While Loop increments and re-runs before Promisekit can finish running and return the proper value in Swift - swift

Question

I'm trying to use a while loop with Promisekit with Alamofire to chain four GET requests, return a value, and rerun the four requests with a new parameter. This is the current code that I'm using:
var index = 0
var count = classDictionary["class"]!.count-1
while index <= count {
firstly {
parseBooksXML(index)
}.then { abrevCode in
self.parseBooksXML2(index, key: abrevCode)
}.then { courseNumber in
self.parseBooksXML3(index, key: courseNumber)
}.then { instructorCode in
self.parseBooksXML4(instructorCode)
}
index += 1
}
Each of the first three functions returns a promised string value which is then passed onto the next function until the fourth and final function calls another function to parse the downloaded HTML using Kanna.
Ideally I would like all four functions to be called and completed after which the index will increment and run the loop again using the new index number. As a note, the index in passed onto the functions as a way to identify which index in an array a value should be compared to.
For clarity, I have included the code for the parseBooksXML functions below:
func parseBooksXML(index: Int) -> Promise<String> {
return Promise {fulfill, reject in
let headers = [
"Referer": "URL"
]
Alamofire.request(.GET, "URL", headers: headers)
.responseData { response in
switch response.result {
case .Success:
let xml = SWXMLHash.parse(response.data!)
do {
let range = self.classDictionary["class"]![index].rangeOfString("[a-zA-Z]{2,4}", options: .RegularExpressionSearch)
let result = self.classDictionary["class"]![index].substringWithRange(range!)
try self.abrevCode = (xml["departments"]["department"].withAttr("abrev", result).element!.attribute(by: "id")!.text)
}
catch {
print("Error: \(error)")
}
fulfill(self.abrevCode)
case .Failure(let error):
print(error)
}
}
}
}
func parseBooksXML2(index: Int, key: String) -> Promise<String> {
return Promise {fulfill, reject in
let headers = [
"Referer": "URL"
]
Alamofire.request(.GET, "URL", headers: headers)
.responseData { response in
switch response.result {
case .Success:
let xml = SWXMLHash.parse(response.data!)
do {
let range = self.classDictionary["class"]![index].rangeOfString("\\d\\d\\d", options: .RegularExpressionSearch)
let result = self.classDictionary["class"]![index].substringWithRange(range!)
try self.courseNumber = (xml["courses"]["course"].withAttr("name", result).element?.attribute(by: "id")?.text)!
}
catch {
print("Error: \(error)")
}
fulfill(self.courseNumber)
case .Failure(let error):
print(error)
}
}
}
}
func parseBooksXML3(index: Int, key: String) -> Promise<String> {
return Promise {fulfill, reject in
let headers = [
"Referer": "URL"
]
Alamofire.request(.GET, "URL", headers: headers)
.responseData { response in
switch response.result {
case .Success:
let xml = SWXMLHash.parse(response.data!)
do {
let range = self.classDictionary["class"]![index].rangeOfString("[a-zA-Z]{1,3}?\\d?\\d?\\d?$", options: .RegularExpressionSearch)
let result = self.classDictionary["class"]![index].substringWithRange(range!)
try self.instructorCode = (xml["sections"]["section"].withAttr("instructor", self.classTeacher[index]).element?.attribute(by: "id")?.text)!
}
catch {
print("Error: \(error)")
}
fulfill(self.instructorCode)
case .Failure(let error):
print(error)
}
}
}
}
func parseBooksXML4(key: String) -> Void {
let headers = [
"Referer": "URL"
]
Alamofire.request(.GET, "URL", headers: headers)
.responseData { response in
switch response.result {
case .Success:
self.parseISBN(String(data: response.data!, encoding: NSUTF8StringEncoding)!)
case .Failure(let error):
print(error)
}
}
}
Any help would be appreciated!

Answer 1

You need to use when:
let count = classDictionary["class"]!.count-1
let promises = (0..<count).map { index -> Promise<ReplaceMe> in
return firstly {
parseBooksXML(index)
}.then { abrevCode in
self.parseBooksXML2(index, key: abrevCode)
}.then { courseNumber in
self.parseBooksXML3(index, key: courseNumber)
}.then { instructorCode in
self.parseBooksXML4(instructorCode)
}
}
when(fulfilled: promises).then {
//…
}

Answer 2

Since parseBooksXML4 call is async, you should wrap parseBooksXML4() call to return promise and wait for that to finish before increment index.
firstly {
parseBooksXML(index)
}.then { abrevCode in
self.parseBooksXML2(index, key: abrevCode)
}.then { courseNumber in
self.parseBooksXML3(index, key: courseNumber)
}.then { instructorCode in
self.parseBooksXML4(instructorCode)
}.then { _ in
index += 1
}
}