* Opens a virtual file and returns its file descriptor.

* @param {VirtualFileHandle} entry The virtual file handle

* @returns {number} The file descriptor

*/

function openVirtualFd(entry) {

const fd = VFS_FD_MASK | nextFd++;

const vfd = new VirtualFD(fd, entry);

openFDs.set(fd, vfd);

return fd;

}

/**

* Gets a VirtualFD by its file descriptor number.

* @param {number} fd The file descriptor number

* @returns {VirtualFD|undefined}

*/

function getVirtualFd(fd) {

return openFDs.get(fd);

}

/**

* Closes a virtual file descriptor.

* @param {number} fd The file descriptor number

* @returns {boolean} True if the fd was found and closed

*/

function closeVirtualFd(fd) {

return openFDs.delete(fd);

}

module.exports = {

VFS_FD_MASK,

VirtualFD,

openVirtualFd,

getVirtualFd,

closeVirtualFd,

};