1 files changed, 114 insertions, 0 deletions
diff --git a/promises.lua b/promises.lua
new file mode 100644
index 0000000..fb86af7
--- /dev/null
+++ b/promises.lua
@@ -0,0 +1,114 @@
+local PromisePrototype = {}
+
+function PromisePrototype:__run_handler(func, ...)
+	local values = {pcall(func, ...)}
+
+	if table.remove(values, 1) then
+		self:__resolve_raw(unpack(values))
+	else
+		self:__reject_raw(values[1])
+	end
+end
+
+function PromisePrototype:__add_child(promise)
+	if self.state == "resolved" then
+		promise:__resolve(unpack(self.values))
+	elseif self.state == "rejected" then
+		promise:__reject(self.reason)
+	else
+		table.insert(self.__children, promise)
+	end
+end
+
+function PromisePrototype:__resolve_raw(...)
+	self.state = "resolved"
+	self.values = {...}
+	self.reason = nil
+
+	for _, child in ipairs(self.__children) do
+		child:resolve(...)
+	end
+end
+
+function PromisePrototype:__reject_raw(reason)
+	self.state = "rejected"
+	self.values = nil
+	self.reason = reason
+
+	local any_child = false
+
+	for _, child in ipairs(self.__children) do
+		child:reject(reason)
+	end
+
+	assert(any_child, "Uncaught (in promise): " .. reason)
+end
+
+function PromisePrototype:resolve(...)
+	assert(self.state == "pending")
+
+	if self.__on_resolve then
+		self:__run_handler(self.__on_resolve, ...)
+	else
+		self:__resolve_raw(...)
+	end
+end
+
+function PromisePrototype:reject(reason)
+	assert(self.state == "pending")
+
+	if self.__on_reject then
+		self:__run_handler(self.__on_reject, reason)
+	else
+		self:__reject_raw(reason)
+	end
+end
+
+function PromisePrototype:then_(func)
+	local promise = Promise()
+	promise.__on_resolve = func
+
+	self:__add_child(promise)
+
+	return promise
+end
+
+function PromisePrototype:catch(func)
+	local promise = Promise(function() end)
+	promise.__on_reject = func
+
+	self:__add_child(promise)
+
+	return promise
+end
+
+Promise = setmetatable({}, {
+	__call = function(_, resolver)
+		local promise = {
+			state = "pending",
+			__children = {},
+		}
+
+		setmetatable(promise, {__index = PromisePrototype})
+
+		if resolver then
+			resolver(
+				function(...)
+					promise:resolve(...)
+				end,
+				function(...)
+					promise:reject(...)
+				end
+			)
+		end
+
+		return promise
+	end
+})
+
+function Promise.resolve(...)
+	local args = {...}
+	return Promise(function(resolve)
+		resolve(unpack(args))
+	end)
+end