make_model: prelinary loading state support

src/util/make_model.js

@@ -51,7 +51,9 @@ export default (options={}) => {
 		// async states
 		xhr: null,
 		promise: null,
-		loading: false
+		loading: false,
+		loading_offset: null,
+		loading_limit: null
 	}
 
 	// construct the model
@@ -63,6 +65,9 @@ export default (options={}) => {
 		ambient_changed() {
 			return _state.ambient != _state.last_ambient
 		},
+		loading() {
+			return _state.loading
+		},
 
 		// clean state and cache if necessary
 		clean() {
@@ -70,6 +75,8 @@ export default (options={}) => {
 			_state.xhr = null
 			_state.promise = null
 			_state.loading = false
+			_state.loading_offset = null
+			_state.loading_limit = null
 
 			// update ambient state
 			_state.last_ambient = _state.ambient
@@ -97,23 +104,21 @@ export default (options={}) => {
 			if (this.data(offset, limit).length > 0 && !this.data(offset, limit).includes(undefined))
 				return Promise.resolve(this.data(offset, limit))
 
-			// be lazy 2: if there is a promise, return it if ambient matches or
-			// cancel it
-			if (_state.promise != null) {
-				if (this.ambient_changed()) {
+			// be lazy 2: if the model is loading the same slice of data with the
+			// same ambient, return the current promise; otherwise cancel it
+			if (this.loading()) {
+				if (!this.ambient_changed() && _state.loading_offset == offset && _state.loading_limit == limit)
+					return _state.promise
+				else {
 					if (_state.xhr != null) _state.xhr.abort()
 					_state.xhr = null
 				}
-				else
-					return _state.promise
 			}
 
-			// TODO
-			// ambient = select + order + limit/offset
-			// if ambient is changed, cancel currently loading xhr; otherwise return
-			// current promise
+			// update state
+			_state.loading = true
 
-			// now the hard work
+			// construct the promise
 			_state.promise = _configs.api.request({
 				method: 'GET',
 				url: _configs.endpoint,
@@ -189,11 +194,21 @@ export default (options={}) => {
 			if (this.data().length == _cache.count && !this.data().includes(undefined))
 				return Promise.resolve(this.data())
 
-			// be lazy 2: if there is a promise, return it if ambient matches or
-			// cancel it
-			if (_state.promise != null)
-				return _state.promise
+			// be lazy 2: if the model is loading the same slice of data with the
+			// same ambient, return the current promise; otherwise cancel it
+			if (this.loading()) {
+				if (!this.ambient_changed() && _state.loading_offset == offset && _state.loading_limit == limit)
+					return _state.promise
+				else {
+					if (_state.xhr != null) _state.xhr.abort()
+					_state.xhr = null
+				}
+			}
+
+			// update state
+			_state.loading = true
 
+			// construct the promise
 			_state.promise = _configs.api.request({
 				method: 'POST',
 				url: '/rpc/select_all',
@@ -213,10 +228,6 @@ export default (options={}) => {
 
 					return data
 				})
-
-				// clean state
-				_state.promise = null
-				this.reset()
 			}).finally(() => {
 				this.clean()
 			})