Composer: mention tagging now works in middle of text (close #105) (#139)

src/lib/strings/mention-manip.ts

@@ -0,0 +1,37 @@
+interface FoundMention {
+  value: string
+  index: number
+}
+
+export function getMentionAt(
+  text: string,
+  cursorPos: number,
+): FoundMention | undefined {
+  let re = /(^|\s)@([a-z0-9.]*)/gi
+  let match
+  while ((match = re.exec(text))) {
+    const spaceOffset = match[1].length
+    const index = match.index + spaceOffset
+    if (
+      cursorPos >= index &&
+      cursorPos <= index + match[0].length - spaceOffset
+    ) {
+      return {value: match[2], index}
+    }
+  }
+  return undefined
+}
+
+export function insertMentionAt(
+  text: string,
+  cursorPos: number,
+  mention: string,
+) {
+  const target = getMentionAt(text, cursorPos)
+  if (target) {
+    return `${text.slice(0, target.index)}@${mention} ${text.slice(
+      target.index + target.value.length + 1, // add 1 to include the "@"
+    )}`
+  }
+  return text
+}

src/view/com/composer/ComposePost.tsx

@@ -3,10 +3,12 @@ import {observer} from 'mobx-react-lite'
 import {
   ActivityIndicator,
   KeyboardAvoidingView,
+  NativeSyntheticEvent,
   Platform,
   SafeAreaView,
   ScrollView,
   StyleSheet,
+  TextInputSelectionChangeEventData,
   TouchableOpacity,
   TouchableWithoutFeedback,
   View,
@@ -42,6 +44,7 @@ import {
 import {getLinkMeta} from '../../../lib/link-meta'
 import {downloadAndResize} from '../../../lib/images'
 import {UserLocalPhotosModel} from '../../../state/models/user-local-photos'
+import {getMentionAt, insertMentionAt} from '../../../lib/strings/mention-manip'
 import {PhotoCarouselPicker, cropPhoto} from './PhotoCarouselPicker'
 import {SelectedPhoto} from './SelectedPhoto'
 import {usePalette} from '../../lib/hooks/usePalette'
@@ -50,6 +53,11 @@ const MAX_TEXT_LENGTH = 256
 const DANGER_TEXT_LENGTH = MAX_TEXT_LENGTH
 const HITSLOP = {left: 10, top: 10, right: 10, bottom: 10}
 
+interface Selection {
+  start: number
+  end: number
+}
+
 export const ComposePost = observer(function ComposePost({
   replyTo,
   imagesOpen,
@@ -65,6 +73,7 @@ export const ComposePost = observer(function ComposePost({
   const pal = usePalette('default')
   const store = useStores()
   const textInput = useRef<PasteInputRef>(null)
+  const textInputSelection = useRef<Selection>({start: 0, end: 0})
   const [isProcessing, setIsProcessing] = useState(false)
   const [processingState, setProcessingState] = useState('')
   const [error, setError] = useState('')
@@ -198,10 +207,10 @@ export const ComposePost = observer(function ComposePost({
   const onChangeText = (newText: string) => {
     setText(newText)
 
-    const prefix = extractTextAutocompletePrefix(newText)
-    if (typeof prefix === 'string') {
+    const prefix = getMentionAt(newText, textInputSelection.current?.start || 0)
+    if (prefix) {
       autocompleteView.setActive(true)
-      autocompleteView.setPrefix(prefix)
+      autocompleteView.setPrefix(prefix.value)
     } else {
       autocompleteView.setActive(false)
     }
@@ -228,6 +237,16 @@ export const ComposePost = observer(function ComposePost({
     const finalImgPath = await cropPhoto(imgFile.uri)
     onSelectPhotos([...selectedPhotos, finalImgPath])
   }
+  const onSelectionChange = (
+    evt: NativeSyntheticEvent<TextInputSelectionChangeEventData>,
+  ) => {
+    // NOTE we track the input selection using a ref to avoid excessive renders -prf
+    textInputSelection.current = evt.nativeEvent.selection
+  }
+  const onSelectAutocompleteItem = (item: string) => {
+    setText(insertMentionAt(text, textInputSelection.current?.start || 0, item))
+    autocompleteView.setActive(false)
+  }
   const onPressCancel = () => hackfixOnClose()
   const onPressPublish = async () => {
     if (isProcessing) {
@@ -265,10 +284,6 @@ export const ComposePost = observer(function ComposePost({
     hackfixOnClose()
     Toast.show(`Your ${replyTo ? 'reply' : 'post'} has been published`)
   }
-  const onSelectAutocompleteItem = (item: string) => {
-    setText(replaceTextAutocompletePrefix(text, item))
-    autocompleteView.setActive(false)
-  }
 
   const canPost = text.length <= MAX_TEXT_LENGTH
   const progressColor =
@@ -399,6 +414,7 @@ export const ComposePost = observer(function ComposePost({
                 scrollEnabled
                 onChangeText={(str: string) => onChangeText(str)}
                 onPaste={onPaste}
+                onSelectionChange={onSelectionChange}
                 placeholder={selectTextInputPlaceholder}
                 placeholderTextColor={pal.colors.textLight}
                 style={[
@@ -494,18 +510,6 @@ export const ComposePost = observer(function ComposePost({
   )
 })
 
-const atPrefixRegex = /@([a-z0-9.]*)$/i
-function extractTextAutocompletePrefix(text: string) {
-  const match = atPrefixRegex.exec(text)
-  if (match) {
-    return match[1]
-  }
-  return undefined
-}
-function replaceTextAutocompletePrefix(text: string, item: string) {
-  return text.replace(atPrefixRegex, `@${item} `)
-}
-
 const styles = StyleSheet.create({
   outer: {
     flexDirection: 'column',