feat: async validators

Allows asynchronous validation, with the ability to track the validated value for use in the StatusInput as a value that is separate from the entered text.

Async operations are debounced internally to the StatusAsyncValidator.

#### Introduce StatusAsyncValidator component:
- `validate`: the input value to this function is the value sent to `asyncComplete`, which must be called by the validator. Return true when the value from the async operation is valid.
- `asyncComplete`: signal to be called by the validator after the async operation has completed. It should contain the value returned by the async operation that should be validated in `validate`.
- `validatedValue`: This is the valid value returned from the async operation. It it tracked separately so that the input text on the `StatusInput` can remain as entered by the user. Use this property and the `onValidatedValueChanged` signal handler for the “real” value to be used by other components.

src/StatusQ/Controls/StatusInput.qml

@@ -1,6 +1,7 @@
 import QtQuick 2.14
 
 import StatusQ.Core 0.1
+import StatusQ.Core.Backpressure 1.0
 import StatusQ.Core.Theme 0.1
 import StatusQ.Controls 0.1
 import StatusQ.Controls.Validators 0.1
@@ -33,8 +34,9 @@ Item {
     property real leftPadding: 16
     property real rightPadding: 16
     property list<StatusValidator> validators
-    property list<StatusValidator> asyncValidators
+    property list<StatusAsyncValidator> asyncValidators
     property int validationMode: StatusInput.ValidationMode.OnlyWhenDirty
+    property string validatedValue
 
     property var pendingValidators: []
 
@@ -50,7 +52,7 @@ Item {
         statusBaseInput.valid = false
         statusBaseInput.pristine = true
         statusBaseInput.text = ""
-        errorMessage = ""
+        root.errorMessage = ""
     }
 
     function validate() {
@@ -86,19 +88,21 @@ Item {
         }
 
         if (asyncValidators.length && !Object.values(errors).length) {
-            root.pending = true
             for (let idx in asyncValidators) {
                 let asyncValidator = asyncValidators[idx]
-                if (pendingValidators.indexOf(asyncValidator.name) == -1) {
+                asyncValidator.validationComplete.connect(function (value, valid) {
-                    asyncValidator.input = root
+                    updateAsyncValidity(asyncValidator.name, value, valid)
-                    pendingValidators.push(asyncValidator.name)
+                })
-                    asyncValidator.validate(statusBaseInput.text)
+                root.pending = true
-                }
+                pendingValidators.push(asyncValidator.name)
+                asyncValidator.asyncOperationInternal(statusBaseInput.text)
             }
+        } else if (!asyncValidators.length && !Object.values(errors).length) {
+            root.validatedValue = root.text
         }
     }
 
-    function updateValidity(validatorName, result) {
+    function updateAsyncValidity(validatorName, value, result) {
         if (!asyncErrors) {
             asyncErrors = {}
         }
@@ -108,6 +112,7 @@ Item {
                 delete asyncErrors[validatorName]
             }
             errorMessage.text = ""
+            root.validatedValue = value
         } else {
             asyncErrors[validatorName] = result
             for (let idx in asyncValidators) {

src/StatusQ/Controls/Validators/StatusAsyncEnsValidator.qml

@@ -0,0 +1,15 @@
+import StatusQ.Controls 0.1
+import StatusQ.Core.Utils 0.1
+
+StatusAsyncValidator {
+    readonly property string uuid: Utils.uuid()
+
+    name: "asyncEns"
+
+    errorMessage: "ENS name could not be resolved in to an address"
+
+    validate: function (asyncResult) {
+        return Utils.isValidAddress(asyncResult)
+    }
+}
+

src/StatusQ/Controls/Validators/StatusAsyncValidator.qml

@@ -0,0 +1,32 @@
+import QtQuick 2.13
+import StatusQ.Core.Backpressure 1.0
+
+Item {
+    id: statusAsyncValidator
+
+    property string name: ""
+    property string errorMessage: "invalid input"
+    signal asyncComplete(var result)
+    signal validationComplete(var value, bool valid)
+
+    // Prevents firing async operations before time has elapsed. If multiple
+    // calls are attempted, the timer resets each time.
+    property int debounceTime: 600
+
+    property var validate: function (value) {
+        return value === "async result"
+    }
+    property var asyncOperation: function(inputText) {
+        // Do something with the input text. Once completed, fire the
+        // `asyncComplete` signal
+        asyncComplete("async result")
+    }
+
+    readonly property var asyncOperationInternal: Backpressure.debounce(statusAsyncValidator, debounceTime, function(inputText) {
+        statusAsyncValidator.asyncOperation(inputText)
+    })
+
+    onAsyncComplete: function(result) {
+        validationComplete(result, validate(result))
+    }
+}

src/StatusQ/Controls/Validators/StatusValidator.qml

@@ -6,7 +6,6 @@ QtObject {
 
     property string name: ""
     property string errorMessage: "invalid input"
-    property StatusInput input
 
     property var validate: function (value) {
         return true

src/StatusQ/Controls/Validators/qmldir

@@ -2,6 +2,8 @@ module StatusQ.Controls.Validators
 
 StatusAddressValidator 0.1 StatusAddressValidator.qml
 StatusAddressOrEnsValidator 0.1 StatusAddressOrEnsValidator.qml
-StatusValidator 0.1 StatusValidator.qml
+StatusAsyncValidator 0.1 StatusAsyncValidator.qml
+StatusAsyncEnsValidator 0.1 StatusAsyncEnsValidator.qml
 StatusMinLengthValidator 0.1 StatusMinLengthValidator.qml
 StatusMaxLengthValidator 0.1 StatusMaxLengthValidator.qml
+StatusValidator 0.1 StatusValidator.qml

src/StatusQ/Core/Backpressure/Backpressure.qml

@@ -0,0 +1,123 @@
+pragma Singleton
+import QtQuick 2.0
+
+Item {
+
+    id: backpressure
+
+    property var _timers: ({})
+    property int _nextId: 0
+
+    function setTimeout(owner, timeout, callback) {
+        var tid = ++_nextId;
+
+        var cleanup = function() {
+            if (tid !== null) {
+                clearTimeout(tid);
+            }
+        }
+
+        if (!owner) {
+            owner = backpressure;
+        }
+
+        owner.Component.destruction.connect(cleanup);
+
+        var obj = Qt.createQmlObject('import QtQuick 2.0; Timer {running: false; repeat: false; interval: ' + timeout + '}', backpressure, "setTimeout");
+        obj.triggered.connect(function() {
+            callback();
+            obj.destroy();
+            owner.Component.destruction.disconnect(cleanup);
+            delete _timers[tid];
+        });
+        obj.running = true;
+        _timers[tid] = obj;
+        return tid;
+    }
+
+    function clearTimeout(timerId) {
+        if (!_timers.hasOwnProperty(timerId)) {
+            return;
+        }
+        var timer = _timers[timerId];
+        timer.stop();
+        timer.destroy();
+        delete _timers[timerId];
+    }
+
+    function oneInTime(owner, duration, callback) {
+        var pending = false;
+        var timerId = null;
+
+        return function() {
+            if (pending) {
+                return;
+            }
+            pending = true;
+            var args = arguments;
+            callback.apply(null, args);
+            timerId = setTimeout(owner, duration , function() {
+                pending = false;
+            }, duration);
+        }
+    }
+
+    function promisedOneInTime(owner, callback) {
+        var q = priv.loadPromiseLib();
+        var promise = null;
+
+        return function() {
+            var args = arguments;
+            if (promise !== null) {
+                return q.rejected();
+            }
+
+            promise = q.promise(function(fulfill, reject) {
+                fulfill(callback.apply(null, args));
+            });
+
+            promise.then(function() {
+                promise = null;
+            }, function() {
+                promise = null;
+            });
+            return promise;
+        };
+    }
+
+    function debounce(owner, duration, callback) {
+        var timerId = null;
+
+        return function() {
+            var args = arguments;
+
+            if (timerId !== null) {
+                clearTimeout(timerId);
+            }
+
+            timerId = setTimeout(owner, duration, function() {
+                timerId = null;
+                callback.apply(null, args);
+            });
+        }
+    }    
+
+    QtObject {
+        id: priv
+        property var q: null
+
+        function loadPromiseLib() {
+            if (q !== null) {
+                return q.q;
+            }
+
+            q = Qt.createQmlObject('import QtQuick 2.0; import QuickPromise 1.0; Item { property var q: Q;}', backpressure);
+            if (q.hasOwnProperty("qmlErrors")) {
+                console.error("Backpressure: Failed to load QuickPromise. Please check your installation.");
+            }
+            return q.q;
+        }
+
+    }
+
+}

src/StatusQ/Core/Backpressure/LICENSE

@@ -0,0 +1,201 @@
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src/StatusQ/Core/Backpressure/README.md

@@ -0,0 +1,80 @@
+[![Build Status](https://www.travis-ci.org/e-fever/backpressure.svg?branch=master)](https://www.travis-ci.org/e-fever/backpressure)
+[![Build status](https://ci.appveyor.com/api/projects/status/knt6r7gra9dm0oui?svg=true)](https://ci.appveyor.com/project/benlau/backpressure)
+
+Backpressure
+============
+
+Backpressure happens on a stream of data where you are not fast enough to process. 
+This library is designed to provide a few mechanism to handle it.
+
+Installation
+============
+
+    qpm install net.efever.backpressure
+    
+    
+API
+===
+
+```
+import Backpressure 1.0
+```
+
+
+**Backpressure.oneInTime(owner, duration, callback)**
+
+It will create a wrapper function of the callback. Whatever you have invoked the wrapper function, it will execute the callback immediately. Then it will be blocked within duration period. It could prevent to process the same event twice within the duration period.
+
+Example:
+```
+
+Item {
+  id : item
+  property var processClick : Backpressure.oneInTime(item, 500, function(value) { 
+    /* Callback */ 
+  });
+
+  MouseArea {
+    onClicked: {
+       processClick(value);
+    }
+  }
+
+}
+```
+
+If the owner is destroyed, the callback will no longer be able to access.
+
+**Backpressure.debounce(owner, duration, callback)**
+
+If will create a wrapper function of the callback. Whatever you have invoked the wrapper function, it won't execute the callback until the duration period finished. If user invoked the wrapper function again within the period, then the previous call will be dropped, and the timer is restarted.
+
+It will guarantee only the last function call and parameter will be passed to the callback.
+
+Reference: [ReactiveX - Debounce operator](http://reactivex.io/documentation/operators/debounce.html)
+
+**Backpressure.promisedOneInTime(owner, callback)**
+
+This function is similar to oneInTime that will create a wrapper of the callback. But it does not take a timeout value as an argument of the construction function.
+
+Instead, it will convert the return from the callback to a promise object. Then blocks successively calls until the promise is resolved/rejected.
+
+The wrapper function returns a promise represents the result of the callback. If that is blocked, it will simply a rejected promise.
+
+You must install QuickPromise in order to use this funciton.
+
+Example
+```
+
+var timeout = Backpressure.promisedOneInTime(anyItem, function(delay) {
+    return Q.promise(function(fulfill, reject) {
+        Q.setTimeout(function() {
+            fulfill();
+        }, delay);
+    });
+});
+
+var promise1 = timeout(1000); // Pending
+var promise2 = timeout(1000); // Rejected
+
+```

src/StatusQ/Core/Backpressure/qmldir

@@ -0,0 +1,3 @@
+module StatusQ.Core.Backpressure
+
+singleton Backpressure 1.0 Backpressure.qml

src/StatusQ/Core/Utils/Utils.qml

@@ -26,6 +26,10 @@ QtObject {
         const isDomain = /(?:(?:(?<thld>[\w\-]*)(?:\.))?(?<sld>[\w\-]*))\.(?<tld>[\w\-]*)/.test(inputValue)
         return isEmail || isDomain || (inputValue.startsWith("@") && inputValue.length > 1)
     }
+
+    function uuid() {
+        return Date.now().toString(36) + Math.random().toString(36).substr(2, 5)
+    }
 }