From 845c99b7983212a97ad5c01eecb5b2c568955001 Mon Sep 17 00:00:00 2001
From: Vitor Pamplona <vitor@vitorpamplona.com>
Date: Mon, 5 Feb 2024 19:37:21 -0500
Subject: [PATCH] Faster Expandable Text calculator.

---
 .../ui/components/ExpandableRichTextViewer.kt |  2 +-
 .../ExpandableViewComputationBenchmark.kt     | 27 ++++++++--
 .../amethyst/commons/ExpandableTextParser.kt  | 50 ++++++++++---------
 3 files changed, 52 insertions(+), 27 deletions(-)

diff --git a/app/src/main/java/com/vitorpamplona/amethyst/ui/components/ExpandableRichTextViewer.kt b/app/src/main/java/com/vitorpamplona/amethyst/ui/components/ExpandableRichTextViewer.kt
index 325211aa2..fc845ba2a 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/ui/components/ExpandableRichTextViewer.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/ui/components/ExpandableRichTextViewer.kt
@@ -64,7 +64,7 @@ fun ExpandableRichTextViewer(
 ) {
     var showFullText by remember { mutableStateOf(false) }
 
-    val whereToCut = remember(content) { ExpandableTextParser().computeWhereToCutIfPostIsTooLong(content) }
+    val whereToCut = remember(content) { ExpandableTextParser.computeWhereToCutIfPostIsTooLong(content) }
 
     val text by
         remember(content) {
diff --git a/benchmark/src/androidTest/java/com/vitorpamplona/amethyst/benchmark/ExpandableViewComputationBenchmark.kt b/benchmark/src/androidTest/java/com/vitorpamplona/amethyst/benchmark/ExpandableViewComputationBenchmark.kt
index a1c6dbde9..b4e52f3d3 100644
--- a/benchmark/src/androidTest/java/com/vitorpamplona/amethyst/benchmark/ExpandableViewComputationBenchmark.kt
+++ b/benchmark/src/androidTest/java/com/vitorpamplona/amethyst/benchmark/ExpandableViewComputationBenchmark.kt
@@ -24,6 +24,7 @@ import androidx.benchmark.junit4.BenchmarkRule
 import androidx.benchmark.junit4.measureRepeated
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.vitorpamplona.amethyst.commons.ExpandableTextParser
+import com.vitorpamplona.amethyst.commons.nthIndexOf
 import junit.framework.TestCase
 import org.junit.Rule
 import org.junit.Test
@@ -38,18 +39,38 @@ class ExpandableViewComputationBenchmark {
     fun computeTestCase1() {
         benchmarkRule.measureRepeated {
             TestCase.assertEquals(
-                294,
-                ExpandableTextParser().computeWhereToCutIfPostIsTooLong(testCase1),
+                293,
+                testCase1.nthIndexOf('\n', 10),
             )
         }
     }
 
     @Test
     fun computeTestCase2() {
+        benchmarkRule.measureRepeated {
+            TestCase.assertEquals(
+                423,
+                testCase2.nthIndexOf('\n', 10),
+            )
+        }
+    }
+
+    @Test
+    fun computeTestCase1All() {
+        benchmarkRule.measureRepeated {
+            TestCase.assertEquals(
+                293,
+                ExpandableTextParser.computeWhereToCutIfPostIsTooLong(testCase1),
+            )
+        }
+    }
+
+    @Test
+    fun computeTestCase2All() {
         benchmarkRule.measureRepeated {
             TestCase.assertEquals(
                 355,
-                ExpandableTextParser().computeWhereToCutIfPostIsTooLong(testCase2),
+                ExpandableTextParser.computeWhereToCutIfPostIsTooLong(testCase2),
             )
         }
     }
diff --git a/commons/src/main/java/com/vitorpamplona/amethyst/commons/ExpandableTextParser.kt b/commons/src/main/java/com/vitorpamplona/amethyst/commons/ExpandableTextParser.kt
index a194933a0..38b43528a 100644
--- a/commons/src/main/java/com/vitorpamplona/amethyst/commons/ExpandableTextParser.kt
+++ b/commons/src/main/java/com/vitorpamplona/amethyst/commons/ExpandableTextParser.kt
@@ -22,31 +22,35 @@ package com.vitorpamplona.amethyst.commons
 
 class ExpandableTextParser {
     companion object {
-        const val SHORT_TEXT_LENGTH = 350
-        const val SHORTEN_AFTER_LINES = 10
-    }
+        private const val SHORT_TEXT_LENGTH = 350
+        private const val SHORTEN_AFTER_LINES = 10
 
-    fun computeWhereToCutIfPostIsTooLong(content: String): Int {
-        // Cuts the text in the first space or new line after SHORT_TEXT_LENGTH characters
-        val firstSpaceAfterCut =
-            content.indexOf(' ', SHORT_TEXT_LENGTH).let { if (it < 0) content.length else it }
-        val firstNewLineAfterCut =
-            content.indexOf('\n', SHORT_TEXT_LENGTH).let { if (it < 0) content.length else it }
+        fun computeWhereToCutIfPostIsTooLong(content: String): Int {
+            // Cuts the text in the first space or new line after SHORT_TEXT_LENGTH characters
+            val firstSpaceAfterCut =
+                content.indexOf(' ', SHORT_TEXT_LENGTH).let { if (it < 0) content.length else it }
+            val firstNewLineAfterCut =
+                content.indexOf('\n', SHORT_TEXT_LENGTH).let { if (it < 0) content.length else it }
+            val firstLineAfterLineLimits =
+                content.nthIndexOf('\n', SHORTEN_AFTER_LINES).let { if (it < 0) content.length else it }
 
-        // or after SHORTEN_AFTER_LINES lines
-        val numberOfLines = content.count { it == '\n' }
-
-        var charactersInLines = minOf(firstSpaceAfterCut, firstNewLineAfterCut)
-
-        if (numberOfLines > SHORTEN_AFTER_LINES) {
-            val shortContent = content.lines().take(SHORTEN_AFTER_LINES)
-            charactersInLines = 0
-            for (line in shortContent) {
-                // +1 because new line character is omitted from .lines
-                charactersInLines += (line.length + 1)
-            }
+            return minOf(firstSpaceAfterCut, firstNewLineAfterCut, firstLineAfterLineLimits)
         }
-
-        return minOf(firstSpaceAfterCut, firstNewLineAfterCut, charactersInLines)
     }
 }
+
+fun String.nthIndexOf(
+    ch: Char,
+    N: Int,
+): Int {
+    var occur = N
+    var pos = -1
+
+    while (occur > 0) {
+        // calling the native function multiple times is faster than looping just once
+        pos = indexOf(ch, pos + 1)
+        occur--
+    }
+
+    return if (occur == 0) pos else -1
+}