Fix Android visual transformation offset mapping (#164)

* Fix Android visual transformation offset mapping * Code review: Use kotlin test
mirego · Jun 27, 2023 · db760e7 · db760e7
1 parent 0adf657
commit db760e7
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Showing 4 changed files with 142 additions and 10 deletions.
diff --git a/...trikot/viewmodels/declarative/compose/viewmodel/internal/FormattedVisualTransformation.kt b/...trikot/viewmodels/declarative/compose/viewmodel/internal/FormattedVisualTransformation.kt
@@ -9,19 +9,53 @@ internal class FormattedVisualTransformation(private val formatter: (text: Strin
     VisualTransformation {
 
     override fun filter(text: AnnotatedString): TransformedText {
-        val formattedString = formatter(text.text)
+        val originalText = text.text
+        val formattedString = formatter(originalText)
         val offsetDelta = formattedString.length - text.length
-        return TransformedText(
-            text = AnnotatedString(formattedString),
+
+        val offsetMapping: OffsetMapping
+        if (offsetDelta > 0) {
+            val transformedToOriginalMapping = Array(formattedString.length) { -1 }
+            // First we fill mapping from original string
+            for (i in originalText.indices) {
+                transformedToOriginalMapping[formatter(originalText.substring(0, i + 1)).length - 1] = i
+            }
+            // Then we fills the missing indices to advance to the next offset
+            var nextOffset = originalText.length - 1
+            for (offset in transformedToOriginalMapping.indices.reversed()) {
+                if (transformedToOriginalMapping[offset] == -1) {
+                    transformedToOriginalMapping[offset] = nextOffset
+                } else {
+                    nextOffset = transformedToOriginalMapping[offset]
+                }
+            }
+
             offsetMapping = object : OffsetMapping {
                 override fun originalToTransformed(offset: Int): Int {
-                    return offset + offsetDelta
+                    return offset + lengthDelta(offset)
                 }
 
                 override fun transformedToOriginal(offset: Int): Int {
-                    return offset - offsetDelta
+                    return if (offset < transformedToOriginalMapping.size) {
+                        transformedToOriginalMapping[offset]
+                    } else {
+                        originalText.length
+                    }
+                }
+
+                private fun lengthDelta(offset: Int): Int {
+                    val originalSubstring = originalText.substring(0, Integer.min(offset + 1, originalText.length))
+                    val formattedSubstring = formatter(originalSubstring)
+                    return formattedSubstring.length - originalSubstring.length
                 }
             }
+        } else {
+            offsetMapping = OffsetMapping.Identity
+        }
+
+        return TransformedText(
+            text = AnnotatedString(formattedString),
+            offsetMapping = offsetMapping
         )
     }
 }
diff --git a/trikot-viewmodels-declarative/compose/build.gradle.kts b/trikot-viewmodels-declarative/compose/build.gradle.kts
@@ -48,6 +48,8 @@ dependencies {
     api("androidx.compose.ui:ui-tooling:${Versions.JETPACK_COMPOSE_UI_TOOLING}")
     api("io.coil-kt:coil-compose:${Versions.COIL}")
 
+    testImplementation(kotlin("test"))
+
     implementation("org.jetbrains.kotlin:kotlin-reflect:${Versions.KOTLIN}")
 }
 

diff --git a/...trikot/viewmodels/declarative/compose/viewmodel/internal/FormattedVisualTransformation.kt b/...trikot/viewmodels/declarative/compose/viewmodel/internal/FormattedVisualTransformation.kt
@@ -9,19 +9,53 @@ internal class FormattedVisualTransformation(private val formatter: (text: Strin
     VisualTransformation {
 
     override fun filter(text: AnnotatedString): TransformedText {
-        val formattedString = formatter(text.text)
+        val originalText = text.text
+        val formattedString = formatter(originalText)
         val offsetDelta = formattedString.length - text.length
-        return TransformedText(
-            text = AnnotatedString(formattedString),
+
+        val offsetMapping: OffsetMapping
+        if (offsetDelta > 0) {
+            val transformedToOriginalMapping = Array(formattedString.length) { -1 }
+            // First we fill mapping from original string
+            for (i in originalText.indices) {
+                transformedToOriginalMapping[formatter(originalText.substring(0, i + 1)).length - 1] = i
+            }
+            // Then we fills the missing indices to advance to the next offset
+            var nextOffset = originalText.length - 1
+            for (offset in transformedToOriginalMapping.indices.reversed()) {
+                if (transformedToOriginalMapping[offset] == -1) {
+                    transformedToOriginalMapping[offset] = nextOffset
+                } else {
+                    nextOffset = transformedToOriginalMapping[offset]
+                }
+            }
+
             offsetMapping = object : OffsetMapping {
                 override fun originalToTransformed(offset: Int): Int {
-                    return offset + offsetDelta
+                    return offset + lengthDelta(offset)
                 }
 
                 override fun transformedToOriginal(offset: Int): Int {
-                    return offset - offsetDelta
+                    return if (offset < transformedToOriginalMapping.size) {
+                        transformedToOriginalMapping[offset]
+                    } else {
+                        originalText.length
+                    }
+                }
+
+                private fun lengthDelta(offset: Int): Int {
+                    val originalSubstring = originalText.substring(0, Integer.min(offset + 1, originalText.length))
+                    val formattedSubstring = formatter(originalSubstring)
+                    return formattedSubstring.length - originalSubstring.length
                 }
             }
+        } else {
+            offsetMapping = OffsetMapping.Identity
+        }
+
+        return TransformedText(
+            text = AnnotatedString(formattedString),
+            offsetMapping = offsetMapping
         )
     }
 }
diff --git a/...compose/src/test/kotlin/com/mirego/trikot/viewmodels/FormattedVisualTransformationTest.kt b/...compose/src/test/kotlin/com/mirego/trikot/viewmodels/FormattedVisualTransformationTest.kt
@@ -0,0 +1,62 @@
+package com.mirego.trikot.viewmodels
+
+import androidx.compose.ui.text.AnnotatedString
+import com.mirego.trikot.viewmodels.declarative.compose.viewmodel.internal.FormattedVisualTransformation
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class FormattedVisualTransformationTest {
+
+    @Test
+    fun `Given original string "ABCDEFGHI" when transformed to "ABC DEF GHI" then returns the correct mapping positions`() {
+        val formattedVisualTransformation = FormattedVisualTransformation { text: String -> text.chunked(3).joinToString(" ") }
+        val annotatedString = AnnotatedString("ABCDEFGHI")
+        val filter = formattedVisualTransformation.filter(annotatedString)
+
+        assertEquals(0, filter.offsetMapping.transformedToOriginal(0))
+        assertEquals(1, filter.offsetMapping.transformedToOriginal(1))
+        assertEquals(2, filter.offsetMapping.transformedToOriginal(2))
+        assertEquals(3, filter.offsetMapping.transformedToOriginal(3))
+        assertEquals(3, filter.offsetMapping.transformedToOriginal(4))
+        assertEquals(4, filter.offsetMapping.transformedToOriginal(5))
+        assertEquals(5, filter.offsetMapping.transformedToOriginal(6))
+        assertEquals(6, filter.offsetMapping.transformedToOriginal(7))
+        assertEquals(6, filter.offsetMapping.transformedToOriginal(8))
+        assertEquals(7, filter.offsetMapping.transformedToOriginal(9))
+        assertEquals(8, filter.offsetMapping.transformedToOriginal(10))
+        assertEquals(9, filter.offsetMapping.transformedToOriginal(11))
+
+        assertEquals(0, filter.offsetMapping.originalToTransformed(0))
+        assertEquals(1, filter.offsetMapping.originalToTransformed(1))
+        assertEquals(2, filter.offsetMapping.originalToTransformed(2))
+        assertEquals(4, filter.offsetMapping.originalToTransformed(3))
+        assertEquals(5, filter.offsetMapping.originalToTransformed(4))
+        assertEquals(6, filter.offsetMapping.originalToTransformed(5))
+        assertEquals(8, filter.offsetMapping.originalToTransformed(6))
+        assertEquals(9, filter.offsetMapping.originalToTransformed(7))
+        assertEquals(10, filter.offsetMapping.originalToTransformed(8))
+        assertEquals(11, filter.offsetMapping.originalToTransformed(9))
+    }
+
+    @Test
+    fun `Given password string when transformed to * then returns the correct mapping positions`() {
+        val formattedVisualTransformation = FormattedVisualTransformation { text: String -> "*".repeat(text.length) }
+        val annotatedString = AnnotatedString("password")
+        val filter = formattedVisualTransformation.filter(annotatedString)
+
+        for (i in annotatedString.text.indices) {
+            assertEquals(i, filter.offsetMapping.transformedToOriginal(i))
+            assertEquals(i, filter.offsetMapping.originalToTransformed(i))
+        }
+    }
+
+    @Test
+    fun `When text is empty string then returns the correct mapping positions`() {
+        val formattedVisualTransformation = FormattedVisualTransformation { text: String -> text }
+        val annotatedString = AnnotatedString("")
+        val filter = formattedVisualTransformation.filter(annotatedString)
+
+        assertEquals(0, filter.offsetMapping.transformedToOriginal(0))
+        assertEquals(0, filter.offsetMapping.originalToTransformed(0))
+    }
+}