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promise.go
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promise.go
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package promise
import (
"fmt"
"sync"
)
type Promise struct {
pending bool
executor func(resolve func(interface{}), reject func(error))
result interface{}
err error
mutex sync.Mutex
wg sync.WaitGroup
}
type PromiseInterface interface {
Then(onFulfilled func(data interface{}) interface{}, onRejected func(data interface{}) interface{}) *Promise
Catch(rejection func(err error) error) *Promise
Finally(onFinally func() (interface{}, error))
}
func New(executor func(resolve func(interface{}), reject func(error))) *Promise {
var promise = &Promise{
pending: true,
executor: executor,
result: nil,
err: nil,
mutex: sync.Mutex{},
wg: sync.WaitGroup{},
}
promise.wg.Add(1)
go func() {
defer promise.handlePanic()
promise.executor(promise.resolve, promise.reject)
}()
return promise
}
func (promise *Promise) resolve(resolution interface{}) {
promise.mutex.Lock()
if !promise.pending {
promise.mutex.Unlock()
return
}
switch result := resolution.(type) {
case *Promise:
flattenedResult, err := result.Await()
if err != nil {
promise.mutex.Unlock()
promise.reject(err)
return
}
promise.result = flattenedResult
default:
promise.result = result
}
promise.pending = false
promise.wg.Done()
promise.mutex.Unlock()
}
func (promise *Promise) reject(err error) {
promise.mutex.Lock()
defer promise.mutex.Unlock()
if !promise.pending {
return
}
promise.err = err
promise.pending = false
promise.wg.Done()
}
func (promise *Promise) handlePanic() {
e := recover()
if e != nil {
switch err := e.(type) {
case nil:
promise.reject(fmt.Errorf("panic recovery with nil error"))
case error:
promise.reject(fmt.Errorf("panic recovery with error: %s", err.Error()))
default:
promise.reject(fmt.Errorf("panic recovery with unknown error: %s", fmt.Sprint(err)))
}
}
}
func (promise *Promise) Then(onFulfilled func(data interface{}) interface{}, onRejected func(err error) interface{}) *Promise {
return New(func(resolve func(interface{}), reject func(error)) {
result, err := promise.Await()
if err != nil {
if onRejected != nil {
resolve(onRejected(err))
} else {
reject(err)
}
return
}
resolve(onFulfilled(result))
})
}
func (promise *Promise) Finally(onFinally func()) (interface{}, error) {
promise.wg.Wait()
onFinally()
return promise.result, promise.err
}
func (promise *Promise) Await() (interface{}, error) {
promise.wg.Wait()
return promise.result, promise.err
}
func (promise *Promise) Catch(rejection func(err error) error) *Promise {
return New(func(resolve func(interface{}), reject func(error)) {
result, err := promise.Await()
if err != nil {
reject(rejection(err))
return
}
resolve(result)
})
}
func Resolve(resolution interface{}) *Promise {
return New(func(resolve func(interface{}), reject func(error)) { resolve(resolution) })
}
func Reject(err error) *Promise {
return New(func(resolve func(interface{}), reject func(error)) {
reject(err)
})
}