-- how to annotate this function
function ModuleMockerClass:_ensureMockState(f): MockFunctionState<any, any>
	local state = self._mockState[f]
	if not state then
		state = self:_defaultMockState()
		self._mockState[f] = state
	end

	return state
end

function ModuleMockerClass:_defaultMockConfig(): MockFunctionConfig
	return {
		mockImpl = nil,
		mockName = "jest.fn()",
		specificMockImpls = {},
		specificReturnValues = {},
	}
end

function ModuleMockerClass:_defaultMockState()
	return {
		calls = {},
		instances = {},
		invocationCallOrder = {},
		results = {},
	}
end

function ModuleMockerClass:_makeComponent(metadata: any, restore)
	if metadata.type == "function" then
		local mocker = self

		local mockConstructor = function(f, ...)
			local args = { ... }

			local mockState = mocker:_ensureMockState(f)
			local mockConfig = mocker:_ensureMockConfig(f)

			table.insert(mockState.instances, f)
			-- ROBLOX deviation: We use a Symbol meant to represent nil instead of
			-- actual nil values to help with handling nil values
			for i = 1, select("#", ...) do
				if args[i] == nil then
					args[i] = Symbol.for_("$$nil")
				end
			end
			table.insert(mockState.calls, args)

			-- Create and record an "incomplete" mock result immediately upon
			-- calling rather than waiting for the mock to return. This avoids
			-- issues caused by recursion where results can be recorded in the
			-- wrong order.
			local mockResult = {
				type = "incomplete",
				value = nil,
			}

			table.insert(mockState.results, mockResult)
			table.insert(mockState.invocationCallOrder, mocker._invocationCallCounter)
			self._invocationCallCounter = self._invocationCallCounter + 1

			-- ROBLOX deviation: omitted finalReturnValue, thrownError, and
			-- callDidThrowError as we get this state for free with our
			-- pcall error handling

			local ok, result = pcall(function(args_)
				-- ROBLOX deviation: omitted section of code dealing with calling
				-- function as constructor
				local specificMockImpl = Array.shift(mockConfig.specificMockImpls)
				if specificMockImpl == nil then
					specificMockImpl = mockConfig.mockImpl
				end

				if specificMockImpl then
					return specificMockImpl(unpack(args_))
				end

				-- ROBLOX deviation: omitted section on f._protoImpl
				return nil
			end, { ... })

			if not ok then
				mockResult.type = "throw"
				mockResult.value = result

				error(result)
			end

			mockResult.type = "return"
			mockResult.value = result

			return result
		end

		local f = setmetatable({}, { __call = mockConstructor })

		f._isMockFunction = true
		f.getMockImplementation = function()
			return self:_ensureMockConfig(f).mockImpl
		end

		if typeof(restore) == "function" then
			self._spyState.add(restore)
		end

		self._mockState[f] = self._defaultMockState()
		self._mockConfigRegistry[f] = self._defaultMockConfig()

		f.mock = setmetatable({}, {
			__index = function(tbl, key)
				return self:_ensureMockState(f)[key]
			end,
			-- ROBLOX deviation: for now we don't have newindex defined as we don't have any use cases
			-- but it should look something like the following
			-- __newindex = function(table, key, value)
			-- 		local state = self:_ensureMockState(f)
			-- 		state[key] = value
			-- 		return state
			-- 	end
		})

		f.mockClear = function()
			self._mockState[f] = nil
			return f
		end

		f.mockReset = function()
			f.mockClear()
			self._mockConfigRegistry[f] = nil
			return f
		end

		f.mockRestore = function()
			f.mockReset()
			if restore then
				return restore()
			else
				return nil
			end
		end

		-- ROBLOX deviation: omitted mockResolvedValue and mockRejectedValue

		f.mockImplementationOnce = function(fn)
			-- next function call will use this mock implementation return value
			-- or default mock implementation return value
			local mockConfig = self:_ensureMockConfig(f)
			table.insert(mockConfig.specificMockImpls, fn)
			return f
		end

		f.mockImplementation = function(fn)
			-- next function call will use mock implementation return value
			local mockConfig = self:_ensureMockConfig(f)
			mockConfig.mockImpl = fn
			return f
		end

		f.mockReturnValueOnce = function(value)
			-- next function call will return this value or default return value
			return f.mockImplementationOnce(function()
				return value
			end)
		end

		-- ROBLOX deviation: omitted mockResolvedValueOnce and mockRejectedValueOnce

		f.mockReturnValue = function(value)
			-- next function call will return specified return value or this one
			return f.mockImplementation(function()
				return value
			end)
		end

		f.mockReturnThis = function()
			return f.mockImplementation(function(this)
				return f
			end)
		end

		f.mockName = function(name)
			if name then
				local mockConfig = self:_ensureMockConfig(f)
				mockConfig.mockName = name
			end
			return f
		end

		f.getMockName = function()
			local mockConfig = self:_ensureMockConfig(f)
			return mockConfig.mockName or "jest.fn()"
		end

		-- ROBLOX deviation: Since we don't have the new keyword in Lua, we add a
		-- fn.new() function
		f.new = function(...)
			f(...)
			return f
		end

		if metadata.mockImpl then
			f.mockImplementation(metadata.mockImpl)
		end

		return f
	else
		error("Call to _makeComponent with non-function")
	end
end

function ModuleMockerClass:_createMockFunction(metadata, mockConstructor)
	local name = metadata.name
	if not name then
		return mockConstructor
	end

	-- ROBLOX TODO: Implement more advanced case for keeping name rather than just returning mockConstructor
	return mockConstructor
end

function ModuleMockerClass:isMockFunction(fn: any)
	return typeof(fn) == "table" and fn._isMockFunction == true
end