-- module will return a stub module table
local spy = require 'luassert.spy'
local util = require 'luassert.util'
local stubfunc = function() end
local stub = {}

function stub.new(object, key)
  if object == nil and key == nil then
    -- called without arguments, create a 'blank' stub
    object = {}
    key = ""
  end
  assert(type(object) == "table" and key ~= nil, "stub.new(): Can only create stub on a table key, call with 2 params; table, key")
  assert(object[key] == nil or util.callable(object[key]), "stub.new(): The element for which to create a stub must either be callable, or be nil")
  local old_elem = object[key]    -- keep existing element (might be nil!)
  object[key] = stubfunc          -- set the stubfunction
  local s = spy.on(object, key)   -- create a spy on top of the stub function
  local spy_revert = s.revert     -- keep created revert function
  
  s.revert = function(self)       -- wrap revert function to restore original element
    if not self.reverted then
      spy_revert(self)
      object[key] = old_elem
      self.reverted = true
    end
    return old_elem
  end
  
  return s
end

function stub.is_stub(object)
  return spy.is_spy(object) and object.callback == stubfunc
end

local function set_stub(state)
end

assert:register("modifier", "stub", set_stub)

return setmetatable( stub, {
    __call = function(self, ...)
      -- stub originally was a function only. Now that it is a module table
      -- the __call method is required for backward compatibility
      -- NOTE: this deviates from spy, which has no __call method
      return stub.new(...)
    end })