Limit ChangeHistory size to 1000 last changes

Author: Crustack

app/src/main/java/com/philkes/notallyx/utils/changehistory/ChangeHistory.kt

@@ -4,7 +4,10 @@ import android.util.Log
 import com.philkes.notallyx.presentation.view.misc.NotNullLiveData
 import kotlin.IllegalStateException
 
-class ChangeHistory {
+class ChangeHistory(
+    /** Maximum number of changes to keep in memory. Oldest entries are evicted when full. */
+    private val maxSize: Int = 1000
+) {
     private val changeStack = ArrayList<Change>()
     var stackPointer = NotNullLiveData(-1)
 
@@ -19,9 +22,19 @@ class ChangeHistory {
     }
 
     fun push(change: Change) {
+        // Drop all redo entries after current pointer
         popRedos()
+        // If full, evict the oldest entry and shift the pointer accordingly
+        var newStackPointer = stackPointer.value
+        if (changeStack.size >= maxSize) {
+            if (changeStack.isNotEmpty()) {
+                changeStack.removeAt(0)
+                // Shift pointer left because we removed the head
+                newStackPointer = (newStackPointer - 1).coerceAtLeast(-1)
+            }
+        }
         changeStack.add(change)
-        stackPointer.value += 1
+        stackPointer.value = newStackPointer + 1
         Log.d(TAG, "addChange: $change")
     }
 

app/src/test/kotlin/com/philkes/notallyx/changehistory/ChangeHistoryTest.kt

@@ -138,4 +138,67 @@ class ChangeHistoryTest {
 
         override fun undo() {}
     }
+
+    @Test
+    fun `bounded history evicts oldest when capacity reached`() {
+        // Use a small capacity to test eviction behavior
+        changeHistory = ChangeHistory(maxSize = 3)
+        val c1 = TestChange()
+        val c2 = TestChange()
+        val c3 = TestChange()
+        val c4 = TestChange()
+
+        changeHistory.push(c1)
+        changeHistory.push(c2)
+        changeHistory.push(c3)
+        // Next push should evict c1
+        changeHistory.push(c4)
+
+        assertTrue(changeHistory.canUndo.value)
+        // Top of stack is c4
+        assertEquals(c4, changeHistory.lookUp())
+        // Next is c3
+        assertEquals(c3, changeHistory.lookUp(1))
+        // Next is c2
+        assertEquals(c2, changeHistory.lookUp(2))
+        // c1 should be gone
+        assertThrows(ChangeHistory.ChangeHistoryException::class.java) { changeHistory.lookUp(3) }
+    }
+
+    @Test
+    fun `pushing after undo with full capacity drops redos then evicts oldest if needed`() {
+        changeHistory = ChangeHistory(maxSize = 3)
+        val c1 = TestChange()
+        val c2 = TestChange()
+        val c3 = TestChange()
+        val c4 = TestChange()
+        val c5 = TestChange()
+
+        // Fill to capacity
+        changeHistory.push(c1)
+        changeHistory.push(c2)
+        changeHistory.push(c3)
+
+        // Undo 1 -> pointer at c2
+        changeHistory.undo()
+        assertTrue(changeHistory.canRedo.value)
+
+        // Push new change: should drop redo (c3) first, then possibly evict if full when pushing
+        changeHistory.push(c4)
+
+        // Stack should now have [c1, c2, c4] with pointer at top
+        assertEquals(c4, changeHistory.lookUp())
+        assertEquals(c2, changeHistory.lookUp(1))
+        assertEquals(c1, changeHistory.lookUp(2))
+
+        // Push another to force eviction of c1
+        changeHistory.push(c5)
+        assertEquals(c5, changeHistory.lookUp())
+        assertEquals(c4, changeHistory.lookUp(1))
+        assertEquals(c2, changeHistory.lookUp(2))
+        assertThrows(ChangeHistory.ChangeHistoryException::class.java) { changeHistory.lookUp(3) }
+
+        // No redo available after pushes
+        assertFalse(changeHistory.canRedo.value)
+    }
 }

documentation/docs/features/rich-text.mdx

@@ -40,6 +40,8 @@ NotallyX provides undo and redo functionality to help you recover from mistakes
 - **Undo**: Tap the undo icon (curved arrow pointing left) in the toolbar
 - **Redo**: Tap the redo icon (curved arrow pointing right) in the toolbar
 
+_Note: Undo/Redo is limited to the last 1,000 changes_
+
 ## Related Features
 
 - [Task Lists and Subtasks](./task-lists.mdx): Learn how to create and manage task lists