fix(chat): arm the reply swipe only where the bubble is

apps/flipcash/features/messenger/src/main/kotlin/com/flipcash/app/messenger/internal/screens/components/MessageRow.kt

@@ -158,14 +158,14 @@ internal fun MessageRow(
         enabled = bubble != null &&
             !selecting &&
             MessageCapability.Reply in bubble.capabilities,
-        // The avatar column is the target for the person, not for the message: a drag that starts
-        // on someone's picture is reaching for them, and the picture is small enough that arming a
-        // reply from it would mostly catch fingers that missed the tap.
-        senderGutter = if (showsSenderGutter && bubble?.isFromSelf == false) {
-            CodeTheme.dimens.staticGrid.x6
-        } else {
-            0.dp
-        },
+        // A drag arms on the message, not beside it: on someone's avatar it is reaching for them,
+        // and on the empty side of an outgoing row it is reaching for nothing. The one row that
+        // leads with the bubble itself — an incoming message in a DM — keeps its leading edge live.
+        leadingGutter = replyGutterFor(
+            width = CodeTheme.dimens.staticGrid.x6,
+            isFromSelf = bubble?.isFromSelf == true,
+            showsSenderGutter = showsSenderGutter,
+        ),
         onReply = { bubble?.let { onAction(ChatAction.ReplyTo(it)) } },
     )
 

apps/flipcash/features/messenger/src/main/kotlin/com/flipcash/app/messenger/internal/screens/components/SwipeToReply.kt

@@ -36,9 +36,9 @@ import kotlin.math.roundToInt
  * it holds at the end of its own travel, because it marks where the gesture fires and there is
  * nothing further along to mark.
  *
- * [senderGutter] is the width of the avatar column at the row's leading edge, if the row reserves
- * one. A drag that starts inside it is inert — that column is the target for the person, not for
- * the message, and a row that opened there would promise a reply it is not going to send.
+ * [leadingGutter] is the strip at the row's leading edge that the bubble does not reach — see
+ * [replyGutterFor]. A drag that starts inside it is inert: a row that opened from a point that is
+ * not the message would promise a reply it is not going to send.
  *
  * The distances are iOS's, in absolute units rather than the fractions of screen width this was
  * ported with. They have to be: [SwipeToReplyState.progress] is the fraction of the trigger
@@ -49,7 +49,7 @@ import kotlin.math.roundToInt
 @Composable
 internal fun rememberSwipeToReply(
     enabled: Boolean,
-    senderGutter: Dp,
+    leadingGutter: Dp,
     onReply: () -> Unit,
 ): SwipeToReplyState {
     val density = LocalDensity.current
@@ -58,7 +58,7 @@ internal fun rememberSwipeToReply(
 
     val maxPx = with(density) { MAX_TRANSLATION.toPx() }
     val triggerPx = with(density) { TRIGGER_THRESHOLD.toPx() }
-    val gutterPx = with(density) { senderGutter.toPx() }
+    val gutterPx = with(density) { leadingGutter.toPx() }
 
     val reply by rememberUpdatedState(onReply)
 
@@ -128,6 +128,24 @@ internal fun rememberSwipeToReply(
     }
 }
 
+/**
+ * The strip at a row's leading edge that a reply drag may not start in: everything ahead of the
+ * bubble, and nothing of the bubble itself.
+ *
+ * Only one kind of row has its bubble hard against the leading edge — an incoming message in a DM,
+ * which reserves no avatar column and is not pushed inward by one. Every other row leads with
+ * something that is not the message: the avatar column on an incoming row of a group, which is the
+ * target for the person rather than for what they said, and empty transcript on an outgoing row,
+ * where the bubble is aligned to the far side.
+ *
+ * [width] is that one avatar column's width, reused as the outgoing strip so both read the same. It
+ * cannot eat into an outgoing bubble: a bubble stops at 0.78 of the row, which leaves far more than
+ * this to its leading side at every width the app runs at. The one content that fills the row is a
+ * system notice, and those carry no capabilities at all, so no drag on one was ever going to reply.
+ */
+internal fun replyGutterFor(width: Dp, isFromSelf: Boolean, showsSenderGutter: Boolean): Dp =
+    if (!isFromSelf && !showsSenderGutter) 0.dp else width
+
 /**
  * What a row needs from the gesture: the modifier that carries it, and how far it has travelled, so
  * the row can draw the affordance the drag is uncovering.
@@ -161,7 +179,7 @@ internal class SwipeToReplyState(
  * for no visible change.
  */
 private class DragLatch {
-    /** Whether this drag may reply at all — false for one that started in the sender gutter. */
+    /** Whether this drag may reply at all — false for one that started in the leading gutter. */
     var armed = false
 
     /** Whether the threshold haptic has fired. Latched for the rest of the drag, so a finger held

apps/flipcash/features/messenger/src/test/kotlin/com/flipcash/app/messenger/internal/SwipeToReplyTest.kt

@@ -1,7 +1,9 @@
 package com.flipcash.app.messenger.internal
 
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
 import com.flipcash.app.messenger.internal.screens.components.SwipeToReplyState
+import com.flipcash.app.messenger.internal.screens.components.replyGutterFor
 import com.flipcash.app.messenger.internal.screens.components.resist
 import org.junit.Test
 import kotlin.test.assertEquals
@@ -13,11 +15,15 @@ import kotlin.test.assertTrue
  *
  * Mirrors iOS's `ChatSwipeToReplyTests`. The two implementations share these numbers, so a change
  * here is a change to the gesture on both platforms.
+ *
+ * Also where the row arms from, which is a layout question rather than a shared one: the gesture
+ * starts on the bubble and nowhere else.
  */
 class SwipeToReplyTest {
 
     private val max = 64f
     private val trigger = 48f
+    private val gutter = 30.dp
     private val tolerance = 0.01f
 
     @Test
@@ -63,6 +69,28 @@ class SwipeToReplyTest {
         assertEquals(1f, stateAt(max).progress(), tolerance)
     }
 
+    @Test
+    fun `a DM's incoming row arms from its own leading edge`() {
+        assertEquals(
+            0.dp,
+            replyGutterFor(gutter, isFromSelf = false, showsSenderGutter = false),
+        )
+    }
+
+    @Test
+    fun `a group's incoming row does not arm from the avatar column`() {
+        assertEquals(
+            gutter,
+            replyGutterFor(gutter, isFromSelf = false, showsSenderGutter = true),
+        )
+    }
+
+    @Test
+    fun `an outgoing row does not arm from the empty side it is aligned away from`() {
+        assertEquals(gutter, replyGutterFor(gutter, isFromSelf = true, showsSenderGutter = false))
+        assertEquals(gutter, replyGutterFor(gutter, isFromSelf = true, showsSenderGutter = true))
+    }
+
     private fun stateAt(offset: Float) = SwipeToReplyState(
         modifier = Modifier,
         offsetPx = { offset },