local kernel = ...
local vfs = {}
vfs.mounts = { ["$"] = "/" }
local disks = kernel.disks

-- Path handling
local function normalizePath(path)
    local parts = {}
    for part in path:gmatch("[^/]+") do
        if part == ".." then
            if #parts > 0 then table.remove(parts) end
        elseif part ~= "." and part ~= "" then
            table.insert(parts, part)
        end
    end
    return "/" .. table.concat(parts, "/") .. (path:sub(-1) == "/" and "/" or "")
end

local function resolvePath(path)
    local task = kernel.currentTask
    local cwd = task.cwd or "/"

    if path:sub(1,1) ~= "/" then
        path = cwd .. path
    end

    path = normalizePath(path)

    local mountPoint = "/"
    local mountId = "$"
    for k,v in pairs(vfs.mounts) do
        if path:sub(1,#v) == v and #v > #mountPoint then
            mountPoint = v
            mountId = k
        end
    end

    local diskPath = path:sub(#mountPoint + 1)
    return disks[mountId], diskPath
end

-- File object creation
local function newFileObject(disk, handle, mode, path)
    return {
        disk = disk,
        handle = handle,
        mode = mode,
        path = path,
        refcount = 1
    }
end

local function allocFD(task)
    local fd = 0
    while task.fd[fd] do fd = fd + 1 end
    return fd
end

local function allocFD(task)
    -- enforce per-task limit
    local count = 0
    for _ in pairs(task.fd) do count = count + 1 end
    if count >= kernel.config.maxFilesPerTask then
        error("EMFILE") -- Too many open files in this task
    end

    -- find first free FD
    local fd = 0
    while task.fd[fd] do fd = fd + 1 end
    return fd
end

local function checkSystemLimit()
    -- enforce system-wide limit
    local total = 0
    for _, task in pairs(kernel.tasks or {}) do
        for _ in pairs(task.fd) do total = total + 1 end
    end
    if total >= kernel.config.maxOpenFiles then
        error("ENFILE") -- Too many open files in the system
    end
end

-- VFS syscalls
function vfs.open(path, mode)
    local task = kernel.currentTask

    -- check limits
    checkSystemLimit()

    local disk, diskPath = resolvePath(path)
    if not disk then
        error("No disk mounted for path '"..path.."'")
    end

    local handle = disk:open(diskPath, mode)
    if not handle then return nil end

    local file = newFileObject(disk.address, handle, mode, path)
    local fd = allocFD(task)
    task.fd[fd] = file

    return fd
end

function vfs.close(fd)
    local task = kernel.currentTask
    local file = task.fd[fd]
    if not file then error("EBADF") end

    task.fd[fd] = nil
    file.refcount = file.refcount - 1
    if file.refcount == 0 then
        file.handle.close()
    end
    return true
end

function vfs.read(fd, count)
    local file = kernel.currentTask.fd[fd]
    if not file then error("EBADF") end
    if not file.mode:find("r") then error("File not open for reading") end
    return file.handle.read(count)
end

function vfs.write(fd, data)
    local file = kernel.currentTask.fd[fd]
    if not file then error("EBADF") end
    if not file.mode:find("w") then error("File not open for writing") end
    return file.handle.write(data)
end

function vfs.whereis(fd)
    local file = kernel.currentTask.fd[fd]
    if not file then error("EBADF") end
    return file.path
end

-- Filesystem operations
function vfs.mkdir(path)
    local disk, diskPath = resolvePath(path)
    if not disk then error("No disk mounted") end
    return disk:makeDirectory(diskPath)
end

function vfs.remove(path)
    local disk, diskPath = resolvePath(path)
    if not disk then error("No disk mounted") end
    return disk:remove(diskPath)
end

function vfs.attributes(path)
    if type(path) == "number" then
        local file = kernel.currentTask.fd[path]
        if not file then error("EBADF") end
        return disks[file.disk]:attributes(file.path)
    end
    local disk, diskPath = resolvePath(path)
    if not disk then error("No disk mounted") end
    return disk:attributes(diskPath)
end

function vfs.list(path)
    local disk, diskPath = resolvePath(path)
    if not disk then error("No disk mounted") end
    return disk:list(diskPath)
end

function vfs.exists(path)
    local disk, diskPath = resolvePath(path)
    if not disk then return false end
    return disk:directoryExists(diskPath) or disk:fileExists(diskPath)
end

function vfs.type(path)
    if type(path) == "number" then
        local file = kernel.currentTask.fd[path]
        if not file then error("EBADF") end
        return disks[file.disk]:type(file.path)
    end
    local disk, diskPath = resolvePath(path)
    if not disk then error("No disk mounted") end
    return disk:type(diskPath)
end

-- CWD
function vfs.getcwd()
    return kernel.currentTask.cwd
end

function vfs.setcwd(path)
    if path:sub(-1) ~= "/" then path = path .. "/" end
    if path:sub(1,1) ~= "/" then path = "/" .. path end
    kernel.currentTask.cwd = normalizePath(path)
end

-- Mounting
function vfs.mount(diskId, path)
    if kernel.uid ~= 0 then error("Permission denied") end
    if not disks[diskId] then error("Unknown disk '"..diskId.."'") end
    if path:sub(-1) ~= "/" then path = path .. "/" end

    for _,v in pairs(vfs.mounts) do
        if v == path then error("Mount point already used") end
    end
    vfs.mounts[diskId] = path
end

function vfs.unmount(path)
    if kernel.uid ~= 0 then error("Permission denied") end
    for k,v in pairs(vfs.mounts) do
        if v == path then
            vfs.mounts[k] = nil
            return true
        end
    end
    return false
end

function vfs.getMounts()
    return vfs.mounts
end

function vfs.virtdisk(obj)
    kernel.disks[obj.address] = obj
    kernel.log("Registered virtual disk at "..obj.address)
end

-- Redirect file operations to VFS
function vfs.dup(oldfd)
    local task = kernel.currentTask
    local file = task.fd[oldfd]
    if not file then error("EBADF") end

    local newfd = allocFD(task)
    task.fd[newfd] = file
    file.refcount = file.refcount + 1
    return newfd
end

function vfs.dup2(oldfd, newfd)
    local task = kernel.currentTask
    local file = task.fd[oldfd]
    if not file then error("EBADF") end

    if oldfd == newfd then return newfd end

    if task.fd[newfd] then
        vfs.close(newfd)
    end

    task.fd[newfd] = file
    file.refcount = file.refcount + 1
    return newfd
end

-- Syscall registration
kernel.vfs = vfs
kernel.syscalls["VFS_open"]        = vfs.open
kernel.syscalls["VFS_read"]        = vfs.read
kernel.syscalls["VFS_write"]       = vfs.write
kernel.syscalls["VFS_close"]       = vfs.close
kernel.syscalls["VFS_list"]        = vfs.list
kernel.syscalls["VFS_type"]        = vfs.type
kernel.syscalls["VFS_attributes"]  = vfs.attributes
kernel.syscalls["VFS_mkdir"]       = vfs.mkdir
kernel.syscalls["VFS_remove"]      = vfs.remove
kernel.syscalls["VFS_exists"]      = vfs.exists
kernel.syscalls["VFS_mount"]       = vfs.mount
kernel.syscalls["VFS_unmount"]     = vfs.unmount
kernel.syscalls["VFS_getcwd"]      = vfs.getcwd
kernel.syscalls["VFS_setcwd"]      = vfs.setcwd
kernel.syscalls["VFS_whereis"]    = vfs.whereis
kernel.syscalls["VFS_dup"]        = vfs.dup
kernel.syscalls["VFS_dup2"]       = vfs.dup2

kernel.log("VFS module loaded")