Ignore task swipes that start at the screen edge (#90) (#111)

app/src/main/java/de/jeanlucmakiola/agendula/ui/common/EdgeSwipeGuard.kt

@@ -0,0 +1,66 @@
+package de.jeanlucmakiola.agendula.ui.common
+
+import androidx.compose.foundation.gestures.awaitEachGesture
+import androidx.compose.foundation.gestures.awaitFirstDown
+import androidx.compose.foundation.layout.WindowInsets
+import androidx.compose.foundation.layout.systemGestures
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.input.pointer.PointerEventPass
+import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.layout.onGloballyPositioned
+import androidx.compose.ui.layout.positionInWindow
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.platform.LocalLayoutDirection
+import androidx.compose.ui.platform.LocalWindowInfo
+import androidx.compose.ui.unit.dp
+import kotlin.math.abs
+
+/** How far past the system back-gesture zone a horizontal swipe is still ignored. */
+private val EDGE_MARGIN = 24.dp
+
+/**
+ * Swallows horizontal swipes that start near the screen's left or right edge,
+ * before a swipe box below it sees them (#90). A back gesture started just
+ * inside the system's gesture zone otherwise reaches the app as a row swipe.
+ * Taps and vertical scrolls are left alone.
+ */
+@Composable
+fun Modifier.ignoringEdgeSwipes(): Modifier {
+    val density = LocalDensity.current
+    val layoutDirection = LocalLayoutDirection.current
+    val windowWidth = LocalWindowInfo.current.containerSize.width
+    val insets = WindowInsets.systemGestures
+    val margin = with(density) { EDGE_MARGIN.roundToPx() }
+    val leftEdge = insets.getLeft(density, layoutDirection) + margin
+    val rightEdge = windowWidth - insets.getRight(density, layoutDirection) - margin
+    var offsetX by remember { mutableFloatStateOf(0f) }
+    return this
+        .onGloballyPositioned { offsetX = it.positionInWindow().x }
+        .pointerInput(leftEdge, rightEdge) {
+            val slop = viewConfiguration.touchSlop
+            awaitEachGesture {
+                val down = awaitFirstDown(requireUnconsumed = false, pass = PointerEventPass.Initial)
+                val x = offsetX + down.position.x
+                if (x > leftEdge && x < rightEdge) return@awaitEachGesture
+                var horizontal = false
+                while (true) {
+                    val change = awaitPointerEvent(PointerEventPass.Initial).changes
+                        .firstOrNull { it.id == down.id } ?: break
+                    if (!horizontal) {
+                        val delta = change.position - down.position
+                        when {
+                            abs(delta.x) > slop -> horizontal = true
+                            abs(delta.y) > slop -> break
+                        }
+                    }
+                    if (horizontal) change.consume()
+                    if (!change.pressed) break
+                }
+            }
+        }
+}

app/src/main/java/de/jeanlucmakiola/agendula/ui/tasklist/TaskListScreen.kt

@@ -112,6 +112,7 @@ import de.jeanlucmakiola.agendula.domain.TaskFilter
 import de.jeanlucmakiola.agendula.domain.TaskSection
 import de.jeanlucmakiola.agendula.domain.TaskSections
 import de.jeanlucmakiola.agendula.ui.common.LocalUse24HourFormat
+import de.jeanlucmakiola.agendula.ui.common.ignoringEdgeSwipes
 import de.jeanlucmakiola.agendula.ui.common.priorityAccent
 import de.jeanlucmakiola.agendula.ui.lists.ListEditorSheet
 import de.jeanlucmakiola.agendula.ui.lists.listWriteFailureMessage
@@ -655,7 +656,7 @@ private fun TaskRow(
 
     SwipeToDismissBox(
         state = dismissState,
-        modifier = modifier.fillMaxWidth().padding(horizontal = 16.dp).then(gap),
+        modifier = modifier.ignoringEdgeSwipes().fillMaxWidth().padding(horizontal = 16.dp).then(gap),
         // dismissDirection (not targetValue) tracks the live drag, so the colour +
         // icon reveal as you swipe rather than only once the threshold is crossed.
         backgroundContent = { SwipeBackground(dismissState.dismissDirection, task.isCompleted) },
@@ -1037,7 +1038,7 @@ private fun SubtaskRow(
     val gap = if (lastInRun) Modifier else Modifier.padding(bottom = 2.dp)
     SwipeToDismissBox(
         state = dismissState,
-        modifier = modifier.fillMaxWidth().padding(horizontal = 16.dp).then(gap),
+        modifier = modifier.ignoringEdgeSwipes().fillMaxWidth().padding(horizontal = 16.dp).then(gap),
         backgroundContent = { SwipeBackground(dismissState.dismissDirection, task.isCompleted) },
     ) {
     Surface(