move cursor in whole codepoints on space / delete swipe

and when space-swiping across emoji, send fake arrow keypress instead (discouraged, but avoids e.g. splitting pirate flag emoji and thus justified)
fixes #859

app/src/main/java/helium314/keyboard/keyboard/KeyboardActionListenerImpl.kt

@@ -6,6 +6,9 @@ import helium314.keyboard.latin.LatinIME
 import helium314.keyboard.latin.RichInputMethodManager
 import helium314.keyboard.latin.common.Constants
 import helium314.keyboard.latin.common.InputPointers
+import helium314.keyboard.latin.common.StringUtils
+import helium314.keyboard.latin.common.loopOverCodePoints
+import helium314.keyboard.latin.common.loopOverCodePointsBackwards
 import helium314.keyboard.latin.inputlogic.InputLogic
 import helium314.keyboard.latin.settings.Settings
 import kotlin.math.abs
@@ -80,7 +83,23 @@ class KeyboardActionListenerImpl(private val latinIME: LatinIME, private val inp
     override fun onMoveDeletePointer(steps: Int) {
         inputLogic.finishInput()
         val end = inputLogic.mConnection.expectedSelectionEnd
-        val start = inputLogic.mConnection.expectedSelectionStart + steps
+        var actualSteps = 0 // corrected steps to avoid splitting chars belonging to the same codepoint
+        if (steps > 0) {
+            val text = inputLogic.mConnection.getSelectedText(0)
+            if (text == null) actualSteps = steps
+            else loopOverCodePoints(text) {
+                actualSteps += Character.charCount(it)
+                actualSteps >= steps
+            }
+        } else {
+            val text = inputLogic.mConnection.getTextBeforeCursor(-steps * 4, 0)
+            if (text == null) actualSteps = steps
+            else loopOverCodePointsBackwards(text) {
+                actualSteps -= Character.charCount(it)
+                actualSteps <= steps
+            }
+        }
+        val start = inputLogic.mConnection.expectedSelectionStart + actualSteps
         if (start > end) return
         inputLogic.mConnection.setSelection(start, end)
     }
@@ -120,29 +139,44 @@ class KeyboardActionListenerImpl(private val latinIME: LatinIME, private val inp
 
     private fun onMoveCursorHorizontally(rawSteps: Int): Boolean {
         if (rawSteps == 0) return false
-        var steps = rawSteps
         // for RTL languages we want to invert pointer movement
-        if (RichInputMethodManager.getInstance().currentSubtype.isRtlSubtype) steps = -steps
+        val steps = if (RichInputMethodManager.getInstance().currentSubtype.isRtlSubtype) -rawSteps else rawSteps
         val moveSteps: Int
         if (steps < 0) {
-            val availableCharacters = inputLogic.mConnection.getTextBeforeCursor(64, 0)?.length ?: return false
-            moveSteps = if (availableCharacters < -steps) -availableCharacters else steps
+            var actualSteps = 0 // corrected steps to avoid splitting chars belonging to the same codepoint
+            val text = inputLogic.mConnection.getTextBeforeCursor(-steps * 4, 0) ?: return false
+            loopOverCodePointsBackwards(text) {
+                if (StringUtils.mightBeEmoji(it)) {
+                    actualSteps = 0
+                    return@loopOverCodePointsBackwards true
+                }
+                actualSteps -= Character.charCount(it)
+                actualSteps <= steps
+            }
+            moveSteps = -text.length.coerceAtMost(abs(actualSteps))
             if (moveSteps == 0) {
                 // some apps don't return any text via input connection, and the cursor can't be moved
                 // we fall back to virtually pressing the left/right key one or more times instead
-                while (steps != 0) {
+                repeat(-steps) {
                     onCodeInput(KeyCode.ARROW_LEFT, Constants.NOT_A_COORDINATE, Constants.NOT_A_COORDINATE, false)
-                    ++steps
                 }
                 return true
             }
         } else {
-            val availableCharacters = inputLogic.mConnection.getTextAfterCursor(64, 0)?.length ?: return false
-            moveSteps = availableCharacters.coerceAtMost(steps)
+            var actualSteps = 0 // corrected steps to avoid splitting chars belonging to the same codepoint
+            val text = inputLogic.mConnection.getTextAfterCursor(steps * 4, 0) ?: return false
+            loopOverCodePoints(text) {
+                if (StringUtils.mightBeEmoji(it)) {
+                    actualSteps = 0
+                    return@loopOverCodePoints true
+                }
+                actualSteps += Character.charCount(it)
+                actualSteps >= steps
+            }
+            moveSteps = text.length.coerceAtMost(actualSteps)
             if (moveSteps == 0) {
-                while (steps != 0) {
+                repeat(steps) {
                     onCodeInput(KeyCode.ARROW_RIGHT, Constants.NOT_A_COORDINATE, Constants.NOT_A_COORDINATE, false)
-                    --steps
                 }
                 return true
             }

app/src/main/java/helium314/keyboard/latin/common/StringUtils.java

@@ -625,7 +625,7 @@ public final class StringUtils {
         return false;
     }
 
-    public static boolean mightBeEmoji(final String s) {
+    public static boolean mightBeEmoji(final CharSequence s) {
         int offset = 0;
         final int length = s.length();
         while (offset < length) {

app/src/main/java/helium314/keyboard/latin/common/StringUtils.kt

@@ -109,7 +109,7 @@ fun String.decapitalize(locale: Locale): String {
 
 fun isEmoji(c: Int): Boolean = mightBeEmoji(c) && isEmoji(newSingleCodePointString(c))
 
-fun isEmoji(s: String): Boolean = mightBeEmoji(s) && s.matches(emoRegex)
+fun isEmoji(s: CharSequence): Boolean = mightBeEmoji(s) && s.matches(emoRegex)
 
 fun String.splitOnWhitespace() = split(whitespaceSplitRegex)