--[[
	Constructs a new Promise with the given initializing callback.

	This is generally only called when directly wrapping a non-promise API into
	a promise-based version.

	The callback will receive 'resolve' and 'reject' methods, used to start
	invoking the promise chain.

	Second parameter, parent, is used internally for tracking the "parent" in a
	promise chain. External code shouldn't need to worry about this.
]]

function Promise._new(traceback, callback, parent)
	if parent ~= nil and not Promise.is(parent) then
		error("Argument #2 to Promise.new must be a promise or nil", 2)
	end

	local self = {
		-- Used to locate where a promise was created
		_source = traceback,

		_status = Promise.Status.Started,

		-- A table containing a list of all results, whether success or failure.
		-- Only valid if _status is set to something besides Started
		_values = nil,

		-- Lua doesn't like sparse arrays very much, so we explicitly store the
		-- length of _values to handle middle nils.
		_valuesLength = -1,

		-- Tracks if this Promise has no error observers..
		_unhandledRejection = true,

		-- Queues representing functions we should invoke when we update!
		_queuedResolve = {},
		_queuedReject = {},
		_queuedFinally = {},

		-- The function to run when/if this promise is cancelled.
		_cancellationHook = nil,

		-- The "parent" of this promise in a promise chain. Required for
		-- cancellation propagation upstream.
		_parent = parent,

		-- Consumers are Promises that have chained onto this one.
		-- We track them for cancellation propagation downstream.
		_consumers = setmetatable({}, MODE_KEY_METATABLE),
	}

	if parent and parent._status == Promise.Status.Started then
		parent._consumers[self] = true
	end

	setmetatable(self, Promise)

	local function resolve(...)
		self:_resolve(...)
	end

	local function reject(...)
		self:_reject(...)
	end

	local function onCancel(cancellationHook)
		if cancellationHook then
			if self._status == Promise.Status.Cancelled then
				cancellationHook()
			else
				self._cancellationHook = cancellationHook
			end
		end

		return self._status == Promise.Status.Cancelled
	end

	coroutine.wrap(function()
		local ok, _, result = runExecutor(
			self._source,
			callback,
			resolve,
			reject,
			onCancel
		)

		if not ok then
			reject(result[1])
		end
	end)()

	return self
end

function Promise.new(executor)
	return Promise._new(debug.traceback(nil, 2), executor)
end

function Promise:__tostring()
	return string.format("Promise(%s)", self:getStatus())
end
