refactor: improve URLDetector readability

- UrlDetector: simplify space handler in readDefault() — both branches
  of if/else were calling the same readEnd(InvalidUrl), making the
  conditional dead code; now we always call readEnd after attempting
  to read the domain
- UrlDetector: remove redundant inner buffer.isNotEmpty() check in
  readEnd(), already guarded by the outer condition
- UrlDetector: rename processColon() parameter from length to
  startLength to eliminate the var length = length self-shadowing
- UrlDetector: replace ArrayList<Url>() with mutableListOf<Url>()
  for idiomatic Kotlin
- DomainNameReader: replace lastSection.deleteRange(0, lastSection.length)
  with lastSection.clear() which expresses the intent directly
- DomainNameReader: move isDotPercent() and isXn() extension functions
  from inside the class body to private file-level functions — extension
  functions defined on a class instance are unusual and confusing

https://claude.ai/code/session_01Pci2AC45yQxQw6F6g7jWdd

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/utils/urldetector/detection/DomainNameReader.kt

@@ -30,6 +30,17 @@ import com.vitorpamplona.quartz.utils.urldetector.detection.CharUtils.splitByDot
 import kotlin.math.max
 import kotlin.math.min
 
+/** Returns true if the string is a percent-encoded dot (%2e or %2E). */
+private fun String.isDotPercent() = this == "%2e" || this == "%2E"
+
+/** Returns true if the string is an internationalized domain label using Punycode (xn-- prefix). */
+private fun String.isXn() =
+    this.length > 3 &&
+        (this[0] == 'x' || this[0] == 'X') &&
+        (this[1] == 'n' || this[1] == 'N') &&
+        this[2] == '-' &&
+        this[3] == '-'
+
 /**
  * The domain name reader reads input from a InputTextReader and validates if the content being read is a valid domain name.
  * After a domain name is read, the returning status is what to do next. If the domain is valid but a specific character is found,
@@ -134,7 +145,6 @@ class DomainNameReader(
     var isIpV6 = false
         private set
 
-    fun String.isDotPercent() = this == "%2e" || this == "%2E"
 
     /**
      * Reads and parses the current string to make sure the domain name started where it was supposed to,
@@ -424,13 +434,6 @@ class DomainNameReader(
         return checkDomainNameValid(ReaderNextState.ValidDomainName, null)
     }
 
-    fun String.isXn() =
-        this.length > 3 &&
-            (this[0] == 'x' || this[0] == 'X') &&
-            (this[1] == 'n' || this[1] == 'N') &&
-            this[2] == '-' &&
-            this[3] == '-'
-
     fun labelCount() = dots + (if (currentLabelLength > 0) 1 else 0)
 
     /**
@@ -700,7 +703,7 @@ class DomainNameReader(
                     hexSection = true // reset hex to true
                     hexDigits = 0 // reset count for hex digits
                     numSections++
-                    lastSection.deleteRange(0, lastSection.length) // clear last section
+                    lastSection.clear() // clear last section
                 }
 
                 else -> {

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/utils/urldetector/detection/UrlDetector.kt

@@ -52,7 +52,7 @@ class UrlDetector(
     /**
      * Stores the found urls.
      */
-    private val urlList: ArrayList<Url> = ArrayList<Url>()
+    private val urlList = mutableListOf<Url>()
 
     /**
      * Keeps track of certain indices to create a Url object.
@@ -89,18 +89,12 @@ class UrlDetector(
             // read the next char to process.
             when (val curr = reader.read()) {
                 ' ' -> {
-                    // space was found, check if it's a valid single level domain.
+                    // space found; if we have a scheme, attempt to read the domain before resetting
                     if (buffer.isNotEmpty() && hasScheme) {
                         reader.goBack()
-                        val domain = buffer.substring(length)
-                        if (!readDomainName(domain)) {
-                            readEnd(ReadEndState.InvalidUrl)
-                        } else {
-                            readEnd(ReadEndState.InvalidUrl)
-                        }
-                    } else {
-                        readEnd(ReadEndState.InvalidUrl)
+                        readDomainName(buffer.substring(length))
                     }
+                    readEnd(ReadEndState.InvalidUrl)
                     length = 0
                 }
 
@@ -220,8 +214,8 @@ class UrlDetector(
      * @param length first index of the previous part (could be beginning of the buffer, beginning of the username/password, or beginning
      * @return new index of where the domain starts
      */
-    private fun processColon(length: Int): Int {
-        var length = length
+    private fun processColon(startLength: Int): Int {
+        var length = startLength
         if (hasScheme) {
             // read it as username/password if it has scheme
             if (!readUserPass(length)) {
@@ -648,12 +642,9 @@ class UrlDetector(
     private fun readEnd(state: ReadEndState?): Boolean {
         // if the url is valid and greater then 0
         if (state == ReadEndState.ValidUrl && buffer.isNotEmpty()) {
-            // Add the url to the list of good urls.
-            if (buffer.isNotEmpty()) {
-                var url = buffer.toString()
-                if (url.lastOrNull() in CANNOT_END_URLS_WITH) url = url.dropLast(1)
-                urlList.add(currentUrlMarker.createUrl(url))
-            }
+            var url = buffer.toString()
+            if (url.lastOrNull() in CANNOT_END_URLS_WITH) url = url.dropLast(1)
+            urlList.add(currentUrlMarker.createUrl(url))
         }
 
         // clear out the buffer.