Ignore clicks outside the start/end of a line (#3380)

* Ignore clicks outside the start/end of a line

`LinkMovementMethod` has a bug in its calculation of the clickable width of a span on a line. If the span is the last thing on the line the clickable area extends to the end of the view. So the user can tap what appears to be whitespace and open a link.

Previous code tried to fix this by adding a zero-width space after the link so that `LinkMovementMethod` wouldn't consider it empty. However the ZWS was selected by copy/paste operations, resulting in junk results if users tried to copy the link.

Fix this by subclassing `LinkMovementMethod` and fixing the click detection code to ignore clicks that are outside the bounds of the line that was clicked on.

Remove the code that adds the ZWS.

Fixes https://github.com/tuskyapp/Tusky/issues/1567

* Assume arguments are all non-null

* Use `object` for singleton

* getInstance as a one-liner

app/src/main/java/com/keylesspalace/tusky/util/LinkHelper.kt

@@ -11,7 +11,8 @@
  * Public License for more details.
  *
  * You should have received a copy of the GNU General Public License along with Tusky; if not,
- * see <http://www.gnu.org/licenses>. */
+ * see <http://www.gnu.org/licenses>.
+ */
 @file:JvmName("LinkHelper")
 
 package com.keylesspalace.tusky.util
@@ -21,12 +22,15 @@ import android.content.Context
 import android.content.Intent
 import android.graphics.Color
 import android.net.Uri
+import android.text.Spannable
 import android.text.SpannableStringBuilder
 import android.text.Spanned
 import android.text.method.LinkMovementMethod
 import android.text.style.ClickableSpan
 import android.text.style.URLSpan
 import android.util.Log
+import android.view.MotionEvent
+import android.view.MotionEvent.ACTION_UP
 import android.view.View
 import android.widget.TextView
 import androidx.annotation.VisibleForTesting
@@ -68,7 +72,7 @@ fun setClickableText(view: TextView, content: CharSequence, mentions: List<Menti
             setClickableText(it, this, mentions, tags, listener)
         }
     }
-    view.movementMethod = LinkMovementMethod.getInstance()
+    view.movementMethod = NoTrailingSpaceLinkMovementMethod.getInstance()
 }
 
 @VisibleForTesting
@@ -125,13 +129,6 @@ fun setClickableText(
 
     removeSpan(span)
     setSpan(customSpan, start, end, flags)
-
-    /* Add zero-width space after links in end of line to fix its too large hitbox.
-     * See also : https://github.com/tuskyapp/Tusky/issues/846
-     *            https://github.com/tuskyapp/Tusky/pull/916 */
-    if (end >= length || subSequence(end, end + 1).toString() == "\n") {
-        insert(end, "\u200B")
-    }
 }
 
 @VisibleForTesting
@@ -199,12 +196,10 @@ fun setClickableMentions(view: TextView, mentions: List<Mention>?, listener: Lin
             append("@")
             append(mention.localUsername)
             setSpan(customSpan, start, end, flags)
-            append("\u200B") // same reasoning as in setClickableText
-            end += 1 // shift position to take the previous character into account
             start = end
         }
     }
-    view.movementMethod = LinkMovementMethod.getInstance()
+    view.movementMethod = NoTrailingSpaceLinkMovementMethod.getInstance()
 }
 
 fun createClickableText(text: String, link: String): CharSequence {
@@ -322,3 +317,35 @@ fun looksLikeMastodonUrl(urlString: String): Boolean {
 }
 
 private const val TAG = "LinkHelper"
+
+/**
+ * [LinkMovementMethod] that doesn't add a leading/trailing clickable area.
+ *
+ * [LinkMovementMethod] has a bug in its calculation of the clickable width of a span on a line. If
+ * the span is the last thing on the line the clickable area extends to the end of the view. So the
+ * user can tap what appears to be whitespace and open a link.
+ *
+ * Fix this by overriding ACTION_UP touch events and calculating the true start and end of the
+ * content on the line that was tapped. Then ignore clicks that are outside this area.
+ *
+ * See https://github.com/tuskyapp/Tusky/issues/1567.
+ */
+object NoTrailingSpaceLinkMovementMethod : LinkMovementMethod() {
+    override fun onTouchEvent(widget: TextView, buffer: Spannable, event: MotionEvent): Boolean {
+        val action = event.action
+        if (action != ACTION_UP) return super.onTouchEvent(widget, buffer, event)
+
+        val x = event.x.toInt()
+        val y = event.y.toInt() - widget.totalPaddingTop + widget.scrollY
+        val line = widget.layout.getLineForVertical(y)
+        val lineLeft = widget.layout.getLineLeft(line)
+        val lineRight = widget.layout.getLineRight(line)
+        if (x > lineRight || x >= 0 && x < lineLeft) {
+            return true
+        }
+
+        return super.onTouchEvent(widget, buffer, event)
+    }
+
+    fun getInstance() = NoTrailingSpaceLinkMovementMethod
+}