RAII-based fault-tolerant(?) tempfile module - ABSOLUTELY UNTESTED, WRITTEN IN A DISCORD CHATBOX, (doesn't work no `__gc` in Luau)

raii_tempfile.luau

--> RAII-based fault-tolerant(?) tempfile module

local fs = require("@lune/fs")

local CHARSET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
local function randId(len: number?, rng: () -> number) 
  local bytes = {}
  for _ = 1, len do
      local byte = math.random(1, #CHARSET)
      table.insert(bytes, string.sub(CHARSET, byte, byte))
  end

  return table.concat(bytes)
end

-- borderline useless micro-opt but mulberry32 is simpler than pcg32, why not
local function mulberry32(seed: number)
    local state = bit32.band(seed, 0xFFFFFFFF)
    return function()
        state = bit32.band(state + 0x6D2B79F5, 0xFFFFFFFF)
        local t = state
        t = bit32.bxor(t, bit32.rshift(t, 15))
        t = bit32.band(t * (1 | t), 0xFFFFFFFF)
        t = bit32.bxor(t, t + bit32.rshift(t, 7))
        t = bit32.bxor(t, bit32.rshift(t, 3))
        return bit32.band(t, 0xFFFFFFFF) / 4294967296
    end
end

local TempfileInner = {}

type TempfileFields = { _name: string, _options: TempfileOptions, _rng: () -> number }
export type Tempfile = typeof(setmetatable({} :: TempfileFields, { 
  __index = TempfileInner,
  __gc = function(self: TempfileFields) end
}))

export type TempfileOptions = {
  prefix: string?,
  suffix: string?,
  idLength: number?,
  rng: (() -> number)?,
}

local function tempName(options: TempfileOptions)
  local prefix = options.prefix or ""
  local suffix = options.suffix or ""
  local idLength = options.idLength or 7
  local rng = options.rng or mulberry32(os.time())

  return `{prefix}-{randomId(idLength)}{suffix}`
end

function tempfile(options: TempfileOptions?): Tempfile
  local optionsInner = options or {}
  
  local rng = mulberry32(os.time())
  optionsInner.rng = optionsInner.rng or rng
  
  return setmetatable({
    _name = tempName(optionsInner)
    _rng = rng,
    _options = _options,
  } :: Tempfields, {
    __index = TempfileInner,
    __gc = function(self: TempfileFields)
      fs.removeFile(`/tmp/{self._name}`)
    end
  })
end

function TempfileInner.create(self: Tempfile): string
    -- TODO: make this cross platform
    for _ = 1, 5 do
      local path = `/tmp/{self._name}`
      local ok = pcall(fs.writeFile, path, "") -- TODO: consider checking err type

      if not ok then
         self._rng = mulberry32(os.time())
         self._name = tempName(self._options)
         continue
      end
      
      return path
    end

    error("Had 5 tempfile colissions, giving up, boss")
end

function TempfileInner.write(self: Tempfile, contents: string)
   local path = self:create()
   return fs.writeFile(path, string)
end

function TempfileInner.read(self: Tempfile): buffer
  return buffer.fromstring(fs.readFile(`/tmp/{self._name}`))
end

return tempfile