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promise.lua
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promise.lua
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---------
-- promise library/module
-- Port of https://github.com/rhysbrettbowen/promise_impl/blob/master/promise.js
-- and https://github.com/rhysbrettbowen/Aplus
-- Source: https://github.com/Billiam/promise.lua
local State = {
PENDING = 'pending',
FULFILLED = 'fulfilled',
REJECTED = 'rejected',
}
local function callable_table(callback)
local mt = getmetatable(callback)
return type(mt) == 'table' and type(mt.__call) == 'function'
end
local function is_callable(value)
local t = type(value)
return t == 'function' or (t == 'table' and callable_table(value))
end
local transition, resolve, run
local prototype = {
is_promise = true,
state = State.PENDING
}
local mt = { __index = prototype }
local reject = function(promise, reason)
transition(promise, State.REJECTED, reason)
end
local fulfill = function(promise, value)
transition(promise, State.FULFILLED, value)
end
transition = function(promise, state, value)
if promise.state == state
or promise.state ~= State.PENDING
or ( state ~= State.FULFILLED and state ~= State.REJECTED )
then
return
end
promise.state = state
promise.value = value
run(promise)
end
function prototype:next(on_fulfilled, on_rejected)
local promise = Promise.new()
table.insert(self.queue, {
fulfill = is_callable(on_fulfilled) and on_fulfilled or nil,
reject = is_callable(on_rejected) and on_rejected or nil,
promise = promise
})
run(self)
return promise
end
resolve = function(promise, x)
if promise == x then
reject(promise, 'TypeError: cannot resolve a promise with itself')
return
end
local x_type = type(x)
if x_type ~= 'table' then
fulfill(promise, x)
return
end
-- x is a promise in the current implementation
if x.is_promise then
-- 2.3.2.1 if x is pending, resolve or reject this promise after completion
if x.state == State.PENDING then
x:next(
function(value)
resolve(promise, value)
end,
function(reason)
reject(promise, reason)
end
)
return
end
-- if x is not pending, transition promise to x's state and value
transition(promise, x.state, x.value)
return
end
local called = false
-- 2.3.3.1. Catches errors thrown by __index metatable
local success, reason = pcall(function()
local next = x.next
if is_callable(next) then
next(
x,
function(y)
if not called then
resolve(promise, y)
called = true
end
end,
function(r)
if not called then
reject(promise, r)
called = true
end
end
)
else
fulfill(promise, x)
end
end)
if not success then
if not called then
reject(promise, reason)
end
end
end
run = function(promise)
if promise.state == State.PENDING then return end
minetest.after(0, function()
-- drain promise.queue while allowing pushes from within callbacks
local q = promise.queue
local i = 0
while i < #q do
i = i + 1
local obj = q[i]
local success, result = pcall(function()
local success_fn = obj.fulfill or function(x) return x end
local failure_fn = obj.reject or function(x) error(x) end
local callback = promise.state == State.FULFILLED and success_fn or failure_fn
return callback(promise.value)
end)
if not success and obj.reject == nil then
-- replace reason
result = promise.value
end
if not success then
reject(obj.promise, result)
else
resolve(obj.promise, result)
end
end
for j = 1, i do
q[j] = nil
end
end)
end
function Promise.new(callback)
local instance = {
queue = {}
}
setmetatable(instance, mt)
if callback then
callback(
function(value)
resolve(instance, value)
end,
function(reason)
reject(instance, reason)
end
)
end
return instance
end
function prototype:catch(callback)
return self:next(nil, callback)
end
function prototype:resolve(value)
fulfill(self, value)
end
function prototype:reject(reason)
reject(self, reason)
end
-- resolve when all promises complete
function Promise.all(...)
local promises = {...}
local results = {}
local state = State.FULFILLED
local remaining = #promises
local promise = Promise.new()
local check_finished = function()
if remaining > 0 then
return
end
transition(promise, state, results)
end
for i,p in ipairs(promises) do
p:next(
function(value)
results[i] = value
remaining = remaining - 1
check_finished()
end,
function(value)
results[i] = value
remaining = remaining - 1
state = State.REJECTED
check_finished()
end
)
end
check_finished()
return promise
end
-- resolve with first promise to complete
function Promise.race(...)
local promises = {...}
local promise = Promise.new()
Promise.all(...):next(nil, function(value)
reject(promise, value)
end)
local success = function(value)
fulfill(promise, value)
end
for _,p in ipairs(promises) do
p:next(success)
end
return promise
end