first pass at a tag input in composer

src/view/com/composer/Composer.tsx

@@ -48,6 +48,7 @@ import {LabelsBtn} from './labels/LabelsBtn'
 import {SelectLangBtn} from './select-language/SelectLangBtn'
 import {EmojiPickerButton} from './text-input/web/EmojiPicker.web'
 import {insertMentionAt} from 'lib/strings/mention-manip'
+import {TagInput} from './TagInput'
 
 type Props = ComposerOpts & {
   onClose: () => void
@@ -380,6 +381,14 @@ export const ComposePost = observer(function ComposePost({
               <QuoteEmbed quote={quote} />
             </View>
           ) : undefined}
+
+          <View
+            style={[
+              pal.border,
+              {borderTopWidth: 1, paddingVertical: 10, marginTop: 10},
+            ]}>
+            <TagInput max={8} />
+          </View>
         </ScrollView>
         {!extLink && suggestedLinks.size > 0 ? (
           <View style={s.mb5}>

src/view/com/composer/TagInput.tsx

@@ -0,0 +1,129 @@
+import React from 'react'
+import {
+  TextInput,
+  View,
+  StyleSheet,
+  NativeSyntheticEvent,
+  TextInputKeyPressEventData,
+  Pressable,
+} from 'react-native'
+import {
+  FontAwesomeIcon,
+  FontAwesomeIconStyle,
+} from '@fortawesome/react-native-fontawesome'
+
+import {Text} from 'view/com/util/text/Text'
+import {usePalette} from 'lib/hooks/usePalette'
+
+function Tag({
+  tag,
+  removeTag,
+}: {
+  tag: string
+  removeTag: (tag: string) => void
+}) {
+  const pal = usePalette('default')
+  return (
+    <Pressable
+      accessibilityRole="button"
+      onPress={() => removeTag(tag)}
+      style={state => ({
+        opacity: state.hovered || state.pressed || state.focused ? 0.8 : 1,
+        outline: 0,
+      })}>
+      <Text type="xs-medium" style={[styles.tag, pal.viewLight, pal.textLight]}>
+        #{tag}
+      </Text>
+    </Pressable>
+  )
+}
+
+export function TagInput({max}: {max: number}) {
+  const pal = usePalette('default')
+  const input = React.useRef<TextInput>(null)
+  const [value, setValue] = React.useState('')
+  const [tags, setTags] = React.useState<string[]>([])
+
+  const onKeyPress = React.useCallback(
+    (e: NativeSyntheticEvent<TextInputKeyPressEventData>) => {
+      if (e.nativeEvent.key === 'Enter') {
+        const _tags = value.trim().split(' ').filter(Boolean)
+
+        if (_tags.length > 0) {
+          setTags(Array.from(new Set([...tags, ..._tags])).slice(0, max))
+          setValue('')
+        }
+
+        setTimeout(() => {
+          input.current?.focus()
+        }, 100)
+      } else if (e.nativeEvent.key === 'Backspace' && value === '') {
+        setTags(tags.slice(0, -1))
+      }
+    },
+    [max, value, tags, setValue, setTags],
+  )
+
+  const onChangeText = React.useCallback((value: string) => {
+    const sanitized = value.replace(/^#/, '')
+    setValue(sanitized)
+  }, [])
+
+  const removeTag = React.useCallback(
+    (tag: string) => {
+      setTags(tags.filter(t => t !== tag))
+    },
+    [tags, setTags],
+  )
+
+  return (
+    <View style={styles.outer}>
+      {!tags.length && (
+        <FontAwesomeIcon
+          icon="tags"
+          size={14}
+          style={pal.textLight as FontAwesomeIconStyle}
+        />
+      )}
+      {tags.map(tag => (
+        <Tag key={tag} tag={tag} removeTag={removeTag} />
+      ))}
+      {tags.length >= max ? null : (
+        <TextInput
+          ref={input}
+          value={value}
+          onKeyPress={onKeyPress}
+          onChangeText={onChangeText}
+          style={[styles.input, pal.textLight]}
+          placeholder="Add tags..."
+          autoCapitalize="none"
+          autoCorrect={false}
+          autoComplete="off"
+          accessible={true}
+          accessibilityLabel="Add tags to your post"
+          accessibilityHint={`You may add up to 8 tags to your post, including those used inline.`}
+        />
+      )}
+    </View>
+  )
+}
+
+const styles = StyleSheet.create({
+  outer: {
+    flexDirection: 'row',
+    flexWrap: 'wrap',
+    alignItems: 'center',
+    gap: 8,
+  },
+  input: {
+    flexGrow: 1,
+    minWidth: 100,
+    fontSize: 13,
+    paddingVertical: 4,
+  },
+  tag: {
+    paddingVertical: 4,
+    paddingHorizontal: 8,
+    borderRadius: 4,
+  },
+})

src/view/index.ts

@@ -98,6 +98,7 @@ import {faUsersSlash} from '@fortawesome/free-solid-svg-icons/faUsersSlash'
 import {faX} from '@fortawesome/free-solid-svg-icons/faX'
 import {faXmark} from '@fortawesome/free-solid-svg-icons/faXmark'
 import {faChevronDown} from '@fortawesome/free-solid-svg-icons/faChevronDown'
+import {faTags} from '@fortawesome/free-solid-svg-icons/faTags'
 
 export function setup() {
   library.add(
@@ -199,5 +200,6 @@ export function setup() {
     faX,
     faXmark,
     faChevronDown,
+    faTags,
   )
 }